The average protein content of soybean is 30% ~ 40%, which is 4 ~ 5 times that of general cereals. The composition and proportion of various essential amino acids also meet the needs of human body. Except methionine, the rest are similar to protein, which is the best source of high-quality protein.
The fat content of soybean is 15% ~ 20%. It is a yellow liquid at room temperature, and the digestibility of human body is as high as 97.5%. It belongs to high-quality vegetable oil. Soybean fat is rich in unsaturated fatty acids, such as oleic acid, linoleic acid and linolenic acid, accounting for about 85% of the total fat. In addition, soybeans contain more lecithin. Therefore, soybean has high nutritional value.
The carbohydrate content in soybean is 25% ~ 30%, and insoluble fiber accounts for about half. Its components are complex, including raffinose, stachyose and arabinose, which are used by bacteria in human colon to produce gas. Generally speaking, the nutritional value of carbohydrates in soybean and its products is not high, and it is an optional food for diabetics.
Soybean is rich in inorganic salts such as phosphorus, iron and calcium, which is obviously more than that of cereals. However, due to the existence of anti-nutritional factors, the digestion and absorption rate of calcium and iron is not high.
The content of B vitamins such as vitamin B 1, vitamin B2 and nicotinic acid in soybean is several times higher than that in cereal, and it also contains a certain amount of carotene and vitamin E. In addition, bean sprouts contain more vitamin C.
Although soybean has high nutritional value, it contains many harmful substances, which will affect the nutritional value and quality of soybean if processing measures are not taken to remove it. The main anti-nutritional components are: ① trypsin inhibitor. It interferes with protein's digestion and leads to pancreatic hypertrophy. ② flatulence factors. Raffinose and stachyose in soybean are fermented by intestinal microorganisms to produce carbon dioxide, hydrogen and a small amount of methane, thus causing flatulence. ③ Phytic acid. Phytic acid chelates with zinc, calcium, iron and magnesium, which affects its absorption and utilization. (4) Plant lectin. Coagulant is a substance that agglutinates red blood cells of animals. There are at least four kinds of protein in soybean, which can agglutinate red blood cells of rabbits and rats.
Most anti-nutritional factors are unstable to heat, which can be eliminated by far-infrared heating and moist heat treatment. Infrared rays have strong penetrating power, and can inactivate anti-nutritional factors with unstable heat in a short time, which is energy-saving and time-saving. Wet heat treatment is the most common and effective treatment method. Soybeans can be soaked for several hours, and then steamed with atmospheric steam for 30 minutes. Cooking soybean milk for 5 ~ 10 minutes can also effectively eliminate the anti-nutritional factors in soybean.