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CLOSE THIS BOOKThe Winged Bean: High-Protein Crop for the Humid Tropics (BOSTID, 1981, 41 p.)
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENTAcknowledgments
VIEW THE DOCUMENTPreface
VIEW THE DOCUMENT1 Summary
VIEW THE DOCUMENT2 Agronomy
VIEW THE DOCUMENT3 Food Use and Nutritive Value
VIEW THE DOCUMENTAppendix A. Pests and Diseases
VIEW THE DOCUMENTAppendix B. Selected Readings
VIEW THE DOCUMENTAdvisory Committee on Technology Innovation
VIEW THE DOCUMENTBoard on Science and Technology for International Development

3 Food Use and Nutritive Value

Edible legumes will play an increasing role in meeting food needs in times of food shortages and widespread malnutrition. For human nutrition the winged bean is a plant with outstanding qualities. With the exception of its stems and roots, all of its parts-leaves, flowers, shoots, immature pods, immature and ripe seeds, and tubers-are edible, palatable, and highly nutritious. Yet, for the most part, winged bean is still grown in Papua New Guinea and South and Southeast Asia as a subsistence crop in gardens or backyards. These regions, however, are typical of the humid tropical zone that encompasses large belts of Central and South America, the Caribbean, Africa, Oceania, and West Asia, where good sources of protein are limited and the plant is little known. It is uncommon for an edible crop with such high protein content to grow in these regions.

The amounts of major nutrients, such as protein, minerals, and vitamins, in the various winged bean parts are shown in Tables 2 through 6. The common characteristic of all parts of the winged bean is the relatively high protein content. Seeds and tubers are particularly protein rich.

Pods

Pods are the most popular part of the plant in most countries where the winged bean is grown. They are probably the easiest part of the winged bean to introduce as food. The young, tender pods may be eaten raw, sliced, or chopped. They may be used in salads, soups, stews, and curries, and may be bolted in water or coconut milk, or sauteed in oil. Their flavor is similar to that of green beans.

In Papua New Guinea pods too fibrous to eat whole are often steamed in oil drums or the "mumu" pit, or baked in open fires; the seeds and mucilage are then scraped out and eaten. Alternatively, the half-ripe seeds can be removed from the pod and cooked like green peas.

The composition of nutrients in the immature pods does not differ significantly from that found in green pods of other leguminous plants. The average protein content is 2.4 g per 100 g of edible portion.

TABLE 2. Composition of Different Parts of the Winged Bean


Flowers

Leaves

Immature

Unripe

Ripe

Tubers



Pods

Seeds

Seeds



Watera

84.2-87.5

64.2-85.0

76.0-93.0

35.8-88.1

8.7-24.6

54.9-65

Energy(mJ)b

0.17(av.)

0.20(av.)

0.19(av.)

0.10-0.71

1.61-1.89

0.63(av.)

Protein

2.8-5.6

5.0-7.6

1.9-4.3

4.6-10.7

29.8-39.0

3.0-15.0

Fat

0.5-0.9

0.5-2.5

0.1-3.4

0.7-10.4

15.0-20 4

0.4-1.1

Carbohydrate
(total)

3.0-8.4

3.0-8.5

1.1-7.9

5.6-42.1

23.9-42

27.2-30.5

Fiber


3.0-4.2

0.9-3.1

1.0-2.5

3.7-16.1

1.6-17.0

Ash

0.8

1.0-2.9

0.4-1.9

1.0

3.3-4.9

0.9-1.7

a Values expressed as g per 100 g fresh weight show the ranges reported by authors cited in footnote to Table 4.
b mJ = megajoules. 4.184 mJ = 1,000 (dietary) kilocalories

The immature pod provides bulk of comparatively low energy content, but it is a beneficial vegetable because of the minerals and vitamins it contains.

Winged bean pods are cooked and eaten widely in many countries; no adverse effects have been reported and no antinutritional factors (see below) have been reported in cooked immature pods.

Seeds

The mature dry seeds are the most nutritious part of the winged bean. Their outstanding nutritive quality is based, above all, on their high protein content (30-42 percent) and their favorable amino acid composition. The seeds also contain high amounts of edible oil (15-20 percent). With the exception of the soybean and the peanut, no other commonly consumed food legume can rival the winged bean in the combination of protein and oil. Winged bean seeds can be steamed, boiled, fried, roasted, fermented, or made into milk, tofu (bean curd), or tempeh.

The winged bean seed contains about as much protein and nutritional energy as the soybean and some find it more palatable. Like most beans, mature winged beans contain antinutritional substances (see below), but somewhat less than in soybeans. Seeds should be soaked overnight, then boiled in water until tender. (The soaking liquid should be discarded.) If seeds are soaked in a hot, 1-percent sodium bicarbonate solution, the hard seed coats are more easily removed. (Mature seeds are more difficult to dehull by this process, since the cotyledons swell and press firmly against the hull.)

When fried or baked, winged bean seeds make a delicious nut-like snack. The high temperature breaks open the tough seed coat. It is not certain, however, whether this method of cooking removes the antinutritional substances contained in the ripe dried seed.

TABLE 3. Mineral Content in Different Parts of the Winged Beena


Leaves

Immature Pods

Ripe Seeds

Tubers

Potassium

80-436

205-381

1110-1800

550

Phosphorus

52-98

26-69

200 - 610

30-64

Sulfur


380

21

Calcium

113-260

53-330

80-370

25-40

Magnesium

54

58

110-255

23

Sodium

2.5-18

3.0-3.4

14-64

33

Iron

2.0-6.2

0.2-2.3

2.0-18.0

0.5-3.0

Manganese

1.5

2.2

4 - 25

10

Zinc

1.4

0.2

3.1-5

1.3

Copper

0.5

0.6

1.3

1.3

a Values expressed as mg per 100 g fresh weight show the ranges reported by authors cited in footnote to Table 4.

The quality of the protein of heat-processed seeds has been tested in several animal experiments. The values for the protein-efficiency ratio (PER) and for the net protein utilization (NPU) of winged bean seeds, as compared with the soybean and the peanut, are presented in Table 7. Both values for winged bean compare well with those for the soybean, indicating that the nutritive value of the two seed proteins is similar.

The amino acid composition is also similar to that in soybeans. Like most legume seeds, the winged bean is relatively deficient in the sulfur-containing amino acids.* Since the winged bean is rich in available lysine, it could supplement cereal diets, which are lysine deficient.

The high quality of the seed protein was evident in experiments conducted with children suffering from kwashiorkor. A mixture of winged bean plus corn, enriched with a small amount of skim milk, showed nutritional efficiency not significantly different from that found in a diet in which most of the protein was derived from cow's milk.!

Table 6 shows the fatty acid composition of winged bean oil compared with that of soybean and peanut oils. The oil is nutritionally of slightly lower quality than soybean oil. Its fatty acid composition resembles that of peanut oil in that it also contains higher amounts of long-chain saturated fatty acids. But it also contains approximately 60 percent of unsaturated fatty acids.

TABLE 4. Vitamin Content in Different Parts of the Winged Bean


Leaves

Immature Pods

Ripe Seeds

Vitamin A IU

5,240-20,800

300-900


Thiarnin mg/100 g

3,6a

0.06-0.24

0.08 - 1.7

Riboflavin mg/100 g

2.6a

0.08-0.12

0.2-0.5

Pyridoxin

1.0a

2.0a

0.1-0.25

Niacin mg/100 g

15.0a

0.5-1.2

3.1-4.6

Folic acid yg/100 g

67a


25.6-63.5

Ascorbic acid mg/100g

14.5-128

20-37

Trace

Tocopherols mg/100 g

3.5a

0,5

22.8

a Values on dry weight basis. All the remaining values are expressed on fresh weight basis.

Data shown in Tables 2, 3 and 4 were reported variously by Bailey, 1968; Brown, 1954; Cernyetal., 1971; Claydon, 1975 and 1980; Ekpenyong and Borchers, 1980; FAO/USDHEW, 1972; IITA, 1971-74; Institute of Nutrition, Philippines, 1957; Jaffe and Korte, 1976; Kapsiotis, 1968; Pospisil et al., 1971; Rachie, 1974; Ravelli et al., 1980; Rockland et al., 1979; Sastrapradja and Aminah, 1975; Svabova and Cerny, 1977; Watson, 1971; Wong, 1975, and L. St. Lawrence, personal communication.

Winged bean oil contains behenic acid (as does peanut oil), but although this may reduce its digestibility, it seems unlikely to have other ill effects. Experiments conducted with both malnourished and well-nourished infants in whom full-fat winged bean flour was used for a period of 4 months gave no evidence of ill effects.* To the contrary, children in all these groups flourished.

Winged bean oil not only contains acceptable amounts of unsaturated fatty acids.(especially linoleic), but, in contrast to soybean oil, the content of linolenic acid is quite low, giving winged bean oil the advantage of greater stability. Winged bean oil also contains a high measure of tocopherols (vitamin E)-an antioxidant that improves the utilization of vitamin A in the human body. Some varieties are reported to have levels higher than those of soybean or corn oils.

Extracting oil from winged bean seeds leaves a high-protein meal. From extensive tests on three continents it has been learned that infants fed winged bean meal suffer little or no flatus discomfort. Analysis has shown that the level of raffinose and stachyose (sugars that lead to flatulence) is less in winged bean than in soybean. A typical comparison of the two seed meals follows."

TABLE 5. Amino Acid Composition of Different Parts of the Winged Beana

Amino Acid

Leaves

Immature

PodsSeeds

Tubers

Isoleucine

238-356

156-266

242-350

171

Leucine

450-713

282-430

453-564

229

Lysine

162-500

219-416

413-600


Methionine

75-163

56-63

38-87

48

Cysteine



73-162

14

Total S-cont.

161-187

272

114-193

62

Phenylalanine

294-463

181-213

214-419

106

Tyrosine

238-456

119-125

195-431

72

Total aromatic

585-710

527

409-850

178

Threonine

247-300

175-231

256-300


Tlyptophan

58-131

59

47-69

150

Valine

300-402

188-319

242-344


Arginine



400-469


Histidine


169-183


a Values expressed as mg per g N.
Data from Cerny et al.,1971; Chubb, 1980; Claydon, 1978; Ekpenyong and Borchers,1980; Gillespie and Blagrove, 1980; Jaffe and Korte, 1976; Ravelli et al., 1980; Wong, 1975.

Sugars

Winged Bean

Soybean

Glucose

trace

trace

Galactose

trace

trace

Sucrose

5.0 percent

4.8 percent

Raffinose

1.0 percent

1.3 percent

Stachyose

2.5 percent

3.5 percent

In storage winged bean seeds show remarkable resistance to bruchid beetles, which are major pests of stored legumes. Experiments have shown that although the beetles lay eggs, the larvae that hatch die in their first or second instars after eating the seeds. The cause is not yet understood.

Tubers

Winged bean tubers are popular in Burma and in the Highlands of Papua New Guinea. They can be boiled, steamed, fried or baked. The brown skin peels off readily (after about 40 minutes of cooking), leaving a white or cream-colored flesh that is firm and moist, with a distinctive nutty, earthy flavor. They are always eaten cooked.

TABLE 6. Fatty Acid Composition of Seeds of Winged Bean, Peanut, and Soybeana

Fatty Acid

Winged seen

Peanut

Soybean

14: 0 Myristic

0.1-0.4

0.1-0.5

0.1-0.3

16: 0 Palmitic

7.4-9.8

7.3-12.9

6.8-11.5

16: 1 Palmitoleic

0.1-0.8

0.9-2.4

0.1-1.0

18: 0 Stearic

2.8-6.9

2.6-6.3

1.4-5.5

18: 1 Oleic

24.5-41.6

42.0-65.7

22.0-55.0

18: 2 Linoleic

27.2-31.3

16.8-38.2

49.8-60

18: 3 Linolenic

1.0-2.0

1.5

2-10

20: 0 Arachidic

1.3-2.2

0.6-2.4

0.3-0.4

20: 1 Gadoleic

2.5-4.0

1.1-1.4

0.6

22:0 Behenic

6.1-15.9

1.8-3.5

0.1-0.3

22: 1 Erucic

0-0.8

-

-

24: 0 Lignoceric

1.0-3.4

0.8-1.5

-

Solidifying point, °C

8-15

0-3

-7- -12

iodine Value

82-95

81-106

125-138

% Unsaponifiable matter

2.4-2.9

0.4-1.0

0.7-1.6

Saponification value

176

188-196

188-196

% Free fatty acids

0.5

2.7

0.9

a Values as percentage whole oil.
Data from Cerny et al., 1971; Chubb, 1980; Claydon, 1980 and in press; Drew Eoods 1970; Ekpenyong and Borchers, 1980; Garcia and Palmer, 1979; Hilditch and Williams, 1964; and L. St. Lawrence, personal communication.

The tubers have an extraordinarily high protein content of 8-20 percent (dry weight) compared with 1-5 percent for cassava, potatoes, and the common cultivars of most root crops.* Not only is the protein content high, but the tubers are also rich in carbohydrates, which provide energy. This rare combination makes the winged bean tuber unusual among tropical root crops. Although the composition of the tuber protein appears poor because it is deficient in sulfur-containing amino acids, the high amount of crude protein could nevertheless make the winged bean tuber a valuable food in those regions where starchy, protein-deficient foods such as cassava, sweet potato, yam, and plantain are staples.

There is little information on the antinutritional (alkaloid negative) factors in winged bean tubers except that trypsin-inhibitor activity has been found and some tannin is present in the peel.

TABLE 7. Nutritive Value of Winged Bean Seed Protein in Rat Diets


10% Protein


16% Protein

Protein Component of Diet

PER

NPU

PER

Winged Bean

1.6-2.38

55.0

2.00

Peanut

1.53

46.2


Skim milk

3.04

73.2

2.37

Winged bean plus corn

2.70

65.7

2.20

Peanut plus corn

1.92

54.7

1.82

Soybean

2.1-2.4

56.0


Data from Cerny et al., 1971; Ekpenyong and Borchers, 1980; Jaffe and Korte, 1976; Liener, 1972; Ravelli et al., 1980.

Leaves and Shoots

Winged bean sprouts and shoots may be eaten either raw or cooked as green vegetables. Usually only the top three sets of leaflets are eaten, since they are the most tender; they taste slightly sweet.

The crude-protein content of winged bean leaves is similar to that found in edible leaves of other plants such as cassava and tarot Young leaves have higher protein content and digestibility than mature leaves.

The leaves have a relatively low Iysine content but an uncommonly high content of tryptophan (see Table 5), a nutritionally essential amino acid. Even a small amount of winged bean leaves can thus greatly improve tryptophan-deficient diets- for example, those based on corn.

Adding cooked winged bean leaves to the diets of weaned infants and preschool children should be beneficial because of the favorable content of minerals, and especially of the vitamin A precursor beta-carotene. The amount of vitamin A equivalent in winged bean leaves (up to 20,000 international units per 100 g of edible portion) ranks among the highest ever recorded in green leaves of tropical plants." This is important; in some developing nations many children go blind because of vitamin A deficiency.

Excessive consumption of raw winged bean leaves has been reported in Indonesia as producing dizziness, nausea, and flatulence. Small amounts of cyanogenic glycosides have been found in the stems. Even though no such adverse effects have been reported from other countries, consumption of large amounts of raw winged bean leaves is not recommended, especially for small children. Properly cooked leaves, however, appear to be safe to eat, even in quantity.

Flowers

Flowers have a sweet taste because of the nectar they contain. When steamed or fried, they have the color and consistency of mushrooms. When lightly cooked, they make an attractive garnish.

Although not important nutritionally in terms of quantity, the protein content of the flowers appears to be fairly high compared with edible flowers of other better-known tropical plants such as banana and Sesbania grandiflora.

Antinutritional Factors

Winged bean seeds are known to contain several antinutritional factors, of which the most closely examined have been the trypsin and chymotrypsin inhibitor." Other antinutritive factors are amylase inhibitors, phytohemaglutinins, cyanogenic glycosides, and perhaps saponins. Further studies, especially of the usual cooked products, are needed.

The winged bean seed-inhibitor activity can be safely eliminated only by using moist heat; for example, steaming the seeds in an autoclave at 130°C for 10 minutes. The same result can be achieved by soaking seeds for approximately 10 hours and then boiling them for 30 minutes.

Processing

Commercial processing of the winged bean is just beginning. Laboratory efforts to make flour from the seed are underway in certain parts of Asia and Africa and in the United States. Similarly, in Thailand and Ghana oil has been pressed from seed, with the oil seed cake being used experimentally for animal feed. A gruel for weaning infants has been produced in Ghana and Czechoslovakia. Mixed with corn, it provides the nutritive equivalent of milk. In Thailand a similar gruel made of winged bean meal, rice, and banana is being fed to refugees from Cambodia.

Because of the similarity of the winged bean seed to the soybean in chemical composition, interest has been expressed in duplicating many foods made from soy. Tempeh and tofu are made commercially in Indonesia from the winged bean seed. It is possible that these might even be improved through use of the white or cream-colored seed rather than the dark-coated seed now used.

Both a white milk and a chocolate-flavored milk have been made from the seed in Thailand and sterilized for longer shelf life. Researchers in Thailand also have made tasty snacks from winged bean tubers sliced thin, fried and salted, or softened in sugar syrup.

Immature winged bean pods are used in pickles commercially available in South India.

One researcher in Indonesia has made a coffee substitute by roasting the seed (the grounds are edible), and a tobacco substitute from the dried leaf. These products can be expected to be free of alkaloids.

Sprouted winged bean seed can also be an alternative to mung bean sprouts for village or commercial use.

Use as Animal Feed

Except for occasional use of the dried haulm, there is only scattered information on the deliberate use of the winged bean plant as a livestock food. Unprotected plants, however, are eagerly and almost totally consumed by livestock.

Experiments are underway in Korea, Sri Lanka, and India to use the unprocessed vegetation as green silage. Work is in progress in Thailand and Malaysia to use the ground-up seed as a constitutent of animal and poultry feed. Experimental pellets for animal feed have been manufactured in Thailand using various parts of the plant, but these have tended to break apart in shipping and handling. A new, more stable pellet has now been developed, using 20 percent winged bean seed meal and 80 percent cassava flour. These feed pellets are eaten readily by livestock, but experiments are still needed to determine their nutritional value.

The dry pod residue left after the seeds have been threshed out has 10 percent protein and has been tested satisfactorily in animal feeds. In Thailand this pod residue is being used successfully as a medium for growing straw mushrooms (Volvariella).

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