Ipomoea batatas

Scientific Name Vernacular Names

Ipomoea batatas (L.) Lamk Afrikaans: Patat;

Albanian: Patate E Ëmbël;
Angola: €Kapa (Umubumbu), Batata-Doce,
Synonyms Batata-Da-Ilha (Portuguese);
Arabic: Ba Ta Tah Helua;
Batatas edulis (Thunb.) Choisy, Batatas edulis Argentina: Yety;
(Thunberg ex Murray) Choisy; Convolvulus Aymara: Pua, Tipali, Tuctuca;
batatas L.; Convolvulus chrysorrhizus Soland. ex Benin: Kukundu (Yoruba);
G. Forster, Convolvulus candicans Solander ex Brazil: Batata Doce, Batata Da Ilha, Batata Da
Sims; Convolvulus edulis Thunb., Convolvulus Terra (Portuguese);
edulis Thunberg ex Murray, Ipomoea batatas var. Bolivia: Apichu;
edulis (Thunb.) Kuntze, Ipomoea batatas var. Burkina Faso: Tingo (Baoulé), Téguibo,
edulis (Thunberg ex Murray) Makino, Ipomoea Déguibo, Bassi (Guéré);
batatas var. lobata Gagnepain & Courchet, Burmese: Myonk-Ni;
Ipomoea chrysorrhiza (Soland. ex G. Forster) Cameroon: Makeu, Ton’ho-La (Bamileke);
Peter, Ipomoea edulis (Thunberg ex Murray) Chamorro: Kamote;
Makino; Ipomoea fastigiata Sweet. Chinese: Bai Shu, Di Gua, Fan Shu, Gan Shu;
Comoros: Maniyambatsi (Great Comoros);
Chuukese: Kómwu, Kómwuti, Kómwuutiy,
Family Omwuti, Sachúmayimwo, Yomwuutiy;
Cuba: Boniato;
Convolvulaceae Cook Islands: Ku‘Ara, Kūara, Kūmala, Kūmara,
Kumara (Maori);
Croatian: Indijski Krumpir, Slatki Krumpir;
Common/English Names Danish: Batat, Sød Kartoffel;
Democratic Republic of Congo: Matembele
Sweet Potato Bangi (Lingala), Mabelenge, Mibabanga

© Springer Science+Business Media Dordrecht 2016 92

T.K. Lim, Edible Medicinal and Non-Medicinal Plants: Volume 10, Modified Stems, Roots, Bulbs,
DOI 10.1007/978-94-017-7276-1_5
Ipomoea batatas 93

(Ngombe), Matembele (Swahili), Tshilunga Marquesan: Kūma’a;

(Tshiluba); Nigeria: Ipotato (Ndokwa Delta State), Odunkun
Dutch: Bataat, Zoete Aardappel; (Ogun State);
Estonian: Bataat, Okariin; Niuean: Kumara, Simala;
Ethiopia: Siquar-Dinich (Omotic); Madagascar: Vomanga (Agnalazaha Forest,
Fiji: Kawai Ni Vavalangi, Kumala, Kumara, Southeastern Madagascar);
Ndambithi, Wa Uvi; Marshallese: Piteto;
French: Batate, Patate Douce; Mexico: Camotli;
Gabon: Émongo (Baduma), Amongo (Bakèlè), Norwegian: Søtpoteter;
Gémongo (Baléngi), Mongo (Balumbu, Palauan: Emutii;
Bavové), Imongo (Banzabi), Lungu (Bapunu), Panama: Kuwas:
Lifita (Bavili), Mbongo (Benga), Imongo Papua New Guinea: Kaukau, Kaema;
(Béséki, Ngowé), Égwèta (Ivéa, Mitsogo), Paraguay: Yety;
Mongu (Bavarama, Bavungu, Eshira), Peru: Apichu, Kumara;
Lémongho, Futa (Mindumu), Mongo Y’onigi Philippines: Tigsi (Bisaya), Tugi (Bontok), Lapni
(Mpongwè, Nkomi, Namôngha (Ifugao), Kamote (Tagalog), Panggi-Bagun
(Fang),Orungu), Ofogola (Galoa); (Sulu);
German: Batate, Süsskartoffel; Polish: Słodki Ziemniak;
Greek: Glikopatata; Popular Republic of Congo: Osokoro (Kôyô);
Guatemala: Chin, Sis, Is; Portuguese: Camote, Papas, Batata Doce;
Haiti: Patate Dôce; Pukapukan: Kūmala;
Hawaiian: ‘Uala, ‘Wala; Rarotongan: Kūmara;
Honduras: Mabi; Russian: Batat;
Hungarian: Édes Burgonya; Samoan: ‘Umala;
I-Kiribati: Te Kumara; Senegal: Juifata (Diola);
India: Lalalu (Bengali), Batata, Bataka, Kannagi, Serbian: Slatki Krompir;
Sakariu (Gujarati), Mitha Alu, Shakar Kanda, Slovak: Sladký Zemiak, Ocarina;
Sakarkand (Hindi), Genasu (Kanada), South Africa: Ubhatata (Northern Maputaland,
Chakkare Kilangu (Malayalam), Batata, Kwazulu-Natal Province);
Bataka, Ratala, Ratalu (Marathi), Kanh Spanish: Batata, Boniato, Papas, Camote, Papa
(Oriya), Carkkaraivalli, Ciignikkilangu, Dulce, Moniato, Cumala Huasca, Cumal
Sakkaravelleikilangu, Vattaalagnkilangu, Huasca, Cumara, Curiti, Jarissi Jabo;
Vellikkilangu (Tamil), Chelagadda (Telugu); Swahili: Anago, Dankoli, Dantiu, Kiazi, Kinkio,
Indonesia: Ubi Jalar, Ubi Keladek, Ketel Rambat Veeazee, Viazi Vitamu;
(Javanese), Huwi Boled (Sundanese); Swedish: Sötpotatis;
Italian: Patata Americana, Patata Dolce, Batata; Tahitian: Umara, ‘Umara;
Ivory Coast: Tingo (Baoulé), Gonenbi (Ebrie), Thai: Mam-Thet;
Téguibo, Déguibo, Bassi (Guéré); Togo: Patate Douce (French);
Japanese: Imo, Kara Imo, Kan Sho, Satsuma- Tongan: Kumala, Kumara;
Imo, Ryuukyuu Imo; Tuamotuan: Kūmara;
Kenya: Ngwaci (Kikiyu), Mîrîyo (Central Turkish: Sarmaşık Patatesi, Tatlı Patates, Yer
Province), Elması;
Khmer: Dâmlô:Ng Chvië; Uganda: Mboli (Bulamogo Country), Pot-Ecok
Korean: Goguma; (Luganda), Akarandura, Enkoora (Rutooro),
Kwara‘Ae: Butete; Lumonde (Sango Bay, Southern Uganda);
Laotian: Man Kè:W; Ulithian: Komoti;
Lithuanian: Saldžiųjų Bulvių; Uruguay: Boniato;
Malaysia: Ubi Keladi, Ubi Keladek, Keledek; Vanuatu: Kūmala;
94 Convolvulaceae

Venezuela: Chaco; the progenitor of I. batatas, and I. tabascana,

Vietnamese: Khoai Lang, Khoai Mon; inter-specific hybrid between these two species.
Welsh: Tatws Melys;
Woleaisan: Gamwuutiy;
Yapese: Gamuti, Kamote, Kamuut Agroecology

Sweet potato is adaptable to a wide range of cli-

matic conditions from the warm humid tropics to
Origin/Distribution mild sub-temperate zones from near sea level to
2000 m elevation. It has tolerance to low temper-
Available evidence shows that sweet potato origi- ature in the higher altitudes, but is frost-sensitive.
nated from the neotropics, either Central or South It grows best on sandy loams that are well-drained
American lowlands with subsequent dispersal to and fertile and is intolerant of water logging and
North America, Europe, Africa, Asia and the is usually grown in on mounds or ridges. It can be
Pacific islands (Zhang et al. 2000; Gichuki et al. grown in clayey soils, but tuberous yield can be
2003). Results of AFLP molecular studies sup- affected. It can be grown in semi-arid conditions.
ported the hypothesis that Central America was Soils below a pH of 5 are at a risk of aluminium
the primary centre of diversity and most likely toxicity and below pH 4.5 (other than organic
the centre of origin of sweet potato and Peru- soils). Aluminium will severely reduce the
Ecuador should be regarded as a secondary cen- growth and development of sweet potato.
tre of sweet potato diversity (Zhang et al. 2000).
This was confirmed by subsequent polymorphic
RAPD molecular studies that found the primary Edible Plant Parts and Uses
centre of diversity probably had two distinct
genepools (Gichuki et al. 2003). It was proposed The tuberous roots and leaves and young shoots
that the dispersal of the sweet potato from its ori- are eaten. The starchy tuberous roots are by far
gin may have mainly involved varieties from the most important product. In some tropical
Central America/Caribbean as opposed to variet- areas, sweet potato is a staple food-crop.
ies from South America. There was an indication Sweet potato leaves are a common side dish in
that new genepools may be evolving in Africa Chinese cuisines, often boiled with garlic and
and Asia due to hybridization and adaptation to vegetable oil and dashed with salt before serving.
the local environments. New Guinea is consid- In Taiwan, they are commonly found at biàndāng
ered to be the most important secondary centre of restaurants, as well as dishes featuring the sweet
genetic diversity for sweet potato, particularly potato root. In Malaysia, the leaves are fried with
the highlands region (Yen 1974). Combining garlic and sambal belacan. The young leaves and
nuclear and chloroplast data, Roullier et al. vine tips of sweet potato leaves are also widely
(2013) showed that New Guinea sweet potato consumed as a vegetable in west African coun-
landraces were principally derived from the tries (Guinea, Sierra Leone and Liberia, for
northern neotropical genepool (Caribbean and example). In PNG and the south Pacific islands,
Central America), but that some South American the young leaves and shoots are sometimes eaten
clones may also have been introduced, either as greens. Leaves eaten cooked in water, coconut
early by Polynesians themselves or (more likely) cream or stir fried with chillies, garlic and dried
later by whalers and missionaries and through shrimps, onion. One common recipe using shoot
twentieth-century movements across the Pacific. tips is ‘sweet potato tip soup’ made up of sweet
It is cultivated worldwide and widely naturalized potato shoot tips, butter/cooking oil, chopped
in the tropics and sub-tropics. onion, flour, milk . The leaves are a good addition
Srisuwan et al. (2006), using cytogenetic to soups and are reported to be an excellent food
approaches, found that Ipomoea trifida might be for babies, pregnant women, and breast-feeding
Ipomoea batatas 95

mothers. One recipe is called Baby’s delight – In Japan, sweet potato is used as a vegetable in
sweet potato leaves, small pieces of pumpkin, tempura, in Yaki-imo (roasted sweet potato) a
fish, coconut cream. delicacy in winter, and in Daigaku-imo a baked
Tubers can be eaten raw and taste somewhat sweet potato dessert. In Imo-gohan, slices or
like a sweet carrot. Tubers are usually eaten small chunks of sweet potato are cooked in rice.
cooked, boiled or baked or roasted. They are used Sweet potato is also served in nimono (Japanese
in various food dishes, cakes, buns, soups, cas- foods such as fish, meat and vegetables that are
seroles, pies, fries and chips. simmered in a seasoned broth) or nitsuke (a sea
Sweet potatoes may be baked in an earth oven food dish) boiled and flavoured with typically
or they may be boiled or steamed. Steamed/ soy sauce, Mirin (sweetened Japanese rice wine
boiled chunks, for a simple and healthy snack, of used for cooking) and Dashi (Japanese soup
sweet potato may be boiled in water or cooked in stock). Sweet potato is also used in sweet potato
the microwave. Baked sweet potato serves as an paste ball called Imo-kinton or a Japanese con-
alternative to potato and can be eaten as it is or fectionary called wagashi.
with brown sugar and butter. They may be eaten Significant amounts of sweet potato are being
as they are or mashed with milk or coconut processed into industrial starch, alcohol, noodles
cream. In the Dominican Republic, they are (Plate 7) and other products, especially in China
served for breakfast. Sweet potato butter can be and Korea. In China, sweet potato is also
cooked into a gourmet spread. In America, cara- processed into a myriad of products for local con-
melized sweet potatoes are prepared with brown sumption and export such as sweet potato pow-
sugar, marshmallows, maple syrup, molasses or der, starch, flour, frozen cubes, sweet potato
other sweet ingredients, and served as a side dish, puree, dried and dehydrated slices, chips, candied
a traditional dish especially on Thanksgiving. dried slices and noodles. In the Shandong and
Sweet potato pie is another favourite American Sichuan provinces of China, transparent cello-
dish. Sweet potato fries are another common phane noodles are made from starch extracted
preparation, and are made by julienning and deep from sweet potato, an important crop in China’s
frying sweet potatoes. Sweet potato chips can be small farming systems. In Korea, sweet potato
sliced, fried and eaten. Sweet potato is a staple starch is commonly employed to make the popu-
food for people in north-eastern Uganda where lar Korean sweet potato vermicelli, a type of cel-
sun-dried slices called ‘Amukeke’ or sun-dried lophane noodles called dang myun, dangmyun,
crushed tubers called ‘Inginyo’ are the important tang myun, tangmyu. The dang myun noodles are
modes of preparation. Amukeke is mainly for glassy and transparent and have a very interesting
breakfast, eating it with peanut sauce and a cup of chewy texture and are very long, slippery and
tea. Inginyo will be mixed with cassava flour and almost elastic. The most common Korean dish
tamarind, this food is called ‘atapa’. People eat using dang myun is japchae, a beef stir-fry using
‘atapa’ with smoked fish cooked in peanut sauce sesame and soy. Another favourite dish using
or with dried cowpea leaves cooked in peanut dang myun is ‘Cold dang myun noodle salad’.
sauce. Sweet potato is also fermented and made into
Cooked sweet potato can be made into a vari- alcohol and spirits, e.g., Shōchū – a Japanese
ety of dishes in soups, stews, curries and stir fry. spirit made from fermentation of rice and sweet
Mashed with a little coconut cream, fish and potato; Soju – Korean alcoholic beverage, often
green vegetables; it makes a good baby food. One mistaken as rice wine, but actually almost always
popular dish in Fiji is called ‘Meal in coconut made in combination with other ingredients such
shell’ which comprises clean shelled and halved as wheat, barley or sweet potatoes. Sweet potato
coconut, small sweet potato, coconut milk, green bread and flour (100 %) are also marketed as
leaves, tomato and spring onions. Sweet potato hypoallergenic for people who cannot tolerate
buns are made with sweet potato cooked and grain breads and flours.
mashed, milk, self-rising flour and lemon juice.
96 Convolvulaceae

Purple-fleshed sweet potato is rich in antho- oxidant enhancer and colour source in industrial
cyanins and is used as a natural food colourant powder soups, gravy, extruder snacks and some
with nutritious and health benefits; the deep pur- bakery products. Sweet potato tubers were pro-
ple paste and flour made from cv. ‘Ayamurasaki’ cessed into non-alcoholic beverages flavoured
are used for the preparation of noodles, bread, with citrus lime and ginger in Ghana (Wireko-
jams, sweet potato chips, confectionery, juices Manu et al. 2010).
and alcoholic beverages (Yamakawa et al. 1998; Vacuum frying (1.33 kPa), with the aid of a
Suda et al. 2003). These foods and beverages de-oiling mechanism, was used to produce low-
using purple-fleshed are being sold in shops at fat sweet potato chips (Ravli et al. 2013). The
stations, airports and tourist resorts in the final oil content of the vacuum-fried chips was
Kyushu-Okinawa area in Japan. Studies found 60 % lower than those found in traditionally fried
that extruded ready-to-eat breakfast cereals sweet potato chip, which indicated that the de-
(RTEBCs) made from 100 % of sweet potato oiling mechanism was crucial in vacuum-frying
flour (SPF), and 75 %/25 % SPF/whole-wheat processing. Studies by Johnson et al. (2010)
bran (WWB) and extrusion cooking were well- found that high fructose syrup, a highly valued
liked and acceptable to sixth graders attending an sweetener for the food and beverage industries,
elementary school in Auburn, Alabama, but the could be produced from sweet potato flours and
100 % WWB was unacceptable (Dansby and their blends with cereal flours.
Bovell-Benjamin 2003).
Tubers of Turkish sweet potato cv. Hatay
Kirmizi can be consumed not only in steamed, Botany
boiled and fried forms but also can be processed
into food products, such as muffins, cookies, bis- A sprawling, low, herbaceous annual (Plate 1),
cuits, breakfast foods with longer shelf-life, and with fusiform or elongated subterranean tubers;
improved characteristics (Tokusoglu and Yildirim tuber skin colour ranging from between red, pur-
2012). Also, sweet potato Hatay Kirmizi can be ple, brownish, yellowish-brown and white and
processed into flour and used as a thickener, anti- tuber flesh colour white yellow, orange and

Plate 1 Sweet potato planting

Ipomoea batatas 97

Plate 2 (a–d) Variously coloured sweet potato tubers

purple (Plates 2, 3). Stems prostrate or ascend- ovules per cell and one simple style. Fruit a
ing, green or purplish, glabrous or pilose, much novoid or depressed globose, non-fleshy capsule.
branched, rooting at nodes and with milky sap. Seeds glabrous.
Leaves alternate, ovate-orbicular, entire or pal-
mately 3-7-lobed or -parted, subcordate or cor-
date, 4–15 cm long, 3–11 cm wide, on 3–15 cm Nutritive/Medicinal Properties
long petioles (Plates 4, 5, and 6). Inflorescences
axillary; peduncle 3–18 cm long, 1–several-flow- Tuber Nutrients/Phytochemicals
ered; pedicels 3–12 mm long; bracts lanceolate
and deciduous. Sepals sub-equal, the inner some- Raw sweet potato tuber (per 100 g edible portion
what longer, oblong to elliptic-oblong, 7–12 mm proximate) was reported to have the following
long by 3–5 mm wide, acute and mucronate, sub- nutrient values: water 77.28 g, energy 86 kcal
coriaceous. Corolla violet or lilac (Plate 5), white (359 kJ), protein 1.57 g, total lipid 0.05 g, ash
above, campanulate, 3–4.7 cm long. Stamens 5, 0.99 g, carbohydrate 20.12 g, total dietary fibre
adnate to the perianth, free and alternating with 3.0 g, total sugars 4.180 g, minerals – Ca 30 mg,
the corolla lobes. Anthers dehiscing via longitu- Fe 0.61 mg, Mg 25 mg, P 47 mg, K 337 mg, Na
dinal slits. Ovary syncarpous, superior with two 55 mg, Zn 0.30 mg, Cu 0.151 mg, Mn 0.258 mg,
98 Convolvulaceae

Plate 3 White-purple-fleshed
tuber

Plate 4 Bronze-coloured
young foliage

Se 0.6 mcg; vitamin C 2.4 mg, thiamin 0.078 mg, fatty acids 0.018 g, 16:0 (palmitic acid) 0.018 g,
riboflavin 0.061 mg, niacin 0.557 mg, panto- 18:0 (stearic acid) 0.001 g, total monounsatu-
thenic acid 0.800 mg, vitamin B-6 0.209 mg, rated fatty acids 0.001 g, 18:1 undifferentiated
total folate 11 μg, total choline 12.3 mg, vitamin (oleic acid) 0.001 g, total polyunsaturated fatty
A 14187 IU, vitamin A RAE 709 μg, β-carotene acids 0.014 g, 18:2 undifferentiated (linoleic
8509 μg, α-carotene 7 μg, vitamin E acid) 0.013 g, 18:3 undifferentiated (linolenic
(α-tocopherol) 0.26 mg, β-tocopherol 0.01 mg, acid) 0.001 g, phytosterols 12 mg, amino acids –
vitamin K (phylloquinone) 1.8 μg; total saturated tryptophan 0.031 g, threonine 0.083 g, isoleucine
Ipomoea batatas 99

Plate 5 Old leaves and flower

0.055 g, leucine 0.092 g, lysine 0.066 g, methio-

nine 0.029 g, cystine 0.022 g, phenylalanine
0.089 g, tyrosine 0.034 g, valine 0.0.086 g, argi-
nine 0.055 g, histidine 0.031 g, alanine 0.077 g,
aspartic acid 0.382 g, glutamic acid 0.155 g, gly-
cine 0.063, proline 0.052 g and serine 0.088 g
(USDA–ARS 2014). Sweet potato storage roots
of 10 sweet potato varieties were found to con-
tain the following flavonoid (%DW) quercetin
0.68 %, myricetin 0.09 %, luteolin 0.01 %, api-
genin 0 %, kaempferol 0.01 % and total flavo-
noids 0.85 % (Ojong et al. 2008).
The proximate nutrient composition of fresh,
boiled and baked sweet potatoes were respectively
as follows: dry matter 31.07–33.76 g, 33–37.65 g,
36.55–40.65 g; ash 2.13–2.54 g, 2.19–2.60 g,
2.31–2.62 g; crude fibre 2.33–2.65 g, 2.45–
2.76 g, 2.11–2.64 g; protein 4.29–5.08 g, 4.36–
5.03 g, 3.54–4.56 g; starch 63.90–64.89 g,
49.22–57.43 g, 55.80–60.22 g; ascorbic acid
14.07–20.18, 24.77–37.15, 19.43–
27.88 mg/100 g dw; glucose 2.73–4.68 mg, 1.34–
3.94 mg, 1.72–4.90 mg/g dw; fructose 1.43–4 mg,
1.42–3.75 mg, 1.24–3.38 mg/g dw; sucrose
56.94–59.97 mg, 48.99–61.50 mg, 55.52–
64.36 mg/gdw; maltose not detected, 48.13–
122.81 mg, 48.52–56.27 mg/g dw; β-carotene
content 5.63–15.63 mg; 3.28–12.64 mg, 1.15–
10.07 mg/g dw; retinol activity equivalent (RAE)
Plate 6 Purplish-stalked sweet potato leaves sold in values 169.5–439.6 μg, 102.3–353.1 μg, 31.65–
markets 260.5 μg/100 g wet basis, respectively (Dincer
100 Convolvulaceae

Plate 7 Sweet potato noodles

et al. 2011). Both the boiling and baking treat- Sucrose concentration was always greater than
ments resulted in a significant reduction in the either monosaccharide. Dessert sweet potato
β-carotene content and therefore in the RAE val- types generally have a cream coloured to orange
ues of the sweet potato samples. Generally, the flesh and dry weight content ranging from 17.7 to
treated samples had a higher dry matter content 26.3 % with starch contents ranging from about
than the fresh samples. The protein content of all 13.0 to 22.0 % (Picha 1987). Dry matter (DM)
samples decreased significantly during baking, content and free sugar composition (g/100 g FW)
while it did not change during boiling. The boil- of raw tubers of nine sweet potato genotypes
ing process led to significant degradation in were: DM 18–30.6 %, total sugars 3.37–6.80 g,
starch. DPPH antiradical activity of sweet pota- fructose 0.23–1.48 g, glucose 0.33–1.87 g and
toes was enhanced by heat treatment via the for- sucrose 1.36–4.14 g (Lewthwaite et al. 1997). In
mation of phenolic compounds. Total phenolic cooked tuber of the same lines, total sugars was
content of the samples increased with both bak- 6.69–10.24 g, fructose 0.22–1.39 g, glucose
ing and boiling treatments. 0.34–1.72 g, sucrose 1.31–4.15 g and maltose
Total sugars in stored, raw staple sweet potato 2.44–5.51 g. A strong linear relationship exists
types range from 2.9 to 3.2 % on a fresh weight between fructose, glucose and sucrose content in
(FW) basis (Picha 1985). The major sugars in raw and baked roots All the clones produced con-
raw roots: sucrose, fructose and glucose and their siderable amounts of maltose during cooking,
contents range from 1.3 to 2.5 %, 0.4 to 0.7 % which was significantly related to % dry weight.
and 0.4 to 1.0 %, respectively. Total sugars in Sucrose was the major sugar during all stages of
stored, raw dessert sweet potato types range from development from 7 to 19 weeks after transplant-
4.6 to 5.5 % on a FW basis (Picha 1985). ing, representing at least 68 % of total sugars
Corresponding sucrose, fructose and glucose across all sweet potato cultivars and dates (La
contents range from 2.8 to 4.1 %, 0.3 to 1.2 % Bronte et al. 2000). Fructose and glucose content
and 0.2 to 1.5 %, respectively. Maltose was the profiles varied among and within cultivars during
major sugar and sucrose the secondary sugar in development. Cultivars ranking the highest in
all cultivars at harvest (Picha 1986). Maltose total sugars had either more monosaccharides to
decreased during curing and over long-term stor- compensate for lower sucrose content or more
age. Sucrose, glucose and fructose concentra- sucrose to compensate for a lower monosaccha-
tions increased during curing and through at least ride content. Cultivars with high dry weight and
4 weeks of storage in the orange-flesh cultivars. alcohol insoluble (solids (starch)) could be
Ipomoea batatas 101

selected early during storage root development. cose absorption capacity determinations of the
Sugar and non-volatile acid contents (g/100 g dry DF of sweet potato varieties had respective
matter) in raw and baked roots of six sweet potato ranges of 8.11–12.56 mL/g, 3.54–6.15 g/g, 1.43–
cultivars were reported by Wang and Kays (2003) 2.48 g/g and 0.54–1.27 mmol/g.
respectively as: sucrose 5.61–21.34 g; 5.67– Major components of non-protein-nitrogen
26.25 g; glucose 0.31–6.31 g; 0.65–6.31 g; fruc- fraction of ‘Jewel’ sweet potato at 107 storage
tose 0.25–5.50 g; 0.44–6.75 g; galactose days were asparagine 61 %, aspartic acid 11 %,
0.03–0.13 g; 0–0.18 g; inositol 0.09–0.22 g; glutamic acid 4 %, serine 4 % and threonine 3 %
0.06–0.31 g; maltose 0–0.03 g; 5.18–29.08 g; (Purcell and Walter 1980). Levels of most amino
malic acid 0.39–1.59 g; 0.40–2.01 g; citric acid acids changed with time. The dry matter, protein
0.07–0.41 g; 0.05–0.49 g and quinic acid 0.24– and starch contents of the sweet potatoes were
0.62 g; 0.4–0.72 g. significantly changed by baking and boiling
Fresh sweet potato and sweet potato flour while the ash and crude fibre contents did not dif-
were reported to have the following nutrient com- fer as significantly (Dincer et al. 2011). The
position (w/w db), respectively: moisture content β-carotene contents of baked and boiled sweet
73.1, 7.7 %; total sugars in glucose equivalent potatoes were lower than those of fresh sweet
75.0, 77 %, glucose 2.4, 2.1 %; fructose 2.6, potatoes; however, the total phenolic and ascor-
1.6 %, sucrose 8.0, 15.8 %, fibre 10, 3 %; pro- bic acid contents of the baked and boiled sweet
teins 3.5, 6.6 %, lipids 0.4, 1.8 % and ash 4.1, potatoes were higher than those of the fresh sam-
2.7 % (Lareo et al. 2013). The mean concentra- ples. Generally, the antiradical activity of the
tion (mg/kg wet weight) of mineral nutrients and sweet potatoes increased with the treatments.
toxic metal determined in white-, red- and Sucrose, glucose and fructose were quantified as
orange-fleshed sweet potato varieties were free sugars in all fresh sweet potatoes; however,
respectively reported as: Na 564, 324, 559.6 mg; maltose was determined in the treated samples.
K 4510, 4094, 4551 mg; Ca 536.3, 789.1, Studies by Roxas et al. (1985) found the
321.7 mg; Mg 706.2, 562.2, 422.2 mg; Cu 1.264, absence of oligosaccharides in the storage roots
1.452, 1.156 mg; Fe 7.195, 6.637, 4.817 mg; Mn of sweet potatoes. They found only monosaccha-
2.713, 2.58, 1.742 mg; Zn 2.499, 2.523, 1.742 mg; rides and sucrose in the samples. The sum of glu-
Cr 0.034, 0.023, 0.022 mg; Ni 0.056, 0.045, cose, fructose and sucrose accounted for 85–96 %
0.030 mg; Cd 0.001, 0.004, 0.001 mg and PB and 17–54 % of total soluble sugars identified in
0.002, 0.005, 0.001 mg (Luis et al. 2014). extracted fractions of raw and cooked sweet
Commercial sweet potato fibre was found to be potato tubers (Truong et al. 1986). Verbascose
mainly composed of glucose (88.4 %), but small was found in trace amounts, stachyose was not
amounts of other sugars were also detected detected. Starch content of raw and cooked sam-
(Salvador et al. 2000). Sweet potato cell wall ples ranged from 33–73 to 32–61 %. Starch deg-
materials had the highest amount of pectin and radation products maltose, maltotriose were
galacturonic acid. present in cooked samples coeluted with cellobi-
The average yield and dietary fibre (DF) con- ose and raffinose, respectively. The tubers con-
tent of DF products from 10 sweet potato variet- tained 0.23–0.4 % cellobiose and negligible
ies were 9.97 and 75.19 %, respectively (Mei raffinose. The concentrations of indigestible oli-
et al. 2010). Average contents of cellulose, lignin, gosaccharides were too low to account for the
pectin and hemicellulose were 31.19, 16.85, flatulence that accompanied sweet potato as a
15.65 and 11.38 g/100 g of dry matter in DF staple food. The sugar composition of fresh and
products, respectively. The relative monosaccha- baked sweet potatoes (% DW basis) were deter-
ride contents of DF were in the order glucose > mined respectively as: total sugars (4.50–8.41 %,
uronic acid > galactose > arabinose > xylose > 15.11–19.14 %), fructose (0.24–1.06 %, 0.26–
rhamnose > mannose. Swelling capacity, water- 0.86 %), sucrose (2.52–7.77 %, 1.53–5.02 %),
holding capacity, oil-holding capacity and glu- glucose (0.39–2.02 %, 0.31–1.37 %), maltose
102 Convolvulaceae

(0–0.39 %, 8.81–13.97 %) (Lai et al. 2013). predominant fatty acids were stearic, palmitic,
Maltose increased dramatically after baking. The oleic, linoleic and linolenic. The amount of lipo-
starch granules of fresh sweet potato were oval- philic extractives in sweet potato root ranged
shaped and generally <20 μm, but after the bak- from 0.87 to 1.32 % dry weight (Cordeiro et al.
ing treatment starch granules completely 2013). Fatty acids and sterols were the major
gelatinized. families of compounds identified. The most
Purple sweet potato wine was found to have abundant saturated and unsaturated fatty acids
the following proximate compositions (per were hexadecanoic acid (182–428 mg/kg) and
100 mL): total soluble sugar (TSS), 2.25° Brix; octadeca-9,12-dienoic acid (133–554 mg/kg),
starch, 0.15 g; total sugar, 1.35 g; total acidity, respectively. β-Sitosterol was the principal phy-
1.34 g tartaric acid; phenol, 0.36 g (caffeic acid tosterol, representing 55.2–77.6 % of this family,
equivalent); anthocyanin, 55.09 mg; tannin, followed by campesterol. Long-chain aliphatic
0.64 mg; lactic acid, 1.14 mg; ethanol, alcohols and α-tocopherol were also detected, but
9.33 %(v/v) and pH, 3.6 (Ray et al. 2012). in smaller amounts.
Sugawara and Miyazawa (1999) reported
Lipids sweet potato roots to contain (mg/100 g) 67 mg
Changes in fatty acid composition of Georgia total glycolipids comprising 9.7 mg monogalac-
Red and Centennial varieties of sweet potatoes tosyldiacylglycerols (MGDG), 22.6 mg digalac-
were observed during storage and appeared to be tosyldiacylglycerols (DGDG), 15 mg acylated
mere pronounced at low storage temperatures (10 steryl glucoside (ASG), 5.6 mg steryl glucoside
and 4.5 °C) (Boggess et al. 1967). The most con- (SG) and 14.1 mg ceramide monohexoside
sistent changes found were an increase in tetraco- (CMH).
sanoic acid and a decrease in short-chain saturated
acids. The Centennial variety contained higher Starch
levels of total lipids, which were generally The physicochemical and functional properties
reflected in higher levels of the three fractions, of starch of 14 sweet potato lines (10 white), (2
(1) non-phospholipids, (2) cephalin and (3) leci- yellow), (1 dark purple), (1 dark orange) were
thin. The increase in total lipids and the individ- determined as: organic matter 85.45–99.48 %,
ual lipid fractions with storage is indicative of ash 2.81–6.45 %, protein 3.96–5.13 %, fibre
two processes that may have occurred in the 2.11–3.96 %, starch 15.2–28.1 %, sugars 1.51–
stored roots. The lipids may have become more 3.9 %, dry matter 26.8–33.3 %, extractable starch
extractable as the respiring potato underwent 16.8–21.1 %, starch swelling volume 32.5–
compositional changes, or lipids were being syn- 50 mg/g, solubility 7.15–13.65 %, amylose
thesized from non-lipid components. 0.311–0.337, peak viscosity 2924–3902 cP;
Lipid composition (% total lipid weight) of breakdown 1080–2541 cP, final viscosity 2098–
cured Centennial sweet potatoes consisted of: 4530 cP, setback 800–1683.5 cP and pasting
neutral lipids 42.1 – triglycerides 26.9 %, steryl temp 65.9–77.50 °C (Moorthy et al. 2010).
esters 6.1 %, diglycerides 3.8 %, hydrocarbons The proximate compositions and physico-
2.8 %, sterols (free) 2.5 %; glycolipids 30.8 % – chemical properties of 21 Caribbean sweet pota-
monogalactosyl diglycerides 13.6 %, digalacto- toes were reported by Aina et al. (2012) as:
syl diglyceride 6.3 %, cerebroside 4.7 %, moisture (8.0–12.4 %), protein (0.0–0.2 %), ash
esterified steryl glucoside 3.5 %, unknown 2.1 %, (0.1–0.5 %), and reducing (0.3–2.3 %) and non-
steryl glucoside 0.6 %; phospholipids 27.1 % – reducing sugar (0.1–0.2 %) contents of starches
phosphatidyl ethanolamine 7.8 %, phosphatidyl were significantly different among the cultivars.
chlorine 7.0 %, phosphatidyl inositol 5.1 %, Amylose content varied significantly between
unknown 3.0 %, cardiolipid 1.6 %, phosphatidyl 12.8 and 21.3 %. Swelling power and solubility
glyceride 1.2 %, phosphatidyl serine 1.1 % and ranged between 7.8–31.1 % and 1.5–9.6 %,
phosphatidic acid 0.4 % (Walter et al. 1971). The respectively. Pasting properties such as peak vis-
Ipomoea batatas 103

cosity measured in Rapid Visco Units (143.2– the angular frequency range employed. Irish
288.8 RVU), breakdown viscosity (29.4–162.6 potato starch paste exhibited higher paste clarity
RVU) and setback viscosity (15.0–78.8 RVU), and lower syneresis than sweet potato starch
pasting temperature (73.5–87.7 °C) and time to paste. Irish potato has superior properties for
pasting temperature (3.6–4.5 min) varied signifi- application as thickener while sweet potato is
cantly among the cultivars. Breakdown viscosity better in withstanding severe processing condi-
was poorly correlated with final viscosity attained tions. The pasting properties showed wide ranges
(R2 = − 0.0507); however, pasting temperature of variation among twenty sweet potato cultivars
was correlated (R2 = 0.479) with setback viscos- and lines, and the amylose content ranged
ity. The variability observed in the physicochem- between 13.3 and 17.2 % (Katayama et al. 1999).
ical properties of the starches was related to Analysis of variance showed that the varietal dif-
specific requirements for use in the production of ferences were significant at 0.1 % level for the
noodles, pasta and inclusion in bread and wean- pasting temperature, setback, amylose content
ing food formulations. The physico-chemical and starch content. The differences among lines
properties of sweet potato starch of Nigerian and years were significant at 1 % level for the
varieties were reported by Nwokocha et al. pasting temperature, peak viscosity and break-
(2014) as follows: 12.03 % moisture, 0.11 % ash, down. The estimated heritability values of the
0.12 % fat, 0.05 % nitrogen, 0.07 % phosphorus, pasting temperature, peak viscosity, setback,
27.7 % amylose; particle characteristics: particle amylose content and starch content were 0.80,
number 97, maximum diameter 27 mm, mini- 0.49, 0.77, 0.88 and 0.85, respectively. The amy-
mum diameter 2.0 mm, mean diameter 9.15 mm, lose content showed significant positive correla-
length/diameter 1.17, roundness 0.77; gelatiniza- tions in both years with the pasting temperature,
tion properties: onset temperature 72.8 °C, peak the peak viscosity temperature and the setback.
temperature 74.9 °C, completion temperature The starch content did not show any significant
76.6 °C, gelatinization range 4.2 °C, endothermic correlation with the pasting properties and the
enthalpy 11.85 J/g; pasting properties: pasting amylose content. High amylopectin content of
temperature 75 °C, temperature at peak viscosity sweet potato starch was associated with a high
89 °C, peak viscosity during heating (PV) gelatinization temperature and correspondingly
265BU, viscosity at 95 °C 250 BU, viscosity less susceptibility to α-amylase attack (Zhang
after 30 min holding at 95 °C (HPV) 180 BU, vis- and Oates 1999). The hydrolysis pattern was cor-
cosity on cooling to 50 °C (CPV) 350 BU, stabil- related with the degree of hydrolysis. Extensive
ity ratio (HPV/PV) 0.7`, setback ratio (CPV/ surface erosion was shown to indicate a high
HPV) 1.94. Irish potato had a paste clarity of 4.9 degree of hydrolysis, whereas less surface ero-
and syneresis of 10.75 % based on 1 % and syn- sion indicated less degradation.
eresis on 5 % aqueous starch pastes. Irish potato Sweet potato SP1-W-YR variety showed the
had larger starch granules, higher phosphorus highest extracted starch with about 17.52 %, fol-
and lower amylose contents than sweet potato lowed by SP2-P-P cultivar with 15.54 % (Thao
starch. It also exhibited a lower gelatinization and Noomhorm 2011). The starches from all
temperature, higher swelling power and amylose sweet potato varieties were high in apparent amy-
leaching compared to sweet potato starch. Sweet lose content ranging from 28.06 to 34.52 %. The
potato starch exhibited a higher pasting tempera- protein content in starches from all sweet potato
ture, higher paste stability, and setback ratio and cultivars ranged from 0.15 to 0.23 % db, ash con-
greater stability to shear thinning than Irish tent was 0.110–0.282 % and lipid content in SP2-
potato starch. The rheological properties indi- P-P and SP3-P-Y starches, which was 0.084 and
cated non-Newtonian behaviour for the two 0.061 %, respectively. The protein and lipid
starch pastes. The storage and loss moduli of the played important roles in retention of amylose in
two starch pastes were frequency-dependent with starch noodles during cooking, resulting in mini-
values higher for sweet potato at all points within mizing cooking losses. For all sweet potato vari-
104 Convolvulaceae

eties, the starch granule shapes were with α-amylase activity in the first 60 days stor-
heterogeneous and no noticeable difference, age. Trypsin inhibitor activity (TIA) in the fresh
including small or largely polygonal and circle- roots varied among genotypes from 3.90 to 21.83
shaped particles. The mean length of SPS gran- U/mg. Storage had little influence on TIA level.
ules ranged from 14 to 17 μm. The pasting There was considerable genotypic variation in
temperature for sweet potato starches ranged digestibility, with up to 27 % reduction in digest-
from 80.1 °C (SP4-OP-O starch) to 82.3 °C (SP1- ibility after 120 days in storage. Glucose and
W-YR starch). The peak viscosity of all sweet sucrose concentration increased early in storage
potato starches ranged from 403.06 RVU for and then remained fairly constant. Storage
SP1-W-YR starch to 473.63 for SP4-OP-O reduced flour pasting viscosities, with up to
starch. Among sweet potato starches, SP1-W-YR nearly a 30 % decline in peak viscosity. Earlier,
starch was the most stable to temperature and Takahata et al. (1994) reported that although
shear treatment, followed by SP4-OP-O, SP2- β-amylase activity decreased with an increase in
P-P and SP3-P-Y starches in descending order. In temperature in all sweet potato lines, it had
another study, moisture, protein, ash, lipid and greater heat stability in the high maltose line than
phosphorus content of the starches from 11 sweet in the other lines. Starch gelatinization of high
potato cultivars varied from 3.86 to 6.52 %, 0.28 maltose lines occurred at a lower temperature
to 0.75 %, 0.10 to 0.47 % and 0.00 to 0.02 %, than did that of other lines. The flour and raw
respectively (Abegunde et al. 2013). Amylose starches isolated from red and white sweet potato
content varied between 13.33 and 26.83 %. The cultivars had high amylose content (32–34 %),
starches differed in their mean granule sizes, par- similar gelatinization characteristics with onset
ticle size distribution and susceptibility to pan- temperature of 67 °C and enthalpy of 10.5–
creatin hydrolysis. Swelling power and solubility 11.0 J/g and exhibited a Ca-type X-ray diffrac-
ranged from 13.46 to 26.13 g/g and 8.56 to tion pattern (Osundahunsi et al. 2003). Both
18.77 %, respectively. Higher retrogradation ten- starches had well-correlated and high solubiliza-
dency was observed in pastes of starches of high tion and swelling temperatures, starting at
amylose content. Gelatinization temperature and 80 °C. Pasting properties of the white cultivar
enthalpy ranged from 55.54 to 69.11 °C and 6.40 exhibit lower tendency for retrogradation. Water
to 11.89 J/g, respectively. Pasting properties and oil absorption capacities were low for both
including peak viscosity (134–255 BU), break- red and white flours. When parboiled, both culti-
down viscosity (91–162 BU), setback viscosity vars showed improved water absorption capacity
(26–112 BU), peak time (5.97–7.03 min) and and decreased least gelation concentration. It was
pasting temperature (67.20–73.00 °C) varied sig- concluded that the white cultivar should be pre-
nificantly among the sweet potato starches. ferred when low retrogradation tendency was
Phosphorus content of the starches had substan- required.
tial effect on their swelling power showing posi- Unit chain length distributions of amylopec-
tive correlations. There was significant positive tins and their φ,β-limit dextrins (reflecting amy-
correlation between swelling power and solubil- lopectin internal part) from 11 Chinese sweet
ity of the starches. Thermal and pasting parame- potato genotypes were characterized and found
ters also showed significant correlations. Zhang to be highly correlated to the thermal and pasting
et al. (2002) reported that most sweet potato gen- properties of granular starches (Zhu et al. 2011).
otypes in their study showed a slight decrease in The weight-based unit chain length profiles of
starch content during 0–180 days of storage, but whole amylopectin and their internal parts both
in the genotype Hi-dry, it decreased substantially. had three distinguishable major groups with
Alpha-amylase activity increased during the first approximate range of DP 6–36, 37–68 and >69
2 months of storage, followed by a decrease with for amylopectins and DP 3–25, 26–55, and >55
continued storage to a level similar to that at har- for φ,β-limit dextrins. Among different geno-
vest. The decline in starch content was correlated types, two different patterns of Bfp (fingerprint
Ipomoea batatas 105

B-chains, DP 3–7) were observed for φ,β-limit carotenoid of the following cultivars: Centennial,
dextrins, whereas Afp (fingerprint A-chains, DP Heart Gold, Anapolis, Acadian, Morada Inta,
6–8) for whole amylopectins were consistent. Vineland Bush and clone CNPH. Luteochrome
Reconstruction of amylopectins from their φ,β- was the principal carotenoid of Monalisa, IAC-
limit dextrins revealed that B-chains with internal 2-71 and SRT-252 cultivars. For raw roots, the
DP > 20 possessed an external chain length cor- vitamin A value varied from 1 retinol equiva-
responding to the average value DP 12.8. A lents/100 g for IAC-2-71 cultivar to 3703 retinol
pomegranate concept was proposed for sweet equivalents/100 g for Acadian. For cooked roots,
potato starch granule (Lian et al. 2012). Similar Acadian cultivar presented the highest provitamin
to the structure of pomegranate, out-layer of the A activity, with 4021 retinol equivalents/100 g.
starch granule was deemed equivalent to skin of A series of carotenoids with a 5,6-dihydro-5,6-
pomegranate, the double-helix blocklets repre- dihydroxy-β-end group, named ipomoeaxanthins
sented the garnet of pomegranate, the amylopec- A (1), B (2), C1 (3) and C2(4) were isolated
tin clusters with one reducing end at hilum, from the flesh of yellow sweet potato
equivalent to primary body of pomegranate, con- ‘Benimasari’ (Maoka et al. 2007). Their structures
stitute the basic structure of the starch granule, in were determined to be (5R,6S,3′R)-5,6-dihydro-
the special parts of the clusters, lots of blocklets β,β-carotene-5,6,3′-triol (1), (5R,6S,5′R,6′S)-
formed and increased, similar to the formation of 5,6,5′,6′-tetrahydro-β,β-carotene-5,6,5′6′-tetrol
garnet of pomegranate. (2),(5R,6S,5′R,8′R)-5′,8′-epoxy-5,6,5′,8′-tetrahydro-
β,β-carotene-5,6-diol (3) and (5R,6S,5′R,8′S)-
Carotenoids 5′,8′-epoxy-5,6,5′,8′-tetrahydro-β,β-carotene-
Major carotenes and epoxide derivatives identi- 5,6-diol (4).
fied in Centennial sweet potatoes included All-trans-β-carotene was the major provita-
β-carotene 86.35 %, phytoene 2.55 %, phytoflu- min A carotenoid in the roots and the mean con-
ene 1.95 %, ζ carotene 1.77 %, α-carotene 0.9 %, tent of seven improved orange-fleshed sweet
α-carotene 5′,6′-epoxide 1.05 %, luteochrome potato (OFSP) cultivars ranged from 108 to
0.21 %, mutatochrome 0.84 %, γ-carotene 0.77 %, 315 mg/g dry matter (Bengtsson et al. 2008). The
cis-γ-carotene 0.13 %, aurochrome 0.05 %, retention of all-trans-β-carotene was 78 % when
β-carotene 5,6,5′,6′-diepoxide 0.05 % and eight OFSP were boiled in water for 20 min. When
unknowns (Purcell and Walter 1968). Total caro- OFSP were steamed for 30 min the retention was
tene content determined was 0.13 mg/g fw or 77 %, whereas deep-frying OFSP roots for
0.45 mg/g dw. Monohydroxycarotenoids and 10 min resulted in retention levels of 78 %.
polyhydroxycarotenoids isolated from Centennial Drying slices of OFSP roots at 57 °C in a forced-
sweet potato were cryptoxanthin 5,6,5′6′-diepox- air oven for 10 h reduced the all-trans-β-carotene
ide 0.06 %, hydroxyl-α-carotene 5′,8′-epoxide content by 12 %. Solar drying and open-air sun
0.01 %, cryptoxanthin 5,6,5′,8′-diepoxide 0.25 %, drying OFSP slices to a moisture content of 10 %
cryptoxanthin 5,8-epoxide 1.10 %, hydroxyl–ζ- resulted in all-trans-β-carotene losses of 9 and
carotene 0.06 %, lutein 5,6-epoxide 0.17 %, cis- 16 %, respectively. The cis-isomer 13-cis-β-
violaxanthin 0.09 %, violaxanthin 0.06 %, 10 carotene was found in noticeable amounts in all
unknowns, 2 hydrocarbon mixtures and a mono- processed samples, but not in any raw samples.
hydroxy mixture. The formation of 13-cis-β-carotene correlated
Seven carotenoids: β-carotene; β-carotene- with the original amount of all-trans-β-carotene
5,6,5′6′-diepoxide; β-carotene-5,6-epoxide; found in the raw OFSP root. The main carotenoid
luteochrome; α-zeacarotene; β-zeacarotene and identified in Nigerian sweet potato varieties was
aurochrome were identified in 10 Brazilian raw pro-vitamin A carotenoid, (β-carotene) in its
and cooked sweet potatoes (Almeida-Muradian trans-cis isomers, namely: all-trans, 9-cis, 13-cis
and Penteado 1993). β-carotene was the main and 15-cis β-carotene isomers (Ukom et al.
106 Convolvulaceae

2011). Trans-β-carotene had the highest concen- method of processing (Vimala et al. 2011). The
tration in all four varieties followed by 9-cis-β- highest retention was observed in oven drying
carotene and 13-cis-β-carotene, respectively. (total carotenoids 90–91 % and β-carotene
Nitrogen fertilizer significantly increased trans- 89–96 %) followed by boiling (total carotenoids
cis isomers of β-carotene with incremental nitro- 85–90 % and β-carotene 84–90 %) and frying
gen fertilizer application up to 80 kg N/ha. (total carotenoids 77–85 % and β-carotene
From sweet potato variety CYY95-26, 72–86 %). The lowest retention of total carot-
278.1 mg/kg of β-carotene was extracted (Lien enoids (63–73 %) and β-carotene (63–73 %) was
et al. 2012). The major carotene of CYY95-26 recorded in the sun drying method. Studies by
was all-trans-β-carotene. CYY95-26 also con- Bechoff et al. (2010) found that losses of carot-
tained small amount of 9-cis-β-carotene and enoids (about 70 %) of orange-fleshed sweet
13-cis-β-carotene which were carotene isomers. potatoes during 4 months storage were consid-
Four Brazilian sweet potato cultivars presented ered to be more of a nutritional constraint to the
high levels of carotenoids in raw roots, utilization of dried sweet potato than losses
predominantly all-trans-β-carotene (79.1– occurring during drying (15 % or less). Two
128.5 mg/100 g DW) (Donado-Pestana et al. orange-fleshed varieties (Resisto and W-119)
2012). The other carotenoids in raw roots were contained significantly more β-carotene, chloro-
13-cis-β-carotene (8.8–9.6 mg), 9-cis-β-carotene genic acid and vitamin C than the two cream-
(4.9–6.1 mg), 5,6-epoxy-β-carotene (7.0– fleshed varieties (Bosbok and Ndou) (Rautenbach
11.3 mg), lutein (0.1–0.4 mg) and zeaxanthin et al. 2010). Thermal processing decreased the
(0.1–0.2 mg). The total phenolic compounds var- carotenoid and vitamin C content of all the vari-
ied among cultivars raw roots (1.30–1.93 mg eties, but increased the chlorogenic acid content
GAE/g DW), flour (0.96–1.56 mg/g) and heat and antioxidant capacity (ORAC, FRAP and
treatments (1.05–2.05 mg/g DW). In most cases, ABTS). Drought stress appeared to increase the
the heat treatments resulted in a significant β-carotene, vitamin C and chlorogenic acid con-
decrease in the carotenoids and phenolic com- tents as well as the antioxidant capacity of some
pounds contents as well as antioxidant capacity of the sweet potato varieties, especially W-119.
(DPPH and ABTS assays). Processing of flour
presented the greatest losses of major carotenoids Polysaccharides and Glycosides
and phenolics. The carotenoid profile of sweet Soluble pectins of sweet potatoes increased dur-
potato flour was all-trans-β-carotene (45.4– ing curing and protopectin decreased correspond-
79.7 mg/100 g DW), 13-cis-β-carotene (2.7– ingly (Heinze and Appleman 1943). At storage
4.7 mg), 9-cis-β-carotene (1.2–2.1 mg), temperature, the protopectin increased again
5,6-epoxy-β-carotene (3.8–6.5 mg), lutein (0.1– while pectin decreased. The polysaccharide
0.3 mg) and zeaxanthin (0.1–0.2 mg). Orange- PSPP (purified sweet potato polysaccharide), iso-
fleshed cv. Benihayto contained 18.7 mg/100 g lated and purified from sweet potato root, was
fresh weight of β-carotene comparable to US cul- found to be a (1→6)-α-D-glucan with a molecular
tivars (Takahata et al. 1993). The average retinol weight of 53.2 kDa (Zhao et al. 2005). Four poly-
equivalent of representative cultivars (Resisto, saccharide components named as PPSP, PPSPII,
Benihayto, Santo Amaro, Caromex and Red PPSPIII and PPSPIV were purified from purple
Jeweel) was 2.8 which equaled the maximum sweet potato (Jiang et al. 2011). PSPI was mainly
value of carrot cultivars. No carotenoids were composed of glucose and galactose, PPSP II was
found in the yellowish-white cultivars. Orange- composed of glucose and had a typical absorp-
fleshed sweet potato was found to have 85 μg/g tion peak of β-D-glucose chitosan pyranose, PPSP
all-trans-β-carotene and 4 μg/g α-carotene and III was a glycoprotein showing a protein absorp-
no lycopene (Pacheco et al. 2014). tion peak.
Studies found that the extent of retention of Batatins I (1) and II (2), two ester-type dimers
carotenoid in sweet potato roots varied with the of acylated pentasaccharides, were isolated from
Ipomoea batatas 107

the hexane-soluble extract of sweet potato solution pH 7.9. These conditions yielded about
(Escalante-Sánchez and Pereda-Miranda 2007). 10.24 % of pectin vs. 10.27 % for the predicted
Both polymers 1 and 2 represented dimers of value. The degree of esterification and gel
compound batatinoside I, a new polyacylated strength of extracted pectin with disodium phos-
macroyclic pentasaccharide also isolated from phate solution in the optimized condition were
the plant. The hexane-soluble extract from sweet 11.2 % and 115.6 g, respectively.
potato roots yielded five new lipophilic oligosac- Linalyl-β-glucoside (LBG), α-terpinyl-β-
charides of jalapinolic acid, batatinosides II-VI glucoside (TBG), neryl-β-glucoside (NBG) and
(1–5), as well as the known pescapreins I (6) and geranyl-β-glucoside (GBG) in sweet potatoes
VII (7) and murucoidin I (8), which are part of were identified as trimethylsilyl derivatives (Ohta
the purgative resin glycoside mixture (Escalante- et al. 1991). Amounts of these monoterpene
Sánchez et al. 2008). Compounds 1 and 2 were alcohol-β-glucosides were from 36.9 μg/kg sweet
tetraglycosidic lactones of operculinic acid potato of LBG to 189 μg/kg sweet potato of
C. The pentasaccharide structures for compounds TBG. In contrast, 75.8 μg/1 distillation residue of
3 and 4 were confirmed to be macrolactones of TBG and traces of other monoterpene alcohol-β-
simonic acid B, and that characterized for 5 was glucosides occurred in the distillation residue.
derived from operculinic acid A. All compounds β-glucosidase (β-D-glucoside glucohydrolase) in
contained an esterifying residue that was com- shiro-koji were purified using p-nitrophenyl-β-
posed of a long-chain fatty acid, n-decanoic acid glucoside (PNPG), and three active fractions, one
(capric) or n-dodecanoic acid (lauric). In com- major fraction and two very minor fractions,
pound 3, an additional short-chain fatty acid, were found. hiro-koji β-glucosidases were active
(2S)-methylbutyric acid, was also identified. on tested β-glucosides except for LBG and
Batatins III–VI (1–4), glycolipid ester-type TBG. Five new ether-soluble resin glycosides
dimers, were isolated from sweet potato tuberous (jalapins), simonins I–V, were isolated from
roots (Rosas-Ramírez et al. 2011). These ester- sweet potato roots (Noda et al. 1992). Simonin I
type dimers consisted of two units of the hetero- was characterized as an example of resin glyco-
tetrasaccharide operculinic acid C. Each unit was side with aromatic acid (trans-cinnamic acid) as
esterified by a different amount and type of acid a component organic acid.
residues: (2S)-methylbutanoic, cinnamic, deca- Two new resin glycosides, batatosides I and II,
noic (capric) and dodecanoic (lauric) acids. and five known compounds, friedelin, scopoletin,
Purification of the chloroform-soluble resin gly- octadecyl caffeate, β-sitosterol and daucosterol,
cosides from yellow-skinned sweet potato roots were isolated sweet potato roots (Yin and Kong
yielded six oligosaccharides, batatin VII (1) and 2008). Three new pentasaccharide resin glycosides,
batatinosides VII–IX (2–4), together with the batatosides III–V (1–3), were isolated from sweet
known resin glycosides pescaprein I and bata- potato (Yin et al. 2008a). Batasin III was elucidated
tinoside IV (Rosas-Ramírez and Pereda-Miranda as (S)-jalapinolic acid 11-O-α-L-rhamnopyranosyl-
2013). Operculinic acid A was identified as pen- (1→3)-O-[3-O-trans-4-O-(S)-2-methylbutyryl-α-L-
tasaccharide glycosidic core structure for com- rhamnopyranosyl-(1→4)]- O -[2- O- ( S )-2-
pounds 2 and 4, and simonic acid B for 3. Batatin methylbutyryl]-α-L-rhamnopyranosyl-(1→4)-O-α-
VII (1) represented a dimer of the known bata- L-rhamnopyranosyl-(1→2)-O-β-D-fucopyranoside,
tinoside IV, consisting of two units of simonic intramolecular 1,2″-ester. Batatoside IV was
acid B. Four factors were found to significantly elucidated as (S)-jalapinolic acid 11-O-α-L-
affect the pectin yield from sweet potato in the rhamnopyranosyl-(1→3)-O-α-L-rhamnopyranosyl
following order: solution pH > extraction time > (1→4)]- O -[2- O -( S )-2-methylbutyryl]- α - L -
extraction temperature > liquid/solid ratio (Zhang rhamnopyranosyl-(1→4)-O-α-L-rhamnopyranosyl-
and Mu 2011). The selected optimal extraction (1→2)-O-β-D-fucopyranoside, intramolecular
conditions were liquid/solid ratio 20:1, extraction 1,3″-ester. Batatoside V was characterized as (S)-
time 3.3 h, extraction temperature 66 °C and jalapinolic acid 11-O-α-L-rhamnopyranosyl-
108 Convolvulaceae

(1→3)-O-[2-O-trans-cinnamoyl-4-O-n-decanoyl- methylbutyric, trans-cinnamic and n-decanoic

α - L -rhamnopyranosyl-(1→4)]- O -[2- O-n - acids.
dodecanoyl]-α-L-rhamnopyranosyl-(1→4)-O-α-L-
rhamnopyranosyl-(1→2)-O-β-D-fucopyranoside, Proteinaceous Compounds
intramolecular 1,3″-ester. Seven new resin glyco- Ipomoein, a globulin, was isolated from sweet
sides, batatosides A–G, along with two known com- potato by enzymic action and found to have prop-
pounds, batatinoside I and simonin IV were isolated erties similar to those of albumin (Jones and
from the tubers (Yin et al. 2008b). Four compounds Gersdorff 1931). Sucrose synthetase with molec-
were isolated from sweet potato and identified as ular weight of 540,000 was isolated from sweet
citrusin C, caffeic acid, 3,4-di-O-caffeoylquinic potato roots (Murata 1971). The enzymes were
acid and 1,2,3,4-tetrahydro-β-carboline-3-carboylic postulated to be involved in the breakdown of
acid (Yin et al. 2008c). Nine new lipo- sucrose in sweet potato root tissues instead of the
oligosaccharides, batatosides H–P, were isolated sucrose-synthesizing reaction. A marked rise in
from sweet potato tubers (Yin et al. 2009). They the phenylalanine ammonia-lyase activity and
were characterized as tetra- or pentasaccharides that the polyphenol synthesis was observed in sliced
formed a macrolactone with the aglycone, (11S)- roots of a sweet potato (Minamikawa and Uritani
hydroxyhexadecanoic acid (jalapinolic acid). Six 1965). The enzyme activity was found to be
compounds batatinoside I, citrusin C, octadecyl localized in the root tissue adjacent to the sliced
caffeate, β-amyrin acetate, caffeic acid and scopole- surface. The results suggested the important role
tin were isolated from the chloroform extract of of phenylalanine ammonia-lyase in the polyphe-
sweet potato tubers (Yin et al. 2012). nol synthesis and de novo synthesis of the enzyme
Two known ether-soluble resin glycosides protein molecule in the sliced tissues.
simon IV and operculin VII were isolated from Phenylalanine ammonia-lyase (PAL) was not
sweet potato roots with four new glycosides present in fresh sweet potato tissue, but appeared
which were tetra- or pentasaccharide monomers in in response to cut injury, reaching a maximum,
which the sugar moieties were partially acylated and then decreasing, in parallel with PAL activity
by organic acids and combine with the aglycone, (Tanaka and Uritani 1976, 1977).
jalapinolic acid, to form a macrocyclic ester Under all curing conditions, NPN increased
(Noda and Horiuchi 2008). Compound I was and protein N decreased indicating protein hydro-
characterized as (11S)-[[O-4-O-n-dodecanoyl-α- lysis, which was higher at higher curing tempera-
L -rhamnopyranosyl-(1→4)-O -2-O-n -decanoyl- tures. Fairly consistent increases in basic N,
α-L-rhamnopyranosyl-(1→4)-O-α-L- amide N, residual N occurred in all lots, but a
rhamnopyranosyl-(1→2)- β - D - fucopyranosyl] consistent increase in amino-N occurred only in
oxy]-jalapinolic acid, intramolecular 1,2-ester those lots cured at high temperatures of 35 and
(1) and compound 2 elucidated as (11S)-[[O-α-L- 40 °C. The nitrogen distribution during storage at
rhamnopy-ranosyl-(1→3)- O -[(2- O - trans - 10–12 °C remained fairly stable during storage.
cinnamoyl)-(4-O-isobutanoyl) The amide N, basic N and residual N increased
a- L -rhamnopyranosyl-(1→4)]- O -2- O -(2 S )- slightly in most lots towards the end of storage
methylbuthanoyl-α-L-rhamnopyranosyl-(1→4)- period. A temperature of 30 °C was found opti-
O-α-L-rhamnopyranosyl-(1→2)-β-D- mal for curing; higher temperature was unsuit-
fucopyranosyl]oxy]-jalapinolic acid, able because of internal break down during
intramolecular 1,2-ester. Compounds 3 and 4 curing. Nearly half of the nitrogen contained in
consisted of the same glycosidic acid, simonic sweet potato may be recovered as a concentrate
acid B and differed only in the organic acid resi- containing > 80 % protein, which were found to
due; compound 3 had isobutyric, trans-cinnamic be limiting in sulphur-containing amino acids but
and n-decanoic acids, while compound 4 had having excess of lysine (Purcell et al. 1978).
Ipomoea batatas 109

Highly polymerized free polysomes were formed starch phosphorylase. β-Amylase was abundant
in sweet potato root tissue in response to wound- throughout the root at all times, and its high lev-
ing (Oba et al. 1982). The degree of polymeriza- els did not directly affect starch degradation
tion also increased to greater than 15-mers. rates. Starch phosphorylase protein level
Polysomes were organized from pre-existing free remained constant, while its extractable activity
ribosomes in fresh tissues immediately after increased. Starch content decreased during sweet
wounding; synthesis of new ribosomes may potato seed root germination.
occur after 6 h when the rate of polysome forma- Two forms of trypsin inhibitors with molecu-
tion decreased. lar weights of 31 and 21 kDa were found in sweet
Ipomeamarone 15-hydroxylase was found to potato roots and they were different from those
be a cytochrome P-450-dependent, mixed- found in the leaves (Wang and Yeh 1996). The
function oxygenase (Fujita et al. 1982). Its activ- level of trypsin inhibitory activity was closely
ity was found in a microsomal fraction from related with pest resistance. Trypsin inhibitors
cut-injured and Ceratocystis fimbriata-infected (TIs) (73, 38 and 22 kDa) were purified from
sweet potato root tissues, but was not found in storage roots, sprouted roots and sprouts of sweet
fresh tissue of sweet potato roots. The major sol- potato variety Tainong 57 (Hou and Lin 1997b).
uble protein of sweet potato roots had an appar- Polyamines cadaverine, spermidine and sperm-
ent molecular weight of 25 KDa and accounted ine were found in all TI hydrolysates with differ-
for 60–70 % of the total soluble protein extracted ent amounts in storage roots, sprouted roots and
from fresh tissue (Li and Oba 1985). This protein sprouts. TIs purified from the sprouts had higher
was identified as antigenic component A which polyamine titers, which were expressed as nmol/
was degraded into peptides of lower molecular μg protein, than those from sprouted roots or
weights (9500–20,000) after storage, cutting or storage roots. Trypsin inhibitors from sweet
fungal infection of the roots. Another major pro- potato were found to have dehydroascorbate
tein, β-amylase, was also identified. Cutting, reductase and monodehydroascorbate reductase
infection or storage of root tissue also resulted in activities (Hou and Lin 1997b). Sweet potato
the production of new isozymes of peroxidase, trypsin inhibitor (SPTI) exhibited thioltransferase-
acid phosphatase and esterase. Acid phosphatase like and glutathione S-transferase (Huang et al.
of sweet potato root tissue was found to consist 2009). Trypsin inhibitor with molecular weight
of five components (Asahi et al. 1967). All com- 23 kDa was purified from sweet potato (Jaw et al.
ponents hydrolyzed various phosphate com- 2007). A proteinaceous invertase inhibitor, desig-
pounds including phosphomonoester- and nated ITI-L, with molecular weight of 10 kDa
pyrophosphate-linkages. Their optimum pH val- was purified from sweet potato leaves. It was
ues were in the range of pH 5 to 6. In sweet potato thermostable (90 % of the activity remained after
root tissue, cinnamic acid 4-hydroxylase activity incubation at 100 °C for 20 min) (Wang et al.
increased markedly in response to cut injury, and 2003).
reached a maximum after 1 day of incubation Sweet potato tuberous roots contained large
(Tanaka et al. 1974). The patterns of development quantities of two proteins named sporamins A
and successive decline were similar to those for and B, were monomeric forms with similar M,s
phenylalanine ammonia-lyase activity. The (25,000) (Maeshima et al. 1985). They were very
enzyme may be involved in the cytochrome similar to each other with respect to amino acid
P-450 mediated electron transport system. Sweet composition, peptide map and immunological
potato storage roots were found to contain high properties. Sporamin was found to account for
amounts of extractable amylolytic enzymes more than 80 % of the total soluble proteins of
(Hagenimana et al. 1994). These storage roots tuberous roots of sweet potato, but very little, if
also have a very high starch content. Three major any, in other tissues of the same plant (Hattori
amylolytic enzymes were identified in sweet et al. 1985; Maeshima et al. 1985). Northern blot
potato storage roots: α-amylase, β-amylase and analysis showed that sporamin mRNA is approx-
110 Convolvulaceae

imately 950 nucleotides in length and is specifi- to have the highest level in the storage roots;
cally present in tuberous roots and very little, if those corresponding to TRX2 and TRX3 were
any, in leaves, petioles and non-tuberous roots. detected at the next higher level in flowers. In
Nucleotide sequence of the cDNA predicted a 37 Western blot analysis, the thioredoxins were
amino acid extension in the precursor at the found to have the highest level in the storage
amino-terminus of the mature protein. Sporamin roots and veins, higher level in leaves, and very
consisted of two polypeptide classes, A and B low levels in sprouts of storage root and roots.
(Maeshima et al. 1985; Murakami et al. 1986). The three thioredoxin h genes of sweet potato
The sporamin cDNA clones could also be classi- storage roots displayed differential gene expres-
fied into sporamin A and B sub-families based on sion patterns, which may be associated with the
their sequence homologies, with intra-sub-family diverse roles and functions. Sweet potato storage
homologies being much higher than inter-sub- root thioredoxin h2 was found to have dehydro-
family homologies. Sporamin, a vacuolar storage ascorbate (DHA) reductase and monodehydro-
protein of tuberous roots of sweet potato, was ascorbate (MDA) reductase activities (Huang
synthesized by membrane-bound polysomes as a et al. 2008a).
precursor which contained a 16 amino acids-long An arabinogalactan-protein (WSSP-AGP) with
propeptide that follows the N-terminal signal weight-average molecular weight of 126,800 g/
peptide (Nakamura et al. 1993). A precursor to mol was isolated from the tuberous cortex of the
sporamin, expressed in transformed cells of white-skinned sweet potato (Ozaki et al. 2010). It
tobacco suspension-cultured cell line BY-2, was was found to consist of 95 % (w/w) carbohydrate
sequentially processed from the N-terminus and and 5 % (w/w) protein with high contents of
correctly targeted to the vacuole. Sporamin com- hydroxyproline, alanine and serine and sugar com-
prised two distinct homology groups, sub- position of α-L-Rha:α-L-Ara:β-D-Gal:β-D-GlcA in
families A and B (Sun et al. 2009). Sporamin B a molar ratio of 1.0:4.1:7.6:1.3. Structural analysis
Q40091|Q40091_IPOBA was isolated as the indicated that WSSP-AGP is a (1→3)-β-D-galactan
major sporamin B from sweet potato cv. 55-2 highly branched at O-6 with (1→6)-β-D-galactan,
tuber and found to have potent trypsin inhibitory in which the branched chains are substituted at the
activity. Sporamin accounts for about 60–80 % of O-3 position with α-L-Araf-(1→ and α-L-Araf-
total soluble protein in sweet potato tubers, and (1→5)-α-L-Araf-(1→ and at the O-6 position typi-
possessed significant amino acid sequence iden- cally with α-L-Rhap-(1→4)-β-D-GlcAp-(1→ as
tity with some Kunitz-type trypsin inhibitors terminating groups.
(Yeh et al. 1997). It was suggested that sporamin Potentially valuable proteins could be
may have a defense role as a protease inhibitor, in extracted from sweet potato peel, a waste product
addition to its role as a storage protein. Sporamin of sweet potato processing (Maloney et al. 2012).
was reported to be constitutively expressed in the The highest yield of protein extraction was
tuberous root and not normally expressed in the obtained by mixing blanched sweet potato peel-
stem or leaves, but this protein was expressed ings with 59.7 mL of 0.025 mM NaCl per g peel
systemically in response to wounding and other and then precipitating with 6.8 mM CaCl2. More
abiotic stresses (Senthilkumar and Yeh 2012). than 370 protein spots in sweet potato tuberous
These dual expression patterns at the transcrip- roots were reproducibly detected by two-
tional level revealed that the complex regulatory dimensional gel electrophoresis, in which 35
mechanism of sporamin was modulated by envi- spots were upregulated (orange-fleshed cv Yulmi
ronmental stresses. vs. purple-fleshed cv. Shinjami) or uniquely
Three full-length cDNA clones, designated expressed (only Yulmi or Shinjami) in either of
TRX1, TRX2 and TRX3 encoding different but the two cultivars (Lee et al. 2012). Of these 35
similar thioredoxin h polypeptides, were isolated protein spots, 23 were expressed in Yulmi and 12
from sweet potato storage roots (Huang et al. were expressed in Shinjami. Fifteen proteins
2004a). All three thioredoxin genes were found were identified in Yulmi and eight proteins in
Ipomoea batatas 111

Shinjami. The proteins identified in Yulmi were the highest in the storage roots, followed by that
catechol oxidase I, putative oxalyl-CoA decar- in sprout. In the Japanese purple-fleshed sweet-
boxylase, α-amylase, 2 semialdehyde dehydro- potato cultivar, Ayamurasaki, which accumulated
genase family protein, disulfide-isomerase anthocyanin in the storage roots, three types of
precursor-like protein, anionic peroxidase swpa, IbMYB1 gene sequences, named IbMYB1-1,
putative beta-1,3-glucanse precursor, cysteine IbMYB1-2a and IbMYB1-2b were found
proteinase inhibitor (phytocystatin), amino acid whereas in the spontaneous mutant, AYM96,
transporter, sporamin A precursor, sporamin B, lacking anthocyanin, only IbMYB1-1 was found
unnamed protein product and 3 unknown protein. (Tanaka et al. 2012). An IbGrx cDNA encoding a
The proteins identified in cv Shilmi were PSG- putative dithiol glutaredoxin was cloned from
RGH7 resistance protein, 2 sporamin B precur- sweet potato (Chi et al. 2012). Glutaredoxins
sor, flavanone 3-hydroxyrase, aldo-ketose play an important role in the reduction of protein
reductase, peroxidase precursor and two unknown glutathione-mixed disulphides
protein. In Yulmi, α-amylase and isomerase In response to fungal infection, protein
precursor-like protein were uniquely expressed increased 10–30 % in diseases tissues and pro-
or upregulated and activities of α-amylase, mono- teins of supernatant, mitochondrial and micro-
dehydroascorbate reductase and dehydroascor- somal fractions (Uritani and Stahmann 1961). In
bate reductase were higher than in Shinjami. In diseased tissues, free amino acids namely leu-
Shinjami, peroxidase precursor and aldo-keto cine, isoleucine, proline, valine, tyrosine and
reductase were uniquely expressed or upregu- lysine were increased with a concomitant
lated and peroxidase and aldo-keto reductase decrease of amides and alanine. New antigenic
activities were higher than in Yulmi. PSG-RGH7 components were detected in the infection site of
resistance protein uniquely expressed only in cv. resistant cultivar. One such compound was iden-
Shinjami was evaluated more resistant than cv. tified as a peroxidase. Microsomes, especially
Yulmi against the root-knot nematode, 73S units, were increased following infection as
Meloidogyne incognita on the basis of shoot and compared to healthy tissues. The IPO (ipomoe-
root growth. Egg mass formation was 14.9-fold lin) wound-inducible gene was isolated from
less in Shinjami than in Yulmi. A cDNA encod- sweet potato cv Tainung 57 (Jih et al. 2003).
ing a small cysteine-rich protein designated When sweet potato was wounded, both hydrogen
defensin (SPD1) was isolated from sweet potato peroxide and nitric oxide were produced to regu-
storage roots (Huang et al. 2008c). It was found late the expression of the IPO gene and enhance
that defensin (SPD1) had both dehydroascorbate the plant’s defense system. Ipomoelin, one of the
(DHA) reductase and monodehydroascorbate wound-inducible proteins of sweet potato, was
(MDA) reductase activities. SPD1 was also found to be a Jacalin-related lectin that possessed
shown to inhibit the growth of both fungi and carbohydrate-binding properties and may play a
bacteria. A defensin protein (SPD1) with antioxi- role in plant defense (Chang et al. 2012). IPO
dant activities in-vitro and ex-vivo was isolated showed high binding ability to methyl α-D-
from sweet potato storage roots (Huang et al. mannopyranoside (Me-Man), methyl α-D-
2012). glucopyranoside (Me-Glc), and methyl
A novel cyclophilin-type peptidylprolyl isom- α-D-galactopyranoside (Me-Gal) forming carbo-
erase protein (SPPPI) was isolated from sweet hydrate complexes.
potato storage roots (Liao et al. 2012). This
cDNA encoded a pro-protein of 260 amino acids Cytokinins
with a predicted molecular mass of 27,658 Da. The cytokinins, 9-β-D-glucopyranosyl-6-(3-
Genomic Southern blot analyses using the full- methyl-2-butenylamino)purine (IPG) (Hashizume
length SPPPI cDNA probe revealed a multi-gene et al. 1982a) and cis-zeatin riboside (236 ng/kg)
family in the sweet potato genome. Both the cor- were isolated and identified from sweet potato
responding mRNA and protein level were found tubers (Hashizume et al. 1982b). Three major
112 Convolvulaceae

cytokinins were isolated from sweet potato Phenolic Compounds

ribosyl 9-β-D-ribosyl trans-zeatin (trans- RZ), and Anthocyanins
9-β-D-ribosyl cis zeatin (cis-RZ) and 9-β-D- Two major anthocyanins in purple sweet potato
glucopyranosyl-6-(3-methyl-2-butenylamino) were identified as cyanidin 3-caffeylferulysophor
purine (IPG) (Suye et al. 1983). RZ = 9-β-D- oside-5-glucoside of cyanidin and peonidin
ribofuranosyl-6-(4-hydroxy-3-methyl-2- - 3-caffeylferulysophoroside-5-glucoside (Odake
butenylamino)purine. The presence and levels et al. 1992). Two major pigments and two minor
of 14 cytokinin species were determined in pigments were found in fresh sweet potato tissue
the developing tuberous roots of sweet slices, the major pigments were identified as
potato (Sugiyama and Hashizume 1989). The peonidin-3-diglucoside-5-glucoside with three
following structures were assigned: trans- molecules of ferulic acid and one molecule
and cis-zeatin, trans- and cis-ribosylzeatin, of caffeic acid and peonidin-3-diglucoside-5-
trans- and cis-glucosylzeatin, trans- and cis-2- glucoside with two molecules of ferulic acid
methylthioribosylzeatin, dihydrozeatin riboside, and one caffeic acid (Shi et al. 1992). Two
N6-isopentenyladenine, N6-isopentenyladenosine, new acylated anthocyanins isolated from
9-glucosyl-N6-isopentenyladenine and trans- and sweet potato storage roots were identified as the
cis-zeatin riboside. Trans-zeatin, trans-zeatin 3-O-(6-O-trans-caffeyl-2-O-β-glucopyranosyl-
riboside and N6-(δ2-isopentenyl)adenosine β-glucopyranoside)-5-O-β-glucoside of cyanidin
6
(i Ado) were found to be the major cytokinins in and peonidin (Goda et al. 1997). Among
the small tubers (≤5 mm diameter) of sweet nine anthocyanins isolated from purple
potato (Matsuo et al. 1983). During tuber devel- sweet potatoes, the structures of three major
opment, cytokinin levels were high in tubers hav- anthocyanins were elucidated as 3-O-(6-O-trans-
ing a diameter below 12 mm, minimal in tubers caffeyl)-2-O-(6-O-trans-caffeylglucopyransoyl-
with a diameter of 22.5 mm and then gradually β-D-glucopyranosyl-5-O-(β-D-glucopyranosyl)-
increased as the tuber developed. The presence peonidin; 3-O-(6-O-trans-caffeyl)-2-O-(6-O-
and levels of trans- and cis-ribosyl zeatin, trans-feruloylglucopyransoyl-β-D-
trans- and cis-zeatin, N6-isopentenyladenosine glucopyranosyl-5- O -( β - D -glucopyranosyl)-
and 6-(3-methyl-2-butenylamino)-9-β-D-gluco- peonidin; and 3-O-(6-O-trans-caffeyl)-2-O-(6-
pyranosylpurine were determined in the root, and O-p - hydroxylbenzoylglucopyranosyl- β - D -
the stem and leaf of young sweet potato plants glucopyranosyl-5- O -( β - D -glucopyranosyl)-
(Sugiyama et al. 1983). The level of 6-(3-methyl- peonidin (Lee et al. 1997). Eight acylated
2-butenylamino)-9- β - D - glucopyranosylpurine anthocyanins were isolated from purple sweet
was found to be the highest in both the root, and potato storage roots; of these, six pigments were
the stem and leaf. trans-ribosyl zeatin were pres- identified as diacylated anthocyanins of cyanidin
ent at a high level in the root. The ratio of the and peonidin: cyanidin 3-O-(2-O-(6-O-p-
trans- and cis-isomers of zeatin in the root, and in hydroxybenzoyl-β-D-glucopyranosyl)-6-O-(E)-
the stem and leaf were determined to be 10 and c a ff ey l - β - D - g l u c o p y r a n o s i d e ) - 5 - O - β - D -
2.4, respectively. Matsuo et al. (1988) found the glucopyranoside; cyanidin 3-O-(2-O-(6-O-(E)-
levels of (i6Ado) and abscisic acid (ABA) were caffeyl- β - D -glucopyranosyl)-6- O -( E )-caffeyl-
much lower than that of trans-ZR throughout β-D-glucopyranoside)-5-O-B-D-glucopyranoside;
tuber development. The longitudinal distribution cyanidin 3-O-(2-O-(6-O-(E)-ferulyl-β-D-gluco-
of the cytokinins and ABA in the developing p y r a n o s y l ) - 6 - O - ( E ) - c a ff ey l - β - D - g l u c o -
sweet potato tubers showed that the level of IPG pyranoside)-5-O-B-D-glucopyranoside; and
was higher than trans-RZ and the levels of trans- peonidin 3-O-(2-O-(6-O-(E)-ferulyl-β-D-gluco-
ZR were higher in parts of the proximal side of pyranosyl)-6- O -( E )-caffeyl- β - D -glucopyrano-
the stem than in other lower parts of the tubers. side-5-O-B-D-glucopyranoside; peonidin 3-O-
The level of IPG was higher than trans-RZ with (2-O-(6-O-(E)-caffeyl-β-D-glucopyranosyl)-6-O-
maximum level of 270 μg/kg fresh weight. ( E )-caffeyl- β - D -glucopyranoside)-5- O - B - D -
Ipomoea batatas 113

glucopyranoside; and peonidin 3-O-(2-O-(6- phoroside-5-glucoside; cyanidin 3-feruloyl-p-co

O-p-hydroxybenzoyl-β-D-glucopyranosyl)-6-O- umarylsophoroside-5-glucoside; cyanidin 3-(6″,
( E )-caffeyl- β - D - glucopyranoside)-5- O - B - D - 6′′′-dicoumarylsophoroside)-5-glucoside, peoni-
glucopyranoside (Terahara et al. 1999). The din 3-feruloyl-p-coumarylsophoroside-5-
following anthocyanins were isolated and identi- glucoside; peonidin 3-(6″, 6″′-dicoumarylso-
fied from a highly pigmented callus induced from phoroside)-5-glucoside and two unidentified
the storage root of purple-fleshed sweet potato compounds (Tian et al. 2005). Four Japanese
cultivar Ayamurasaki: cyanidin 3-O-sophoroside- purple sweet potato cultivars were categorized
5-O-glucoside; 3-O-(2-O-(6-O-(E)-p-coumaroyl- into two groups based on variation in two major
β-D-glucopyranosyl)-β-D-glucopyranoside)-5-O- pigments, cyanidin-3-(6′′-caffeoylsophoroside)-
β-D-glucopyranoside (Terahara et al. 2000); 5-glucoside and peonidin-3-(6′′-caffeoylso-
cyanidin 3-O-(2-O-(6-O-(E)-caffeoyl-β-D-gluco- phoroside)-5-glucoside; the cultivars Chiran
pyranosyl)- β - D -glucopyranoside)-5- O - β - D - Murasaki and Purple Sweet showed a high con-
glucopyranoside; cyanidin 3-O-(2-O-(6-O-(E)- tent of peonidin derivatives (peonidin type),
p -coumaroyl- β - D -glucopyranosyl)-6- O -( E )- whereas the varieties Tanegashima Murasaki and
caffeoyl- β - D -glucopyranoside)-5- O - β - D - Naka Murasaki were classified as cyanidin types
glucopyranoside; cyanidin 3-O-(2-O-(6-O- (Montilla et al. 2010). The non-acylated 3-sopho-
(E)-p-coumaroyl-β-D-glucopyranosyl)-6-O-(E)- roside-5-glucoside of cyanidin, the monoacylated
p -coumaroyl- β - D -glucopyranoside)-5- O - β - D - cyanidin-3-(6′′-caffeoylsophoroside)-5-
glucopyranoside; and peonidin 3-O-(2-O-(6-O- glucoside as well as three diacylated major pig-
(E)-p-coumaroyl-β-D-glucopyranosyl)-6-O-(E)- ments,cyanidin-3-(6′′,6′′′-dicaffeoylsophoroside)-
p -coumaroyl- β - D -glucopyranoside)-5- O - β - D - 5-glucoside, cyanidin-3-(6′′-caffeoyl-6′′′-p-
glucopyranoside (Terahara et al. 2004). hydroxy-benzoylsophoroside)-5-glucoside and
Twenty-six anthocyanins were detected and peonidin-3-(6′′-caffeoyl-6′′′-p-hydroxybenzoyl-
characterized in the aqueous extract of a purple sophoroside)-5-glucoside were also isolated.
line cell line generated from the storage root Four anthocyanins were isolated and purified
of purple-fleshed sweet potato (Ipomoea batatas from purple sweet potato: peonidin 3-O-(6-O-(E)-
cv. Ayamurasaki): cyanidin 3-sophoroside-5- c a ff e o y l - 2 - O - β - D - g l u c o p y r a n o s y l - β - D -
glucoside; cyanidin 3,5-diglucoside; pelargonidin glucopyranoside)-5-O-β-D-glucoside (1), cyani-
3-sophoroside-5-glucoside; peonidin 3-sophoro- din 3-O-(6-O-p-coumaroyl)-β-D-glucopyranoside
side-5-glucoside; cyanidin 3-p-hydroxybenzoyl- (2), peonidin 3-O-(2-O-(6-O-(E)-caffeoyl-β-D-
sophoroside-5-glucoside; cyanidin 3-(6″- g l u c o p y r a n o s y l ) - 6 - O - ( E ) - c a ff e o y l - β - D -
caffeoylsophoroside)-5-glucoside; peonidin 3-p- glucopyranoside)-5-O-β-D-glucopyranoside (3),
hydroxybenzoylsophoroside-5-glucoside; peoni- peonidin 3-O-(2-O-(6-O-(E)-feruloyl-β-D-gluco-
din 3-caffeoylsophoroside-5-glucoside; cyanidin pyranosyl)-6-O-(E)-caffeoyl-β-D-
3-(6″- p -coumarylsophoroside)-5-glucoside; glucopyranoside)-5-O-β-D-glucopyranoside (4)
cyanidin 3-(6″-feruloylsophoroside)-5-gluco- (Qiu et al. 2009). The purities of 1–4 were 95.5,
side; peonidin 3-(6″-p-coumarylsophoroside)-5- 95.0, 97.8 and 96.3 %, respectively. The follow-
glucoside; peonidin 3-(6″-feruloylsophoroside)-5- ing anthocyanins were found in purple sweet
glucoside; pelargonidin 3-feruloylsophoroside- potato: cyanidin-3-sophoroside-5-glucoside;
5-glucoside;cyanidin3-(6″,6′′′-dicaffeoylsophoroside)- peonidin-3-sophoroside-5-glucoside; cyanidin-
5-glucoside; cyanidin 3-caffeoylsophoroside- 3-(6″,6′′′-dicaffeoylsophoroside)-5-glucoside;
5-glucoside; cyanidin 3-(6″-caffeoyl-6′′′- cy a n i d i n - 3 - ( 6 ″ - c a ff e oy l - 6 ‴ - p - h y d r o x y -
feruloylsophoroside)-5-glucoside; cyanidin 3- benzoylsophoroside)-5-glucoside; cyanidin-3-
caffeoyl- p -coumarylsophoroside-5-glucoside; ( 6 ″ - c a ff e o y l s o p h o r o s i d e ) - 5 - g l u c o s i d e ;
peonidin3-caffeoyl-p-hydroxybenzoyl-sophoroside- cy a n i d i n - 3 - ( 6 ″ - c a ff e oy l - 6 ‴ - f e r u l oy l s o -
5-glucoside; peonidin 3-caffeoylsophoroside-5-g phoroside)-5-glucoside; peonidin-3-(6″,6‴-
lucoside; peonidin 3-feruloyl-p-caffeoylso- dicaffeoylsophoroside)-5-glucoside;
114 Convolvulaceae

p e o n i d i n - 3 - ( 6 ″ - c a ff e oy l s o p h o r o s i d e ) - 5 - were cyanidin-caffeoy-fumaroysophoroside-3-O-
glucoside; peonidin-3-(6″-caffeoyl-6‴-p-hydroxy- glucoside, peonidin-caffeoyl-hydroxybenzoyl-3-
benzoylsophoroside)-5-glucoside; and peonidin- O-glucoside, peonidin-caffeoyl-sophoroside-3-
3-(6″-caffeoyl-6‴-feruloylsophoroside)-5- O-glucoside and peonidin-caffeoyl-fumaroyl-
glucoside (Montilla et al. 2011). Seventeen sophoroside-3-O-glucoside (Liu et al. 2013). A
anthocyanins were identified in purple-fleshed dimer of galloyl procyanidin was also found.
Stokes Purple and NC 415 varieties with five Purple-fleshed sweet potato P40 cultivar con-
major compounds: cyanidin 3-caffeoylsophorosi tained anthocyanins up to 13 mg/g dry matter and
de-5-glucoside; peonidin 3-caffeoylsophoroside- a total 12 acylated anthocyanins were identified:
5-glucoside; cyanidin 3-caffeoyl-p-hydroxy- cyanidin 3-caffeoyl-p-hydroxybenzoyl sophoro-
benzoylsophoroside-5-glucoside; peonidin 3- side-5-glucoside (16.43 %), peonidin 3-caffeoyl
caffeoyl- p -hydroxybenzoyl-sophoroside- 5- sophoroside-5-glucoside (19.72 %), cyanidin
glucoside and peonidin-caffeoyl-feruloylso- 3-(6″-caffeoyl-6″-feruloylsophoroside)-5-gluco-
phoroside-5-glucoside (Truong et al. 2010). The side (12.10 %), cyanidin 3-sophoroside-5-gluco-
other anthocyanin compounds were cyanidin side (9.25 %), cyanidin 3-p-hydroxybenzoyl
3-sophoroside-5-glucoside, peonidin 3-sophoro- sophoroside-5-glucoside (8.83 %), cyanidin
side-5-glucoside, cyanidin 3-p-hydroxybenzoyl- 3-(6″-caffeoyl sophoroside)-5-glucoside (4.74 %),
sophoroside-5-glucoside, pelargonidin compound, peonidin 3-p-hydroxybenzoyl sophoroside-
cyanidin 3-(6″-feruloylsophoroside)-5-gluco- 5-glucoside (1.29 %), cyanidin 3-(6″-feruloyl
side, cyanidin 3-caffeoylsophoroside-5-gluco- sophoroside)-5-glucoside (8.09 %), peonidin
side, cyanidin 3-(6″-feruloylsophoroside)-5- 3-(6″-feruloyl sophoroside)-5-glucoside (1.72 %),
glucoside, cyanidin 3-(6″,6‴-dicaffeoylsopho- cyanidin 3-(6″,6″-dicaffeoyl sophoroside-5-glu-
roside)-5-glucoside, cyanidin 3-(6″-caffeoyl-6‴- coside (9.56 %), peonidin 3-caffeoyl-p-hydroxy-
feruloylsophoroside)-5-glucoside, benzoyl sophoroside-5-glucoside (6.32 %) and
peonidin-dicaffeoylsophoroside-5- peonidin 3-(6″-caffeoyl-6″-feruloyl sophoroside)-
glucoside,cyanidin 3-caffeoyl-p-coumarylsopho- 5-glucoside (1.53 %) (Xu et al. 2013). Baking did
roside-5-glucoside. Okinawa variety showed 12 not impact overall anthocyanins, but steaming,
pigments with 3 major peaks identified as cyani- high pressure cooking, microwaving and frying
din3-caffeoylsophoroside-5-glucoside,cyanidin3-(6″,6‴- significantly reduced 20 % of total anthocyanins.
dicaffeoylsophoroside)-5-glucoside and cyanidin Monoacylated anthocyanins showed a higher
3-(6″-caffeoyl-6‴-feruloylsophoroside)-5- resistance against heat than di- and non-acylated.
glucoside. Steam cooking had no significant Among which, cyanidin 3-p-hydroxybenz-
effect on total anthocyanin content or the antho- oylsophoroside-5-glucoside exhibited the best
cyanin pigments. Cyanidin and peonidin were the thermal stability. Studies found that X-ray irra-
major anthocyanidins in the acid hydrolyzed diation treatment at doses up to 1000 Gy could
extracts. Thirteen anthocyanins were identified in reduce microbial populations while maintaining
the purple-fleshed sweet potato cultivar Jihei the physical quality and anthocyanin content of
No. 1 (Li et al. 2013a). The main anthocyanins purple-fleshed sweet potato cubes up to 14 days
were 3-sophoroside-5-glucoside derivatives from of storage (Oner and Wall 2013).
cyanidin and peonidin, acylated with p-hydroxy- Optimal conditions for anthocyanin and phe-
benzoic acid, ferulic acid or caffeic acid. A nolic content extraction from purple sweet potato
unique anthocyanin, delphinidin-3,5-diglucoside, using response surface methodology were drying
was also found. Eight kinds of anthocyanins temperature 62.91, 60.94 °C; citric acid concen-
with a yield of 90.02 % were extracted from tration 1.38, 1.04 %; and soaking time 2.53,
purple sweet potatoes by aqueous two-phase 2.24 min, respectively (Ahmed et al. 2011). The
extraction, and the major anthocyanins experimental value of anthocyanin content was
Ipomoea batatas 115

19.78 mg/100 g and total phenolic content was a high anthocyanin content than in clones with
61.55 mg/g. Twenty-seven different anthocya- a low anthocyanin content. Seven unknown
nins were tentatively identified in the sweet pota- aminoacyl sugars were isolated from the
toes in four Korean purple-fleshed sweet potato polar extracts of sweet potatoes (Dini et al.
varieties (Borami, Mokpo 62, Shinzami, and 2006b). Their structures were elucidated
Zami) (Lee et al. 2013). Borami was found to be as β-D-fructofuranosyl-(2 →1)-α-D-[2-O-valyl]-
a rare sweet potato variety with an exceptionally glucopyranoside; β-D-fructofuranosyl-(2→1)-
high quantity of pelargonidin-based anthocya- α-D-[2-O-tyrosyl]-glucopyranoside; β-D-fructo-
nins. Major anthocyanins in the crude extracts of furanosyl-(2→1)- α - D -[2- O -threonyl]-gluco-
peel, flesh and whole roots of 10 Chinese pyranoside; β-D-fructofuranosyl-(2→1)-α-D-[2-
purple-fleshed sweet potato genotypes were iden- O-hystidyl]-glucopyranoside; 2-β-D-fructofu-
tified as peonidin or cyanidin 3-sophoroside- ranosyl-(2→1)-α-D-[2-O-alanyl]-
5-glucoside and their acylated derivatives, glucopyranoside; β-D-fructofuranosyl-(2→1)
e.g., peonidin 3-sophoroside-5-glucoside, peoni- -α-D-[2-O-tryptophanyl]-glucopyranoside and
din 3-(6″-p-feruloylsophoroside)-5-glucoside β - D -fructofuranosyl-(2→1)- α - D -[2- O -glycyl]-
and cyanidin 3-(6″-p-feruloylsophoroside)-5- glucopyranoside.
glucoside (Zhu et al 2010). The main hydroxy- Chlorogenic acid and related components
cinnamic acid derivatives were identified as were isolated from sound sweet potato, yielding
mono- and dicaffeoylquinic acids (e.g., caffeic acid by alkaline hydrolysis (Rudkin and
5-O-caffeoylquinic acid and 3,5-di-O- Nelson 1947). Quinic acid was found in sweet
caffeoylquinic acid) and caffeoyl-hexoside. potato root in response to cutting (Minamikawa
These main phenolic compounds identified were 1967).
important contributors to the total antioxidant Four isomers of caffeoylquinic acid and an
capacity of the tested sweet potato samples. unidentified phenolic acid compound were found
The periderm cork cells (skin), but not those in 14 sweet potato cultivars (Thompson 1981). A
of the adjacent parenchyma cells, of sweet potato koji (Aspergillus awamori) extract hydrolyzed
tubers were found to contain high concentrations caffeoylquinic acid derivatives from sweet potato,
of anthocyanins (Philpott et al. 2009). Acid chlorogenic acid, 3,4-di-O-caffeoylquinic acid,
hydrolysis of the periderm extract followed by 3,5-di-O-caffeoylquinic acid, 4,5-di-O-
HPLC indicated the presence of the anthocyani- caffeoylquinic acid and 3,4,5-tri-O-caffeoylquinic
dins cyanidin and peonidin. The pattern of antho- acid to caffeic acid (Yoshimoto et al. 2005).
cyanin accumulation in sweet potato roots was Chlorogenic acid, isochlorogenic acid (several
characterized into three distinctive phases: (1) an isomers possible), caffeic acid, neochlorogenic
initial rapid increase during the 3rd to 6th week, acid and ‘Band 510’(4-[[4-(3,4-dihydroxyphenyl)-
(2) no change or a slight decrease during the 6th 1 - o x o - 2 - p r o p e ny l ] o x y ] - 1 , 3 , 5 - t r i h y d r o -
to 12th week and (3) a slight increase during the xycyclohexanecarboxylic acid) were identified in
12th to 17th week (Yoshinaga et al. 2000). mRNA sweet potato peelings (Sondheimer 1958). The
levels of dihydroflavonol 4-reductase (DFR), one levels were 335, 603, 11.53 and 548 mg/100 g dw
of the key enzymes of the anthocyanin biosyn- respectively. Chlorogenic (7.92–20.27 mg/100 g
thetic pathway, was expressed throughout the fw), isochlorogenic acid-1 (0.74–4.29 mg), iso-
stage of storage root development and appeared chlorogenic acid-2 (5.52–23.21 mg) were the
to be the most abundant at the 6th week, and most abundant phenolics comprising 80 % of the
declined at the 9th week, which coincided with total in sweet potato. The phenolic contents
the change in anthocyanin content. The rate of ranged from 14.18–51.24 mg/100 g fw depend-
increase in anthocyanin content during the 3rd to ing on cultivar. 4-O-Caffeoylquinic (1.29–
6th week was significantly higher in clones with 3.66 mg) was found in three cultivars.
116 Convolvulaceae

Trans-cinnamic acid-2-14C, p-coumaric acid-2- with higher concentrations correlated with wee-
14
C and caffeic acid-2-14C were administered to vil resistance (Anyanga et al. 2013). 2,4-Di-tert-
discs of sweet potato roots and incorporation of butylphenol was isolated from sweet potato (Choi
each radioactive compound into chlorogenic acid et al. 2013). Two constituents were isolated from
was compared (Kojima et al. 1969). The data purple sweet potato, 6,7-dimethoxycoumarin and
suggested that chlorogenic acid was synthesized 5-hydroxymethyl-2-furfural by combination of
through either or both of two major pathways, silica gel column and high-speed counter-current
phenylalanine → t-cinnamate → t-cinnamoyl chromatography (He et al. 2012).
derivative → p-coumaroyl derivative → chloro- Phenolics (chlorogenic acid, neochlorogenic
genic acid and phenylalanine → t-cinnamate → acid, isochlorogenic acid isomers A, B and C and
p-coumarate → p-coumaroyl derivative → chlo- an unknown compound in sweet potato decreased
rogenic acid. The intermediate compound V was in the order: outer tissues (6.29 mg/100 g fw,
found to be the first intermediate after trans-cin- 43.47 %) > skin (4.81 mg, 34.71 %) > inner
namic acid and to be a conjugate of t-cinnamic (3.05 mg, 21.44 %) (Walter and Schadel 1981).
acid and some sugar different from quinic acid or Phenols in the inner tissues were uniform
shikimic acid (Kojima and Uritani 1972a, 1972b; throughout the root while the outer tissues of the
1973). Also, it was found that chlorogenic acid stem end and root end were found to contain
was not the final product, but was metabolized to more phenolics than the mid-root outer tissues.
isochlorogenic acid in sweet potato tissues. Thus, about 78 % of the phenolics were found
Compound V was determined to be β-1- localized in the skin and outer 5 mm of root tis-
cinnamoyl-D-glucose (Kojima and uritani 1972a). sues. Walter and Purcell (1980) showed that the
Trans-cinnamic-2-14C and quinic acid –G-3H1 amount of darkening in homogenized sweet
were selectively incorporated into the aromatic potato was directly proportional to the concentra-
and non-aromatic moieties of chlorogenic acid, tions of phenolics and that the majority of the
respectively (Kojima and uritani 1972b). Slicing phenolics were esters formed between quinic
of sweet potato released enzymes involved in the acid (1,3,4,5-tetrahydroxycyclohexanecarboxyl
biosynthesis of phenolics leading to the produc- ic acid) and caffeic acid ([3-(3,4-dihydroxyphenyl)-
tion of phenolic compounds, mainly chlorogenic 2-propenoic acid], i.e., chlorogenic acids.
and isochlorogenic acids, and isomers of dicaf- Significant differences were found in the distri-
feoylquinic acid. bution of carbohydrates, organic acids and phe-
Sweet potato root periderm contained 0.008 to nolics among four sweet potato cultivars (Son
7.97 mg/g dry weight caffeic acid and the highest et al. 1991). Cultivars more resistant to weevils
content was 0.047 mg/g in the cortex tissues i.e., Regal and Resisto had higher concentration
(Harrison et al. 2003). Chlorogenic acid contents of malic acid than the most susceptible cv
were determined in periderm and cortex tissues Centennial. Concentration (mg/g FW) of carbo-
of sweet potato roots (Peterson et al. 2005). On a hydrates and organic acids in the root periderm
dry weight basis, contents of the chlorogenic tissues (outer 3 mm) of four sweet potato culti-
content in the periderm tissues ranged from 33 to vars were : α-glucose 0.51–2.26 mg, β-glucose
214 μg/g tissue and in the cortex from 1416 to 0.89–3.98 mg, sucrose 19.47–46.6 mg, inositol
4213 μg/g tissue (181 to 1384 μg/g FW). Sweet 27.16–59.27 mg, total sugars 27.16–59.27 mg,
potato root surface and epidermal extracts malic acid 0.25–1.49 mg, fructose and citric acid
showed significant variation in phenolic com- 2.52–10.41 mg, quinic acid 0.69–1.51 mg; and
pound concentration of hexadecylcaffeic acid, phenolics; chlorogenic acid 0.69–1.72 mg, caf-
hexadecylcoumaric acid, heptadecylcaffeic acid, feic acid 0.34–1.38 mg, dicaffeoylquinic acid (1)
octadecylcaffeic acid, octadecylcormaric acid 0.89–3.44 mg, dicaffeoylquinic acid (2) 0.74–
and 5-O-caffeoylquinic acid (chlorogenic acid), 2.94 mg, rutin 0.13–0.58 mg and total phenolics
Ipomoea batatas 117

3.79–9.17 mg. Sucrose was the major water- storage and remained nearly constant or decreased
soluble carbohydrate. In periderm tissues (outer) over time. Also, a non-caffeoylquinic acid com-
of cv Centennial stored for 3 months, 3-O-CQA ponent, identified as caffeoyl sucrose [CSu,
(chlorogenic acid), 5-O-CQA (neochlorogenic 6-O-caffeoyl-(β-D-fructofuranosyl-(2→1))-α-D-
acid), 4-O-CQA, dicaffeoylquinic acids and rutin glucopyranoside] increased during storage, espe-
(quercetin-3-β-D-rutinoside) were detected. cially in cv. ‘J-Red’ at 15 °C. Of five phenolic
Four different polyphenolic compounds were acids, caffeic acid, chlorogenic acid, 4,5-di-O-
isolated from methanolic and hydromethanolic caffeoylquinic acid, 3,5-di-O-caffeoylquinic acid
extracts of Ipomoea batatas tuber flour (Dini and 3,4-di-O-caffeoylquinic acid, identified in
et al. 2006a). Their structures were determined as sweet potato storage roots, chlorogenic acid was
4,5-di-O-caffeoyldaucic acid; 4-O-caffeoylquinic the most abundant (Truong et al. 2007). Steam
acid; 3,5-di-O-caffeoylquinic acid and 1,3-di-O- cooking resulted in statistically non-significant
caffeoylquinic acid). Six major phenolic increases in the concentration of total phenolics
compounds in raw sweet potato were identified and all the individual phenolic acids identified.
as β-D-fructofuranosyl 6-O-caffeoyl-α-D-- Five colourless caffeoyl monomers were isolated
glucopyranoside (FCG), chlorogenic acid from purple-fleshed sweet potato cv. Ayamurasaki
(5-O-caffeoylquinic acid or 5-CQA), caffeic and identified as: 5-caffeoylquinic acid;
acid, 4,5-CQA (4,5-di-O-caffeoylquinic acid), 6- O -caffeoyl- β - D - fructofuranosyl-(2–1)- α - D -
3,5-CQA (3, 5-di-O-caffeoylquinic acid) and 3,4- glucopyranoside; trans-4,5-dicaffeoylquinic
CQA (3,4-di-O-caffeoylquinic acid) (Takenaka acid; 3,5-dicaffeoylquinic acid and
et al. 2006). Two further compounds from heated 4,5-dicaffeoylquinic acid (Zhao et al. 2014).
sweet potato were identified as 3-CQA Total phenolic content in purple-fleshed sweet
(3-O-caffeoylquinic acid) and 4-CQA potato (PFSP) ranged from 313.6 to 1483.7 mg
(4-O-caffeoylquinic acid). There was an obvious chlorogenic acid equivalent/100 g fresh weight
decrease in caffeic acid derivatives during the (fw), and anthocyanin contents between 51.5 and
boiling of cube-shaped blocks of sweet potatoes. 174.7 mg anthocyanins/100 g fw (Steed and
They also decreased in a mixture of freeze-dried Truong 2008). Unlike orange-fleshed sweet pota-
sweet-potato powder and water maintained at toes (OFSP), the steamed roots of PFSP formed a
room temperature. When the mixture of pow- thick paste, which required a process modifica-
dered sweet potato and water was heated at tion to produce flowable purees. Rheological
100 °C, there was only a negligible decrease in testing indicated that adjusting the dry matter of
the total amount of phenolic compounds, and PFSP to 18–21 % produced purees with flow
portions of 5-CQA and 3,5-CQA were found to properties similar to the OFSP purees.
be isomerized to 3-CQA, 4-CQA, 3,4-CQA and
4,5-CQA. The content and composition of the Miscellaneous Compounds including
phenolic compounds in sweet potatoes differed Alkaloids, Saponins, Terpenoids
between fresh and long-stored ones, as did their Polyhydroxylated nortropane alkaloids calyste-
response to heating. The main polyphenolic com- gines A3, B1, B2 and C1 were detected in sweet
ponents found in four Japanese cultivars were potato (Asano et al. 1997). Calystegine A3, B1, B3
chlorogenic acid (ChA) and 3,5-di-O- were isolated from sweet potato root sample from
caffeoylquinic acid (3,5-diCQA) (Ishiguro et al. Panana (Schimming et al. 1998). From Japan,
2007). ChA level increased more at 5 °C than at sweet potato aerial part samples calystegine B1
15 °C, whereas that of 3,5-diCQA was greater at and B2 were found but no biogenetic precursors
15 °C. Caffeoylquinic acids and radical scaveng- were determined; from Panama, sweet potato
ing activity in cv. ‘Murasakimasari’, which con- root calystegine A3 and B1 were found and bioge-
tained a large amount of anthocyanin in flesh netic precursors found in the biosynthesis of
tissue, were extremely high at the beginning of calystegines were 3-oxotropane (tropinone),
118 Convolvulaceae

3-β-hydroxytropane (pseudotropine) and coryniformis, respectively, was developed by

3-β-hydroxynortropane (norpseudotropine) Nguyen et al. (2013). The method produced
(Schimming et al. 2005). From Mexico, sweet 122.91–198.32 g/L of L-lactic acid with yields of
potato aerial part samples, calystegines B1, B2, B3 90.11–84.92 % (w/w) and 122.49–186.40 g/L
were found and from roots calystegines A5, B1, D-lactic acid with yields of 90.11–84.92 % (w/w).
B2, were found and biogenetic precursors found Sweet potato roots (non-boiled/fully-boiled)
were 3-oxotropane (tropinone), 3-β-hydro- were fermented with Lactobacillus plantarum
xytropane (pseudotropine), 3-oxonortropane MTCC 1407 at 28 °C for 48 h to make lacto-juice
(nortropinone) and 3-β-hydroxynortropane (Panda and Ray 2007). There were no significant
(norpseudotropine). The dihydroxynortropane variations in biochemical constituents (pH, 2.2–
alkaloid was isolated from sweet potato (Asano 3.3; lactic acid, 1.19–1.27 g/kg root; titratable
et al. 2001). acidity, 1.23–1.46 g/kg root, etc.) of lacto-juices
A novel indole-type alkaloid, named ipomine prepared from non-boiled and fully-boiled sweet
A, was isolated from sweet potato hairy roots potato roots except β-carotene concentration
(Yuan et al. 2004). Triterpene saponins were iso- [130 mg/kg (fully boiled roots) and 165 mg/kg
lated from sweet potato tuber flour and identified (non-boiled roots)]. The panelist evaluation
as oleanolic acid-3-O-[β-D-glucopyranosyl- scores ranged from 3–4.8 (in a hedonic scale of
(1→2)- β - D -galactopyranosyl-(1→2)- β - D - 1–5) from moderate liking to very much liking of
glucuronopyranosyl]-28-O-β-D-glucopyranoside sweet potato lacto-juice.
(sandrosaponin IX) (161.20 mg/100 g dry weight)
and oleanolic acid-3-O-[β-D-galactopyranosyl- Volatiles
(1→3)- β - D -glucuronopyranosyl]-28- O - β - D - Thirty volatile compounds were identified from
glucopyranoside (14.67 mg/100 g dry weight) baked ‘Jewel’ sweet potatoes: methanol, ethanol,
(Dini et al. 2009). Both saponins were moderate acetone; diethylether; dichloromethane;
in relation to commercial standards when tested 2,3-butanedione (doacetyl); 3-methylpentane;
by DPPH and FRAP assay. Five sesquiterpenes hexane, tetrahydrofuran; methylcyclopentane;
in the volatiles from sweet potato storage roots 2,3-pentaedione; methylbenzene (toluene);
and leaves that attracted sweet potato weevils 2-methyltetrahydrofuran-3-one; furfuraldehyde;
were identified as copaene, trans-caryophyllene, dimethylbenzene (xylene); isobutyronitrile;
γ-humulene, γ-cadinene and γ-elemene 2-pyrone; heptanal; 2-furyl methyl ketone; benz-
(Nottingham et al. 1989a) and triterpenol acetate aldehyde; 5-methyl-2-furaldehyde; trimethylben-
from root surface (Nottingham et al. 1989b). Two zene (mesitylene); octanal; 2-pentylfuran;
pentacyclic triterpenoids were isolated from phenylacetaldehyde; nonanal; linalool; decanal;
sweet potato tubers: beohmerol and boehmeryl β-ionone; and 4-(2,2,3,3-tetramethylbutyl)phe-
acetate (Son et al. 1990). Boehmeryl acetate from nol (Purcell et al. 1980). During heat treatment of
sweet potato tuber was found to be an oviposi- sweet potatoes, maltose concentration increased
tional stimulant for sweet potato weevil, Cylas from 0.03 % fresh weight at 25 °C to 4.33 % at
formicarius elegantulus. 80 °C, at which temperature maximum synthesis
Alkaloids, saponin, tannins, steroids, antho- occurred (Sun et al. 1994). Microwave pre-
cyanins, flavonoids, anthraquinones, oxalate and treatment (2 or 4 min) resulted in a significant
trypsin inhibitors, phytate (35 mg/100 g) and decrease in amounts of maltose and volatiles
coumarin was found in sweet potato but not phlo- formed. At 80 °C, approximately 80 % of malt-
batannin and cyanogenic glycosides (Anbuselvi ose synthesis was inhibited when pre-treated
and Muthumani 2014). with microwave. It was found that maltose repre-
A bioprocess for L- and D-lactic acid produc- sented a primary precursor for many of the vola-
tion from raw sweet potato through simultaneous tile compounds emanating from baked ‘Jewel’
saccharification and fermentation by sweet potatoes and the formation of these vola-
Lactobacillus paracasei and Lactobacillus tiles appeared to involve both enzymatic and
Ipomoea batatas 119

thermal reactions. Twelve experimental lines of furyl alcohol and β-ionone were found in the
sweet potatoes could be classified on the basis of non-polar fraction. Acetol, furyl aldehyde,
27 volatiles (Tiu et al. 1985). Five volatiles were 5-methyl-2-furfural, furfuryl alcohol and
associated with good flavour and eight volatiles 5-hydroxymethyl-2-furfural were found in the
with cultivars having poor flavour. Twenty-one polar fraction.
volatile compounds consisting of aldehydes, Volatile emanating from baked roots of sweet
ketones, furans, pyridine, alcohols, terpenes and potato cultivars ‘Jewel’ and ‘GA90-16’ were:
palmitic acid were identified in the steam distil- pyridine; 1,2,4-cyclopentanetriol; 1,2,4-trimethyl
lates from Jewel, Tainung 57 and a breeding line benzene; 3-furaldehyde; xylene; 2-furmethanol;
(No. 99) (Horvat et al. 1991). Maltose, sucrose, pyridine; 1,2,4-cyclopentanetriol; 1,2,4-trimethyl
glucose and fructose were isolated and identified. benzene; 3-furaldehyde; xylene; 2-furmethanol;
Maltose, the principal sugar formed during furfuryl alcohol; 2-acetyl furan; benzaldehyde;
cooking, ranged from 0.07 % in the breeding line 5-methyl-2-furfural; 2-pentyl furan; 2,3-pentane-
No. 99 to 5.3 % in Tainung 57. Twenty-three dione; phenylacetaldehyde; limonene; 3,4-dihy-
volatiles emanated from baked Jewel sweet dropyran; 2-acetyl pyrrole; maltol; linalool;
potatoes: 2,3-pentadione, acetol; 2,3-butandione; isopulegone; 4,5-dimethyl-4-hexen-3-one; gera-
methylpropanoate; isobutyl alcohol; 2- niol; 2,4-nonadienal; 2-napthalenone; cyclohexa-
methyl-2-hexene; oxabicyclo(2,2,1) heptanes; nol; n-decanal; 2,2-dimethyl-1,3-cyclohexanediol;
2-furancarboxaldehyde; 2-furmethyl ketone; 2,3-nonadecanediol; 2,4-decadienal; octyl
2-furmethanol; isomaltol; benzaldehyde; 5- ketone; germacrene D; caryophyllene; cyperene;
methyl-furfural; phenylacetaldehyde; β-cyclocitral; β-farnesene; α-copaene; α-bisabolene; bohlmann
2-acetyl pyrrole; maltol; 2-methyl-furaote; 176; 2(4H)-benzofuranone; β-ionone; nerol,
3,5-dihydroxy-2-methyl, 5,6-dihydrogen-4- 4-decanolide; unknown; tetradecanoic acid;
pyrone; 5-hydroxymethyl furaldehyde; C17 10-heneicosene; palmitic acid; octadecanol;
hydrocarbon; C18 hydrocarbon; and C19 hydrocar- 1-nonadecanol; and 9,12-octadecadienoic acid
bon (Sun et al. 1993). The major components (Wang et al. 1998). Of 46 compounds identified,
identified from baked Jewel and Centennial sweet 38 were odour-active. Curing had a pronounced
potatoes were similar: acetol; 2-furancarboxalde- effect on aroma intensity and quality. Uncured
hyde; 2-furmethyl ketone; 2-furanmethanol; roots yielded only 37 % (cv. ‘Jewel’) and 12 %
5-methyl-furfural; phenylacetaldehyde; maltol; (‘GA90–16’) of the total amount of odour-active
2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran- volatiles of cured roots and had substantially
4-one; 5-hydroxy-methyl-2-furancarboxaldehyde. depressed aromas. Certain compounds were not
Volatile compounds identified from conven- obtained from freshly harvested roots (i.e., only
tionally baked and thermolyzed sweet potatoes 22 of 38 compounds were present in ‘GA90–16’
were similar except for the presence of acetic and 34 of 37 in ‘Jewel’). Curing appeared to
acid (thermolyzed) and phenylacetaldehyde enhance the synthesis of α- and β-amylase, which
(baked) sweet potatoes (Sun et al. 1995). The in turn facilitates starch hydrolysis during baking
common compounds to both baked and thermo- and formation of monosaccharides that acted as
lyzed sweet potatoes were: acetol; furyl aldehyde; precursors for critical volatile flavour
2-acetylfuran; benzaldehyde; 5-methyl-2-furfu- components.
ral; furfuryl alcohol; 3,4-dihydropyran; Volatiles (49) emanating from baked ‘Jewel’
3-hydroxy-2-methyl-4-pyrone (maltol); 2-hydro- sweet potatoes were: pyridine; 1,2,4-cyclopenta-
xyacetyl furan; 5-hydroxymethyl-2-furfural and netriol; 1,2,4-trimethyl benzene; 3-furaldehyde;
an unknown. All the aforementioned compounds xylene; 2-furmethanol; 2-furancarboxaldehyde;
except for phenylacetaldehyde and β-ionone 2-acetyl furan; benzaldehyde; 5-methyl-2-furfu-
were found in the insoluble sweet potato fraction. ral; 2-pentyl furan; 2,3-pentanedione; phenylac-
Acetol, furyl aldehyde, 5-methyl-2-furfural, fur- etaldehyde; limonene; 3,4-dihydropyran; 2-acetyl
120 Convolvulaceae

pyrrole; maltol; linalool; isopulegone; respectively. From aroma extract dilution

4,5-dimethyl-4-hexen-3-one; geraniol; 2,4-nona- analysis, four compounds contributed to the
dienal; 2-napthalenone; cyclohexanol; n-decanal; aroma from each cooking method. In addition,
2,2-dimethyl-1,3-cyclohexanediol; 2,3-nonadec- cooking method specific aroma contributing
anediol; 2,4-decadienal; octyl ketone; methyl compounds accounted for the unique aroma of
geranate; germacrene D; β-caryophyllene; each of the cooked products.
β-farnesene; α-copaene; α-bisabolene; bohlmann Wang and Kays (2003) described an analytical
176; 2(4H)-benzofuranone; β-ionone; nerolidol; means of assessing flavour which is amenable to
4-decanolide; unknown; tetradecanoic acid; large numbers of sweet potato lines to be screened
10-heneicosene; palmitic acid; octadecanol; and allows initial selection decisions to be made
1-nonadecanol; 9,12-octadecadienoic acid, silane without the use of sensory panels. For this, they
and squalene (Wang and Kays 2000). Three com- found 19 critical aroma compounds and their
pounds, phenylacetaldehyde (perfume), maltol relative weighting factors in six baked sweet
(caramel) and methyl geranate (2,6-octadienoic potato clones: Maillard/caramelization prod-
acid, 3,7-dimethyl-, methyl ester) (sweet candy) ucts – maltol 138.9; 5-methyl-2-furfural 444.4;
possessed the highest flavour dilution (FD) val- 2-acetyl furan 227.3; 3-furaldehyde 0.7;
ues (1500) via AEDA. 2-Acetyl furan (baked 2-furmethanol 7.1; Strecker degradation prod-
potato), 2-pentyl furan (floral), 2-acetyl pyrrole ucts – benzaldehyde 380.9; phenylacetaldehyde
(sweet, caramel), geraniol (sweet floral) and 50.5; β-carotene degradation products – β-ionone
β-ionone (violet) had FD values of 1000. These 625; 1,2,4-trimethyl benzene 296; lipid degrada-
compounds were deemed to be the most potent tion products – 2-pentyl furan 833.3;
odourants in baked ‘Jewel’ sweet potatoes. 2,2-decadienal 666.7; 2,4-nonadienal 333.3;
Additionally, 1,2,4-trimethyl benzene, n-decanal trace; terpenoids – linalool 1000; gera-
2-furmethanol, benzaldehyde, 5-methyl-2- niol 2500; methyl geranate trace; cyperene 1.0;
furfural, linalool, isopulegone, n-decanal, α-copaene 266.7 and sesquiterpene (MW204)
2,4-decadienal, octyl ketone, α-copaene, 100 (Wang and Kays 2003)
4-decanolide and one unidentified compound Flavour volatile components identified in
were also contributors to the aroma. Kansho-shochu (sweet potato spirit) included:
Thirty-seven odour-active compounds of ethanol, ethyl hexanoate, ethyl octanoate;
which 36 were identified from ‘Jewel’ sweet 1-octen-3-ol; furfural; linalool; ethyl decanoate;
potatoes cooked by baking, boiling and micro- diethyl succinate; α-terpineol; citronellol; ethyl
waving (Wang and kays 2001). These compounds phenylacetate; nerol; β-phenylethyl acetate; ethyl
were: pyridine; 1,2,4-trimethyl benzene; laurate; geraniol; β-phenylethyl alcohol;
3-furaldehyde; xylene; 2-furmethanol; 2-acetyl- nerolidol; ethyl myristate; ethyl cinnamate; ethyl
furan; benzaldehyde; 5-methyl-2-furfural; palmitate; ipomeamarone; farnesol; cetyl alco-
2-pentyl furan; 2,3-pentanedione; phenylacetal- hol; ethyl stearate; ethyl oleate, ethyl linoleate
dehyde; limonene; 3,4-dihydropyran; 2-acetyl (Ohta et al. 1990). The monoterpene alcohols lin-
pyrrole; maltol; linalool; isopulegone; geraniol; alool, α-terpineol, citronellol, nerol and geraniol,
2,4-nonadienal; cyclohexanol; n-decanal; together with ethyl phenyl acetate and ethyl cin-
2,2-dimethyl-1,3-cyclohexanediol; 2,3-nonadec- namate qualitatively contributed to the sensory
anediol; 2,4-decadienal; octyl ketone; methyl property of Kansho-shochu flavour. They also
geranate; β-caryophyllene; β-farnesene; found terpene alcohols linalool, α-terpineol,
α-copaene; α-bisabolene; bohlmann 176; 2(4H)- nerol, geraniol and p-menth-2-en-7ol in raw
benzofuranone; β-ionone; nerolidol; 4-decano- grated sweet potato and nerol, geraniol and
lide, unknown and tetradecanoic acid. Compared p-menth-2-en-7ol in steamed sweet potato.
with conventional baking, boiling and microwav- The following volatiles emanated from stor-
ing yielded only 54.26 % and 6.43 % of the rela- age roots of four sweet potato cultivars over 24 h:
tive total yield of aroma-active compounds, 1,2-dimethylbenzene; 6-methyl-5-hepten-2-one;
Ipomoea batatas 121

1,4-dichlorobenzene; p-cymene; dl-limonene; the alcohol fraction C18, C20, C22 and C24,
diethylbenzene; undecane; neroloxide; naphtha- saturated primary alcohols were the major com-
lene; nerol; Z-citral; E-citral; 1-methylnaphtha- ponents. Chain lengths of fatty alcohol of root
lene; 2-methylnaphthalene; methylgeranate; suberin were C18 68.3 %, C19 0.5 %, C20 15.5 %,
alkazene; δ-cadinene; α-copaene; β-elemene; C21 1.7 %, C22 6.1 %, C23 0.5 %, C24 3.0 %, C25
cyperene; trans-caryophyllene; germacrene D; 0.4 %, C26 3 %, C27 0.1 %, C28 0.6 %, C29 0.2 %
α-humulene; cis-α-bisabolene; ylangene; and C30 0.1 %. C16 and C18 dicarboxylic acids
β-selinene, α-muurolene; α-gurjunene, 1S,cis- were the major dicarboxylic acids of the suberin.
calamenene (Wang and Kays 2002). The follow- Chain length of dicarboxylic acids of root
ing volatiles emanated from aerial parts of four suberin were C15 0.2 %, C16 6.6 %, C17 2.4 %,
sweet potato cultivars over 24 h: 1,2-dimethyl- C18:1 80.5 %, C19 0.7 %, C20 0.2 % and C21 0.4 %.
benzene; 1,4-dichlorobenzene; p-cymene; dl- The composition of the ω-hydroxy acid fraction
limonene; undecane; naphthalene; nerol; was quite similar to that of the dicarboxylic
1-methylnaphthalene; 2-methylnaphthalene; acids; 18-hydroxy-octadec-9-enoic acid was the
alkazene; α-copaene; β-elemene; cyperene; major component. Chain lengths of ω-hydroxy
trans-caryophyllene; germacrene D; cis-α- acids of root suberin were C16: 4.9 %, C18:1
bisabolene; ylangene; β-selinene, α-muurolene; 90.7 %, C18 1.3 %, C20 0.3 %, C22 0.3 %, C24
1S,cis-calamenene; β-ocimene; (E)-4,8- 0.5 %, C26 0.9 % and C28 0.7 %. The amount of
dimethyl-1,3,7-nonatriene; zingiberene; and (E)- wax extracted from the periderm of the storage
β-farnesene. The sesquiterpene volatile fraction organs including sweet potato ranged from 2 to
was repellent to female sweet potato weevil 32 μg/cm2 (Espelie et al. 1980). The hydrocar-
(SPW, Cylas formicarius elegantulus) with bons from the suberin layer had a broader chain-
α-gurjunene, α-humulene and ylangene active in length distribution, a predominance of shorter
the concentration range emanating from storage carbon chains and a higher proportion of even-
roots. The aerial plant parts emanated a higher numbered carbon chains than the leaf alkanes
composite concentration of sesquiterpenes than from the same plants. The major components of
storage roots. Differences in the relative attrac- the free and esterified fatty alcohols and fatty
tion among four sweet potato cultivars to female acids had an even number of carbon atoms, and
SPW was inversely correlated with the composite were similar in chain-length distribution to their
concentration of headspace sesquiterpenes. counterparts found covalently attached to the
suberin polymers. Also extracted from the
Suberin and Waxes suberin associated waxes were polar compo-
Suberin, isolated from sweet potato, was finely nents which included fatty alcohols and fatty
powdered and depolymerized with 14 % boron acids in a conjugated form, and ω-hydroxy acids
trifluoride in methanol and the soluble mono- and dicarboxylic acids.
mers were fractionated into phenolic fraction Ceramides and glucocerebrosides containing
17 %, aliphatic fraction 6 % and soluble fraction the three different long-chain bases
Δ4,Δ8
26 % (Kolattukudy et al. 1975). The aliphatic 4,8-sphingadienine (d18:2 ), 4-hydroxy-8-
fraction consisted of 36 % ω-hydroxy acids, sphingenine (t18:1Δ8), and 8-sphingenine
21 % dicarboxylic acids, 5 % fatty acids, 4 % (d18:1Δ8) acylated to saturated and unsaturated
fatty alcohols and 3 % polar compounds. Among hydroxy- and non-hydroxy fatty acids with 16–26
the fatty acids, very long chain acids (>C20) were carbon atoms were detected in sweet potatoes
the dominant components. Chain length of fatty and potatoes (Bartke et al. 2006). For ceramides
acids of root suberin were C16 0.9 %, C17 0.2 %, and glucocerebrosides 4,8-sphingadienine
C18:U 3.9 %, C18 1.1 %, C19 0.09 %, C20 0.9 %, C21 (d18:2Δ4,Δ8) was found as the major long-chain
0.08 %, C22 3.3 %, C23 0.3 %, C24 4.7 %, C25 base, with lesser amounts of 4-hydroxy-8-
0.5 %, C26 16.6 %, C27 1.6 %, C28 20.2 %, C29 sphingenine (t18:1Δ8) and 8-sphingenine
7.5 %, C30 34.3 %, C31 3.7 % and C32 0.4 %. In (d18:1Δ8). 2-(α-)hydroxypalmitic acid (C16:0 h)
122 Convolvulaceae

was the major fatty acid, which was found to be fraction of diseased tissue suggested that some
acylated to the long-chain bases. The analyzed metabolic alteration of this fraction might occur
samples of potatoes and sweet potatoes showed in response to infection. Tracer studies with the
amounts of approximately 0.1–8 μg/kg single use of 2-14C-acetate revealed that the infected tis-
ceramides and amounts up to 500 μg/kg gluco- sue of diseased sweet potato roots with black rot
cerebrosides, with C16:0 h-glucosyl-4,8-sphing- was incapable of synthesizing ipomeamarone
adienine as the major component. from acetate, but was capable of synthesizing it
from some intermediate(s) which was produced
Toxins and Phytoalexins from acetate by the non-infected tissue in a short
Ipomeamarone, a phytoalexin, was first reported period. The incorporation of mevalonate-2-14C
as a stress metabolite of unknown structures in into ipomeamarone in sweet potato root tissue
old damaged sweet potatoes in 1943 (Hiura infected by Ceratocystis fimbriata was demon-
1943). The bitter substance produced in black strated, but the rate was low when compared with
rot-infected sweet potato was identified as ipo- acetate-2-14C (Oshima and Uritani 1968). The
moeamarone, an open-chain ketone with two data supported the participation of mevalonate in
oxide rings and two ethylenic linkages (Ohno ipomeamarone synthesis as an intermediate.
1952). It yielded a liquid keto-acid and oxalic Acetate-2-14C, pyruvate-3-14C and citrate-2,4-14C
acid by oxidation with potassium permanganate were incorporated into ipomeamarone in sweet
at room temperature, and acetone, acetic acid, potato root tissues infected by Ceratocystis fim-
oxalic acid and a liquid acid by oxidation with briata (Oba et al. 1970). Rates of incorporation
the same reagent at 100 °C. Also, similarities of 14C, from these three substances, into the
were noted between ipomeamarone and ngaione. CHCl3-CH3OH-soluble lipid fraction and ipo-
The correct accepted structure of ipomeamarone meamarone were of the following order: acetate
was elucidated through a series of oxidative deg- > pyruvate > citrate. Labelled studies showed that
radation by Kubota and co-workers (Kubota and farnesol-2-14C was incorporated into ipomeama-
Ichikawa 1954; Kubota 1958; Kubota and rone (Oguni and Uritani 1970). Incorporation of
Matsuura 1958; Kubota et al. 1965). Subsequent ethanol-2-14C into furanoterpenoids such as ipo-
studies by Kubota and Matsuura (1958) estab- meamarone in sweet potato infected with the
lished ipomeamarone and ngaione to be enantio- black rot fungus, Ceratocystis fimbriata, was
mers, both having a cis-configuration. When demonstrated by Oguni and Uritani (1971). The
sweet potato root tissue was infected by rate of incorporation of ethanol-2-14C into ipo-
Ceratocystis fimbriata, terpenes like ipomeama- meamarone was about twofold more efficient
rone was synthesized in the adjacent non-infected than for acetate-2-14C. The results suggested that
region and accumulated in the infected region; ethanol was utilized for lipid synthesis after being
also chlorogenic acid increased in non-infected directly converted to acetyl CoA via acetalde-
tissues adjacent to infected tissues (Akazawa and hyde, and it appeared likely that a CoA-linked
Wada 1961). Akazawa and Uritani (1962) aldehyde dehydrogenase operated in sweet potato
hypothesized that the biosynthesis of ipomeama- root tissue infected with C. fimbriata.
rone in the sweet potato root infected by 3-hydroxy-3-methylglutaryl coenzyme, a
Ceratocystis fimbriata might be induced by the reductase, was detected in the non-infected root
alteration of the tricarboxylic acid cycle in the tissues and found to participate in the synthesis of
host tissues. Tracer studies showed although ipomeamarone (Suzuki et al. 1974). Fresh sweet
there was no significant change in lipid ester potato root tissue had a very low activity of
groups in both infected and non-infected tissues, 3-hydroxy-3-methylglutaryl coenzyme A reduc-
increase in phospholipids was found in diseased tase; however, when infected by Ceratocystis fim-
tissue (Imaseki et al. 1964). Sterol isolated from briata, the enzyme activity increased rapidly, and
fresh material was identified with β-sitosterol. reached a maximum in 2 days, thereafter, the
Chromatographic patterns of non-phospholipid activity decreased rapidly (Suzuki et al. 1975).
Ipomoea batatas 123

Optimal activity of 3-hydroxy-3-methylglutaryl (1975). Two glucosides of coumarin derivatives,

coenzyme A reductase occurred at pH 7·3 to 7·5. skimmin (umbelliferone-7-β-glucoside) and sco-
An abnormal semicarbazone was formed by polin (scopoletin-7-β-glucoside) were isolated
removal of two molecules of water when ipo- from sweet potato roots infected with black rot
meanine, one of the constituents of black rot- (Minamikawa et al. 1964). β-hydroxy-β-
infected sweet potato, was treated with methylglutaric acid derivative was synthesized
semicarbazide (Kubota et al. 1965). Structural from acetyl CoA by a cell-free system from non-
formulae were assigned to semicarbazone and an infected tissues adjacent to the infected region of
abnormal semicarbazone of an ester, an interme- sweet potato infected with black rot (Oshima and
diate in the synthesis of ipomeanine in fungal- Uritani 1967). A phytoalexin-like compound was
rotted sweet potato (Kubota and Ichikawa 1954). isolated from sweet potato root tissue infected by
From the volatile component of sweet potatoes the black-rot fungus, Ceratocystis fimbriata, and
infected by Ceratostomella fimbriata (black rot identified as 14-hydroxy-ipomeamarone and
disease), four β-substituted furans, namely ipo- called ipomeamaronol (Kato et al. 1973).
meamarone, batatic acid, ipomeanine and β-furan 4-hydroxydehydromyoporone was mainly con-
carboxylic acid were isolated (Kubota 1958). verted to 4-hydroxymyoporone and a little to
Sweet potato roots infected by the black rot dehydroipomeamarone, and ipomeamarone, in
fungus, Ceratocystis fimbriata, produced umbel- Ceratocystis fimbriata-infected sweet potato
liferon (7-hydroxy coumarin) and scopletin tissues (Inoue and Uritani 1980a). Furano-
(6-methoxy-7-hydroxy coumarin) (Uritani and sesquiterpene reductase reduced dehydroipomea-
Hoshiya 1953; Minamikawa et al. 1962), escule- marone and 4-hydroxydehydromyoporone to
tin (Minamikawa et al. 1962), along with poly- ipomeamarone and 4-hydroxymyoporone, respec-
phenols chlorogenic acid, isochlorogenic acid, tively, in fungal-inoculated sweet potato tissues
caffeic acid and their derivatives were produced (Inoue and Uritani 1980b). The enzyme was
in the tissue adjacent to the wounded surface or located in the microsomal fraction and required
infected region of sweet potato storage roots NADPH but not NADH.
(Uritani and Muramatsu 1953; Uritani and A new stress toxic furano-sesquiterpene
Miyano 1955). The formation of these coumarins metabolite of sweet potato was isolated and iden-
was very low in the uninfected or uninoculated tified as 1-(3-furoyl)-4,8-dimethyl-7-hydroxy-
cut tissues, indicating that coumarin synthesis 1,6-nonanedione (7-hydroxymyoporone) (Burka
occurred after infection (Minamikawa et al. et al. 1974). Its toxicity was similar to that of the
1963). well known phytoalexin, ipomeamarone. This
A new hepatotoxic metabolite, ipomeama- compound was produced along with other toxic
ronol, was isolated and described from mold- furanoterpenoids in response to certain exoge-
damaged sweet potatoes (Kato et al. 1971; Yang nous stimuli. The lowest limit of detection of
et al. 1971). The toxic furan ipomeamarone was ipomeamarone in damaged sweet potatoes
detected in damaged sweet potato (Wood and was 2 ng (Wood and Huang 1975). Four lung-
Huang 1975). A phytoalexin dehydroipomeama- toxic furanoterpenoids produced by sweet
rone, a sesquiterpenoid, was isolated from sweet potatoes following microbial infection were
potato root tissues infected by the black rot fun- identified as 4-ipomeanol (1-(3-furyl)-4-
gus, Ceratocystis fimbriata (Oguni and Uritani hydroxy-1-pentanone), the isomeric 1-ipomeanol
1973; 1974). Dehydroipomeamarone was found (1-(3-furyl)-1-hydroxy-4-pentanone), the corre-
to be an intermediate precursor in the biosynthetic sponding diketone, ipomeanine (1-(3-furyl)-
pathway of the phytoalexin, ipomeamarone 1,4-pentanedione), and the diol, 1,4-ipomeadiol
(Oguni 1974). The hepatotoxin ipomeamarone (1-(3-furyl)-1,4-pentanediol) (Boyd et al. 1974).
and lung-oedema toxins 4, ipomeanol and ipo- In addition to ipomeamarone and other hepato-
meanine, were found in several sweet potato sam- toxins, a series of 1-(3-furyl)-1,4-dioxygenated
ples in the United Kingdom by Coxon et al. pentanes were isolated from sweet potatoes
124 Convolvulaceae

infected with Fusarium solani (Burka and Wilson the 18-h incubated cut tissue together with
1976). Burka and Kuhnert (1977) demonstrated chemical elicitors of furano-terpene production.
that the tetrahydrofuran ring was cleaved so that Two new compounds, 7-hydroxycostal and
ipomeamarone was converted to 4-hydroxymyo- 7-hydroxycostal, were isolated from infected
porone. The following phytoalexins (μg/g fresh sweet potatoes as members of a new class of
weight) were isolated from mercuric chloride sweet potato phytoalexins (Schneider and
stressed sweet potatoes: myoporone 39 μg, Nakanishi 1983). Nine new sesquiterpenes
6-hydroxymyoporol 109 μg and 1-hydroxymyo- related biosynthetically to ipomeamarone, the
porol 53 μg (Burka and Iles 1979). 6-myoporol well-known sweet potato phytoalexin, were
was two to three times more toxic than isolated from Ceratocystis fimbriata-infected
ipomeamarone. sweet potato root tissue (Schneider et al. 1984).
A new sesquiterpenoid, 4-hydroxydehydro- They were identified as 9-hydroxyfarnesoic
myoporone, was isolated from Ceratocystis fim- acid; ipomeatetrahydrofuran; (Z)-1,6-dioxoiso-
briata-infected sweet potato root tissue (Inoue dendrolasin; (E)-1,6-dioxoisodendrolasin;10-
et al. 1977). Injury to sweet potato tissue by a hydroxyipomeabisfuran; 4-hydroxymyoporonol;
poison such as HgCl2 caused changes very simi- 4-hydroxymyoporonol ketal and two butenolides
lar to those induced by inoculation with 6-oxodendrolasinolide and ipomeamaronolide.
Ceratocystis fimbriata, namely faster respiration, Furanoterpenoids including ipomeamarone
increase of polyphenols and coumarins in adja- and ipomeamaronol were isolated from sweet
cent, sound tissue and production of ipomeama- potato root tissues infected with Ceratocystis fim-
rone (Uritani et al. 1960). Myoporone and briata (Shen 1997). Plenodomus destruens,
6-myoporol (Burka and Iles 1979) and Diaporthe batatatis, Diplodia tubericola,
1-(3′-furyl)-6,7-dihydroxy-4,8-dimethylnonan- Fusarium solani and Ceratocystis fimbriata
1-one (Burka 1978) were isolated from stress induced accumulation of relatively high concen-
sweet potatoes. Treatment of sweet potato slices trations of ipomeamarone (63–16, 523 μg/g),
with 0.1 % HgCl2 three times within 24 h caused 4-ipomeanol (5–236 μg/g) and 1,4-ipomeadiol
production of ipomeamarone in both the injured (ND–1406 μg/g) in sweet potatoes (Clark et al.
and the adjacent tissue which did not brown. The 1981). Macrophomina phaseoli and Sclerotium
following phytoalexins dehydroipomeamarone, rolfsii induced accumulation of relatively high
ipomeamaronol, 4-hydroxydehydromyoporone, concentrations of ipomeamarone (ND–
4-hydroxymyoporoine were detected in sweet 23.346 μg/g) and 4-ipomeanol (4–227 μg/g), but
potato root tissues infected by Ceratocystis fim- did not induce accumulation of 1,4-ipomeadiol.
briata (Inoue and Uritani 1979). Four sesquiter- Rhizopus stolonifer and Erwinia carotovora
pene stress metabolites, 6-oxodendrolasin induced accumulation of relatively low concen-
(8.5 μg/g), 6-hydroxydendrolasin (1.2 μg/g), trations of ipomeamarone (58–2675 μg/g),
9-oxofarnesol (0.7 μg/g) and 9-hydroxyfarnesol 4-ipomeanol (from not detectable [ND] to
(12.9 μg/g) were isolated from mercuric chloride- 112 μg/g) and 1,4-ipomeadiol (ND–16 μg/g).
treated sweet potatoes (Burka et al. 1981). Oba Streptomyces ipomoeae, Monilochaetes infuscan,
and Uritani (1981) found that furano-terpene pro- and internal cork virus did not induce accumula-
duction in sweet potato root tissue treated with tion of detectable levels of ipomeamarone,
chemicals, such as HgCl2, l-alanine and CAMP 4-ipomeanol or 1,4-ipomeadiol. Mercuric acetate
was inhibited by antibiotics, such as cyclohexi- induced accumulation of low concentrations
mide, blasticidin S, puromycin and chloramphen- of total furanoterpenoids, ipomeamarone,
icol when the antibiotics were administered to 1-ipomeanol, 1,4-ipomeadiol. Fusarium oxyspo-
the tissue immediately after cutting. However, rum f. sp. batatas did not induce accumulation
furano-terpene production was not inhibited by of furanoterpenoids in sweet potato vines.
antibiotics when they were administered to Concentrations of 4-ipomeanol and
Ipomoea batatas 125

1,4-ipomeadiol were highest in tissue infected istration, the label was mainly incorporated into
with certain isolates of Diplodia tubericola and the two unknown fractions.
Fusarium solani. Sweet potato disks treated with
50 mM mercuric acetate and incubated for 2
weeks at 30 °C contained 1657 μg total furano- Leaf/Stem/Nutrients/Phytochemicals
terpenoids, 1075 μg ipomeamarone, 3 μg
4-ipomeanol and 5 μg 1,4-ipomeadiol perg Sweet potato leaves provide a dietary source of
tissue. vitamins, minerals, antioxidants, dietary fibre
The bitter principle of sweet potato roots and essential fatty acids (Johnson and Pace
destroyed by the sweet potato weevil, Cylas for- 2010). Bioactive compounds contained in this
micarius elegantulus, was isolated and proved to vegetable play a role in health promotion by
be ipomeamarone, which had originally been iso- improving immune function, reducing oxidative
lated from fungus-infected sweet potatoes stress and free radical damage, reducing cardio-
(Akazawa et al. 1960). When sweet potato root vascular disease risk and suppressing cancer cell
tissues were infested by the larvae of sweet potato growth. Research had affirmed the potential car-
weevil, Cylas formicarius and West Indian sweet dioprotective and chemopreventive advantages of
potato weevil, Euscepes postfasciatus, furano- consuming sweet potato leaves, thus indicating
terpenoids namely ipomeamarone, dehydroipo- that increased consumption of this vegetable
meamarone, 4-hydroxymyoporone, should be advocated. The levels of Fe, Ca and Mg
ipomeamaronol and component A and coumarins essential trace elements of Cr, Co, Ni, Cu and Zn
umbelliferone and scopoletin were produced in in 11 lines of sweet potato leaves were similar to
brown necrotic layer formed during the infesta- those of common green leafy vegetables (Taira
tion (Uritani et al. 1975). et al. 2013). The ratio of K and Na for the seven
Sweet potato had been found to accumulate lines of sweet potato leaves was higher than that
umbelliferone and scopoletin after biotic and abi- of spinach, indicating that sweet potato leaves
otic stresses (Matsumoto et al. 2012) In the bio- may be used in antihypertensive diet. The sele-
synthesis of the coumarins, they found that Ib1 nium and manganese contents were higher in all
proteins exhibited ortho-hydroxylation activity the sweet potato leaves than in other green leafy
toward feruloyl coenzyme A (CoA) to form sco- vegetables, such as spinach and water spinach.
poletin. Ib2 proteins catalyzed ortho- Crude protein ranged from 16.78 to 25.39 %;
hydroxylation of feruloyl-CoA and also of crude fibre from 9.75 to 12.14 %; crude fat from
p-coumaroyl-CoA to form scopoletin and umbel- 0.38 to 1.91 %; ash content from 8.71 to 11.60 %;
liferone, respectively. Fungal and chitosan treat- moisture content (fwb) ranged from 80.16 to
ments increased levels of umbelliferone and its 88.20 %; carbohydrate values from 53.29 to
glucoside (skimmin) in the tubers, and expres- 59.01 % and calorific values ranged from 1344.00
sion of the Ib2 gene was induced concomitantly. to 1399.00 kJ/g (316.66–329.76 cal/g) for the
Two sesquiterpenoids phytoalexins, called sweet potato leaves (Oduro et al. 2008). Elemental
components A1 and A2, were isolated from sweet analysis of the leaves in mg/100 g dry matter
potato root tissue either infected by Ceratocystis (DM) indicates the sweet potato leaves contained
fimbriata or injured by HgCl2 (Ito et al. 1984). appreciable levels of calcium (1310.52–1402.27)
Both components inhibited germination and and iron (9.62–23.02).
term-tube growth of Ceratocystis fimbriata-oak Fresh sweet potato leaves contained the fol-
strain. When 14C-component A2 was supplied to lowing nutrient value per 100 g edible portion
diseased tissue discs, the label was efficiently proximate: water 86.81 g, energy 42 kcal
incorporated into dehydroipomeamarone, ipo- (175 kJ), protein 2.49 g, total lipid 0.51 g, ash
meamarone, ipomeamaronol and component B1, 1.36 g, carbohydrate 8.82 g, total dietary fibre
indicating it to be a close precursor of these com- 5.3 g, Ca 78 mg, Fe 0.97 mg, Mg 70 mg, P 81 mg,
ponents. In the case of 14C-component A1 admin- K 508 mg, Na 6 mg, Se 0.9 mcg; vitamin C
126 Convolvulaceae

11 mg, thiamin 0.156 mg, riboflavin 0.345 mg, crude protein 26.37, 37.06 %; total ash 12.87,
niacin 1.130 mg, pantothenic acid 0.225 mg, 20.41 %, crude fibre 16.01, 21.48 %, total lipid
vitamin B-6 0.190 mg, folate DFE 1 μg, vitamin 3.11, 3.27 %; soluble carbohydrates 41.62,
A RAE 189 μg, vitamin A 3778 IU, β-carotene 17.76 %; ascorbic acid 305.58, 273.17 mg/100 g,
2217 μg, α-carotene 42 μg, β-cryptoxanthin carotenoids 44.18, 53.32 mg/100 g, Fe 15.22,
58 μg, lutein-zeaxanthin 14,720 μg, vitamin K 17.48 mg/100 g; Ca 3457, 4255 mg/100 g, oxa-
(phylloquinone) 302.2 μg, total saturated fatty lates 3730.50, 2901.50 mg/100 g and polyphe-
acids 0.110 g, 16:0 (palmitic acid) 0.1 g, 18:0 nols 5.28, 22.16 mg/100 g (Mwanri et al. 2011).
(stearic acid) 0.01 g, total monounsaturated fatty Drying with salt and cooking with lemon reduced
acids 0.020 g, 18:1 undifferentiated (oleic acid) polyphenols significantly, with retention of 42
0.020 g, total polyunsaturated fatty acids 0.228 g, and 56 % respectively, while cooking with lemon
18:2 undifferentiated (linoleic acid) 0.192 g, 18:3 lowered significantly the oxalate levels.
undifferentiated (linolenic acid) 0.036 g; amino Two major anthocyanins in purple sweet
acids – tryptophan 0.035 g, lysine 0.228 g, methi- potato were identified as cyanidin 3-caffeylferuly
onine 0.086 g, cystine 0.047 g, flavones – api- sophoroside-5-glucoside of cyanidin and peoni-
genin 0.1 mg, luteolin 0.1 mg, flavonols – kaempferol din 3-caffeylferulysophoroside-5-glucoside
2.1 mg, myricetin 4.4 mg and quercetin 16.9 mg (Odake et al. 1992).
(USDA-ARS 2014). Sweet potato leaves of ten Fifteen anthocyanins of acylated cyanidin and
sweet potato varieties were found to contain the peonidin types were identified in sweetpotato
following flavonoid (% DW) quercetin 0.98 %, leaves: cyanidin 3-sophoroside-5-glucoside;
myricetin 0.12 %, luteolin 0.23 %, apigenin peonidin3-sophoroside-5-glucoside; p-hydro-
0.38 %, kaempferol 0.07 %, total flavonoids xybenzoylated (cyanidin 3-sophoroside-5-
1.79 % (Ojong et al. 2008). Sweet potato purple glucoside); caffeoylated (cyanidin3-sophoroside-
and green leaves were found to contain the flavo- 5-glucoside); p-hydroxybenzoylated (peonidin-
nols quercetin (852.63; 83.22 μg/g dw), and 3-sophoroside-5-glucoside); caffeoylated (peoni-
morin (3266.11; 9376.21 μg/g dw) and anthocy- din 3-sophoroside-5-glucoside); feruloylated
anidins cyanidin (1437.32 μg/g Dw, not detected (cyanidin 3-sophoroside-5-glucoside); cyanidin
(nd)) and malvidin (30.37 μg/g DW, nd), respec- 3-(6,6′-caffeoyl-p-hydroxybenzoylsophoroside)-
tively (Chao et al. 2014). Innami et al. (1998) 5-glucoside; cyanidin 3-(6,6′-dicaffeoylso-
reported the nutrient composition of freeze-dried phoroside)-5-glucoside; cyanidin 3-(6-
sweet potato leaf powder as follows: moisture caffeoylsophoroside)-5-glucoside; cyanidin
3.9 %, protein 29.5 %, fat 5.5 %, ash 10.4 %, car- 3-(6,6′-caffeoylferuloylsophoroside)-5-gluco-
bohydrates 10 % and total dietary fibre 40.7 %. A side; peonidin 3-(6,6′-dicaffeoylsophoroside)-
soluble dietary fibre (SDF) was extracted from 5-glucoside; peonidin 3-(6,6′-caffeoyl-p-
the sweet potato leaf powder (Ishida et al. 2004). hydroxybenzoylsophoroside)-5-glucoside; cyan-
This substance was found to show high viscosity idin 3-(6-caffeoylsophoroside)-5-glucoside and
and to be mainly composed of xylose (34.7 %) peonidin 3-(6,6′-caffeoylferuloylsophoroside)-
and uronic acid (38.8 % as galacturonic acid). 5-glucoside (Islam et al. 2002a).
The average contents of minerals and vitamin From sweet potato leaves five compounds
in the leaves of cv. ‘Suioh’ were 115 mg Ca, were isolated and identified as β-sitosterol, frie-
1.8 mg Fe, 3.5 mg Carotene, 7.2 mg vitamin C, delin, acetyl-β-amyrin, caffeic acid and quercetin
1.6 mg vitamin E and 0.56 mg vitamin K per (Tan et al. 1995). Eight compounds: β-amyrin
100 g fresh weight leaves (Islam 2006). The acetate, friedelin, epifriedelanol, n-triacontanol,
nutrient and antinutrient (oxalate and polyphe- β-sitosterol (5), ethyl caffeate, scopoletin and
nol) content of green midrib sweet potato leaves daucosterol were isolated from sweet potato
and purple midrib sweet potato leaves were leaves (Luo and Kong 2005a). Six different poly-
determined to be respectively as: moisture con- phenolic compounds were identified and quanti-
tent 85.63, 86.28 %; dry matter 14.37, 13.72 %; fied in sweet potato leaves (Islam et al. 2002b,
Ipomoea batatas 127

2003a, b). The relative levels of polyphenolic ity, antimutagenic activity, anticancer, antidiabe-
acids were as follows: 3,5-di-O-caffeoylquinic tes and antibacterial activity in-vitro or in-vivo
acid > 4,5-di-O-caffeoylquinic acid > chloro- which may be helpful for maintaining and pro-
genic acid (3-O-caffeoylquinic acid) > 3,4-di-O- moting human health.
caffeoylquinic acid > 3,4,5-tri-O-caffeoylquinic Methanol extracts of vine latex of four sweet
acid > caffeic acid. The highest 3,4,5-tri-O- potato cultivars yielded hexadecyl, octadecyl and
caffeoylquinic acid and 4,5-di-O-caffeoylquinic eicosyl p-coumarates (Snook et al. 1994). Both
acid occurred at 221 and 1183.30 mg/100 g dry Z- and E-isomers of the phenolic acid were found,
weight, respectively. Six caffeoylquinic acid with the latter predominating. Trace quantities of
derivatives were quantified and divided into three hexadecyl (Z)- and (E)-ferulates were also identi-
categories based on the leaf polyphenol content: fied in ester concentrates. Levels of octadecyl
high, medium and low polyphenol accumulator (E)-p-coumarate ranged from 0.7 % fresh weight
(Islam et al. 2003b). The caffeic acid and deriva- in cv. Resisto to almost 2 % in cv. Jewel, while
tives were positively correlated with the total the hexadecyl ester levels were only 1/4 to 1/3
polyphenol contents, and the correlation coeffi- these values. Levels of the Z-esters were 1/10 to
cients varied widely among the different catego- 1/20 of the levels of the corresponding E-isomers.
ries. Most of the phenolic compounds were Levels of the esters in cv. Jewel sweetpotato root
highest in leaves from plants grown at 20 °C latex were 2–10-fold the levels in the vine latex,
without shading except 4,5-di-O-caffeoylquinic while the ratio of E-esters to Z-esters was found
acid (Islam et al. 2003a). The results indicated to be 7–14-fold.
that growing leaves under moderately high tem- Sweet potato leaves, petiole and stem were
peratures and in full sun enhanced the accumula- found to contain folic acid and polyphenols
tion of phenolic components. These phenolics (Taira et al. 2007). The amounts of folic acid and
exhibited various kinds of biological activities – polyphenol in eligible parts (leaf and petiole),
radical scavenging, antimutagenic, anticancer- except in cv Okinawa 100 species, contained
ous, antidiabetic and antimicrobial activities higher amounts than stems and were similar to
(Islam 2006). Of five phenolic acids caffeic acid, amounts of spinach. Miyanou 36 had the highest
chlorogenic acid, 4,5-di-O-caffeoylquinic acid, amounts of folic acid.
3,5-di-O-caffeoylquinic acid and 3,4-di-O- Sweet potato leaves were found to contain
caffeoylquinic acid identified in sweet potato functional polyphenols, such as caffeic acid
storage leaves, 3,5-di-O-caffeoylquinic acid and/ (CA), chlorogenic acid (ChA), 4,5-di-
or 4,5-di-O-caffeoylquinic acid were predomi- caffeoylquinic acid (4,5-diCQA), 3,5-diCQA,
nant (Truong et al. 2007). Sweetpotato leaves had 3,4-diCQA and 3,4,5-triCQA (Taira and Ohmine
the highest phenolic acid content followed by the 2011). High-speed counter-current chromatogra-
peel, whole root and flesh tissues. phy was used to isolate and purify four caf-
Sweet potato leaves were found to contain a feoylquinic acid derivatives and a mixture of two
high content of polyphenolics in comparison flavonoids from sweet potato leaves (Li et al.
with 12 kinds of the major commercial vegeta- 2012). The caffeoylquinic acid derivatives were
bles (Yoshimoto et al. 2006). The polyphenolics 3-O-caffeoylquinic acid (1), 4,5-di-O-
were composed of caffeic acid (CA) and five caffeoylquinic acid (4), 3,5-di-O-caffeoylquinic
kinds of caffeoylquinic acid derivatives, 3-mono- acid (5) and 3,4-di-O-caffeoylquinic acid (6).
O-caffeoylquinic acid (chlorogenic acid, ChA), The mixture of flavonoids was separated by pre-
3,4-di-O-caffeoylquinic acid (3,4-diCQA), parative high-performance liquid chromatogra-
3,5-di-O-caffeoylquinic acid (3,5-diCQA), phy into quercetin-3-O-β-D-galactopyranoside
4,5-di-O-caffeoylquinic acid (4,5-diCQA) and (2) and quercetin-3-O-β-D-glucoside (3). The
3,4,5-tri-O-caffeoylquinic acid (3,4,5-triCQA). purities of compounds 1–6 were 95.8 % (5.4 mg),
These polyphenolics showed various kinds of 99.5 % (6.1 mg), 98.7 % (15.1 mg), 97.8 %
physiological functions, radical scavenging activ- (14.5 mg), 96.2 % (10.3 mg) and 96.8 % (7.8 mg),
128 Convolvulaceae

respectively. The following phenolic compounds amounts of at least four caffeoyl-feruloylquinic

were identified in the leaves of 20 sweet potato acids. Chlorogenic acids were not detected in
cultivars: quinic acid; hydroxybenzoic acids; sweet potato root.
hydroxycinnamic acids; caffeic acid; p-coumaric Young leafy shoots were reported to be rich in
acid; ferulic acid; sinapic acid; chlorogenic acid; proteins and a good source of vitamin B1 thia-
5-CQA, 5-O-caffeoylquinic acid; 3-CQA, 3-O- mine, riboflavin B2, folic acid and ascorbic acid
caffeoylquinic acid; 4-CQA, 4-O-caffeoylquinic and a good source of β-carotene (Villareal et al
acid; 3,4-diCQA, 3,4-di-O-caffeoylquinic acid; 1979a, b, 1985, Woolfe 1992). The leaves had
3,5-diCQA, 3,5-di-O-caffeoylquinic acid; 4,5- higher levels of Fe, P, K, Mg and Se than the
diCQA, 4,5-di-O-caffeoylquinic acid; 3,4,5- tubers. Yields of sweet potato tips varied from 10
triCQA, 3,4,5-tri-O-caffeoylquinic acid; FQA, to 16 t/ha in weight and 61 to 352/m2 in number,
feruloylquinic acid; CFQA, caffeoyl-feru- whilst yields of marketable roots varied from 1 to
loylquinic acid (Luo et al. 2013). Two dihexo- 16 t/ha (Villareal et al. 1979b). The tips appeared
sides (such as quercetin-O-dihexoside) and one to provide an excellent source of vitamin B2, a
hexoside of quercetin (quercetin-3-O-hexose- vitamin often deficient in Asian diets. Cultivar
hexoside) were also characterized. differences in dry matter, fibre, ash, vitamin B2
Three chemical compounds fumaric acid, suc- and oxalate were also observed. Wide variation
cinic acid and 7,3′,4′-trimethylquercetin were was found in the morphological characteristics of
isolated from sweet potato leaves and stems (Liu sweet potato leaf tips which were acceptable as a
et al. 1991). Five flavonoid compounds were iso- vegetable for human consumption in terms of
lated from sweet potato leaves and identified as: yield, palatability, tenderness and nutritive traits
tiliroside, astragalin, rhamnocitrin, rhamnetin (Villareal et al. 1979a). Among the leaf types
and kaempferol (Luo and Kong 2005b). Six com- evaluated, Kinangkong (a fine leaf cultivar) pro-
pounds were isolated from 90 % ethanol leaf duced the highest yield, and had the highest
extract and identified as tetracosane, myristic amount of protein, lowest oxalate and fairly high
acid, β-sitosterol, β-carotene, daucosterol and dry matter, making it a very desirable leafy
quercetin (Lv et al. 2009). Sweet potato leaves vegetable.
were found to contain per 100 g dry weight, Antia et al. (2006) reported sweet potato
345.65 mg alkaloids, 328.44 anthraquinones and leaves to contain an appreciable amount of nutri-
phenolic compounds 662.02 mg (Pochapski et al. ents, vitamins and mineral elements and low lev-
2011). els of toxicants and should be included in diets to
Ipomoea batatas stems were found to contain supplement our daily allowance needed by the
sapons, flavonoids, phlobatannins, tannins and body. Their analyses reported that sweet potato
alkaloids (Essiett and Ukpong 2014). The stem leaves had the following nutrient composition
had the following proximate composition: 10 % (per 100 g dm): crude protein 24.85 %, crude fat
moisture, 7.2 % ash, 5.05 % crude fibre, 9.4 % 4.90 %, crude fibre 7.20 %, ash 11.10 %, carbo-
crude protein, 4.65 % lipid, 73.7 % carbohydrate hydrate 51.95 %, moisture content 82.21 %, calo-
and 374.25 kcal energy value. It also contained rific value 351.30 kcal, vitamin A 0.672 mg/100 g,
antinutrients (mg/100 g) – hydrogen cyanide vitamin C 15.20 mg/100 g. The elemental analy-
0.103 mg, total oxalate 90.8 mg, soluble oxalate sis of the leaves in mg/100 g, zinc 0.08 mg, potas-
66 mg, phytate 1.25 mg and 4.51 mg tannins. sium 4.05 mg, sodium 4.23 mg, manganese
Caffeoylquinic acids were quantitatively the (4.64 mg, calcium 28.44 mg, magnesium 340 mg
major sub-group of chlorogenic acids detected in and iron 16 mg. The antinutrient composition for
the stem and the only sub-group detected in the phytic acid, cyanide, tannins and total oxalate
leaves (Zheng and Clifford 2008). This sub-group were 1.44, 30.24, 0.21 and 308.00 mg/100 g,
was dominated by 5-caffeoylquinic acid. The respectively. Studies in Japan (Ishida et al. 2000)
stem also contained three feruloylquinic acids, reported that sweet potato leaves contain a large
3,5- and 4,5-dicaffeoylquinic acid, and small amount of protein, showing high amino acid
Ipomoea batatas 129

score. Any part of sweet potato was rich in dietary tuber portion of the plant contained more than >
fibre and in particular, leaves were soluble dietary 3.0 % per g by dry weight. Through enzymatic
fibre and stems were insoluble dietary fibre, hydrolysis 45 % ferulic acid, 29 % vanillin, 16 %
respectively. Mineral content, particularly iron, vanillic acid and negligible (about 0.5 %) cin-
and vitamin content such as carotene, vitamin namic acid were obtained from the stems. The
B2, vitamin C and vitamin E were high in leaves amount of vanillic acid and vanillin released were
in comparison with other vegetables. Furthermore, 11.04 and 14.69 mg/g, respectively, when incu-
polyphenol and flavonoid content in leaves are bated with 1.0 % Viscozyme L for an hour, com-
comparatively high. These results suggest that pared with only 7.47 and 8.30 mg/g, respectively,
the whole parts of sweet potatoes should be uti- when incubated for an hour with 1.0 %
lized as valuable foodstuffs to cope with future Ultraflo L.
changes in food supply and demand, particularly The aerial parts of Ipomoea batatas were
in developing countries. Sweet potato leaves are found to produce four new resin glycosides, des-
excellent source of lutein with levels from ignated as ipomotaosides A, B, C and D were
34–68 mg/100 mg depending on varieties isolated from sweet potato dried aerial parts
(Khachatryan et al. 2003). This places sweet (Yoshikawa et al. 2010).
potato leaves second in lutein content after mari- Three kinds of pure polysaccharide, named
gold flowers, and number one among edible veg- PSPV I, PSPV II and PSPVIII, respectively, were
etables. Lutein, an antioxidant carotenoid obtained from sweet potato vines (SPV) (Luo
(3,3′-dihydroxy-D-carotene), has been identified and Gao 2008). PSPV I had a molecular weight
as a dietary strategy that can delay the onset of of 6.278 × 104 D and was mainly composed of
age-related macular degeneration (AMD). AMD xylose, mannose and glucose. PSPV II and
is a medical condition predominantly found in PSPVIII had molecular weights of 3.801 × 104 D
elderly adults in which the centre of the inner lin- and 1.418 × 104 D, respectively. PSPVII was
ing of the eye, known as the macula area of the mainly composed of mannose and galactan and
retina, suffers thinning, atrophy and in some PSPVIII mainly composed of glucose, xylose
cases, bleeding. This can result in loss of central and rhamnose. Sweet potato leaves were found to
vision, which entails the inability to see fine contain galactolipids: 53,940 mg/kg monogalac-
details, to read or to recognize faces. Sweet tosyldiacylglycerols (MGDG) and 22,640 mg/kg
potato leaves may help in the fight against age- digalactosyldiacylglycerols (DGDG) (Napolitano
related macular degeneration (AMD). The crude et al. 2007).
protein, crude fibre, crude fat, carbohydrate and Two forms of trypsin inhibitors with molecu-
ash contents of leaves from 40 sweet potato culti- lar weights of 31 and 14 kDa were found in sweet
vars ranged between 16.69–31.08, 9.15–14.26, potato leaves and they were different from those
2.08–5.28, 42.03–61.36 and 7.39–14.66 g/100 g found in the roots (Wang and Yeh 1996). A pro-
dry weight (DW), respectively (Sun et al 2014b). teinaceous invertase inhibitor, designated ITI-L,
According to the index of nutritional quality, with molecular weight of 10 kDa was purified
sweet potato leaves were good sources of protein, from sweet potato leaves. It was thermostable
fibre and minerals, especially K, P, Ca, Mg, Fe, (90 % of the activity remained after incubation at
Mn and Cu. The correlation coefficient between 100 °C for 20 min) (Wang et al. 2003). High-
antioxidant activity and total polyphenol content quality and intact total RNA with a yield of
was the highest (R2 = 0.76032), indicating that 0.2 mg/g fresh weight was isolated from leaf
polyphenols were important antioxidants in blade, petiole, stem, fibrous root, thick root and
sweet potato leaves. storage root purple-fleshed sweet potato (Zhou
Sweet potato was reported to be a particularly et al. 2009).
rich source of ferulic acid (Min et al. 2006). The Chen et al. (2008b) found that elevation of
tuber contained 0.54 % per g dry weight; the non- cytosolic Ca2+ by ethylene may stimulate protein
130 Convolvulaceae

phosphatase and mitogen-activated protein Antioxidant Activity

kinase kinase activation (MAPKK), which finally
activated ipomoelin gene expression in sweet Of 21 sweet potato cultivars with different flesh
potato. They also found that cyclic guanosine colours, purple-fleshed cultivars which contained
monophosphate (cGMP) was necessary for anthocyanins, had the highest tert-butylperoxyl
expression of wounding-responsive microRNAs radical (t-BuOO·)· scavenging activities (Furuta
miR828, which repressed the expression of et al. 1998). Those cultivars with purple flesh also
IbMYB and IbTLD, leading to accumulation of had the highest antioxidative activities against
lignin and hydrogen peroxide to participate in the lipid peroxidation induced by auto-oxidation of
plant defense mechanisms (Lin et al. 2012a). In a linoleic acid. Most of the sweet potato cultivars
recent subsequent study, they found wounding in with white, white-yellow, yellow and orange
leaves repressed IbHO expression and carbon flesh had low t-BuOO· scavenging and antioxida-
monoxide production, induced hydrogen perox- tive activities; however, some of them had higher
ide generation and extracellular signal-regulated activities. In all sweet potato cultivars tested, the
kinase (ERK) phosphorylation and then stimu- t-BuOO· scavenging activities were higher with
lated ipomoelin expression (Lin et al. 2014). an increase in the total phenolic content. Due to
Three sweet potato metallothionein genes, cyste- its high phenolic and anthocyanin content, purple
ine-rich, low molecular weight, metal-binding sweet potato exhibited high antioxidant activity
proteins, type 1 (IbMT1), type 2 (IbMT2) and (Cevallos-Casals and Cisneros-Zevallos 2002).
type 3 (IbMT3) were found to respond differen- Antioxidant activity and total phenolic content
tially to abiotic stress and heavy metal toxicity were 3.2 and 2.5 times higher, respectively, than
(Kim et al. 2014). IbMT1 was predominantly that of a blueberry variety assayed. Antioxidant
expressed in leaves, roots and callus. IbMT2 activity in purple sweet potato skin was found to
transcript was detected only in stems and fibrous be almost three times higher than in the rest of the
roots, whereas IbMT3 was strongly expressed in tissue. Acylated anthocyanins isolated from a
leaves and stems. The levels of IbMT1 expres- highly pigmented callus induced from the storage
sion were strongly elevated in response to Cd and root of purple-fleshed sweet potato cultivar
Fe, and moderately higher in response to Cu. The Ayamurasaki exhibited both higher stability and
IbMT3 expression pattern in response to heavy higher DPPH radical scavenging activity than
metals was similar to that of IbMT1. Exposure to corresponding nonacylated cyanidin and peoni-
abiotic stresses such as methyl viologen (MV; din 3-O-sophoroside-5-O-glucosides (Terahara
paraquat), NaCl, polyethylene glycol (PEG) and et al. 2004).
H2O2 up-regulated IbMT expression; IbMT1 Purple-fleshed sweet potato containing antho-
responded strongly to MV and NaCl, whereas cyanin pigments displayed a potent antioxidative
IbMT3 was induced by low temperature and activity (Oki et al. 2002; 2003) An 80 % ethanol
PEG. A 16-amino-acid peptide, IbACP (Ipomoea extract from purple-fleshed sweet potato cultivars
batatas anticancer peptide), was isolated from harvested exhibited a 1,1-diphenyl-2-
sweet potato leaves (Chang et al. 2013). picrylhydrazyl (DPPH) radical-scavenging activ-
The presence and levels of zeatin, ribosylze- ity of 8.6–49.0 μmol expressed as Trolox
atin, 9-glucosylzeatin ([9G] Z), N6- equivalent/g of fresh weight. Oki et al. (2002)
isopentenyladenosine and 9-glucosyl- found that the dominant DPPH radical-scavengers
N6-isopentenyladenine ([9G] iP) were deter- in sweet potato purple-fleshed cultivars
mined in calluses of sweet potato plant (Sugiyama ‘Ayamurasaki’ and ‘Kyushu-132’ were anthocya-
et al. 1988). The levels of [9G]iP and [9G]Z were, nins rather than phenolic compounds, while those
respectively, 3.6 and 2.7 μg per 100 g fw of the in ‘Miyanou-36’ and ‘Bise’ were phenolic com-
callus derived from the tuberous root of sweet pounds, such as chlorogenic acid. ‘Ayamurasaki’
potato. and ‘Kyushu-132’ were rich in anthocyanins with
Ipomoea batatas 131

peonidin aglycon, whereas ‘Miyanou-36’, ‘Bise’ stress and increasing the glutathione (GSH) lev-
and ‘Tanegashimamurasaki’ contained cyanidin els (Sakatani et al. 2007). Embryos exposed to
aglycon. Steed and Truong (2008) reported that heat shock without anthocyanins showed a sig-
the DPPH radical-scavenging activities of purple- nificant decrease in blastocyst formation rate and
fleshed sweet potatoes were 47.0–87.4 μmol tro- GSH content and an increase in intracellular
lox equivalent (TE)/g fw, and the oxygen radical reactive oxygen species (ROS) compared with
absorbance capacity (ORAC) values were non-heat-shocked embryos.
between 26.4 and 78.2 μmol TE/g fw. Oki et al. The polyphenolic compound 4,5-di-O-
(2003) developed a simple and rapid spectropho- caffeoyldaucic acid from sweet potato tuber
tometric method for selecting breeding lines of exhibited higher antioxidant activity in both
breeding lines of purple-fleshed sweet potato cul- DPPH and FRAP methods compared to that of all
tivars with a high DPPH radical-scavenging antioxidant standards, l-ascorbic acid, tert-butyl-
activity. In-vitro antioxidant assay trans-4,5- 4-hydroxy toluene (BHT) and gallic acid used at
dicaffeoylquinic acid from purple sweet potato the same molar concentration (Dini et al. 2006a,
cv Ayamurasaki showed significant antioxidant 2006b). Two components, cyanidin 3-O-(2-O-(6-
activities (Zhao et al. 2014). O -( E )-caffeoyl- β - D -glucopyranosyl)- β - D -
Purple sweet potato anthocyanin exhibited glucopyranoide)-5-O-β-D-glucopyranoside and
1,1-diphenyl-2-picrylhydrazyl (DPPH) radical- peonidin 3-O-(2-O-(6-O-(E)-caffeoyl-β-D-
scavenging activity and effectively inhibited lipid glucopyranocyl)-β-D-glucopyranoide)-5-O-β-D-
peroxidation initiated by Fe2+ and ascorbic acid glucopyranoside, which were detected in the
in rat brain homogenates (Cho et al. 2003). plasma, protected low-density lipoprotein from
Philpott et al. (2004) demonstrate in-vitro anti- oxidation at a physiological concentration. At a
oxidant activity by a mottled purple-fleshed concentration of 0.5 mg/mL, the reducing power
sweet potato anthocyanins, where an additive of purple sweet potato (PSP) anthocyanins,
effect with hydroxycinnamic acids was observed. L-ascorbic acid (L-AA) and butylated hydroxy-
They asserted that sweetpotato could be eaten toluene (BHT) reached 0.572, 0.460 and 0.121,
several hundred grams at a time and as a staple respectively (Jiao et al. 2012; Jiao et al. 2014).
could confer superior health protection against a PSP anthocyanins exhibited high DPPH and
variety of degenerative disease processes by superoxide anion radicals-scavenging activities;
anthocyanic varieties of sweet potato in compari- for DPPH. IC50 values were PSP anthocyanins
son to most common fruits and vegetables. 6.94 μg/mL, L-AA 6.10 μg and BHT 123.46 μg/
Anthocyanins from purple sweet potato (PSP) mL; for superoxide anion radical-scavenging
showed stronger 1,1-diphenyl-2-picrylhydrazyl activity IC50 values were PSP anthocyanin
(DPPH) radical-scavenging activity than antho- 3.68 μg/mL, L-AA 10.01 μg/mL and BHT 50 μg/
cyanins from red cabbage, grape skin, elderberry mL. Sixteen kinds of anthocyanins cyanidin,
or purple corn, and eight major components of peonidin and mono- and diacylated forms of
the anthocyanins from PSP showed higher levels cyanidin and peonidin were detected.
of activity than ascorbic acid (Kano et al. 2005). The total antioxidant activity (hydrophilic +
In PSP anthocyanin-injected rats and PSP lipophilic ORAC (oxygen radical absorbance
beverage-administered human volunteers, DPPH capacity)) was highest (14.7–29.2 μmol TE/g
radical-scavenging activity in the urine increased. fresh weight (fw)) for NC415 (purple-fleshed),
The elevation of plasma transaminase activities orange-fleshed (5.89–10.3 μmol TE/g fw) and
induced by carbon tetrachloride was depressed in lowest (2.72–3.33 μmol TE/g fw) for Xushu 18
rats administered PSP anthocyanin solution. (white-fleshed) (Teow et al. 2007). The
Results of in-vitro studies indicated that purple hydrophilic-ORAC values were significantly cor-
sweet potato anthocyanins maintained the intra- related with the DPPH (R2 = 0.859) and
cellular redox balance of heat-shocked bovine 2,2′-azinobis(3-ethyl-benzothiazoline-6-sulfonic
embryos by reducing intracellular oxidative acid) (ABTS) (R2 = 0.761) values. However, the
132 Convolvulaceae

lipophilic-ORAC values were poorly correlated tuber extract showed strong DPPH radical-scav-
with the b-carotene contents (R2 = 0.480). The enging activity of about 83 % (Arockiamary et al.
total phenolic contents (0.011–0.949 mg chloro- 2014). In ferric reducing antioxidant power
genic acid equivalent/g fw) were highly corre- (FRAP) assay, the extract showed increased
lated with the hydrophilic-ORAC (R2 = 0.937) absorbance which was directly related to the
and DPPH (R2 = 0.820) values. Purple sweet combined or total reducing power of the electron-
potato (PSP) ethanol extract (100-fold diluted) donating antioxidants. Nitric oxide radical inhi-
showed stronger radical (2,2-diphenyl-1- bition was 41 %. About 73 % of superoxide anion
picrylhydrazyl radical) scavenging activity than was inhibited, followed by 72 % of hydrogen per-
the water extract of PSP and the ethanol extract oxide radical-scavenging activity.
of YSP (up to a sixfold higher activity) (Park El Far and Taie (2009) found that the domi-
et al. 2010). The ethanol extract of PSP also nant DPPH radical-scavengers of Abees, the
exhibited the highest increase in ferric reducing Egyptian orange-fleshed sweet potato cultivar,
ability among all extracts. Cupric ion-mediated was due to the presence of anthocyanins and phe-
LDL oxidation was strongly inhibited by the eth- nolic compounds rather than flavonoids, while in
anol extract of PSP, with similar potency to vita- the genotype 199062.1 it was attributed flavo-
min C treatment. noids and in genotype 199004.2 was due to phe-
Small sweet potato roots (≈4 g root weight) nolic compounds. The DPPH and ABTS
had a higher antioxidant activity and phenolic radical-scavenging activities of Egyptian sweet
content compared with full-sized marketable potato cultivars varied from 1.10 to 1.72 and 0.85
roots (≈300 g root weight) (Padda and Picha to 1.51 μmol trolox equivalent (TE)/g dw, respec-
2007). Phenolic content in marketable roots was tively (Bellail et al. 2012). The reducing power
significantly higher in the cortex tissue than in between 0.1 and 0.25 mg chlorogenic acid equiv-
the internal pith tissue. The highest total phenolic alent (mg ChAE)/g dry weight basis (dw) and
content [chlorogenic acid equivalents (10.3 mg/g total phenolic content ranged from 0.53 to
dry weight)] and antioxidant activity [Trolox 0.87 mg ChAE/g dw. The most abundant indi-
equivalents (9.7 mg/g dry weight)] was found in vidual phenolic acids in processed flesh roots tis-
cortex tissue of small-sized roots. Antioxidant sues were chlorogenic acid followed by
activity of different sweet potato genotypes roots 3,5-dicaffeoylquinic acid. Total phenolic con-
ranged from 1.3 to 4.6 mg/g dry weight (DW) tents were highly correlated with RP, DPPH and
Trolox equivalent (Padda and Picha 2008). Total ABTS, also the correlation between DPPH and
phenolic content, expressed in terms of chloro- ABTS values were significantly high. Thermal
genic acid equivalent, in different sweet potato processing significantly increased the total phe-
genotypes ranged from 1.4 to 4.7 mg/g DW. The nolic content, as well as individual phenolic acids
highest total phenolic content and antioxidant and antioxidant capacity of all the cultivars under
activity were observed in a purple-fleshed geno- study. Purple sweet potato cv. NCPuR02-020 was
type. Chlorogenic acid and 3,5-dicaffeoylquinic found to contain the highest levels of all phenolic
acid were the predominant phenolic acids, components (Grace et al. 2014). A decrease in
while caffeic acid was the least abundant in phenolic components was observed after curing
most genotypes. The highest content of chloro- and storage. Levels of carotenoids were signifi-
genic acid (422.4 μg/g DW) was present in cantly increased over curing and storage times. In
a white-fleshed cultivar ‘Quarter Million’ contrast, antioxidant activity and ascorbic acid
imported from Jamaica. However, a purple- gradually decreased with storage. The DPPH
fleshed genotype had the highest amounts of scavenging activity of purple sweet potato wine
3,5-dicaffeoylquinic (485.6 μg/g DW), 3,4-dicaf- was 58.95 % at a dose of 250 μg/mL (Ray et al.
feoylquinic (125.6 μg/g DW), 4,5-dicaf- 2012).
feoylquinic (284.4 μg/g DW) and caffeic The thioredoxin h protein from sweet potato
(20.5 μg/g DW) acids. Ipomoea batatas aqueous storage roots at a concentration of 12.5 mg/mL
Ipomoea batatas 133

exhibited the highest activity (expressed as TBARS values were obtained from root samples
0.37 mM ABTS* radical cation being cleared) in of sweet potato, and followed by stems and
a total antioxidant status test (Huang et al. 2004b). leaves, indicating that leaf sample showed the
In the DPPH staining thioredoxin h appeared as strongest antioxidant activity (Boo et al. 2005).
white spots when it was diluted to 50 mg/mL (a Sweet potato leaves had a significantly higher
final amount of 15 μg). The reducing power, Fe2+- phenolic content and antioxidant activity than
chelating ability, FTC activity and protection roots (Padda and Picha 2007). Young, immature
against hydroxyl radical-induced calf thymus unfolded leaves had the highest total phenolic
DNA damage were also found with the thiore- content (88.5 mg/g dry weight) and antioxidant
doxin h protein. It was suggested that thioredoxin activity (99.6 mg/g dry weight). Chlorogenic
h might contribute to its antioxidant activities acid was the major phenolic acid in root and leaf
against hydroxyl and peroxyl radicals. tissues with the exception of young immature
Antioxidant activities of the raw, boiled, leaves in which the predominant phenolic acid
steamed and fried sweet potato was 78.76, 89.67, was 3,5-dicaffeoylquinic acid. Sweet potato cul-
97.92 and 57.89 % (as DPPH radical inhibition tivars with yellow flesh and leaf part exhibited
percent), respectively (Tokusoglu and Yildirim strong antioxidant activities. Studies showed that
2012). With steaming process, radical inhibition flavonoids of sweet potato vines had a strong
percent increased 1.24-fold. Anthocyanin level of scavenging effect on DPPH (Ding et al. 2010).
Turkish sweet potato cv Hatay Kirmizi (as Their scavenging activity on superoxide radicals
cyanidin-3-glucoside (C3G) equivalent) was was stronger than that of rutin, and the scaveng-
determined as 11,992 mg/100 g) (Tokusoglu and ing activity on hydroxyl radical was higher than
Yildirim 2012). Anthocyanins were detected as that of rutin and vitamin C. Additionally, they
13,767 mg/100 g; 24,756 mg/100 g; exhibited strong antioxidant activities in the lin-
6755 mg/100 g in boiled, steamed and fried sweet oleic acid model system. Of six sweet potato
potatoes, respectively. The total anthocyanins varieties, leaves of the Indon variety showed the
increased 1.14-fold after boiling process and highest level of total phenolic contents at 5.35 g
increased 3.22-fold after steaming process and GAE/100 g DW (Hue et al. 2012). The flavonoid
decreased 1.78-fold after frying process. It was contents in the leaves ranged from 96 ± 47.6 μg/g
determined that steaming process was the most in Indon variety to 263.5 ± 43.5 μg/g in Batu
effective among the heat-treated sweet potatoes. Biasa variety. In DPPH radical scavenging activ-
Dark green sweet potato leaves exhibited ity in leaves, the Indon and Biru Putih variety had
DPPH radical-scavenging activity with an EC50 the highest and lowest scavenging activities of
of 4 nmol and polyphenol antioxidant index in 372.4 μg/mL (IC50) and 597.61 μg/mL (IC50),
free radical scavenging of 595.2 (Thu et al. 2004). respectively. All varieties, except Biru Putih,
Total polyphenol in the leaves was determined as showed high radical scavenging activity com-
30.3 μmol catechin/g and free polyphenols as pared to the ascorbic acid standard. Besides, all
23.6 μmol catechin/g. In the DPPH assay, it was the leaf varieties also showed increment in their
found that sweet potato leaf ethanol extract had reducing power with increasing concentrations.
the highest radical-scavenging activity, followed The total antioxidant capacity of sweet potato
by leaf vein water extract (Huang et al. 2004c). In leaves was 42.94 % as compared to ascorbic acid.
the reducing power activity assay, it was found Purple-leaved sweet potato, an indigenous
that the leaf water extract had the highest reduc- Taiwanese vegetable, was found to have higher
ing power activity, followed by ethanol vein antioxidant activity than green sweet potato
extract. The highest FTC (ferric thiocyanate) leaves, which could be attributable to its higher
activity was found in the ethanol vein extract. contents of anthocyanidin content 275.60 unit/g
Among all the extracts, the highest amount of DW, polyphenols 22.80 mg GAE (gallic acid
total phenolic and flavonoid compounds was equivalent)/g DW, 67.66 mg Que (quercetin)/g
found in the ethanol vein extract. The highest DW, flavonols 23.82 mg Que/g DW. In contrast,
134 Convolvulaceae

green leaves had anthocyanidin content not scavenging activity % in ethanol leaf extracts
detected, polyphenols 18.70 mg GAE/g DW, were: A 97.63 %, B 93.94 %, E 56.68 %, D
42.45 mg Que/g DW, flavonols 7.80 mg Que/g 50.04 %, C 34.28 %. The highest antioxidant
DW. (Chao et al. 2014). The IC50 value for DPPH activity 97.63 % was given by the ethanolic
scavenging activity of purple and green sweet extract of red-purple tuber cv. The ethyl acetate
potato leaves were determined respectively as extract of B contained the highest total flavonoid
803.13, 74.67 μg/mL; TEAC value in the leaf (59.79 g QE/100 g). The ethanolic extract from B
methanolic hydrolysate were 162.66; 92.76 μmol had the highest phenolic contents (19.64 g
Trolox/g DW, TEAC value in the ethanolic GAE/100 g), while the highest carotenoid 24.17 g
hydrolysate were 25.58; 10.66 μmol Trolox/g BET/100 g was given by the ethyl acetate extract
DW). The ORAC antioxidant activity in the of C. The total phenolic contents were signifi-
methanolic leaf hydrolysate were hydrophilic cantly correlated with DPPH scavenging activity
ORAC value 1174.98; 786.26 μmol Trolox/g DW in A (leaves of red-purple tubers) with R2 = 0.951
and lipophilic ORAC value 92.43; 143.65 μmol and sample B (leaves of purples tubers) with
Trolox/g DW. R2 = 0.792, but no correlation in sample C, D and
The inhibition of LDL-oxidation of the sweet E. The DPPH scavenging activity in sample A
potato leaf extracts was correlated with the total was negatively correlated with total flavonoid
amounts of caffeic acid derivatives, suggesting contents (R2 = −0.772), while sample B, C, D and
that sweet potato leaves may prevent atheroscle- E had no correlation. The total carotenoid content
rosis via reducing early atherogenesis (Taira and in sample C (leaves of yellow tubers) had correla-
Ohmine 2011). caffeic acid derivatives, 4,5-di- tion with DPPH scavenging activity (R2 = 0.778)
caffeoylquinic acid (4,5-diCQA), 3,5-diCQA, and no correlation in sample A, B, D and E.
3,4-diCQA and 3,4,5-triCQA were the main The 33 kDa trypsin inhibitor, root storage pro-
polyphenol constituents of sweet potato leaf and tein, purified from sweet potato root, exhibited
total amounts of caffeic acid derivatives corre- scavenging activity against 1,1-diphenyl-2-
lated with the polyphenol contents (R2 = 0.94). picrylhydrazyl (DPPH) radical (Hou et al. 2001).
All the caffeoylquinic acid (CQA) derivatives There was positive correlation between scaveng-
from sweet potato leaves indicated an anti-LDL ing effects against DPPH (2 to 22 %) and amounts
(low-density lipoprotein) oxidation activity at of 33 kDa TI (1.92 to 46 pmol). The sporamin B
low concentrations (1–5 μM) and particularly, the protein from sweet potato at a concentration of
activity of 3,4,5-triCQA was remarkably higher 100 μg/mL exhibited highest activity (expressed
than those of 5-CQA and diCQA, such as 4,5- as 4.21 mM Trolox equivalent antioxidative
diCQA, 3,5-diCQA and 3,4-diCQA (Taira et al. value, TEAC) in total antioxidant status test
2013). The antioxidant activity of sweet potato (Huang et al. 2007a). In the DPPH staining spora-
leaves was correlated with the amounts of CQA min B appeared as a white spot when the concen-
derivatives in the range of R2 = 0.69–0.75. The tration was diluted to 25 mg sporamin B/mL
results suggested that sweet potato leaves may (with an absolute amount of 75 μg). Like total
prevent that developing atherosclerosis causes antioxidant status, the reducing power, Fe2+ -che-
the oxidative modification of LDL. DPPH scav- lating ability, FTC activity and protection calf
enging activity % in n-hexane leaf extracts of thymus DNA against hydroxyl radical-induced
sweet potato cultivars with varying tuber colours damage all showed that sporamin B polypeptides
were determined as: B (purple tuber cv) 23.35 %, had significant antioxidant activities. It was
C (yellow tuber cv) 23.18 %, E (orange tuber cv) found that antioxidant activities of sporamin B
19.38 %, A (red-purple tuber cv 8.42 %, D (red- increased from 19 % (0 h) to about 29 % (24 h)
yellow tuber cv) 7.73 % (Fidrianny et al. 2013). after 24 h hydrolysis by pepsin.
The DPPH scavenging activity % in ethyl acetate The cyclophilin-type peptidylprolyl isomer-
leaf extracts were: E 93.26 %, D 91.47 %, C ase protein (SPPPI) isolated from sweet potato
90.01 %, A 77.69 %, B 65.47 %. The DPPH storage roots and CP (calf thymus cytophilin, a
Ipomoea batatas 135

positive control) displayed the highest ABTS might contribute various antioxidant properties
(2,2-azino-bis-(3-ethylbenzothiazoline-6- through its hydrolytic peptides.
sulfonic acid) scavenging ability (15.36 and
17.79 %, respectively) at 100 μg/mL (Liao et al. Clinical Studies
2012). In the DPPH assay, SPPPI and CP were In a randomized, cross-over clinical study
found to have the highest radical-scavenging included 16 healthy adults (7 M, 9 F; aged 20–22
activity (5.78 and 4.05 %, respectively) at 100 μg/ years), 2 weeks consumption of polyphenol-rich
mL. The Fe2+-chelating ability of SPPPI and CP purple sweet potato leaves enhanced urinary total
was found to be the highest (12.47 and 14.576 %) phenol excretion by 24.5 % at day 14 as com-
at 100 μg/mL, respectively. The results suggested pared to day 0, while the low polyphenol diet
SPPPI to be an excellent candidate as a lead com- (LPD) decreased total phenol content in plasma
pound for the development of reductant agent. and urine by 3.3 and 16.3 %, respectively (Chen
Sweet potato protein (SPP) hydrolysates pre- et al. 2008a). Low-density lipoprotein lag time
pared by six enzymes (alcalase, proleather FG- F, and glutathione concentration in erythrocytes at
AS1.398, neutrase, papain and pepsin) exhibited day 14 was significantly enhanced by 15.0 and
antioxidant activity and protective effects on oxi- 33.3 % by PSPL as compared to day 0, respec-
dative DNA damage (Zhang et al. 2012). Alcalase tively. Urinary 8-hydoxy-deoxyguanosine
hydrolysates exhibited the highest hydroxyl (8-OHdG) excretion decreased significantly by
radical-scavenging activity (IC50 1.74 mg/mL) PSPL consumption. The results suggested that
and Fe2+-chelating ability (IC50 1.54 mg/L). polyphenols in 200 g purple sweet potato leaves
Compared with other five hydrolysates, the alca- were bioavailable and could enhance antioxidant
lase hydrolysates had the most abundant <3 kDa defense and decrease oxidative stress in young
fractions. In addition, below 3 kDa fractions of healthy people.
alcalase hydrolysates showed the highest antioxi- Consumption of purple sweet potato leaves
dant activities and protective effects against DNA (PSPL) for 2 weeks by basketball players led to a
damage through both scavenging hydroxyl radi- significant increase of plasma polyphenol con-
cals and chelating Fe2+, which was probably centration and vitamin E and C levels (Chang
because of the increase in several antioxidant et al. 2007). Low-density lipoprotein (LDL) lag
amino acids, such as histidine, methionine, cys- time was significantly longer in the PSPLs group.
tein, tyrosine and phenylalanine, as well as the A significant decrease of urinary 8-hydroxy-2-
hydrophobic amino acids. deoxyguanosine (8-OHdG) was noted; however,
Sweet potato defensin (SPD1), a cystein-rich there was no significant change in plasma gluta-
protein, was found to decrease the production of thione (GSH), total antioxidant status (TAS) and
intracellular peroxide in HepG2 cells (Huang malondialdehyde + 4-hydroxy-2(E)-nonenal
et al. 2012). Four of its peptides, namely GFR, level after consuming the PSPLs diet. It was con-
GPCSR, CFCTKPC and MCESASSK, synthe- cluded that consumption of PSPLs diet for 2
sized by hydrolysis was also tested for antioxi- weeks may reduce lipid and DNA oxidation and
dant activity. In the TEAC assay CFCTKPC modulate the antioxidative status of basketball
performed the best (13.5TE/g dw), even better players during training period.
than reduced glutathione (7.3 μmol TE/g dw). In
the DPPH radical assay, CFCTKPC again had the
highest antioxidant activity (IC50 = 11.3 μM) even Anticancer Activity
better than reduced glutathione (IC50 = 74.3 = μM).
In the lipid peroxidation assay, once again In-Vitro Studies
CFCTKPC performed the best, with an IC50 value Anthocyanin-rich aqueous extracts from cell sus-
of 0.5 μM better than reduced glutathione pension cultures of a high anthocyanin-producing
(1.2 μM). The findings demonstrated that SPD1 sweet potato purple line grown under two differ-
136 Convolvulaceae

ent media conditions, MM (multiplication dependent pathway, which was associated with
medium) and APM (high anthocyanin-producing the activation of caspase-3 and -8.
medium) exhibited higher radical-scavenging Caffeic acid, chlorogenic acid, 3,4-di-O-
activities, 3.8- and 1.4-fold, respectively, than the caffeoylquinic acid, 3,5-di-O-caffeoylquinic
field grown sweet potato storage root (SR) acid, 4,5-di-O-caffeoylquinic acid and 3,4,5-tri-
(Konczak-Islam et al. 2003). The antimutagenic O-caffeoylquinic acid, isolated from sweet potato
activity of all extracts was found to be dose- leaves, dose-dependently depressed cancer cell
dependent. At a dose of 1 mg/plate, the highest proliferation, and the difference in sensitivity
activity exhibited APM (73 % inhibition of Trp- between caffeoylquinic acid derivatives and each
P-1-induced reverse mutation of Salmonella kind of cancer cell was observed (Kurata et al.
typhimurium TA98), followed by MM (54 % 2007). Specifically, 3,4,5-tri-O-caffeoylquinic
inhibition) and SR (36 % inhibition). MM extract acid effectively depressed the growth of human
was the strongest inhibitor of the proliferation of stomach cancer (Kato III), colon cancer (DLD-1)
human promyelocytic leukaemia HL-60 cells. At and a promyelocytic leukaemia cell (HL-60), and
a concentration of 1.6 mg/mL medium during caffeic acid had an exceptionally higher effect
24 h, it suppressed the growth of 47 % of HL-60 against HL-60 cells than other di- and tricaf-
cells. A significantly lower growth suppression feoylquinic acids. Growth suppression of HL-60
effect displayed APM and SR extracts (21 and cells by 3,4,5-tri-O-caffeoylquinic acid was
25 %, respectively). The MM extract, which determined to be the result of apoptotic death of
exhibited the highest RSA and antiproliferation the cells. IbACP (Ipomoea batatas anti-cancer
activities, contained the highest level of anthocy- peptide), isolated from sweet potato leaves, was
anins. Among them, nonacylated cyanidin found to dose-dependently inhibit Panc-1, a pan-
3-sophoroside-5-glucoside predominated. Sweet creatic cancer line, cell proliferation and induced
potato extract caused marked dose-dependent cell death by apoptosis (Chang et al. 2013).
growth inhibition in several human colon carci- Batatosides L and O showed a weak inhibitory
noma cell lines with IC50 values in the range of effect on the growth of Hep-2 cells, while the
20–50 μg/mL for HCT 116, SW480, HT29 and other batatosides proved to be inactive (Yin et al.
SW837 cell lines (Kaneshiro et al. 2005). 2009). The extract from baked sweet potato (cv.
However, the IC50 value was more than 100 μg/ Koganesengan) showed potential cancer-
mL when CaCo2 cells were tested. preventing effects (Rabah et al. 2004). Fractions
The water leaf vein extract of sweet potato had II-a and III suppressed strongly the proliferation
the highest antiproliferative activity in-vitro of human myelocytic leukaemia HL-60 cells
against human lymphoma NB4 cells with an EC50 with apoptosis induction in a dose-dependent
of 449.6 μg/mL, followed by water extract of manner. Moreover, the two fractions markedly
storage root, water extract of leaf, ethanol extract blocked TPA-induced cell transformation in the
of storage root and ethanol extract of leaf (Huang mouse skin JB6 cell line. Both fractions showed
et al. 2004c). Although the ethanol extract of vein markedly strong radical scavenging effects on the
showed strong antioxidant activity, it exhibited DPPH radical, coinciding with the high content
no antiproliferative activity under the experimen- of total phenolic compounds in the fractions.
tal conditions tested. Studies showed that trypsin Sporamin, the major soluble protein with a
inhibitor (TI) from sweet potato tubers inhibited kunitz-type trypsin inhibitory activity, from
cellular growth of NB4 promyelocytic leukaemia sweet potato tuber, exhibited antiproliferative
cells in a time-dependent and dose-dependent effects of human tongue cancer Tca8113 cells
manner, and treatment for 72 h induced a marked partly by induction of apoptosis by downregulat-
inhibition of cellular growth, showing an IC50 of ing Akt/GSK-3 signaling pathway (Yao and Qian
57.1 μg/mL (Huang et al. 2007b). TI caused cell 2011). Of four polysaccharide components of
cycle arrest at the G1 phase and induced apopto- purple sweet potato named as PPSP, PPSPII,
sis in NB4 cells through a mitochondria- PPSPIII and PPSPIV, PPSP II and PPSPIII inhib-
Ipomoea batatas 137

ited Hela and HepG2 tumour cells (Zhao et al. ments and non-invasive real-time bioluminescent
2011). Treatment of human colonic SW480 can- imaging. SPGE did not cause any detectable tox-
cer cells with sweet potato P40 anthocyanin-rich icity to rapidly dividing normal tissues such as
extracts at 0–40 μM of peonidin-3-glucoside gut and bone marrow. In another study, a remark-
equivalent resulted in a dose-dependent decrease ably active polyphenol-enriched fraction, F5, of
in cell number due to cytostatic arrest of cell sweet potato greens extract was found to be
cycle at G1 phase but not cytotoxicity (Lim et al ~100-fold more potent in anticancerous activity
2013). Further, dietary P40 at 10–30 % signifi- than the parent extract as shown by IC50 measure-
cantly suppressed azoxymethane-induced forma- ments in human prostate cancer cells (Gundala
tion of aberrant crypt foci in the colons of CF-1 et al. 2013). F5 fraction was found to be rich in
mice partially in conjunction with a lesser prolif- quinic acid (QA), caffeic acid, its ester chloro-
erative PCNA (proliferating cell nuclear antigen) genic acid and isochlorogenic acids, 4,5-di-CQA,
and a greater apoptotic caspase-3 expression in 3,5-di-CQA and 3,4-di-CQA, especially in QA
the colon mucosal epithelial cells. Purified sweet and chlorogenic acid. Sub-fractionation of F5
potato root protein (SPP) exerted significant anti- resulted in loss of bioactivity, suggesting syner-
proliferative and antimetastatic effects on human gistic interactions among the constituent phyto-
colorectal cancer cell lines, both in-vitro and in- chemicals. Daily oral administration of 400 mg/
vivo (Li et al. 2013b). SPP inhibited the prolifera- kg body wt of F5 inhibited growth and progres-
tion of human colorectal cancer SW480 cells in a sion of prostate tumour xenografts by ~75 % in
dose-dependent manner in-vitro, with an IC50 nude mice.
value of 38.732 μmol/L. Both intraperitoneal (ip) Studies found that inclusion of natural food
and intragastric (ig) administration of SPP sig- anthocyanins, purple sweet potato colour and red
nificantly suppressed growth of intraperitoneally cabbage colour (5 %) to the rat diet could reduce
inoculated human colorectal cancer HCT-8 cells 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyri-
in nude mice to 58.0 and 43.5 % of the controls, dine (PhIP)-associated colorectal carcinogenesis
respectively, after 9 days treatment. Ig and ip in rats initiated with 1,2-dimethylhydrazine
administration of SPP markedly induced a sig- (Hagiwara et al. 2002). Liu et al. (2008) found
nificant decrease in spontaneous pulmonary met- that sweet potato anthocyanins could have inhibi-
astatic nodule formation in C57 BL/6 mice (21.0 tory effect on transplantation tumour of mice,
and 27.3 nodules/lung vs 42.5 5 nodules/lung in and had no obvious toxicity and mutagenicity. At
controls, respectively), after 25 days treatment. doses of 150 mg and 75 mg, the inhibition rates
Moreover, the average weight of primary tumour of mice carcinoma 180 were 45.04 % and
nodules in the hind leg of mice decreased from 36.64 %, respectively, while the inhibition rate of
8.2 g/mice in the control to 6.1 g/mice in the ip mice liver cancer H22 was 33.33 % at 150 mg
group. dose.
Sweet potato greens extract (SPGE) rich in
polyphenols exerted significant antiproliferative
activity in a panel of prostate cancer cell lines Antiviral/Antimicrobial Activity
while sparing normal prostate epithelial cells
(Karna et al. 2011). Mechanistically, SPGE dis- Caffeoylquinic acid derivatives, 3,4,5-tri-O-
rupted cell cycle progression, reduced clonogenic caffeoylquinic acid exhibited a greater selective
survival, modulated cell cycle and apoptosis reg- inhibition of HIV replication than 4,5-di-O-
ulatory molecules and induced apoptosis in caffeoylquinic acid (Mahmood et al. 1993).
human prostate cancer PC-3 cells both in-vitro Purple sweetpotato extract at the tested con-
and in-vivo. Oral administration of 400 mg/kg centration caused 40 % inhibition on the growth
SPGE markedly inhibited growth and progres- of Salmonella enteritidis, but no inhibition
sion of prostate tumour xenografts by ∼69 % in against Escherichia coli (Cevallos-Casals and
nude mice, as shown by tumour volume measure- Cisneros-Zevallos 2002).
138 Convolvulaceae

Antimutagenic Activity The results suggested that the catechol structure

played an important role in the potent antimuta-
Analysis of anthocyanin in sweet potato tubers genicity of anthocyanin pigments. The caf-
revealed a large distribution of anthocyanin pig- feoylquinic acid derivatives, 3-mono-O-
ments in the outer portion and showed that the caffeoylquinic acid (chlorogenic acid, ChA),
content of cyanidin in the outer portion was 3,4-di-O-caffeoylquinic acid (3,4-diCQA), 3,5-di-
higher than in the inner tissues (Yoshimoto et al. O-caffeoylquinic acid (3,5-diCQA), 4,5-di-
(1999a). The strong antimutagenicity of the O-caffeoylquinic acid (4,5-diCQA) and 3,4,5-tri-
purple-fleshed variety Ayamurasaki outer portion O-caffeoylquinic acid (3,4,5-triCQA) and caffeic
was attributed chiefly to the high concentration of acid (CA) isolated from the sweet potato leaf
cyanidin. The extracts from the outer portions of effectively inhibited the reverse mutation induced
Koganesengan, Sunny Red and Joy White variet- by Trp-P-1 on Salmonella typhimurium TA 98
ies showed an antimutagenic activity unlike the (Yoshimoto et al. 2002). The antimutagenicity of
inner ones, suggesting that the antimutagenic these derivatives was 3,4,5-triCQA > 3,4-
component in the outer portions of these varieties diCQA = 3,5-diCQA = 4,5-diCQA > ChA in this
was mainly associated with phenolics. Aqueous order. It was found that the number of caffeoyl
extract from the whole roots of the purple- groups bound to quinic acid played a role in the
coloured sweet potato Ayamurasaki variety effec- antimutagenicity of the caffeoylquinic acid deriv-
tively decreased the reverse mutation induced not atives. The caffeoylquinic acid derivatives iso-
only by Trp-P-1, Trp-P-2, IQ, B[a]P and 4-NQO lated from sweet potato leaves showed high
but also by dimethyl sulphoxide extracts of DPPH radical-scavenging activity (%), and high
grilled beef on Salmonella typhimurium TA 98 antimutagenicity by effectively inhibiting the
(Yoshimoto et al. 1999b). Two anthocyanin pig- reverse mutation induced by Trp-P-1 on
ments purified from purple-coloured sweet- Salmonella typhimurium TA 98 (Islam et al.
potato extract, 3-(6,6′-caffeylferulylsophoroside)- 2003b).
5-glucoside of cyanidin (YGM-3) and peonidin
(YGM-6) effectively inhibited the reverse muta-
tion induced by heterocyclic amines, Trp-P-1, Antidiabetic Activity
Trp-P-2 and IQ in the presence of rat liver micro-
somal activation systems. In-Vitro Studies
Anthocyanins purified from purple-fleshed Sweet potato acylated anthocyanin (YGM)
sweet potato 3-sophoroside-5-glucoside of cyani- extract exhibited potent maltase inhibitory activ-
din and 3-sophoroside-5-glucoside of peonidin, ity with IC50 of 0.36 mg/mL (Matsui et al. 2001).
the anthocyanin derivatives deacylated from the It also inhibited α-amylase action, indicating that
3-(6,6′-caffeylferulylsophoroside)-5-glucoside anthocyanins would have a potential function to
of cyanidin (YGM-3) and 3-(6,6′-caffeylferulylso- suppress the increase in post-prandial glucose
phoroside)-5-glucoside of peonidin (YGM-6) level from starch.
exhibited antimutagenicity activity using
Salmonella typhimurium TA 98 (Yoshimoto et al Animal Studies
2001). A comparison of the antimutagenicity White-skinned sweet potato cortex (WSSP-
between YGM-3 and YGM-6 and the deacylated cortex) was found to have potential hypoglycae-
derivatives showed that the activity of cyanidin mic activity in streptozotocin (STZ)-induced
was stronger than that of peonidin. Deacylation diabetic rats and hereditary diabetic mice (Type
of the peonidin-type pigment markedly decreased II, KK-AY/Ta Jcl, C57BL/KsJ db/db) by oral
this antimutagenicity. Caffeic acid showed the administration (Kusano et al. 1998). However, in
strongest antimutagenicity of the constituent normal rats, serum glucose levels were not
organic acids of the anthocyanin pigments, caf- changed by WSSP-cortex treatment. In glucose
feic acid, ferulic acid and p-hydroxybenzoic acid. tolerance tests, treatment of normal and STZ dia-
Ipomoea batatas 139

betic rats by WSSP-cortex showed increased glu- was estimated to be approximately 30-fold lower
cose tolerance and increased serum insulin levels than that of the therapeutic drug acarbose
like the tolbutamide treatment, whereas the treat- (ED20 = 2.2 mg/kg). A reduction of serum insulin
ment of KK-AY and db/db mice showed increased secretion was also observed corresponding to the
glucose tolerance and decreased serum insulin decrease in blood glucose level (BGL). No sig-
levels different from the tolbutamide treatment in nificant change in BGL was observed when
response to oral glucose load. Results of further sucrose or glucose was ingested, suggesting that
studies suggested that WSSP showed remarkable the antihyperglycaemic effect of the anthocyanin
antidiabetic activity and ameliorated the abnor- was achieved by maltase inhibition, not by
mality of glucose and lipid metabolism by reduc- sucrase or glucose transport inhibition at the
ing insulin resistance (Kusano and Abe 2000). intestinal membrane. After 6 weeks feeding
Hyperinsulinaemia in Zucker fatty rats was started, blood glucose and insulin levels in GK
reduced by 23, 26, 60 and 50 %, respectively, 3, rats fed the 5 % sweet potato leaf (SPL) diet
4, 6 and 8 weeks after starting the oral adminis- group were significantly reduced compared with
tration of WSSP. Similar results were obtained those of the control diet group (Ishida et al.
with troglitazone. In the glucose tolerance test 2004). Effectiveness of SPL on modulation of
after 7 weeks of treatment, increases in blood glucose metabolism in the GK rats was accompa-
glucose levels after glucose loading were inhib- nied by a significant reduction of blood choles-
ited by the administration of WSSP. Glucose tol- terol, especially LDL cholesterol. A soluble
erance was also improved. Blood triacylglyceride mucilaginous, dietary fibre (SDF) was extracted
(TG) and free fatty acid (FFA) lactate levels were from the sweet potato leaf powder. An elevation
lowered by the oral administration of of post-prandial blood glucose level in rats given
WSSP. Similar effects on blood insulin, lipid and 5.0 ml of 20 % glucose solution containing 1 %
lactate levels were observed after the administra- SPL-SDF orally was significantly suppressed as
tion of troglitazone. Body weight gain increased compared with that in the control rats given 20 %
in the troglitazone group, but not in the WSSP glucose solution only. The results suggested that
group, compared to the control group. In histo- the main effective substance of SPL for suppress-
logical examinations of the pancreas of Zucker ing blood glucose elevation was a kind of muci-
fatty rats, remarkable re-granulation of pancre- lage SDF.
atic islet B-cells was observed in the WSSP and Treatment with sweet potato leaf flavones
troglitazone groups after 8 weeks of treatment. extract for 2 weeks resulted in a significant
The antidiabetic component of WSSP was found decrease in the concentration of plasma triglycer-
to be an acidic glycoprotein with molecular ide (TG), plasma cholesterol (TC) and weight in
weight of 22,000 (Kusano et al. 2001). A single non-insulin-dependent diabetes mellitus
oral administration of sweet potato tuber diacyl- (NIDDM) rats (Zhao et al. 2006). Further, the
ated anthocyanin peonidin 3-O-[2-O-(6-O-E- extract markedly decreased fasting plasma insu-
feruloyl-β-D-glucopyranosyl)-6-O-E-caffeoyl-β-- lin level, blood glucose (FBG) level, low-density
D -glucopyranoside]-5- O - β - D -glucopyranoside lipoprotein cholesterol (LDL-C) and malondial-
exerted a potent maltase inhibitory activity with dehyde (MDA) levels and significantly increased
an IC50 value of 200 μM over sucrase inhibition the Insulin Sensitive Index (ISI) and superoxide
in male Sprague–Dawley rats (Matsui et al. dismutase (SOD) level in NIDDM rats. The
2002). When the diacylated anthocyanin results suggested that sweet potato leaf flavone
(100 mg/kg) was administered following maltose extract could control blood glucose and modulate
(2 g/kg), a maximal blood glucose level (BGL) at the metabolism of glucose and blood lipid, and
30 min was significantly decreased by 16.5 % decrease outputs of lipid peroxidation and
compared to vehicle. A minimum 10 mg/kg dose scavenge the free radicals in non-insulin-depen-
of the anthocyanin was necessary for the suppres- dent diabetic rats. Li et al. (2009) demonstrated
sion of glycaemic rise, and the ED20 (69 mg/kg) that sweet potato leaf flavonoids at a dose of
140 Convolvulaceae

100 mg/kg bw exhibited the optimal antidiabetic of SP significantly stimulated glucagon-like pep-
effect on alloxan-induced diabetic mice. The leaf tide-1 (GLP-1) secretion and was accompanied
flavonoid treatment for 28 days resulted in a by enhanced insulin secretion in rats, which
significant decrease in the concentration of fast- resulted in a reduced glycaemic response after
ing blood glucose, total cholesterol and triglycer- glucose injection. In in-vitro studies, it was found
ide in diabetes mellitus mice and significantly that SP and its caffeoylquinic acid derivatives
increased body weight and serum high-density significantly enhanced GLP-1 secretion. Studies
lipoprotein cholesterol. Studies by Ijaola et al. by Chen et al. (2013) found that sweet potato
(2014) showed that oral treatment with 300 mg/ starch (low GI) feeding for 4 weeks could
kg/day of sweet potato leaf extract for 2 weeks improve insulin sensitivity in insulin-resistant
produced the best hypoglycaemic effect rats, possibly by improving the adipocytokine
(69.67 %) in alloxan-induced diabetic rats. The levels, pro-inflammatory status and insulin
highest percentage blood sugar reductions of signalling.
69.67 % was recorded in rats treated with 300 mg/
kg/day, followed by 59.24 % (400 mg/kg/day Clinical Studies
extract) while the least percentage sugar reduc- Ludvik et al. (2002) demonstrated in a random-
tion of 52.18 % was observed in 200 mg/kg/day ized study that ingestion of 4 g Ipomoea batatas
extract. The non-diabetic-induced rats exhibited (Caiapo)/day for 6 weeks reduced fasting blood
steady increase (8.03 %) in their normal glucose glucose and total as well as LDL cholesterol in
level. It was revealed that alloxan induced rats male Caucasian type 2 diabetic patients previ-
treated with 200, 300 and 400 mg/kg/day sus- ously treated by diet alone. The improvement of
tained percentage weight loss of 48.91, 28.66 and insulin sensitivity in the fasting serum intrave-
31.11 %, respectively, compared with non- nous glucose tolerance test FSIGT indicated that
diabetic-induced rats. caiapo exerts its beneficial effects via reducing
Administration of an arabinogalactan-protein insulin resistance. The treatment was well toler-
(WSSP-AGP) from white-skinned sweet potato ated, with no apparent side effects. After treat-
to KKAy mice significantly lowered fasting ment with Caiapo, glycated haemoglobin HbA1c
plasma glucose levels (Ozaki et al. 2010). This decreased significantly from 7.21 to 6.68 %,
indicated that WSSP-AGP played an important whereas it remained unchanged in subjects given
role in the hypoglycaemic effects of white- placebo (7.04 vs. 7.10 %). Fasting blood glucose
skinned sweet potato. Treatment of hyperglycae- levels decreased in the Caiapo group (143.7 vs.
mic db/db mice with sweet potato arabinogalactan 128.5 mg/dL) and did not change in the placebo
protein (WSSP-AGP) decreased plasma glucose group (144.3 vs. 138.2 mg/dL). Mean cholesterol
levels and ameliorated insulin resistance leading at the end of the treatment was significantly lower
to hypoglycaemic effects (Oki et al. 2011). in the Caiapo group (214.6 mg/dL) than in the
Feeding streptozotocin-induced diabetic rats placebo group. A decrease in body weight was
with purple sweet potato flavonoids ameliorated observed in both the placebo group and in the
diabetic symptoms (Jiang et al. 2011). Fasting Caiapo group, probably due to a better-controlled
blood glucose (FBG), GSP (glycated serum pro- lifestyle. In another study, they found that short-
tein), total cholesterol, triglycerides (TG), LDL-C term treatment with 4 g/day of the nutraceutical
were decreased and serum HDL-C levels were Caiapo consistently improved metabolic control
increased in high-, medium-dose groups; while in type 2 diabetic patients by decreasing insulin
FBG, serum GSP, TG, LDL-C were also resistance without affecting body weight, glucose
improved in low dose group. In another study, effectiveness or insulin dynamics (Ludvik et al.
administration of dietary sweet potato leaf extract 2003). No side effects related to the treatment
powder (SP) for 5 weeks significantly lowered were observed. They also confirmed that the
hyperglycaemia in type 2 diabetic mice long-term treatment of Caiapo had beneficial on
(Nagamine et al. 2014). Also, pre-administration glucose control as evidenced by the observed
Ipomoea batatas 141

decrease in HbA1c in type 2 diabetic subjects may prove beneficial for diabetic- or insulin-
(Ludvik et al. 2004). resistant consumers.
Matured sweet potato tubers were cooked by
roasting, baking, frying or boiling then immedi- Reviews/Meta-analyses
ately consumed by the ten non-diabetic test sub- Suksomboon et al. (2011) conducted a meta-
jects (5 males and 5 females; mean age of 27 ± 2 analysis of the effect of herbal supplement on
years) (Bahado-Singh et al. 2011). Samples pre- glycaemic control in type 2 diabetes and nine
pared by boiling had the lowest GI (41–50), while randomized trials (487 patients) that met the cri-
those processed by baking (82–94) and roasting teria of (1) randomized placebo-controlled trial
(79–93) had the highest GI values. The study of single herb aimed at assessing glycaemic con-
indicated that the glycaemic index of Jamaican trol in type 2 diabetes, (2) of at least 8 weeks
sweet potatoes varied significantly with the duration and (3) reporting HbA(1c). They found
method of preparation and to a lesser extent on that supplementation with Ipomoea batatas,
intravarietal differences. Consumption of boiled Silybum marianum and Trigonella foenum-
sweet potatoes could minimize post-prandial graecum significantly improved glycaemic con-
blood glucose spikes and therefore, may prove to trol, whereas Cinnamomum cassia did not. Ooi
be more efficacious in the management of type 2 and Loke (2013) reviewed three randomized con-
diabetes mellitus. In another study, fasted partici- trolled trials ranged from 6 weeks to 5 months in
pants were measured blood glucose levels at 0, duration and involving 140 participants in regards
30, 60, 90 and 120 min after consuming 25 g of to the efficacy of sweet potato vs. placebo inter-
available carbohydrate from ‘Beauregard’ sweet vention for type 2 diabetes mellitus. There was a
potato skin and flesh separately that were sub- statistically significant improvement in glycosyl-
jected to conventional cooking methods: baking ated haemoglobin A1c (HbA1c) at 3–5 months
at 163 °C for 1 h; microwaving for 5 min in a with 4 g/day sweet potato preparation compared
1000 W microwave; dehydrating at 60 °C for to placebo. However, it was concluded that there
16 h; and steaming at 100 °C for 45 min (Allen was insufficient evidence about the use of sweet
et al. 2012). Glycaemic indices calculated from potato for type 2 diabetes mellitus.
these methods for steamed, baked and micro-
waved sweet potato flesh were 63, 64 and 66,
respectively, indicative of a moderate glycaemic Antihyperlipidemic/
index food. However, dehydrated and raw sweet Antiatherosclerotic Activity
potato flesh had a low glycaemic index (41 and
32, respectively). Steamed skin and baked skin, In-Vitro Studies
and raw flesh also had a low glycaemic index of The purple sweet potato (PSP) ethanol extract
30, 34 and 19, respectively. A second experiment (100-fold diluted) showed stronger (up to a six-
confirmed the low glycaemic index of raw sweet fold higher) DPPH radical-scavenging activity
potato, especially the skin, and showed that a than the water PSP extract and the ethanol extract
commercial extract of the sweet potato cortex, of yellow sweet potato (Park et al. 2010). The
Caiapo, tended to lower the glycaemic index of PSP ethanol extract also exhibited the highest
white potato to a level that was not different from increase in ferric-reducing ability among all
the raw sweet potato peel. The physiological extracts. Cupric ion-mediated LDL oxidation
mechanism for the lower glycaemic index was was strongly inhibited by the PSP ethanol extract
not due to a greater release or a greater clearance with similar potency to vitamin C treatment (final
of insulin during the glycaemic response. concentration, 10 mM). The PSP extract strongly
Depending on cooking methods, ‘Beauregard’ inhibited fructose-mediated protein glycation
sweet potato flesh and skin may be considered and also inhibited the uptake of oxidized LDL
low and medium glycaemic index foods, which into human macrophage cells with suppression of
142 Convolvulaceae

malondialdehyde production in the cell culture activated protein kinase signalling pathways in
medium. The data suggested that PSP extract human HepG2 cells and obese mice. Chen et al.
could be used as a putative antiatherosclerotic (2011) found that feeding hyperlipidaemic rats
and antidiabetic agent with strong antioxidant for 6 weeks with purple sweet potato could
functions. Purple sweet potato extract exerted decrease serum lipids (TC, TG and LDL-C) and
antiobesity, antioxidative and anti-inflammatory reduce hepatic oxidative stress. Serum SOD was
in 3 T3-L1 adipocytes in-vitro (Ju et al. 2011). It significantly higher in high- and low-dosage
diminished leptin secretion, suppressed the group than in high-fat control group, whereas
expression of mRNAs of lipogenic and inflam- serum MDA was significantly lower than that in
matory factors and promoted lipolytic action. It high-fat control group.
exhibited DPPH radical-scavenging and ferric- Consumption of purple sweet potato root
reducing activity. affected post-translational modification of plasma
proteins in male Syrian hamsters (Liao et al.
Animal Studies 2013). The results indicated that 95 plasma pro-
Studies found feeding that male Sprague–Dawley teins were identified and 28 post-translational
rats for about 1 month feeding cholesterol-free modifications sites on 26 of these 95 proteins
diet containing dried powder of sweet potato were affected by consumption of purple sweet
leaves at 5 % level as dietary fibre significantly potato. Methylation accounted for the largest per-
decreased hepatic cholesterol level (Innami et al. centage of affected modifications (35.71 %).
1998). A significant increase in faecal weight Also, incorporation of purple sweet potato into
was observed in the group fed the green leaf the diet significantly lowered blood and liver lip-
samples. ids. Consumption of purple sweet potato root
All the dried green leaves increased faecal affected post-translational modification of plasma
excretion of bile acids per gram or per day com- proteins in male Syrian hamsters (Liao et al.
pared with the control group. The results suggest 2013). The results indicated that 95 plasma pro-
that lowering of hepatic cholesterol by powdered teins were identified and 28 post-translational
green leaves was not necessarily due to the same modifications sites on 26 of these 95 proteins
factor, but to the increased faecal excretion of were affected by consumption of purple sweet
bile acids due to inhibited enterohepatic circula- potato. Methylation accounted for the largest per-
tion in animals given the sample. Johnson et al. centage of affected modifications (35.71 %).
(2013) demonstrated that consumption of novel Also, incorporation of purple sweet potato into
green leafy vegetables like sweet potato leaves the diet significantly lowered blood and liver
improved liver fatty acid profiles of spontane- lipids.
ously hypertensive rats (SHRs) and protected Studies showed that rats administered sweet
against elevations in atherogenic fatty acids, potato aqueous extract showed significant reduc-
which may be involved in cardiovascular disease tion in food intake, blood glucose level and body
pathogenesis. SHRs consuming diets containing weight when compared with the control group
such vegetables had significantly greater liver (Olubobokun et al. 2013). It was suggested that
concentrations of γ-linolenic, docosahexaenoic consumption of sweet potato caused a reduction
and docosahexaenoic acids, as well as lower lev- in food intake probably by increasing satiety and
els of lauric, palmitic and arachidonic acids. reduction in weight gain by using up the body’s
Purple sweet potato anthocyanin fraction reserve of fat as a result of the low blood
(200 mg/kg per day) reduced weight gain and glucose.
hepatic triglyceride accumulation and improved APSP (anthocyanins from purple sweet
serum lipid parameters in mice fed an high-fat potato) protected low-density lipoprotein against
diet (HFD) for 4 weeks (Hwang et al. 2011b). oxidation more potently than other anthocyanins
The fraction attenuated hepatic lipid accumula- and L-ascorbic acid in-vitro (Miyazaki et al.
tion through activating adenosine monophosphate- 2008). In apolipoprotein E-deficient mice, APSP
Ipomoea batatas 143

significantly lowered the atherosclerotic plaque NO-scavenging activity of sweet potato leaves
area to about half of the control, the liver level of was correlated with the total amount of polyphe-
thiobarbituric acid-reactive substances as an nol and its main constituents of caffeoylquinic
oxidative stress marker and the plasma level of acid (CQA) derivatives, such as 5-monoCQA,
soluble vascular cell adhesion molecule-1 4,5-diCQA, 3,5-diCQA, 3,4-diCQA and
(sVCAM-1), but showed no effects on body 3,4,5-triCQA. Therefore, the CQA derivatives
weight and cholesterol and lipid levels in the may be responsible for the NO-scavenging activ-
plasma. Shin et al. (2013) demonstrated that mice ity demonstrating that potato leaves may be
fed a high-fat diet containing purple sweet potato promising functional food materials for prevent-
extract (PSPE) presented lower increases in body ing various inflammatory diseases that cause
and adipose tissue weights and reduced occur- excess NO production.
rences of hepatic steatosis than mice that were
fed a high-fat diet without PSPE. The decreased
adiposity induced by PSPE accounted for lower Cognitive Enhancing Activity
serum levels of leptin and a higher adiponectin/
leptin ratio. PSPE administration also resulted in Purple sweet potato colour (anthocyanin rich
a significant decrease in serum and hepatic tri- colour) markedly enhanced cognitive perfor-
glyceride and cholesterol levels and a significant mance, assessed by passive avoidance test in
increase in faecal triglyceride and cholesterol ethanol-treated mice (Cho et al. 2003). Its mem-
levels when compared to the high-fat group. ory enhancing effects may be associated with its
PSPE suppressed the expression of sterol regula- antioxidant properties. Treatment of d-galactose-
tory element-binding protein (SREBP)-1, acyl- treated mice with purple sweet potato colour
CoA synthase (ACS), glycerol-3-phosphate (PSPC), a class of naturally occurring anthocya-
acyltransferase (GPAT), HMG-CoA reductase nins used to colour food, improved spatial learn-
(HMGR) and fatty acid synthase (FAS) in liver ing and memory impairment by reversing the loss
tissue in mice provided the high-fat diet. The of pre- and post-synaptic proteins induced by
results suggested that the antiobesity effect of galactose (Wu et al. 2008). Oral administration of
PSPE in high-fat-fed mice occurred through its purple sweet potato colour (anthocyanin rich)
modulation of lipogenesis in the liver and inhibi- extract to domoic acid-treated mice significantly
tion of dietary lipid absorption. improved their behavioural performance in a
In-vitro and clinical studies of 13 healthy volun- step-through passive avoidance task and a Morris
teers by Nagai et al. (2011) found that sweet potato water maze task (Lu et al. 2012). These improve-
leaves had antioxidant activity leading to the sup- ments were mediated through multiple pathways,
pression of low-density lipoprotein oxidation. involving a stimulation of oestrogen receptor-α-
Ingestion of sweet potato leaves prolonged the lag mediated mitochondrial biogenesis signalling,
time for starting low-density lipoprotein oxidation decreases in the expression of p47phox and
and decreased low-density lipoprotein mobility. gp91phox, decreases in reactive oxygen species
and protein carbonylation were also observed,
along with a blockade of the endoplasmic reticu-
Anti-inflammatory Activity lum stress pathway.
Studies showed that purple sweet potato (PSP)
Leaves of nine Okinawan sweet potato cultivars extract rich in caffeoylquinic acid derivatives
and two comparable sweet potato cultivars sup- with or without anthocyanin had a neuroprotec-
pressed nitrite production, an index of NO in tive effect on mouse brain and could improve the
LPS-stimulated RAW264.7 macrophages (Taira spatial learning and memory of senescence-
et al 2012). In addition, the sweet potato leave accelerated prone mouse strain (SAMP) 8 (Sasaki
extracts decreased the amount of nitrite ions gen- et al. 2013). Additionally, PSP increased brain
erated from NOR3, an NO donor, indicating that cell viability by 141.6 and 133 % as compared to
they had NO-scavenging activity. This Aβ1-42-treated cells.
144 Convolvulaceae

Antihypertensive Activity 190.47 μg/mL SPD1 while that of Captopril was

10 nM (868 ng/mL). ACE inhibitory activity
The purified mucilage from sweet potato tubers increased from 52.47 to about 74.38 % after 24 h
inhibited angiotensin converting enzyme (ACE) hydrolysis. Hydrolysis afforded six peptides,
in a dose-dependent manner (28.7 to 59.8 % ACE namely GFR, FK, IMVAEAR, GPCSR,
inhibition, respectively, at 50 to 400 μg/mL muci- CFCTKPC and MCESASSK, with ACE inhibi-
lage) with IC50 of 364.5 μg/mL while that of cap- tory activity and the IC50 values of individual
topril was 10 nM (8.68 μg/mL) (Huang et al. peptides were 94.25, 265.43, 84.12, 61.67, 1.31
2006). The commercial polysaccharide pectin and 75.93 μM, respectively, suggesting that
(50 to 400 μg/mL) showed no inhibitory activity CFCTKPC might represent the main domain for
against ACE. Trypsin inhibitor (TI), the root stor- the ACE inhibition.
age protein of sweet potato, inhibited angiotensin Studies found that continuous administration
converting enzyme (ACE) in a dose-dependent of colours (anthocyanins) from purple sweet
manner (50–200 μg/mL, with 31.9–53.2 % inhi- potato to spontaneously hypertensive rats for 15
bition) using N-[3-(2-furyl) acryloyl]-Phe-Gly- weeks decreased blood pressure and the heart
Gly (FAPGG) as a substrate (Huang et al. 2008b). rate (Shindo et al. 2007).
The 50 % inhibition (IC50) of ACE activity
required 187.96 μg/mL TI compared to 10 nM
(868 ng/mL) of Captopril. ACE inhibitory activ- Cardioprotective Activity
ity of TI was found to increase from 34 % to
about 8 3 % after 24 h of hydrolysis by pepsin. Studies found that administration of probiotic-
Ten peptides – namely HDHM, LR, SNIP, VRL, fermented purple sweet potato yogurt (PSPY)
TYCQ, GTEKC, RF, VKAGE, AH and KIEL – with high γ-aminobutyric acid (GABA) content
were synthesized and were also found to have inhibited cardiac hypertrophy in spontaneously
ACE inhibitory activity. IC50 values of individual hypertensive rat hearts (Lin et al. 2012b).
peptides were 276.2, 746.4, 228.3, 208.6, 2.3, Abnormal myocardial architecture and enlarged
275.8, 392.2, 141.56, 523.5 and 849.7 μM, sug- interstitial spaces were decreased in PSPY treated
gesting that TYCQ might represent the main rats. The elevated protein levels of cardiac
active site for the ACE inhibition. It was con- hypertrophic-related pathways and hypertension
cluded that sweet potato TI and its hydrolysates were completely reversed by the administration
might be good for control of hypertension and of PSPY. Also, it was found that PSPY may
other diseases when people consume sweet repress the activation of atrial natriuretic peptide
potato tuberous roots. Similarly, sweet potato (ANP) and brain (B-type) natriuretic peptide
storage root thioredoxin h2 and its four peptic (BNP) which subsequently may inhibit the
hydrolysates, namely EVPK, VVGAK, dephosphorylation of the nuclear factor of acti-
FTDVDFIK and MMEPMVK, exhibited angio- vated T-cells, cytoplasmic 3 and ultimately pre-
tensin converting enzyme inhibitory activity vent the progression of cardiac hypertrophy.
(Huang et al. 2011a). The IC50 values of individ- They also found that oral administration of 10 %
ual peptides were 1.73, 1.14, 0.42 and 1.03 mM, probiotic-fermented sweet potato yogurt PSPY
respectively, suggesting that FTDVDFIK might was strong enough to lower cardiac fibrosis in
be the main active site of ACE inhibition. The spontaneously hypertensive rats through the sup-
results for Trx h2 and its hydrolysates suggested pression of toll-like receptor 4 (TLR-4)-related
that consumption of sweet potato storage roots inflammatory pathway (Lin et al. 2013b). They
can aid in the control of hypertension and other suggested that PSPY may be included in diets to
diseases. Sweet potato defensin (SPD1) inhibits help prevent cardiac fibrosis in patients with
angiotensin converting enzyme in a dose- hypertension. In another study, they found that
dependent manner (Huang et al. 2011b). The oral administration of PSPY may attenuate car-
50 % inhibition (IC50) of ACE activity required diomyocyte apoptosis in spontaneously hyper-
Ipomoea batatas 145

tensive rats’ hearts by activating insulin-like eration and lipid peroxidation dose-dependently
growth factor-I receptor (IGF-IR)-dependent sur- (Ye et al. 2010). Concomitantly, cell apoptosis
vival signalling pathways (Lin et al. 2013a). triggered by Abeta characterized with the DNA
Administration of 2,4-di-tert-butylphenol from fragmentation and caspase-3 activity were also
sweet potato increased alternation behaviour in inhibited by PSPA. The results suggested that
mice injected with amyloid-beta peptide Aβ1–42 PSPA could protect the PC-12 cell from Abeta-
(Choi et al 2013). The results suggest that sweet induced injury through the inhibition of oxidative
potato extract could be protective against Aβ- damage, intracellular calcium influx, mitochon-
induced neurotoxicity, possibly due to the anti- dria dysfunction and ultimately inhibition of cell
oxidative capacity of its constituent, apoptosis and may have potential in the treatment
2,4-di-tert-butylphenol. of Alzheimer’s disease and other oxidative-
stress-related neurodegenerative diseases.
Oral administration of purple sweet potato
Neuroprotective Activity anthocyanins (PSPA) to mice significantly
reversed the impairment of motor and explora-
Studies showed that purple sweet potato antho- tion behaviour induced by lipopolysaccharide in
cyanins (PSPA) alleviated D-galactose-induced the open field tasks, and also improve learning
brain aging in old mice by promoting survival of and memory ability in step-through tests (Wang
neurons via PI3K pathway and inhibiting cyto- et al. 2010). The results suggested that PSPA may
chrome C-mediated apoptosis (Lu et al. 2010). be useful for mitigating inflammatory brain dis-
PSPA enhanced open-field activity, decreased eases by inhibition of proinflammatory tumour
step-through latency and improved spatial learn- necrosis factor-alpha (TNF-alpha), interleukin-
ing and memory ability in D-galactose-treated 1beta (IL-1beta) and interleukin-6 (IL-6) in LPS-
old mice by decreasing advanced glycation end- stimulated mouse brain, partially through
products’ (AGEs) formation and the AGE recep- inhibition of extracellular signal-regulated kinase
tor (RAGE) expression, and by elevating (ERK) and phosphorylated c-Jun N-terminal
Cu,Zn-superoxide dismutase (Cu,Zn-SOD) and kinase (JNK) expression and nuclear factor kappa
catalase (CAT) expression and activity. PSPA B (NF-kappaB) signalling. Sweet potato extract
also inhibited cleavage of capase-3 and the significantly reversed amyloid β peptide (Aβ)-
increase in terminal deoxynucleotidyl transferase induced neurotoxicity in ICR mice as assessed by
(TdT)-mediated deoxyuridine triphosphate the passive avoidance test (Kim et al. 2011).
(dUTP) nick-end-labelling (TUNEL)-positive Additionally, it reduced the level of lipid peroxi-
cells in D-galactose-treated old mice. In a sepa- dation and increased catalase activities in brain
rate study, aging mice administrated with PSPA tissue of mice. The results indicated that I. bata-
via oral gavage showed significantly improved tas might be beneficial against Alzheimer’s dis-
behaviour performance in the open field and pas- ease, especially by limiting oxidative stress in the
sive avoidance test compared with D-galactose- brain.
treated mice (Shan et al. 2009). It was found that
PSPA decreased the expression level of glial
fibrillary acidic protein, inducible nitric oxide Immunomodulating Activity
synthase (iNOS), and cyclooxygenase-2, inhib-
ited nuclear translocation of nuclear factor- Studies showed that white-skinned sweet potato
kappaB (NF-kappaB), increased the activity of (AWSSP) increased phagocytic activity and
Cu/Zn-SOD and (CAT), and reduced the content phagosome–lysosome fusion in neutrophils and
of malondialdehyde in the mouse brain. Pre- monocytes in a dose-dependent manner, but had
treatment of PC12 cells with PSPA reduced no significant effect on superoxide anion release
amyloid-beta peptide (Abeta)-induced toxicity, (O2−) from human neutrophils (Miyazaki et al.
intracellular reactive oxygen species (ROS) gen- 2005). The results suggested that AWSSP would
146 Convolvulaceae

be useful in the prevention and improvement of matory response induced by TNF-α in human
diabetic symptoms by stimulating human immu- aortic endothelial cells by modulation of NFκB
nity. In-vivo studies showed that the polysaccha- and MAPK signalling (Chao et al. 2013).
ride PSPP, purified from sweet potato root,
improved the immune system in mice and could
be deemed a biological response modifier (Zhao Antifatigue Activity
et al. 2005). PSPP at the dose of 50 mg/kg, sig-
nificant increments in proliferation of lympho- Oral administration of sweet potato leaf flavo-
cytes and serum IgG concentration were noids to male Kunming mice for 4 weeks exerted
observed. At the dose of 150 and 250 mg/kg, sig- significant antifatigue effects (Li and Zhang
nificant increments were observed in all tested 2013). The leaf extract extended the exhaustive
immunological indexes. A dose-dependent man- swimming time, effectively inhibited the increase
ner was demonstrated in phagocytic function, of blood lactic acid, decreased the level of serum
haemolytic activity and serum IgG concentration, urea nitrogen and increased the hepatic and mus-
but not in proliferation of lymphocytes and natu- cle glycogen content of mice.
ral killer cell activity. In a randomized cross-over
study (two periods, each lasting for 2 weeks)
involving 16 healthy non-smoking adults of nor- Hepatoprotective Activity
mal weight, consumption of purple sweet potato
leaves modulated various immune functions Pre-treatment of rats with purple-coloured sweet
including increased proliferation responsiveness potato juice orally for five consecutive days prior
of peripheral blood mononuclear cells secretion to carbon tetrachloride treatment effectively
of cytokines IL-2 and IL-4 and the lytic activity reduced glutamic-oxaloacetic transaminase
of natural killer cells (Chen et al. 2005). (GOT), glutamate pyruvate transaminase (GPT),
The methanolic extract of sweet potato roots lactate dehydrogenase (LDH) and thiobarbituric
at the concentration range of 10–100 μg/mL acid-reactive substance (TBARS) in serum and
stimulated cell-mediated immune system by liver TBA-RS and oxidized protein levels (Suda
increasing neutrophil phagocytic function and et al. 1997). The results demonstrated ameliorat-
intracellular killing potency of human neutro- ing effects of purple-coloured sweet potato juice
phils (Patil et al. 2007). against carbon tetrachloride-induced liver injury.
Pre-treatment of mice with an anthocyanin
fraction obtained from purple-fleshed sweet
Anti-inflammatory Activity potato protected against acetaminophen
(paracetamol)-induced hepatotoxicity by block-
The resin glycoside ipomotaoside A, isolated ing CYP2E1-mediated paracetamol bioactiva-
from sweet potato aerial parts, were found to tion, by upregulating hepatic glutathione levels,
have inhibitory activity on both cyclooxygenase and by acting as a free radical scavenger (Choi
Cox 1 and Cox 2 (Yoshikawa et al. 2010). Arantes et al. 2009). Studies showed that anthocyanin-
et al. (2014) investigated conformational charac- rich purple sweet potato colour could protect
terization of ipomotaosides A–D in aqueous and mouse liver from d-galactose-induced injury by
non-aqueous solvents. The most abundant con- attenuating lipid peroxidation, renewing the
formation of ipomotaoside A in solution was activities of antioxidant enzymes (Cu, Zn-SOD
employed in flexible docking studies, providing a (superoxide dismutase), catalase and glutathione
structural basis for the compound’s inhibition of peroxidase) and suppressing inflammatory
COX enzymes, further supporting its potential as response by inhibiting the upregulation of the
a new anti-inflammatory agent. Purple sweet expression of NF-kappaB p65, COX-2 and iNOS
potato leaf extract and its components, cyanidin (Zhang et al. 2009). Administration of purple-
and quercetin, inhibited cell adhesion and inflam- fleshed sweet potato fraction to rats effectively
Ipomoea batatas 147

ameliorated liver fibrosis caused by dimethylni- rally occurring alkylating furan from fungal-
trosamine (DMN) (Choi et al. 2010). Additionally, infected sweet potato, at a dose of either 826 or
the fraction inhibited DMN-induced reductions 1032 mg/m2 administered every 3 weeks did not
in rat body and liver weights in a dose-dependent demonstrate a relevant degree of clinical activity
manner and decreased DMN-induced expression against advanced hepatocellular carcinoma
levels platelet-derived growth factor receptors- (Lakhanpal et al. 2001). In a randomized, double-
beta, tumour necrosis factor-alpha and transform- blind, placebo-controlled, parallel study of
ing growth factor-beta. healthy adult men (30–60 years) with borderline
Studies showed that purple sweet potato hepatitis, ingestion of purple sweet potato bever-
anthocyanin could protect mouse liver against age significantly decreased the serum levels of
d-galactose-induced hepatocyte apoptosis via hepatic biomarkers gamma-glutamyl transferase
attenuating oxidative stress, inhibiting the activa- (GGT), aspartate aminotransferase and alanine
tion of caspase-3 and enhancing cell survival sig- aminotransferase, particularly the GGT level
nalling (enhancing the level of antiapoptotic (Suda et al. 2008).
protein Bcl-2 and the activation of PI3K/Akt
pathway) in d-galactose- treated mice (Zhang
et al. 2010). Oral pre-treatment of purple sweet Renoprotective Activity
potato anthocyanin fraction prior to t-tert-butyl
hydroperoxide treatment significantly lowered Purple sweet potato anthocyanin (PSPA)
the serum levels of the hepatic enzyme markers (700 mg/kg per day) reduced body weight, ratio
(ALT and AST), reduced the incidence of liver of urine albumin to creatinine, inflammatory cell
lesion and reduced oxidative stress of the liver by infiltration and collagen IV accumulation in mice
evaluation of malondialdehyde and glutathione fed a high-fat diet (HFD) (60 % fat food) for 20
(Hwang et al. 2011a). In HepG2 cell, the fraction weeks (Shan et al. 2014). PSPA attenuated oxida-
significantly reduced t-BHP-induced oxidative tive stress and kidney tissue damage in the kidney
injury, as determined by cell cytotoxicity, intra- of HFD-treated mice. PSPA inhibited the activa-
cellular glutathione content, lipid peroxidation, tion of kidney IKKβ/NF-κB signalling in HFD-
reactive oxygen species (ROS) levels and cas- treated mice. PSPA also reduced the activation of
pases activation. The hepatoprotective effects NLRP3 inflammasome and decreased the protein
may be partly attributed to its ability to scavenge expression of kidney oxidative stress-associated
ROS and to regulate the antioxidant enzyme AGE receptor (RAGE) and thioredoxin interact-
HO-1 via the Akt and ERK1/2/Nrf2 signaling ing protein (TXNIP) in HFD-treated mice.
pathways. Studies demonstrated that anthocya-
nins of the purple sweet potato attenuated
dimethylnitrosamine-induced liver injury in rats Wound Healing Activity
by inducing nuclear erythroid 2-related factor 2
(Nrf2)-mediated antioxidant enzymes, reducing In the incision wound model, high tensile strength
cyclooxygenase-2 and inducible nitric oxide syn- of the wounded skin was observed in Wistar rats
thase expression and reducing inflammation via treated with sweet potato peel extract gels and the
nuclear factor kappa B (NF-κB) inhibition peel bandage when compared with wounded con-
(Hwang et al. 2011c). Purple sweet potato was trol rats (Panda et al. 2011). The increase in ten-
found to have a preventive effect on acute and sile strength indicated the promotion of collagen
subacute alcoholic liver damage in mice (Sun fibres and that the disrupted wound surfaces were
et al. 2014a). All tested biochemical and histo- being firmly knit by collagen. In the excision
logical parameters were ameliorated after intra- wound model, significant wound closure was
gastric administration of purple sweet potato. observed on the 4th day in rats treated with all
In a phase II study of patients with advanced three peel gel formulations when compared with
hepatocellular carcinoma, 4-ipomeanol, a natu- wounded control rats. A significant increase in
148 Convolvulaceae

hydroxyproline (index for collagen turnover) and bath/acupressure massage (SFA) intervention
ascorbic acid content in the peel gel-treated was found to be a more effective, safe, economi-
animals and a significant decrease in malondial- cal and practical than usual care alone in manag-
dehyde content in the animals treated with ing constipation and satisfaction with defaecation
peel-gel as well as peel bandage was observed in patients hospitalized with ACS (Ren et al.
when compared with the wounded control 2012).
animal. It was concluded that sweet potato
peels possessed a potent wound-healing activity
which may be associated to its antioxidant Radioprotective Activity
property. The peel extract showed the presence
of high levels of polyphenols (anthocyanins Administration of a freshly prepared aqueous
and phenolic acids) and sesquiterpenoids extract of sweet potato tubers to rats, 1 week pre-
(6-myporol, 4-hydroxydehydromyoporone and irradiation and during the period of radiation
ipomeamarone). exposure significantly ameliorated the oxidative
stress in liver and kidney tissues (Darwish et al.
2010). The significant amelioration in oxidative
Antimelanogenic Activity stress was substantiated by improvement of liver
and kidney enzymes. Treatment of rats with
The extract from steamed sweet potato was found sweet potato has significantly reduced the
to suppress the melanogenesis of mouse mela- increase in serum alanine amino transferase
noma B 16 cells (Shimozono et al. 1996). The (ALT), aspartate amino transferase (AST) and
phenolic acids extracted from steamed sweet lactate dehydrogenase (LDH) activity, serum cre-
potato such as chlorogenic acid (ChlA), atinine and urea levels. Furthermore, hypergly-
3,5-dicaffeoylquinic acid (3,5-diCQA), caemia and alteration in lipid profile manifested
3,4-dicaffeoylquinic acid (3,4-diCQA) and by a significant increase in triglycerides (TG),
4,5-dicaffeoylquinic acid (4,5-diCQA) also sup- total cholesterol (TC) and low-density lipopro-
pressed melanogenesis in mice. tein cholesterol (LDL-C) and a significant
decrease in high-density lipoprotein cholesterol
(HDL-C) were improved in sweet potato-treated
Antiulcerogenic Activity irradiated rats compared to those only irradiated.
Pre-treatment of murine thymocytes with purple
Studies showed that methanol sweet potato sweet potato pigments significantly inhibited
60
extract possessed gastroprotective activity as evi- Co γ-ray-induced mitochondria-mediated apop-
denced by its significant inhibition of mean ulcer tosis (Xie et al. 2010). The radioprotective effect
score and ulcer index and a marked increase in might be related to reactive oxygen species scav-
GSH, SOD, CAT, glutathione peroxidase(GPx) enging, the enhancement of the activity of anti-
and glutathione reductase (GR) levels and reduc- oxidant enzymes, the maintenance of
tion in lipid peroxidation in a dose-dependent mitochondrial transmembrane potential and the
manner in cold stress and aspirin-induced gastric sequential inhibition of cytochrome c release and
ulcers in Wistar rats (Panda and Sonkamble downstream caspase and poly ADP-ribose poly-
2012). merase (PARP) cleavage. The cosmetic cream
with 0.61 mg of total anthocyanins (per 100 g
cream) from TNG73 purple sweet potato
Gastroenterologic Activity absorbed approximately 46 % of the incident UV
radiation (Chan et al. 2010). Although the antho-
In a prospective, randomized controlled trial with cyanins absorbed both UV-A and UV-B radia-
a sample of 93 hospitalized patients with acute tion, they were particularly effective against
coronary syndromes (ACS), sweet potato/foot- UV-B rays. Acidic ethanol-extracted anthocya-
Ipomoea batatas 149

nins had better radical-scavenging ability, higher the aortic ring preparations were mainly
total phenolic content and stronger reducing abil- endothelium-dependent, and mediated by nitric
ity than acidic water-extracted anthocyanins. The oxide.
study demonstrated that the addition of anthocy-
anin extracts of purple sweet potato to a cosmetic
cream improved the cream’s UV absorption Vitamin A and Health Enhancement
ability.
Purple sweet potato (PSP) pigments treatment In a study of 90 primary school children aged
prior to 4 Gy (60)Co γ-ray irradiation had a cyto- 5–10 years, consumption of β-carotene-rich
protective activity against γ radiation by increas- orange-fleshed sweet potato was found to
ing murine thymocytes viability and decreasing improve vitamin A status and could play a sig-
apoptosis (han et al. 2011). The protective effect nificant role in developing countries as a viable
of PSP pigments may be involving ROS scaveng- long-term food-based strategy for controlling
ing, p53 depression and Bcl-2/Bax modulation in vitamin A deficiency in children (van Jaarsveld
a caspase-dependent mitochondrial way. et al. 2005). Jamil et al. (2012) found that daily
consumption of orange-fleshed sweet potato for
60 days increased plasma β-carotene concentra-
Adaptogenic Activity tion, but did not increase total body vitamin A
pool size in Bangladeshi women residing in a
In a cross-over designed study of 15 healthy, non- resource-poor community.
trained, young male subjects, consumption of Amagloh et al. (2012) found that sweet potato-
purple sweet potato leaves (PSPL) for 7 days sig- based formulations were superior to enriched
nificantly increased plasma total polyphenols Weanimix (maize-soybean blend) as comple-
concentration and total antioxidant power (i.e., mentary foods for infants in low-income coun-
the ferric-reducing ability of plasma) and tries, based on its higher fructose level (which
decreased exercise-induced oxidative damage makes the porridge naturally sweet) and lower
and pro-inflammatory cytokine secretion (Chang phytate levels compared to the enriched
et al. 2010). However, no significant difference Weanimix.
was found in heat shock protein HSP72 levels
between PSPL and the control groups.
Removal of Trypsin Inhibitory
Activity
Antimicrobial Activity
Trypsin inhibitor activity (TIA) decreased during
Two antifungal (Rhizopus stolonifer) fractions ensilage in sweet potato/maize powder samples
were isolated from the periderm and outer cotex of all treatments while the sweet-potato strips
of sweet potato tubers; one active fraction (SPS) mixed with maize powder (CP) mixture
comprised predominantly caffeic acid and the (7:3, w/w) ensiled for 3 months contained the
second more active fraction contained lowest TIA (Lin et al. 1988). Rats fed on diets
3,5-dicaffeoylquinic acid (3,5-DCQA) with an containing dried SPS-CP (8:2, w/w) showed sig-
EC50 of 2.2 g/L (Stange et al. 2001). nificantly lower body-weight gain than rats fed
on the control diet or ensiled SPS diets, at the end
of the 8th week. They also showed enlargement
Vasorelaxant Activity of the pancreas. The adverse effect of SPS was
associated with TIA which appeared to be pre-
Ipomoea batatas plant extract exhibited more vented to some extent by ensilage. Among the
than 50 % relaxing effect on aortic ring prepara- four cultivars of sweet potatoes, RS-III-2 trypsin
tions (Runnie et al. 2004). The vascular effects on inhibitors were more heat-labile (Kiran and
150 Convolvulaceae

Padmaja 2003). Heating at 100 °C led to rapid cial effects on plasma glucose and total as well as
inactivation of TI of sweet potatoes. Microwave LDL cholesterol levels in patients with type 2
baking and flour preparation were the best meth- diabetes. These effects related to a decrease in
ods to eliminate TI from sweet potatoes. insulin resistance. Another study reported that
Q40091|Q40091_IPOBA was isolated as the increases in blood glucose levels after glucose
major sporamin B from sweet potato cv. 55-2 loading in test animals were inhibited after oral
tuber and found to have potent trypsin inhibitory administration of white skinned sweet potato
activity (Sun et al. 2009). There was a linear rela- (WSSP). WSSP shows remarkable antidiabetic
tionship between trypsin inhibitor activity (Ti activity and improves the abnormality of glucose
activity) and amounts of this sporamin B and lipid metabolism by reducing insulin resis-
(3–18 μg/mL). Heat treatment at more than 90 °C tance. Almost all antidiabetic activity was found
led to a dramatic decrease of trypsin inhibitor in the cortex of WSSP. This active component
efficiency. was presumed to be an acidic glycoprotein
because it contained protein and sugar.
The phenolic compounds caffeic acid and di-
Pharmacokinetic Studies and tricaffeoylquinic acids from sweet potato
leaves were also reported to significantly
Two major anthocyanin components of a depressed cancer cell proliferation. Specifically,
beverage prepared from an extract of the tuber of 3,4,5-tri-O-caffeoylquinic acid effectively
purple sweet potato, cyanidin 3-O-(2-O-(6-O- depressed the growth of three kinds of cancer
( E ) - c a ff e o y l - β - D - g l u c o p y r a n o s y l ) - β - D - cells: stomach cancer (Kato III), a colon cancer
glucopyranoside)-5- O - β - D -glucopyranoside) (DLD-1) and a promyelocytic leukaemia cell
and peonidin 3-O-(2-O-(6-O-(E)-caffeoyl-β-D- (HL-60). Caffeic acid had an exceptionally
glucopyranosyl)-β-D-glucopyranoside)-5-O-β-D- higher effect against HL-60 cells than other di-
glucopyranoside), were detected in the plasma and tricaffeoylquinic acids. The findings indicate
and urine of both rats and humans (Harada et al. that 3,4,5-tri-O-caffeoylquinic acid may have the
2004). The plasma concentration of anthocyanins potential for cancer prevention.
in humans reached a maximum 90 min after One paper reported that flavone extracted
ingestion, and the recovery of anthocyanins in the from sweet potato leaf could control blood glu-
urine was estimated as 0.01–0.03 %. An acylated cose and modulate the metabolism of glucose
anthocyanin, peonidin 3-caffeoylsophoroside-5- and blood lipid, and decrease outputs of lipid per-
glucoside, was detected in the urine of 87 healthy oxidation and scavenge the free radicals in non-
volunteers 2 h after ingestion of purple-fleshed insulin-dependent diabetic rats.
sweet potato beverage with various contents of
anthocyanin (beverage A; 22.1 mg/250 mL, B;
107.8, C; 84.9) (Oki et al. 2006). The mean con- Toxicity Issues
centrations were 15.1 μg/L of urine, 46.6 and
53.3 for beverages A, B and C, respectively. A lung-toxic furanoterpenoid, 4-ipomeanol, was
The tuber and leaves have also been used in isolated from moldy sweet potato (Boyd and
traditional medicine. The leafy shoots are used as Wilson 1972). The toxin was shown to produce a
a galactagogue and as poultice. The leaves are respiratory disease in mice characterized by
used to treat diabetes, hookworm, haemorrhage severe pulmonary oedema, pleural effusion and
and abscesses and reported to be used as a matur- death. Toxicity manifestations of mould-damaged
ative cataplasm. The tuber is used to treat asthma sweet potatoes namely pulmonary oedema,
and are laxative. Tubers are sliced, dried to make emphysema and adenomatosis had been
a tea to allay thirst. described as characteristic disease signs in cattle
Recent researches support their use for type 2 (Wilson et al. 1970; Wilson 1973). The experi-
diabetes. Sweet potato was found to have benefi- mental infection of viable sweet potato slices or
Ipomoea batatas 151

of the intact tubers by fungi resulted in the pro- treatment. The results indicated that type I alveo-
duction of many furanoterpenoid compounds, lar epithelial cells and non-ciliated bronchiolar
some of which were markedly toxic for labora- epithelial cells are most susceptible to
tory and commercial animals (Wilson et al. 4-ipomeanol-induced damage and necrosis in
1971). The respiratory tract toxin, 4-ipomeanol calves. 4-Ipomeanol-induced pulmonary oedema
(1-[3-furyl]-4-hydroxy-1-pentanone) may be in calves occurred prior to ultrastructurally
responsible for the typical lung oedema of cattle demonstrable, mild, alveolar capillary endothe-
that were fed mouldy sweet potatoes as well as a lial cell damage. Also they found that 4-ipomeanol
similar pathological state in mice fed or injected exacerbated interstitial pneumonia in calves
with the pure compound (Boyd et al. 1972). induced by bovine parainfluenza type 3 virus (Li
Four furanoterpenoids produced by sweet and Castleman 1991). Four-ipomeanol-enhanced
potatoes following microbial infection viral pneumonia was characterized in part by
4-ipomeanol, 1-ipomeanol, tipomeanine and extensive hyperplasia of type II alveolar epithe-
1,4-ipomeadiol were found to be acutely toxic to lial cells and by dense aggregates of macrophages
the lungs of experimental animals, characteristi- and neutrophils in alveolar spaces and interalveo-
cally producing pulmonary oedema and conges- lar septa.
tion, following a latent period of several hours The pulmonary toxin, 4-ipomeanol, selec-
after dosing (Boyd et al. 1974). Mice receiving tively alkylated the lungs of rats (Boyd and Burka
lethal doses of the toxins usually die within 24 h, 1978). Time-course and dose–response studies
and pathological findings appeared most often demonstrated a close correlation between the
only in the lungs. However, mice initially surviv- pulmonary alkylation and the lung toxicity of the
ing near-lethal doses of the toxins, particularly compound. The LD50 values (μg/g) of the lung-
1-ipomeanol and 1,4-ipomeadiol, may show evi- toxic furanoterpenoids produced by sweet pota-
dence of nephrotoxicity within 1–3 days. In addi- toes following microbial infection in mice were
tion to ipomeamarone and other hepatotoxins, a determined as follows: 4-ipomeanol 38 μg by
series of 1-(3-furyl)-1,4-dioxygenated pentanes oral administration, 36 μg by intraperitoneal and
were isolated from sweet potatoes infected with 21 μg by intravenous; 1-ipomeanol 79 μg by oral,
Fusarium solani (Burka and Wilson 1976). These 49 μg by intraperitoneal, 34 μg by intravenous;
compounds, especially 1-(3-furyl)-4-hydroxy-1- ipoemanine 26 μg by oral, 25 μg by intraperito-
pentanone (4-ipomeanol) show marked pulmo- neal, 14 μg by intravenous and 1,4-ipomeadiol
nary toxicity in laboratory animals. Cattle given 104 μg by oral, 67 μg by intraperitoneal, 66 μg by
intraruminal administration of 4-ipomeanol, a intravenous administration (Boyd et al. 1974).
furanoterpenoid originally obtained from sweet Durham et al. (1987) found that the histologic
potatoes infected with Fusarium solani (F. severity of Sendai viral pneumonia in young
javanicum), developed a respiratory syndrome adult female C57BL/6 J mice was closely corre-
clinically and histologically indistinguishable lated with increasing doses of the pulmonary
from atypical interstitial pneumonia (Doster et al. toxicant, 4-ipomeanol.
1978). There were oedema and emphysema in Injection of five three-substituted furans, iso-
the lungs and mediastinum. The maximum non- lated from stressed sweet potato root tissue, into
lethal oral dose of 4-ipomeanol was estimated to mice produced temporary neurological effects
be between 7.5 and 9 mg/kg of body weight. followed by development of extensive necrosis in
Studies by Li and Castleman (1990) found sig- the liver (Wilson and Burka 1979). The most
nificant elevations in numbers of neutrophils and toxic was 6-myoporol, with LD50 of 84 mg/kg,
macrophages were recovered by bronchoalveolar comparable to ipomeamarone. The other toxic
lavage at times from 24 to 96 h after 4-ipomeanol- compounds were ipomeamaronol LD50 266 mg/
treatment in calves. Hyperplasia of non-ciliated kg, 4-hydroxymyoporone LD50 235 mg/kg,
bronchiolar epithelial cells and of type II alveolar 7-hydroxymyoporone LD50 200 mg/kg and
epithelial cells were observed at 72 and 96 h after dihydro-7-hydroxymyoporone LD50 184 mg/kg.
152 Convolvulaceae

Fermentation of 6 weeks duration was observed lated diet (Dilworth et al 2008). The results sug-
to inadequately eliminate the lung, liver and kid- gested that the consumption of foods high in
ney toxicity caused by mold-damaged sweet phytic acid may contribute to a reduction in the
potatoes (Thibodeau et al. 2004). In fact, fermen- minerals available for essential metabolic pro-
tation exacerbated the hepatotoxicity of mold- cesses in rats.
damaged sweet potatoes. Also, it was
demonstrated that sweet potato regions lacking
visible mold damage could induce lung and kid- Traditional Medicinal Uses
ney injury, which, however, was preventable by
fermentation. In Burkina Faso and the Ivory Coast, juice from
Microwave and bake cooking operations the leaves are used for gum gargle and gum mas-
destroyed approximately 90 % of the ipomeama- sage (Kerharo and Bouquet 1950), and leaf sap
rone in sweet potato roots (Cody and haard for burns and grounded leaves as enema to pre-
1976). 4-Ipomeanol was more heat stable than vent miscarriage (Bouquet and Debray 1974). In
ipomeamarone, although it also decreased sub- the Popular Republic of Congo (Brazzaville), an
stantially as a result of normal cooking. Catalano infusion of leaves sweet potato and Cassia occi-
et al. (1977) found that ipomeamarone was pri- dentalis, barks stem, branch, trunk of Bridelia
marily concentrated in the blemished and dis- ferruginea, are used as purgative (Bouquet 1969).
eased sweet potato tissues. Neither baking nor In Casamance, Senegal, leaves are boiled and
boiling appeared to promote diffusion of ipomea- used to treat abscess and boils and the hot leaves
marone into the healthy tissues. Also, baking are used as cataflam in cosmetics (Thomas 1972).
appeared to reduce the concentration of this In the Comoros, sweet potato is used for wound
hepatotoxin. healing and analgesic and the leaves sap is used
Sweet potato polyhydroxylated nortropane to treat serious sunburn (Adjanohoun et al. 1982).
alkaloids calystegines A3, B1, B2 and C1 exhibited In Togo, a decoction of the roots and leaves of
inhibitory activity on mammalian liver glucosi- sweet potato and Cassia occidentalis is taken
dases (Asano et al. 1997). Calystegines B1 and C1 orally as a remedy for intercostal and rib pain and
were potent competitive inhibitors of the bovine, the powered mixture of the same is used to treat
human and rat β-glucosidase activities, with Ki scarification pain (Adjanohoun et al. 1986).
values of 150, 10 and 1.9 μM, respectively, for B1 Leaves of Ipomoea batatas, Vernonia amygda-
and 15, 1.5 and 1 μM, respectively, for C1. lina, Plumbago zeylanica are burnt, and the ashes
Calystegine B2 was a strong competitive inhibitor licked with palm oil to treat small pox in Benin
of the α-galactosidase activity in all the livers. (Verger 1995). In Gabon, crushed, macerated
Human β-xylosidase was inhibited by all four leaves of sweet potato is taken orally to facilitate
nortropanes, with calystegine C1 having a Ki of child birth (Raponda-Walker and Sillans 1995).
0.13 μM. Calystegines A3 and B2 selectively In the Democratic Republic of Congo (ex. Zaïre)
inhibited the rat liver β-glucosidase activity. The region of Kisangani, the leaves are used to treat
potent inhibition of mammalian beta-glucosidase erythroderma (exfoliative dermatitis), measles
and alpha-galactosidase activities in-vitro raises and chicken pox (Kalanda and Bolamba 1994).
the possibility of toxicity in humans consuming In Cameroon Yaounde region, leaf pieces are
large amounts of plants that contain these added in food to treat diabetes (Tsabang et al.
compounds. 2001). In Bulamogi, Uganda, the plant is used for
Studies found that Wistar rats fed phytic acid insect stings and leaves used in steam bath as a
extracted from sweet potato or commercial phytic restorative for lameness (Tabuti et al. 2003). In
acid-supplemented diets displayed reduced bone Uganda (Northern sector of Kibale National
calcium levels and had significantly thinner bone Park), an aqueous extract of dry leaves pounded
in the trabecular region, compared to the groups with Passiflora edulis, Coffea canephora, is taken
fed formulated diet or zinc-supplemented formu- orally to treat diarrhoea (Namukobe et al. 2011).
Ipomoea batatas 153

An infusion of the leaves is used by women in the 2004). Sweet potato tuber is used for livestock
Sango Bay area, Uganda, for relaxation of the feed and for the production of starch in South
pelvic region during child birth (Ssegawa and Korea (Min et al. 2006). Studies found sweet
Kasenene 2007). In Ethiopia, the leaves are used potato vine pellet to be a good source of dietary
topically for boils (Giday et al. 2009). In Nigeria supplement, which resulted in significant
(Ndokwa Delta State), the leaves are squeezed improvement in apparent digestibility, rumen fer-
and the sap taken orally as a therapy for stomach mentation and milk yield in lactating dairy cows
problem by the Abbi people (Ogie-Odia and fed on urea-treated rice straw (Phesatcha and
Oluowo 2009). In Ogun state of Nigeria, peels of Wanapat 2013). Megersa et al. (2013) found sup-
sweet potato are macerated and used to treat plementation with sweet potato vine could
tuberculosis (Ogbole and Ajaiyeoba 2010). In replace the conventional concentrate and could
northern Maputaland, KwaZulu-Natal Province, be incorporated with poor quality hay to prevent
South Africa, sweet potato and Tabernaemontana body weight loss of goats in the absence of other
elegans leaves are boiled in water and a decoc- feed supplements.
tion taken thrice daily to treat gonorrhoea (De More than 50 million tons of sweet potato are
Wet et al. 2012). In the Democratic Republic of used for starch production annually around the
Congo, pounded leaves are used as poultice for world (Cheng et al. 2014). A procedure was
breast cancer (Mbuta et al. 2012). The leaves are developed for separately recovering polyphenol
used to treat insect stings and used by the women oxidase (PPO), β-amylase, sporamins and small
of Agnalazaha littoral forest (Southeastern molecular nutrients (SMNs) from sweet potato
Madagascar) to evacuate the placenta during wastewater in starch production. Purified pow-
pregnancy (Razafindraibe et al. 2013). ders of 4.3 × 105 units of PPO, 4.0 × 106 units of
β-amylase, 8.70 g sporamins and 20.2 g SMNs
were obtained from the wastewater of 1 kg sweet
Other Uses potato. A sweet potato medium derived from
baked sweet potato supplemented with 0, 4 or
All parts of the plant are used for an animal feed 8 g/L of a nitrogen source such as yeast extract
and supplement especially in developing coun- was found to be a suitable and low-cost medium
tries. In Papua New Guinea pigs are primarily for the cultivation of Lactobacillus (Hayek et al.
raised on sweet potatoes. In the Canete valley in 2013).
Peru sweet potato supports a modern dairy indus- Cowdung was found to be a good seed for
try. There is growing interest in its potential use direct fermentation of sweet potato to produce
as a component in chicken feed. The vines are biofuels (hydrogen and ethanol) (Chu et al.
also used as mulches and compost. In Taiwan, 2010). Also, acetate and butyrate with small
companies are making alcohol biofuel from quantities of propionate were produced at all pH
sweet potato. In South America, the juice of red values. Sweet potato was identified as a sustain-
sweet potatoes is combined with lime juice to able crop for fuel bioethanol production based on
make a dye for cloth. By varying the proportions both its favourable energy balance and the net
of the juices, every shade from pink to purple to GHG emission reduction (Carrasco-Letelier et al.
black can be obtained. 2013). Studies found sweet potato to be an attrac-
Sweet potato tubers and leafy shoots are used tive raw material for fuel ethanol, since up to
as animal (especially pigs and cattle) feed in 4800 L ethanol per hectare can be obtained
developing countries (Scott 1992). Studies found (Lareo et al. 2013). An energy-saving ethanol
that ensiled sweet potato leaves could replace fermentation technology was developed using
fishmeal and groundnut cake in traditional uncooked fresh sweet potato as raw material for
Vietnamese diets for growing pigs (Van et al. fuel ethanol (Zhang et al. 2013). A mutant strain
2005). There was a significant stimulatory impact of Aspergillus niger isolated from mildewed
of the intake of sweet potato leaves on growth sweet potato was used to produce abundant raw
performance of the growing pigs (Nguyen et al. starch saccharification enzymes for treating
154 Convolvulaceae

uncooked sweet potato storage roots. The ethanol Nigeria 3,400,000 MT, United Republic of
fermentation was carried out by Zymomonas Tanzania 3,018,175 MT, Uganda 2,645,700 MT,
mobilis, and 14.4 g of ethanol (87.2 % of the the- Indonesia 2,483,467 MT, Vietnam 1,422,501
oretical yield) was produced from 100 g of fresh MT, the USA 1,201,203 MT, Ethiopia 1,185,050
sweet potato storage roots. Studies found that MT, Madagascar 1,144,000 MT and India
sweet potato starch residue (SPSR) could be used 1,072,800 MT (FAO 2014).
as starting material to prepare an eco-friendly Patents that have been lodged over the past two
adsorbent to control heavy metal pollution (Hao decades related to alternative functional use of the
et al. 2014). Life-cycle assessment (LCA) of the sweet potato consisted largely under the category
energy efficiency of sweet potato-based bioetha- of ornamental products and alternative products
nol production found the net energy ratio of such as sweet potato chips and fries, and a few
sweet potato-based bioethanol to be 1.48 and the fuel ethanol products (Barnes and Sanders 2012).
net energy gain was 6.55 MJ/L (Wang et al.
2013). Studies by Cai et al. (2010) demonstrated
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