Soybeans are an important source of food for humans and animals. Owing to their content of many biologically active compounds, they can have a beneficial effect on the bodies of humans and animals.
Soybean (Glycine max) is the legume with the highest amino acid score. The content of the sulphur amino acids methionine and cysteine is double when compared to grass pea (Lathyrus sativus), the commercial legume with the lowest content of these essential amino acids.
According to the standard for measuring protein quality, Protein Digestibility Corrected Amino Acid Score, soybean protein has a biological value of 74, whole soybeans 96, soybean milk 91, and eggs 97.
Soybeans contain all the essential amino acids (except methionine), which must be supplied in the diet because they cannot be synthesized by the human body.
The main advantage of soybean for human health, besides the nutritional value provided by its energy and protein content, is the high level of isoflavones genistein and daidzein present in the seeds.
Soybean isoflavones genistein and daidzein are used in medicine at daily doses of 50 mg for the prevention of prostate cancer and breast cancer. This is the equivalent of about 50 g of soybean products or about 30 kg of other legumes.
The protein accumulation is promoted by higher average daily temperature and light rainfall, while lower daily temperature and higher rainfall are conducive to fat accumulation.
Proteins and lipids, and minerals, are the major nutritionally important components of soybeans. Average nutrient content of soybean:
Protein 38g/100g
Fat 18g/100g
Carbohydrate 6.3g/100g
Fibers 22g/100g
Calcium 201mg/100g
Magnesium 220mg/100g
Lipids account for 16–20% of the dry matter of soybeans, and acylglycerols are the main component of soybean oil. Research shows the weather conditions largely modify the nutrient content of soybeans and thereby reduce the impact of agrotechnical factors.
The lipids (crude oil) content of soybeans consists of:
*Triglycerides representing about 96 % of the soybean lipids
*Unsaponifiable lipids (1.6 %) mainly tocopherols (Vit E) and sterols
*Free Fatty acids (0.5 %)
The composition of fatty acids determines the quality of soybean oil. Soybean oil has a high nutritional value because it is a rich source of unsaturated fatty acids, such as oleic, linoleic, and linolenic acids with one, two, and three double bonds.
The total carbohydrate content of soybean is about 30%. Unlike other beans, soya is low in high molecular weight carbohydrates in soya. Soybeans contain 10-13% soluble carbohydrates of which sugars (sucrose, fructose, saccharose, raffinose and stachyose) represent 10-12% and starch 1%.
Many bioactive compounds are isolated from soybean and soy food products including isoflavones, peptides, flavonoids, phytic acid, soy lipids, soy phytoalexins, soyasaponins, lectins, hemagglutinin, soy toxins, and vitamins and more.
Typical flavonoids are kaempferol, quercetin and rutin (the common glycoside of quercetin), belonging to the class of flavonols. Isoflavones (soy phytoestrogens) is a subgroup of flavonoids. The major isoflavones in soybean are genistein, daidzein, and glycitein, representing about 50, 40, and 10% of total isoflavone profiles, respectively.
Soybean and nutritional properties
