Okra, Potential Multiple-Purpose Crop

for the Temperate Zones and Tropics I

FRANKLIN W. MARTIN 2

Immature okra pods are commonly consumed as a vegetable. In addition, okra

has attributes that could permit it to be used for other purposes. Leaves, buds,
and flowers are edible; dried seeds could provide oil, protein, vegetable curd,
and a coffee additive or substitute. Foliage could be used for biomass, and the
dried stems could serve as a source of paper pulp or fuel. The possible gossypol
and cyclopropenoid contents of okraseed must be considered when food or feed
use for monogastrates is contemplated. Although little development work has
been done with okra, available germ plasm appears to be sufficiently diverse to
permit genetic improvement.

The desirability of cultivating multiple-purpose crops cannot be overempha-

sized, for crops that can produce several kinds of useful products make efficient
use of land. The pressure imposed by expanding populations and higher standards
of living will force us to produce food, feed, forage, fiber, foliage and fuel on
increasingly limited land resources.
Okra, Abelmoschus esculentus (L.) Moench, is a widely distributed crop in the
tropics, subtropics, and warmer areas of the temperate zones, now grown chiefly
for its immature seed pods consumed as a vegetable. Recent findings have shown
that okra can be used for other purposes. In spite of little effort dedicated to
development, okra is a potentially important plant. Its major potential uses as a
vegetable, oil and protein source, and source of paper pulp and fuel, or biomass
are compatible.
Okra is an annual crop plant with some tendencies toward the perennial con-
dition. All varieties are sensitive to daylength; short days promote early flower-
ing. Although conventional temperate zone varieties flower during the longest
days of the temperate zone summer, even these flower earlier and plants are
smaller when they are grown under short-day conditions. On the other hand,
some African varieties of okra not seen in the continental United States do not
flower until days are short (Anonymous, 1979). Such varieties have a remarkable
ability to grow vegetatively in the temperate zones. Okraseed needs warm tem-
peratures to germinate, and plants grow best during the warm months. In the
tropics okra can flower throughout the year, but appropriate varieties are nec-
essary for different seasons.
Okra has a high number of chromosomes (2n = 130) and behaves in some
instances as a diploid and in others as a tetraploid. Flowers are structured for
cross-pollination by insects but self-pollination usually occurs. Hand-pollination
and handling of seed are simple processes, and thus controlled breeding is not
difficult, but progress in breeding for some characteristics may require very large
populations and careful evaluation.

1 Received 30 June 1981; accepted 20 January 1982.

2 Research Horticulturist, Mayaguez Institute of Tropical Agriculture, Agricultural Research Ser-
vice, U.S.D.A., Mayaguez, Puerto Rico 00709.

Economic Botany, 36(3), 1982, pp. 340-345

O 1982, by the New York Botanical Garden, Bronx, NY 10458
1982] MARTIN: OKRA 341

PRESENT A N D P O T E N T I A L USES OF OKRA

Leafy vegetable.--The tender leaves of okra are often used as a vegetable in

areas where a wide variety of leaves are used in the diet (west Africa, Southeast
Asia). The leaves of some varieties are somewhat hispid, an objectionable quality
reduced by cooking, but leaves of other varieties are glabrous. The tender shoots,
flower buds, and calyces are often eaten along with the leaves (Irvine, 1952).
Leaves are most frequently cooked as a "spinach" or added to soups and stews.
They are also frequently dried in the sun, crushed or ground to a powder, and
stored for future use.
Okra leaves provide vitamins A and C, protein, calcium, and iron. No toxic
substances have been reported in the leaves.
Fruit vegetable.--Whether boiled, added to soups, or sliced and fried, the pods
have a unique flavor and mucilaginous texture, the latter objectionable to many
people. The appeal of okra to the palate, however, appears to grow.
Edible seeds can be extracted from the pods which are too mature to be eaten
as vegetables. After cooking, the pods are pressed and the seeds are easily re-
moved. They can then be used in place of legumes in soups or in other dishes,
such as with rice. In Turkey the young pods are strung to dry for winter use. In
west Africa the fruits are sliced, sun-dried, ground to a powder, and then stored
until needed. Dried pods or okra powder can easily be rendered edible by boiling.

Coffee substitute.--Mature dried seeds of okra are roasted and ground as a coffee
substitute, or are added to coffee as an adulterant. Use as a "coffee" is wide-
spread and includes El Salvador and other parts of Central America, Africa, and
Malaysia (Burkill, 1935). According ot Carranza-Solfs (1933), the resulting "cof-
fee" has a good aroma and is inoffensive, since it lacks the stimulating effect of
caffeine.
Oil and protein source.--The potential of okraseed as a source of oil was probably
first noted by Jamieson and Baughman (1920), who recognized also the high
protein content. Edwards and Miller (1947) evaluated the characteristics of okra-
seed oil as an edible fat. When extracted by solvents or by pressing, it is greenish
yellow with a pleasant odor. Color and odor can easily be removed. The content
of unsaturated fatty acids, especially linoleic and oleic acids, is high (70%). The
keeping quality of the oil is poor but it is readily hydrogenated as shortening and
could be used as margarine.
About 20% of the weight of the seed is oil. Since one half of the seed weight
is hull, this means that about 40% of the kernel is oil. In comparing seeds of more
than 200 varieties we have found oil content of 13-22% (unpublished data). The
composition of okraseed oil has been studied by Savello et al. (1980), and their
data were compared to those of other studies. The sum percentage of oleic and
linoleic acid was similar in all varieties (60-65%) but the relative proportions
varied.
Okraseed oil of some varieties contains small quantities of cyclopropenoid fatty
acids (Telek and Martin, in press). These fatty acids have strong physiological
effects and are believed to be the cause of suppression of laying when hens eat
the seed meal of Sterculia foetida (Schneider et al., 1962). However, the wide
variation found (0.26--5.59%) in content of this compound in okra suggests that
342 ECONOMIC BOTANY [VOL. 36

a screening of varieties might reveal some with little or none. Cyclopropene fatty
acids can be removed by processing of the oil, including heat treatment.
Edwards and Miller (1947) also considered the residue after extraction of oil
as a possible feedstuff. Residue of the whole seed contained 44% protein, and
relatively high thiamine, niacin, and tocopherol content. In simple trials it ap-
peared to be a suitable ingredient in diets for rats and chicks.
Karakoltsidis and Constantinides (1975) can be credited with the rediscovery
of the value of okraseed as a protein source. They reported the protein content
to be 21%. In screening seeds of a large collection of introductions at the May-
aguez Institute of Tropical Agriculture, it was found that protein content varied
from 18-27% (unpublished data).
The amino acid pattern of okraseed protein is different from that of either
legumes or cereal grains. Limiting amino acids are valine, isoleucine, and lysine
(Savello et al., 1980) or threonine (J. P. Cherry, pers. comm.). Okraseed protein
is rich in tryptophan (94 mg/g N) and has an adequate content of sulfur-containing
amino acids (189 mg/g N). The protein of okra could thus complement that of
legumes or cereal grains in some dietary combinations.
One advantage of okraseed as an oil and protein source is ease of preparation.
Martin and Rubert6 (1979) used a hand mill and sieves to separate a high protein
(33%), high oil (32%) meal from the hull, and showed the usefulness of this meal
in baked products.
Machinery for harvesting okraseed has been developed (Kester, 1951), and the
machinery used for extraction of cottonseed oil is also suitable for okraseed
(Clopton et al., 1948). Recently J. P. Cherry (pers. comm.) has developed a
method of fractionating ground okraseed using a McGill aspirator. (Mention of
a trademark, proprietary product, or vendor does not constitute a guarantee or
warranty of the product by the U.S.D.A. and does not imply its approval to the
exclusion of other products or vendors that may also be suitable.) Three useful
protein fractions can be isolated.
Vegetable curd.--Okra protein and oil can be separated from the hulls by making
a vegetable curd (Martin et al., 1979). The seeds are finely ground in water, and
the aqueous mixture is strained through a cloth filter. Protein is precipitated with
bivalent salts such as magnesium sulfate, or by addition of acid (vinegar or lime
juice) to the heated mixture. The resulting curds are removed from the whey by
filtration. They are washed and can then be pressed. Seed oil is also precipitated
from the aqueous mixture, probably by occlusion, and thus becomes part of the
curd. Curds have a creamy or light yellow color, a background flavor similar to
that of tofu, the vegetable curd from soybean, and a musky, distinctive flavor
associated with okraseed. In experiments in Puerto Rico, a taste panel found the
vegetable curd pleasant to eat. It can be used fresh or cooked in any dish as a
cheese substitute. The protein content of such curds is as high as 43%, and the
oil 52.6%, dry-weight basis (Martin et al., 1979).
Okra vegetable curd has a possible drawback. Seeds reportedly contain gos-
sypol or a gossypol-like compound, which is soluble in oil, and thus is included
in the curd at concentrations several times higher than that of the original seed.
To avoid possible long-term toxicity, it would be desirable to remove the gos-
sypol, if indeed it exists. It is extracted from cottonseed oil with a butanol solution
(Canella and Sodini, 1977).
1982] MARTIN: OKRA 343

Animal feed.qAfter cooking or processing, okraseed might be a useful feed.

Okraseed meal made by grinding and sieving reduced growth of rats when used
as a principal source of protein. However, this inhibition was removed by aging
the ground meal for 4 wk before use, or by extruding the meal with a machine
that heats it substantially (Savello et al., in press).
Studies by P. F. Randel (pers. comm.) show that ground okraseed is a good
source of protein but a poor source of digestible carbohydrate. The tough seed-
coat, if not well ground, impedes solubilization of parts of the kernel.
As a biomass crop.--After all immature pods are removed from the plant, the
remaining green foliage can still be cut and the stem can be uprooted for their
biomass. The dry weight produced may reach 27 tons/ha. This material includes
the following: 11.3% protein, 3.9% oil, 0.17% hydrocarbon, 3.3% polyphenols,
5.3% ash (W. B. Roth, pers. comm.). In other studies, not given in detail here,
the various components of dry matter varied with variety and state of maturity
of the plants. It may be possible to extract protein, oil, and perhaps other sub-
stances and then use the residue for other purposes (see below).
Paper pulp.---The fiber of the okra plant, in common with fibers of other plants
of the Malvaceae, is a good material for making paper. Okra stems contain longer
fibers in their woody cores than most other dicotyledonous plants (Nelson et al.,
1961). The large-stemmed, rapidly growing west African varieties that cannot
flower in the continental United States should be especially valuable for pulp
production.

Fuel.---The thoroughly dried okra stems can be burned as an inexpensive fuel on

the farm. A worldwide shortage of cooking fuel is now apparent and is likely to
become more pronounced, especially in the tropics as forests are destroyed.
Dried okra stems are not dense, and thus are consumed rapidly in fires, producing
considerable heat but not lasting for long, a severe disadvantage. On the other
hand, they do not throw off sparks, smoke extensively, or produce a disagreeable
odor. The use of okra stems as fuel may require the use of a suitable stove, one
that concentrates heat on the cooking pots themselves and does not waste heat
to the air. Such stoves are being developed for the tropics.
The use of okra as a fuel requires removing the stems, drying, and storing
them. It might be useful to uproot the old plants before drying and storing, for
the tough, woody root could also be used as fuel. African varieties of okra that
produce large (up to 10 cm diameter) stems when planted during summer months
can be used for pod and seed production during short days and cut as fuel when
production ceases. With some varieties, regrowth may be feasible for at least a
second season.
Male sterilant.--Gossypol is being tested as an orally adminstered contraceptive
in China (National Coordinating Group on Male Antifertility Agents, 1978), and
is perhaps the most promising material currently available for such purposes.
Gossypol begins to inhibit sperm formation a month after daily doses are begun,
but does not affect testosterone production or secondary sex characteristics.
When gossypol adminstration is terminated, fertility is gradually restored over a
year-tong period. Possible side effects of gossypol on the human must still be
investigated. Okra, among other plants, might serve as a gossypol source, or
344 ECONOMIC BOTANY [VOL. 36

okraseed in the diet might reduce fertility. However, the question of the exact
nature of the gossypol-like compound in okra must be resolved. Low contents of
a terpenoid aldehyde have been demonstrated, and may be the gossypol-like
compound.
Mucilage.--The mucilage of the immature okra fruit is easily obtained when slices
of the fruit are placed in water. When the pod is boiled, the fruit becomes highly
mucilaginous. This mucilage has been used to size paper in Malaysia (Burkill,
1935). Recently the composition and potential use of the mucilage were studied
by Woolfe et al. (1977). It is an acidic polysaccharide with associated minerals
and protein. The polysaccharide is composed of galacturonic acid, rhamnose, and
glucose. The maximum viscosity occurs at neutral pH, and it is unstable when
heated. Okra mucilage is potentially useful as an extender of serum albumin and
as an egg white extender or substitute. Mucilage released on frying slices of okra
is a good thickening agent for gravy.

GENETIC RESOURCES OF OKRA

Abelmoschus includes 6 species in Southeast and Southern Asia and North

Australia (Von Borssum Waalkes, 1966). Southeast Asia is considered by Von
Borssum Waalkes to be the center of origin of the species A. esculentus, but
Zeven and Zhukovsky (1975) consider okra to have originated in the Hindustani
center, possibly from the wild A. tuberculatus Pal & Singh.
Okra seen in the temperate zones is fairly uniform. Martin and others (unpub-
lished data) could not find any consistent subvarietal differences among a collec-
tion of 266 temperate-zone varieties. Nevertheless, Siemonsma (Anonymous,
1979) described 2 distinct types of okra from the Ivory Coast, and has thus
brought to attention the existence of almost perennial races that probably were
unknown to Van Borssum Waalkes. Most of these do not bloom early enough in
the temperate zone summer to set seed. In hybridization among types Martin
(unpublished data) has found F1 hybrids to be partially sterile. The potential of
west African okras to revitalize okra breeding is only now becoming evident.
Some African varieties grown in the temperate zones should easily surpass con-
ventional varieties as fiber and biomass sources.
Standard varieties may be very good. Mangual-Crespo and Martin (1980) re-
ported yields of oil and protein of 612 kg/ha and 658 kg/ha, respectively, in Puerto
Rico. These yields rival those of other oil and protein crops of the temperate
zones and tropics. There is good reason to believe that existing varieties, already
good, can be improved by breeding.
Selection and breeding of okra for yields of plant components other than im-
mature pods have never been practiced, but the germ plasm already available
appears to be adequate to facilitate such efforts to attain genetic improvement.

LITERATURE CITED

Anonymous. 1979. La vafiabilit6 naturelle du mat6riel v6g6tal du gumbo, Abelmoschus esculentus

(L.) Moench. In C6te-D'Ivoire. Centre N6erlandais, Fondation Rattach6e au Centre ORSTOM.
D'Adiopoum6. 1978 Annual Report, p. 2%34. Universit6 Agronomique, Wageningen, Neth-
erlands.
1982] MARTIN: OKRA 345

Burkill, I. H. 1935. A Dictionary of the Economic Products of the Malay Peninsula. Crown Agents
for the Colonies, London.
Canella, M., and G. Sodini. 1977. Extraction of gossypol and oligosaccharides from oil seed meals.
J. Food Sci. 42: 1218--1219.
Carranza-Solis, J. 1933. Monografia del Caf6. Imprenta Nacional de Costa Rica, San Jose, Costa Rica.
Clopton, J. R., R. Ammarette, and H. A. Jeskey. 1948. Chemical studies of oil-bearing seeds. I.
Okra-seed. J. Amer. Oil Chemists' Soc. 25: 401--404.
Edwards, W. R., Jr., and J. C. Miller. 1947. Okra seed oil. Chemurgic Digest 29: 31-33.
Irvine, F. R. 1952. Supplementary and emergency food plants of West Africa. Econ. Bot. 6: 23--40.
Jamieson, G. S., and W. F. Baughman. 1920. Okraseed oil. J. Amer. Chem. Soc. 42: 166.
Karakoltsidis, P. A., and S. M. Constantinides. 1975. Okra seeds: a new protein source. J. Agric.
Food Chem. 23: 1204-1207.
Kester, E. B. 1951. Minor oil-producing crops of the United States. Econ. Bot. 5: 38-59.
Mangual-Crespo, G., and F. W. Martin. 1980. Effects of spacing on seed, protein, and oil production
of four okra varieties. J. Agric. Univ. Puerto Rico 64: 450--459.
Martin, F. W., and R. Rubert6. 1979. Milling and use of okra seed meal at the household level. J.
Agric. Univ. Puerto Rico 63: 1-7.
, and L. Telek, R. Rubert6, and A. G. Santiago. 1979. Protein, oil and gossypol contents of
a vegetable curd made from okra seeds. J. Food Sci. 44: 1517-1519.
National Coordinating Group on Male Anti-fertility Agents. 1978. Gossypol: a new antifertility agent
for males. Chin. Med. J. (English ed.) 4: 417--428.
Nelson, C. H., H. J. Nieschlag, M. E. Daxenbichler, I. A. Wolff, and R. E. Perdue, Jr. 1%1. A
search for new fiber crops. III. Laboratory-scale pulping studies. Tappi 44:319-325.
Savello, P., F. W. Martin, and J. M. Hill. 1980. Nutritional composition of okra seed meal. Agric.
Food Chem. 28:1163-1166.
, --, and . In press. Nutritional value of ground okra seed in rat feeding trials. J.
Food Sci.
Schneider, D. L., A. A. Kurnick, M. G. Vavich, and A. R. Kemmerer. 1%2. Delay of sexual maturity
in chickens by Sterculiafoetida oil. J. Nutr. 77: 403--407.
Telek, L., and F. W. Martin. In press. Okra seed. A potential source for oil and protein in the humid
lowland tropics. In E. H. Pryde, ed., New Sources of Fats and Soils. Amer. Oil Chem. Soc.,
Champaign, IL.
Van Borssum Waalkes, J. 1966. Malesian Malvaceae revised. Blumea 14: 1-213.
Woolfe, M. L., M. F. Chaplin, and G. Otchere. 1977. Studies on the mucilages extracted from okra
fruits Hibiscus esculentus and baobab leaves Adansonia digitata. J. Sci. Food Agric. 28: 519-
529.
Zeven, A. C., and P. M. Zhukovsky. 1975. Dictionary of Cultivated Plants and Tehri Centres of
Diversity. Centre for Agricultural Publishing and Documentation, Wageningen, Netherlands.

Book Review
A n Illustrated M a n u a l of Pacific Coast Trees. Howard E. McMinn and Evelyn Maino.
Reprint of the 1937 edition. 409 pp. illus. University of California Press, Berkeley, 1981.
$6.95 (softcover), $12.95 (hardcover).
This is the first paperback printing of the second, 1937 edition. The book is somewhat
unusual among tree guides in that it accounts for introduced, cultivated species (some 400
of them) as well as native ones (146). The region covered includes California, Oregon,
Washington, and British Columbia. Although some of the scientific names are no longer
current (a list of name changes might have been added as an addendum to the volume)
and the reference list contains no entries more recent than 1934, the book remains useful
for its area.
JWT