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 3
Sourdough Bread
Sudhanshu S. Behera1,* and Ramesh C. Ray2,*

1. IntroducƟon
“Sourdough” is one of the oldest forms of cereal fermentation utilized primarily for
baking purposes and it has been proven to be perfect for upgrading the shelf life,
texture, palatability, and nutritional values of wheat and rye breads. Its main function
is to leaven the dough to produce more aerated bread. In recent years, the traditional
sourdough bread production has gained tremendous success with increasing demand by
the consumers for more organic, tasty and healthy foods (Arendt et al. 2007; Mariotti
et al. 2014; Torrieri et al. 2014).
Traditionally, sourdoughs are obtained by spontaneous fermentation of a mixture
of flour (wheat or rye), water, and salt by the autochthonous culture of homo- and
hetero-fermentative lactic acid bacteria (LAB), in association with yeasts; however,
recent years have seen the use of defined allochthonous starters and control of the
fermentation process. LAB produce a number of metabolites such as organic (lactic and
acetic acid), exopolysaccharides (EPS), anti-microbial substances (i.e., bacteriocins)
and a variety of species specific enzymes (i.e., α-amylase, pectinase, phytase, etc.)
that have been shown to impart beneficial effects on the texture, nutritive values, and
staling of bread. For example, EPS can stimulate the viscoelastic properties of dough,
increase loaf volume, reduce crumb hardiness and enhance the shelf life (Torrieri et al.
2014). In this chapter, we discuss briefly the sourdough microflora, types of sourdough
breads, nutritional implications of sourdough and gluten-free sourdough breads.

1
Department of Biotechnology & Medical Engineering, National Institute of Technology, Rourkela-769008,
India.
Email: ssbehera.nitrkl2013@gmail.com
2
ICAR- Central Tuber Crops Research Institute (Regional Centre), Bhubaneswar-751019, India.
Email: rc_rayctcri@rediffmail.com
* Corresponding authors

© 2016 by Taylor & Francis Group, LLC

 54 Bread and Its Fortification: Nutrition and Health Benefits

2. History of sourdough
Sourdough was likely originated in ancient Egypt around 1500 BC and was the first
form of leavening of dough available to the bakers (Wood 1996). It remained the usual
form of leavening down into the European Middle ages until being replaced by barm
(the foam, or scum, formed on the top of the liquor-fermented alcoholic beverages
such as beer or wine from the brewing process), and then later by purpose-cultured
yeast (Pollock and Cairns 1991).
Historically, the use of sourdough was necessary for rye bread production, because
Baker’s yeast is not suitable as a leavening agent for rye bread, as rye does not contain
enough gluten. The rye bread is basically made from starch in the flour and a known
carbohydrate (pentosans). However, rye amylase is active at significantly higher
temperatures than wheat amylase, causing the structure of bread to deteriorate. The
lower pH of the starter, therefore, inactivates the amylase and allows the carbohydrates
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in the bread to gel and set properly. In the 1920s, the first dough acidifier, a mixture
of pre-gelatinized flour and lactic acid came to the market. Further, the development
of dried sourdoughs as convenient bakery ingredients was also initiated in 1920s and
1930s and resulted finally in early 1970s in the development of naturally fermented
organic dried sourdoughs (Brandt 2007).
The tradition of making sourdough wheat bread is widely used in the
Mediterranean and the Middle East countries and also in the San Francisco bay in
United States since 1849 (De Vuyst and Neysens 2005). In San Francisco sourdough
bread, the predominant strain of Lactobacillus starter, is named as Lactobacillus
sanfranciscensis (Jay et al. 2005).

3. Sourdough microflora
Sourdough is a combination of ground cereals (e.g., wheat or rye) and water that is
spontaneously fermented with a stable culture of LAB and yeast. Broadly speaking,
LAB and yeasts enact an important role in sourdough fermentation processes and the
production of LAB:yeasts in sourdough are generally 100:1 (Ottogalli et al. 1996).
In the process of bread making, yeast offers gas (CO2) that leavens the dough and
the LAB generate lactic acid that gives flavor and delay bread spoilage (De Vuyst
et al. 2009). In general, homo-fermentative LAB play a significant role in most of
the fermented foods, while hetero-fermentative LAB are prevalent in sourdough,
exclusively when prepared conventionally (Corsetti et al. 2003). However, LAB,
both homo- and hetero-fermentative species (Table 1) are mostly responsible for the
process of dough acidification; but yeasts and hetero-fermentative species of LAB
are responsible for the leavening (Gobbetti et al. 1995; Spicher and Brümmer 2001).
With recent improvements in the biodiversity study of sourdough LAB (Table
1), particularly sourdough ecosystems, several novel species have been isolated from
traditional sourdough, such as Lactobacillus mindensis, Lb. spicheri, Lb. rossiae,
Lb. zymae, Lb. acidifarinae, Lb. hammesii, and Lb. nantensis (De Vuyst et al. 2009;
Rizzello et al. 2014). Isolation of novel taxa mainly depends on the cultivation in
selective media and conditions while the distribution of the taxa of LAB is highly
variable from one sourdough ecosystem to another (De Vuyst et al. 2009). So far,

© 2016 by Taylor & Francis Group, LLC

 Sourdough Bread 55

Table 1. Fermenting sourdough species of bacteria (LAB).

Obligate homo-fermentative Obligate hetero-fermentative Facultative hetero-fermentative

Lactobacillus acidophilus Lb. sanfranciscensis Lb. brevis Lb. plantarum
Lb. delbrueckii Lb. fermentum Pediococcus pentosaceus
Lb. farciminis Lb. pontis
Lb. mindensis Lb. reuteri
Lb. amylovorus Lb. fructivorans
Lb. johnsonii Lb. panis
Lb. buchneri Lactobacillus sp.
Adopted from De Vuyst et al. 2009

a few less than 50 different species of LAB, including Lactococcus, Leuconostoc,

Enterococcus, Pediococcus, Streptococcus, and Weissella, have been isolated from
sourdough, Lactobacillus strains are the most frequently observed (Hammes et al.
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2005), while Leuconostoc sp., and Enterococcus sp., are irregularly used or found in
sourdough ecosystem. Among lactobacilli, Lb. sanfranciscensis, Lb. planatarum and
Lb. brevis are most often isolated from sourdough ecosystem. In one report, Gänzle
et al. (2007) communicated that two species of LAB species such as Lactobacillus
acidophilus and Lb. reuteri may be of intestinal origin and, due to cross-contamination,
are found in sourdough ecosystem.
More than 20 species of yeasts (Table 2) are found in sourdough (Gullo et al. 2003).
Saccharomyces cerevisiae is the most commonly found yeast species (De Vuyst et al.
2014). But, the figure of S. cerevisiae may be overestimated due to the lack of reliable
systems for identification and classification of yeasts from this habitat (Vogel 1997).

Table 2. Fermenting sourdough species of yeast.

Species Synonyms
Candida glabrata Torulopsis glabrata
Candida humilis Candida milleri
Debaryomyce shansenii Torulopsis candida
Candida famata
Dekkera bruxellensis Brettanomyces custersii
Issatchenkia orientalis Candida krusei
Kluyveromyces marxianus -
Saccharomyces bayanus Saccharomyces inusitatus
Saccharomyces cerevisiae Saccharomyces fructuum
Saccharomyces exiguous Torulopsis holmii
Candida holmii
Saccharomyces minor
Saccharomyces kluyveri -
Saccharomyces servazzi -
Torulaspora delbrueckii Torulopsis colliculosa,Vandida colliculosa,
Saccharomyces delbrueckii, Saccharomyces
inconspicuous

© 2016 by Taylor & Francis Group, LLC

 56 Bread and Its Fortification: Nutrition and Health Benefits

In particular, yeasts associated with LAB in sourdough are Saccharomyces exiguus,

Candida humilis (formerly described as Candida milleri) and Issatchenkia orientalis
(formerly described as Candida krusei) (Foschino et al. 1999). Moreover, other yeast
species include Pichia anomala (also called Hansenula anomala), Saturnispora saitoi
(also called Pichiasaitoi), Torulaspora delbrueckii, Debaryomyce shansenii and Pichia
membranifaciens (Gobbetti et al. 1994; Succi et al. 2003; Hammes et al. 2005). The
large instability in the number and type of yeast species found depends on several
factors such as degree of dough hydration, type of cereal used, leavening temperature,
and sourdough maintenance temperature (Gobbetti et al. 1994).

4. ClassificaƟon of sourdough producƟon processes

On the basis of the technology applied, three standard protocol of the sourdoughs
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fementation have been followed (Table 3):

• Type I (traditional sourdough),
• Type II (accelerated sourdough), and
• Type III (dried sourdough).
While artisanal and industrial technologies also largely use other conventional
protocols (Gobbetti et al. 2005).

Table 3. Scheme of sourdough production process.

Type I (Traditional sourdough) Type II (Accelerated Type III (Dried sourdough)
sourdough)
Flour, H2O, starter (LAB & yeast), Flour, H 2O, starter (LAB & Flour, H2O, starter (LAB &
NaCl, sugar yeast), NaCl, sugar yeast), NaCl, sugar
↓ ↓ ↓
Mixing Mixing Mixing
↓← Fermentation at RT ↓← Fermentation at ˃RT ↓← Fermentation at ˃RT
Bread dough Bread dough Bread dough
↓←(final pH at 3.8–4.5) ↓← Baking & final pH 3.5 ↓← Baking and drying
Traditional sourdough bread Sourdough II Sourdough III
(e.g., San Francisco sourdough) ↓ ↓
Bread Bread

Adopted from Corsetti and Settanni 2007

4.1 Type I sourdough or tradiƟonal sourdough

Type I sourdough is produced with traditional techniques and are characterized by
continuous, daily refreshment to hold on the microorganisms in an active state and has
very high metabolic activity. The fermentation is carried out in a temperature range
of 20–30°C (68–86°F) and the matrix has a pH range of 3.8–4.5. Traditional San
Francisco sourdough is an example of Type I sourdough and the LAB, Lactobacillus
sanfranciscensis was named for its discovery in San Francisco sourdough starter,
though it is not endemic to San Francisco (Jay et al. 2005; Komlenić et al. 2010).

© 2016 by Taylor & Francis Group, LLC

 Sourdough Bread 57

The starter culture containing Lb. sanfranciscensis for production of San Francisco
French bread is responsible for acid (acetic and lactic acid) production from maltose.

4.2 Type II sourdough or accelerated sourdough

The industrial action of the baking operation and the industrial appeal for faster, most
competent and extensive sourdough fermentation processes resulted in the evolution
of Type II sourdoughs. In the recent trend of industrial bakeries, several altered
accelerated sourdough fermentation processes were present (Stolz and Bocker 1996).
In the Type II sourdough, baker’s yeast or Saccharomyces cerevisiae is incorporated
to leaven the dough and obligate hetero-fermentative LAB such as Lb. pontis,
Lb. panis, Lb. sanfranciscensis, Lb. brevis, Lb. fermentum, Lb. reuteri, Weissela confuse
and Lb. frumenti as well as obligate homo-fermentative such as Lb. acidophilus,
Lb. delbrueckii, Lb. farciminis, Lb. amylovorus (rye), Lb. johnsonii highlight the
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microflora (Table 4) (Jay et al. 2005; Arendt et al. 2007).

In the late stationary phase these microorganisms are commonly found and thus
possess restricted metabolic activity. Moreover, the sourdoughs have a high acid
content (pH less than 3.5) and are fermented within a temperature range of 30 to 50°C
(86 to 122°F) for many days without feedings, which reduces the flora’s metabolic
activity (Sadeghi 2008). This process was adopted by some industry, in part, due to
simplification of multiple-step build typical of Type I sourdoughs (Hui 2007).

Table 4. Classification of sourdough and their characteristics microflora.

Type I sourdough Type II sourdough Type III sourdough

Obligate hetero-fermentative Obligate hetero-fermentative Obligate hetero-fermentative
Lb. sanfranciscensis, Lb. sanfranciscensis, Lb. brevis, Lb. brevis.
Lactobacillus sp. Lb. brevis, Lb. fermentum, Lb. pontis,
Lb. buchneri, Lb. fermentum, Lb. reuteri, W. confusa, Lb. panis,
Lb. fructivorans, Lb. pontis, Lb. frumenti.
Lb. reuteri, W. cibaria.
Obligate homo-fermentative Obligate homo-fermentative Facultative hetero-
Lb. acidophils, Lb. delbrueckii, Lb. acidophilus, Lb. delbrueckii, fermentative
Lb. farciminis, Lb. mindensis, Lb. farciminis, Lb. amylovorus, Lb. plantarum, P. pentosaceus.
Lb. amylovorus. Lb. johnsonii.
Yeasts Yeasts -
Candida humilis No yeast, S. cerevisiae may be
(Candida milleri), Issatchenkia added.
orientalis (Candida krusei).

Lb = Lactobacillus, P = Pediococcus, W = Weissela

4.3 Type III sourdoughs or dried sourdoughs

The type III sourdough is dried doughs in powder forms, which are initiated by defined
starter cultures. They mostly contain LAB that are resistant to drying and are able
to survive in that form. The LAB found in this conditions are either obligate hetero-
fermentative such as Lb. brevis and/or facultative hetero-fermentative like Pediococcus
pentosaceus and Lb. plantarum strains. The drying process such as spray-drying or
drum-drying leads to an increased shelf life of the sourdough and turns it into a stock

© 2016 by Taylor & Francis Group, LLC

 58 Bread and Its Fortification: Nutrition and Health Benefits

product until further use. The dried sourdoughs are easily distinguished in aroma, color
and acid content and are convenient as well as simple in use, resulting in standardized
end products (Stolz and Bocker 1996).

5. Biochemistry of sourdough fermentaƟon

The utilization of carbohydrate source by the LAB, for the production of acetic and
lactic acids are greatly influenced by the associated yeasts and availability of the types
of sugars. Starting from glucose as carbohydrate sources, the homo-fermentative LAB
specifically produce lactic acid through glycolysis/Embden-Meyerhof (EM) pathway
(homo-lactic fermentation), whereas hetero-fermentative LAB produce, apart from
lactic acids, CO2, acetic acids and/or ethanol depending on the availability of substrates
acting as electron acceptors (Ray and Joshi 2014). Gobbetti et al. (2005) reported
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that facultative (e.g., Lb. plantarum and Lb. alimentarius) and obligatory hetero-
fermentative (e.g., Lb. sanfranciscensis and Lb. pontis) LAB follow the biochemical
route of the EM pathway/glycolysis and through 6-phosphogluconate/phosphoketolase
(6-PG/PK) pathway for hexose fermentation respectively, and are commonly found
in the sourdoughs. The facultative hetero-fermentative LAB contains a constitutive,
fructose-1, 6-diphosphate aldolase, the key enzyme of EM pathway/glycolysis that
ferments hexose. The disaccharides cleaved by specific hydrolases (aldolases) and/
or phosphohydrolases to monosaccharides, which enter into EM/6-PG/PK pathways
(Corsetti et al. 2003).
In general, the competitiveness of obligatory hetero-fermentative lactobacilli in
sourdough is described by their integration of maltose and external electron acceptors
(Vogel et al. 2002). At the same time, 6-phosphogluconate/phosphoketolase (6-PG/PK)
pathway, additional energy yield may appear by the action of acetate kinase, which
in the vicinity of electron acceptors, allows the recycling of NAD+ without formation
of ethanol as end product (Gobbetti et al. 2005).
Pentose such as xylulose and ribulose are phosphorylated and converted to
xylulose-5-phosphate or ribulose-5-phosphate respectively, by the action of isomerases
or epimerase and further metabolized through the lower half of the 6-PG/PK pathway
(Ray and Joshi 2014). The pentoses are easily utilized by the obligatory hetero-
fermentative LAB, since they possess a crucial enzyme of the 6-PG/PK pathway,
the phosphoketolase. Further, fermentation of pentose results in the generation of
equimolar quantities of acetic and lactic acids; after all no dehydrogenation steps are
mandatory to reach the intermediate, xylulose-5-phosphate. There will be no evolution
of CO2, while acetyl phosphate undergoes substrate level phosphorylation with the
help of acetate kinase, to produce acetate and ATP.
The LAB, Lb. sanfranciscensis mainly utilize fructose as an external electron
acceptor and reduced to mannitol. The enzyme, mannitol dehydrogenase of
Lb. sanfranciscensis catalyses for both the reduction of fructose to mannitol and the
oxidation of mannitol to fructose in the presence of optimum temperature and pH of
35°C and 5.8–8.0, respectively (Korakli and Vogel 2003). The use of fructose as an
extraneous electron acceptor was also shown in Leuconostoc mesenteroides (Erten
1998). In a nutshell, the practical importance of using extraneous acceptors of electrons

© 2016 by Taylor & Francis Group, LLC

 Sourdough Bread 59

is the change of fermentation quotient (i.e., lactate/acetate molar ratio), which enhance
the baking, sensorial and shelf-life of sourdough breads (Gobbetti 1998; Spicher and
Brümmer 2001).

6. Sourdough breads: tradiƟonal and novel types

6.1 Rye sourdough
Rye flours contain higher levels of pentosans than wheat flour; hence the baking
properties differ significantly. The proteins in rye dough play a lesser role in the crumb
forming process than in wheat dough, because the pentosans usually inhibit the gluten
network. Further, the typical acidic characteristics of sourdough increase the solubility
and swelling properties of pentosans as well as partially inactivate the α-amylase
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activity in rye flour. An excessive amount of α-amylase in rye flour produces not only
a sticky crumb, but, at higher levels, it produces a very open grain and a reduction in
loaf volume by making them more elastic and extensible and confers the acidic flavor
characteristic of rye breads (Arendt et al. 2007).

6.2 Wheat sourdough

The use of sourdough in wheat breads has gained popularity in recent times as a means
to improve the quality and flavor of wheat breads (Arendt et al. 2007). San Francisco
sourdough French bread is an example of wheat products that rely on the process of
souring. Several reports have also stated that the incorporation of LAB in the form of
sourdough notably delays wheat bread staling.

6.3 Gluten-free sourdough

The majority of the gluten-free bakery products in the market are of poor quality
as compared to their wheat counterparts (Arendt et al. 2007). This is mainly due to
the unique properties of gluten, and the absence of a protein network in gluten-free
products. Current research focuses to find out alternate substrates for rye and wheat
such as barley flour and jackfruit seed flour for making bread that celiac patients can
tolerate. The other approach involves the use of such flour with the sourdough starter
to improve the quality of gluten-free matrix. The effects of addition of sourdough
produced using a mixture of brown rice flours, corn starch, buckwheat and soya flour
to a gluten-free bread recipe were investigated (Moore et al. 2007).

6.4 Novel sourdough

There are large number of studies to find alternate substrates, apart from rye and
wheat, to make functional bread using sourdough. Few recent works have been cited
in the following paragraph.
Consumption of whole grain barley foods reduces blood cholesterol and glycemic
index, and promotes weight loss by increasing satiety. However, barley has only been

© 2016 by Taylor & Francis Group, LLC

 60 Bread and Its Fortification: Nutrition and Health Benefits

marginally exploited by the baking industry, due to its deteriorating effect on bread
quality. The use of sourdough can be a strategy to improve the quality of barley bread.
In a recent study, two sourdoughs, made with sole hull-less barley flour or with a
mixture of 50 g/100 g barley and 50 g/100 g wheat flours, were characterized from a
microbiological and technological point of view, in comparison with a sole wheat flour
sourdough. Overall, the results showed that the barley sourdoughs investigated could
be used to obtain barley bread with enhanced nutritional value (Mariotti et al. 2014).
Likewise, the use of sourdough fermentation and mixture of wheat, chickpea, lentil and
bean flours was found to enhance the nutritional, texture and sensory characteristics
of white bread (Rizzello et al. 2012).
Lactobacillus plantarum C48 and Lactococcus lactis subsp. lactis PU1, were
reported to synthesize γ-aminobutyric acid (GABA) (Coda et al. 2010). These
Lactobacillus strains were used as starter for sourdough fermentation of chickpea,
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amaranth, quinoa and buckwheat flours (ratio 5:1:3:1) to enrich the bread with GABA.
The results were compared with wheat flour bread fermented with conventional baker’s
yeast. The non-conventional sourdough bread had the highest concentration of free
amino acids and GABA (ca. 4467 and 504 mg/kg, respectively) concomitant with
high concentration of phenolics and antioxidant activity, and the glycemic index was
lower than the wheat bread (Coda et al. 2010).

7. NutriƟonal implicaƟons
Sourdough fermentation has proved useful in improving the texture and palatability
of whole grain and fiber-rich or gluten-free products and it may stabilize or increase
the levels of bioactive compounds (Katina et al. 2005). The effects of sourdough on
the nutritional quality of bread are shown in Fig. 1.

1. Protein
7. Sourdough &
degradation 2. Increased
coeliac diseases
stability of vitamins
& bioactive

Effects of sour dough

6. Released 3. Enhanced fibre
on nutritional
aroma enriched products
qualityof bread
compounds and their
solubilisation

5. Some EPS 4. Reduction

can act as a in Phytate
prebiotic content

Figure 1. Effect of sourdough on the nutritional quality of bread (Arendt et al. 2007; updated).

© 2016 by Taylor & Francis Group, LLC

 Sourdough Bread 61

7.1 Proteolysis
The degradation of protein during sourdough fermentation is one of the key features
that influence the overall quality of sourdough bread (Gänzle et al. 2008). LAB or
yeast proteinases (either intracellular or extracellular) do not play a major role in
protein hydrolysis in sourdough (Wieser et al. 2008). Instead, proteolysis (breakdown
of proteins into peptides) during sourdough bread fermentation is initiated by wheat
or rye endogenous proteinases that are activated by the low pH. Further hydrolysis
of peptides into amino acids is carried out by intracellular/extracellular peptidases
of LAB (Di Cagno et al. 2004). In addition, most sourdough LAB, and in particular
Lb. sanfranciscensis, prefer peptides uptake rather than amino acids transport (Thiele
et al. 2004).
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7.2 Sourdough on the stability of vitamins and bioacƟve compounds

Intake of whole grain food products is believed to have many health benefits, such
as low starch digestibility, improved blood sugar regulation and lessened risk of
diabetes, cancer, and cardiovascular diseases (Jacobs et al. 1998; Liu et al. 2000;
Pereira et al. 2002).
There are mixed reports on either enhancing or decreasing effects of sourdough
fermentation on the bio-availability of minerals and vitamins in the final products
depending on the types of the sourdough process (Liukkonen et al. 2003). For example,
sourdough fermentation has been reported to increase the folate content of both wheat
and rye breads (Liukkonen et al. 2003; Kariluoto et al. 2004), and in rye fermentation
the levels of folate is found more than double (Kariluoto et al. 2004). Similarly, a
decrease in tocopherol and tocotrienol (Wennemark and Jägerstad 1992) and decrease/
increase in thiamine content were reported depending on the fermentation process
(Ternes and Freund 1988). The presence of yeast assume to support for the formation
of thiamine and folates, especially after long fermentation time (Batifoulier et al.
2005), but the content of thiamine has also been reported to decrease in the baking
process, more in wheat than in rye baking (Martinez-Villaluenga et al. 2009). Overall,
the fermentation step can affect the retention of vitamins in the baking process. For
example, in whole-wheat baking, a short baking process was shown to decrease the
vitamin B1 content, while a prolonged yeast or sourdough fermentation maintained
the content of above vitamins. In the long fermentation process, whole-wheat bread
making with yeast resulted in a 30 percent enrichment in riboflavin (vitamin B2),
but the use of mixed fermentations (yeast with sourdough) did not have a synergistic
effect on B vitamin levels (Batifoulier et al. 2005). It has been observed that during
sourdough preparation vitamin E content had declined.
Sourdough fermentation has been also shown to increase the anti-oxidativity
(DPPH radical scavenging) in the methanol extracted fraction of rye sourdough,
contemporaneously increased the levels of easily extractable phenolic compounds
(Liukkonen et al. 2003). Katina et al. (2005) reported that fermentation of rye bran
with yeast was also shown to increase the level of free ferulic acid. Anson et al. (2012)
reported that wheat bran bio-processed with yeast fermentation in combination with cell

© 2016 by Taylor & Francis Group, LLC

 62 Bread and Its Fortification: Nutrition and Health Benefits

wall hydrolytic enzymes increased the in vitro bio-accessibility of phenolic compounds

as well as the colonic end metabolites 3-phenylpropionic in breads.

7.3 Sourdough in fiber enriched products and solubilisaƟon

Recently, the health benefits of dietary fibers (DF) in food matrices have generated
huge interest because of the several either proven or hypothetical health benefits. As
a consequence, the markets are nowadays flooded with many new high-fiber food
products. In the process of rye sourdough fermentation, endogenous rye proteases,
especially aspartic proteases, hydrolyze rye proteins, mainly secalins. This generates
amino acids and small peptides, which act as flavor precursor (Tuukkanen et al. 2005).
Salmenkallio-Marttila et al. (2001) proposed that pre-fermentation of the wheat
barn with yeast alone or in symbiotic association with LAB improves the loaf volume
and crumb softness of bread during storage. Moreover, the potential activity of
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endogenous enzymes of flour especially, the amylases and proteases, assumed efficient
in sourdough fermentation (Hansen et al. 2002).

7.4 ReducƟon in phytate (anƟ-nutriƟonal factors) content

The cereal grains, legumes and oilseeds generally constitute 1–4 percent by weight
of phytic acid [myo-inositol hexakis (dihydrogen-phosphate) or myo-inositol
hexakiphosphate (IP6)], being a source of myo-inositol (Pandey et al. 2001). It acts as
the major storage form of phosphorous and it strongly chelates metallic cations such as
Ca, Fe, K, Mg, Mn and Zn making them insoluble and thus unavailable for nutrition
(Moroni et al. 2009). Therefore, phytic acid is considered to be an anti-nutritional
factor in humans and animals. Its anti-nutritional properties are due to the presence
of the central hexaphosphate ring, and being the highly charged (contains six anionic
groups) it acts as a chelator of dietary minerals. Moreover, phytic acid complexes
basic amino groups of proteins, subsequently reduced bioavailability of basic amino
acids (Wodzinski and Ullah 1996).
Any type of fermentation process including sourdough promotes degradation of
phytic acid by creating optimal pH for activation of phytases. For example, sourdough
fermentation has been shown to enhance phytate hydrolysis that favors mineral
solubility in case of whole wheat bread as compared to traditional yeast fermentation
(Lopez et al. 2000). Another study has revealed that Lb. sanfranciscensis has phytase
activity and when used as starter for sourdough fermentation in wheat flour, a major
reduction of over 50 percent of the phytate level was found in comparison to un-started
dough (De Angelis et al. 2003).

7.5 Some EPS can act as prebioƟc

Lactobacilli produce EPS that have many beneficial effects on technological properties
of bread, including water absorption of the dough, dough machinability, increased
loaf volume and retarded bread staling (Tieking et al. 2005). LAB during sourdough
fermentation also produces other metabolites such as mannitol, glucose and acetate that
can improve bread quality (Korakli et al. 2003). Further, some of the EPS produced

© 2016 by Taylor & Francis Group, LLC

 Sourdough Bread 63

by LAB have prebiotic properties (Roberfroid et al. 1998). In particular, the levan
produced by Lb. sanfranciscensis LTH2590 is metabolized by bifidobacteria (Korakli
et al. 2003). In a recent study, Torrieri et al. (2014) showed that the addition of 30 g/
100 g of sourdough, obtained using selected EPS producing-LAB, had a positive effect
on bread volume and crumb texture. Shelf life was improved substantially. Further, the
EPS producing LAB sourdough showed higher moisture content, better mechanical
properties during storage and had a protective effect on bread staling.
There are two classes of EPS extra-cellularly produced by LAB: homo-
polysaccharides and hetero-polysaccharides. Homo-polysaccharides are composed
of only one type of monosaccharide and are synthesized by glucan and fructo-
syltransferases using sucrose as the glycosyl donor (Brandt 2007). The lactobacilli
such as Lb. sanfranciscensis (producing fructan), Weissellacibaria MG1 (producing
dextran) and Lactobacillus reuteri VIP (producing reuteran) have positive effect on
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dough rheology and bread texture (Korakli et al. 2003; Brandt 2007; Sandra et al. 2012).

7.6 Aroma compounds

The flavor of leavened baked goods is influenced by several factors such as raw
materials, sourdough process, type of starters, and proofing and baking conditions.
Microbial and enzymatic conversions of carbohydrates, proteins, peptides, and lipids
in the dough result in the formation of alcohols, esters and carbonyls creating flavor
compounds relevant for the crumb odor. The crust odor is influenced by the thermal
reactions during the process of baking (Hansen and Schieberle 2005).
The ratio between lactic acid and acetic acid is an important factor affecting the
aroma of the final bread (Corsetti and Settanni 2007). It is influenced by the fermenting
microorganism, the fermentation temperature and the type of flour (Hansen and
Schieberle 2005). LAB can catalyze reactions such as deamidation, transamination
and decarboxylation, and their amino acid metabolism also contribute to the flavor.
For example, glutamine is converted to glutamate during sourdough fermentation
that imparts taste to the bread (Gänzle et al. 2007). The expression of the arginine
deaminase pathway in Lactobacillus sp. promotes higher production of ornithine, and
thus enhances the formation of 2-acetyl pyrroline that is responsible for the roasty
note of wheat bread crumb (Gänzle et al. 2007).
Similarly proteins as well as lipids also affect the bread quality. Lipids oxidation,
which occurs during flour storage and mixing of the dough, induces the formation
of (E)-2-nonenal and other aldehydes which are key aroma compounds in wheat and
rye breads (Hansen and Schieberle 2005; Vermeulen et al. 2007; Moroni et al. 2009).

7.7 Sourdough and Coeliac disease

Coeliac or celiac disease (CD) is a condition, where the victim’s body reacts to the
gliadin fraction of wheat and the prolamins of rye (secalins), barley (hordeins) and
oats (avidins) (Murray 1999). The inflammation of small intestine due to ingestion of
gluten, leads to the mal-absorption of several important nutrients such as iron, folic
acid, calcium and fat-soluble vitamins.

© 2016 by Taylor & Francis Group, LLC

 64 Bread and Its Fortification: Nutrition and Health Benefits

The Codex Alimentarius Commission (1994, 2000) of the World Health Organization
(WHO) and the Food and Agricultural Organization (FAO) communicate in a draft
revised standard for ‘gluten-free foods’ as:
• Consisting of, or made only from, ingredients which do not contain any prolamins
from wheat or all Triticum species such as spelt (Triticum speltra L.), kamut
(Triticum polonicum L.) or durum wheat, rye, barley, oats or their crossbreed
varieties with a gluten level not exceeding 20 ppm, or
• Consisting of ingredients from wheat, rye, barley, oats, spelt or their crossbreed
varieties which are branded as ‘gluten free’, with a gluten level not exceeding
200 ppm, or
• Any mixture of two ingredients as mentioned above with a level not exceeding
200 ppm (Katina et al. 2005; Arendt et al. 2007).
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8. Future perspecƟves
Sourdough is established technology in improving and diversifying the sensory
quality of bread, and especially in whole grain type baking it is finding good use. The
concept of bran fermentation has also been introduced to assist in bringing more bran
in palatable form for high-fiber baked goods. Fermentation and acid production have
been consistently shown to bring about improved mineral bioavailability. Sourdough
baking is also consistently shown to deliver breads with slow starch digestibility
and hence low glycemic responses, and has shown promise in improving texture of
gluten-free bread for celiac patients. In the future, it can be anticipated that sourdough
processing could be used to design foods with specific gut-mediated health effects,
such as demonstrated changes in composition or activity of intestinal microbiota. The
extracellular polysaccharides produced by lactic acid bacteria could act as selective or
functional substrates for gut microbiota. Production of bioactive peptides remains a yet
quite unexplored potential, which could be accomplished by utilizing the proteolytic
activity of the acidified cereal system. As with other food processing, the challenge
in fermenting cereal raw materials lies in the ability to combine good sensory quality
with demonstrated nutritional and health benefits.

Acknowledgements
The authors thank Dr. Cristina M. Rosell, Food Science Department, Institute of
Agrochemistry and Food Technology, Valencia, Spain and Prof. A.F. El Sheikha,
Department of Biology, Al-Baha University, Al-Baha, Saudi Arabia, for their
suggestions and critically going through the manuscript.
Keywords: Sourdough, spontaneous fermentation, lactic acid bacteria,
exopolysaccharides, bacteriocins, lactic acid, yeasts, Rye sourdough, Wheat sourdough,
Gluten-free sourdough, γ-aminobutyric acid (GABA), DPPH radical scavenging,
Coeliac disease

© 2016 by Taylor & Francis Group, LLC

 Sourdough Bread 65

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