Soyabean / soya bean is a species of “legume” native to East Asia but widely grown in several parts of the world. The main producers of soyabeans are USA – 36%, Brazil -36%, Argentina -18%, China 5% and India 4%. The edible bean is an inexpensive source of good quality proteins and is used and marketed in various forms. Because of its oil content it is often classified as an “oilseed” also.
The Soya plant varies in height from 0.2 to 2.0 meters. Pods, stems and leaves are covered with fine brown or grey hairs. Leaves are trifoliate, having 3-4 leaflets per leaf. Leaflets are 6-15 cms long and 2-7 cms broad. The inconspicuous, self-fertile flowers, white, pink or purple in colour are borne on the axil of the leaf. Leaves off fall before the seeds mature. Fruit bearing hairy pods grow in clusters of 3 to 5 , each 3-8 cms long and containing 2-4 (rarely more) seeds 5-11 mms in diameter.
Small, purple soyabean flowers
Soyabean pods with seeds
Soyabeans of varying sizes come in black, blue, brown, yellow, green or mottled colours. The mature seed has a hard, water-resistent hull/cover with a hilum on one side. At one end of the hilum is a microphyle or small opening allowing absorption of water for sprouting. Seed undergo desiccation and has a long shelf life and gets revived with water absorption through the microphyle. Common with many other legumes, the roots have the ability to fix nitrogen from atmosphere and thus produce the plant proteins in abundance.
Nutritional Value of Soyabeans:
Per 100 gms of raw seeds:
Energy – 446 kcal
Carbohydrates – 30.6 gms
Sugar – 7.33 gm
Dietary Fibres – 9.3 gm
Proteins – 36.49 gms
Water – 8.54 gms
Fat – 19.94 gms ( Saturated. 2.88; Unsaturated 17.06 gms)
Vitamins – A,B1,B2, B3, B5, B6, B9, (B12 -0), C, E K etc
Minerals Ca, Iron, Mg, Mn, Phosp, Pot, (Sodium – 0), Zn etc.
Soyabean oil and protein account for about 60% of dry soya by weight (20 & 40% respectively). The remainder has 35% carbohydrate and 5% ash. Proteins have a high percentage of essential amino acids and heat stable even at high temperatures at cooking. This allows making of such items as tofu, soy milk, textured vegetable proteins etc. Soya is an excellent source of “complete” proteins, as it contains many of the essential amino acids that cannot be manufactured in the human body. Hence it is highly recommended for vegetarians and vegans or those who want to reduce meat in their food. Proteins in soya is favorably comparable to meat, which has the disadvantage of having lot of fat especially saturated fat.
PDCAAS ( Protein Digestibility Corrected Aminoacid Score) is the gold standard in assessing quality of proreins in food and using this standard soy proteins is nutritionally equavalent to meat, eggs and casein for human growth and health. Soyabean protein isolate has biological value of 74, whole soyabean 96, soyabean milk 91 and eggs 97.
The carbohydrates profile includes several varieties of mono, di or polysaccharides and are mainly of soluble or insoluble varieties. The latter constitutes the dietery fibres and may lead to flatulence and abdominal discomfort. These latter effects, however, are absent in many of the processed end products of soya.
Uses of Soyabeans:
Used as fat-free soyabean meal, it is a good and inexpensive source of proteins for animal feeds as well as packaged meals.Soy vegetable oil is another processed end product of soyabean crop. TVP or Textured Vegetable Proteins are ingredients in many meat and diary products.
Non fermented food uses include soy milk and tofu and tofu skin. Fermented foods include soy sauce, fermented bean paste,natto and tempeh.
Soya oil is used in many industrial applications.
Daily use of Soyabeans & products at home:
For human consumption raw soyabeans should be cooked in “wet” heat to destroy the trypsin inhibitors (serine protease inhibitors). Raw soyabeans including the green form are harmful/toxic to humans.
Soyabeans can be cooked to make a large variety of dry dishes or dishes with gravy or some snacks like “tikka”, Soya Dosa, Soya Idlietc
Soya Chunks Pulav
Soya chunks can be used in a variety of Indian dishes like Sambar, Kurma or Pulav and Biriyanietc.
Other marketed soy products like Soy milk, Soya sauce, Soy Yogurt, Breadand Tofu are also used quite commonly.
Use of various soya beans and product s is a simple way to provide high quality proteins particularly suited for vegetarians and vegans, who would otherwise be taking protein deficient daily food.
Health Benefits of Soy Foods:
Soyabeans contain some chemicals called “phytoestrogens” with action similar, but much weaker than the human female hormone oestrogen. Isoflavones is one of the predominant phytoestrogen found in soyabeans, found manly in soya nuts and tempeh. In addition to oestrogen like action, it is also a strong antioxidant.
# Post-menopausal symptoms: Taking soyabeans and products like soy milk, tofu or bread is believed to help reduce post-menopausal hot flushes since the Isoflavones act somewhat like hormone replacement therapy, if taken is sufficient quantity.More studies are needed to confirm this theory. Soy consumption can reduce hot flushes from 1.9 to 45 %. To get this benefit the subject needs to take 500 ml of soy milk or 100gms of tofu or 4-5 slices of soy linseed bread.
# Coronary heart disease: Oestrogen/Isoflavones in soyabeans along with its high protein content has been shown to lower total cholesterol and LDL (bad cholesterol) and help increase HDL (good cholesterol) and thus has protective action against coronary artery disease. Isoflavones alone are not quite helpful, but effects are substantial along with other soy proteins and additionally with a high carbohydrate diet, supposed to help in breakdown of isoflavones. About 25 gms of soy proteins or 4 servings of soy daily is recommended.
Other possible health benefits are:
- Lowers blood pressure.
- Increases elasticity of arterial wall.
- Reduces risk of osteoporosis.
- Protective action against cancers of breast, colon, prostate and skin.
- Helpful in management of endometriosis.
- Has anti-inflammatory effects also.
For getting most of the above health benefits one needs to take soyabeans or products containing 30 to 50 mgs of isoflavones. Isoflavone content of some of the common soy products are as follows:
- Half a cup of soyabeans – 40-75 mgs of isoflavones.
- Quarter cup of soy flour – 40 to 69 mgs.
- 250 ml of soy drink – 15 to 60 mgs.
- One 115 g block of tofu – 13 to 43 mgs.
- One container of soy yoghurt – 26 mgs.
- Two slices of soy bread – 7 to 15 mgs.
- One teaspoon of soy sauce – 0.4 to 2.2 mgs.
Words of caution:
- Fermented soy products like soy sauce are high in salt.
- Choose whole soy foods like soy milk, soy yoghurt, soy bread and tofu.
- Make sure that soy foods are made from whole soyabeans and not from soy isolates.
- Make sure that the products contain soy proteins and not just added isoflavones.
Soyabeans cultivation is mainly for its high protein content said to be twice as much proteins per acre than other vegetables or grain crops, 5-10 times more protein per acre than land set aside for grazing animals to make milk and up to 15 times more proteins per acre than land set aside for meat production.
Be knowledgeable, follow healthy life style and enjoy good health,
Compiled by Dr M Mohan Rao,
Formerly Managing Director & Chief Surgeon,
Dr U Mohan Rau Memorial Hospital, Chennai.
Visit : www.mohanraohosptal.com