Soybean has many uses. It is mainly pressed to extract soybean oil, after which a soybean meal remains, which is a rich source of protein. Soybean oil can be used for the production of edible oils such as kitchen oil, salad oil and others through refining and deep processing. Soybean oil is also used for the production of printing ink and biodiesel. Soybean meal is mainly used for the production of compound feed. It is the main protein source in feed for livestock farming. The native soybean meal produced under low-temperature conditions is mainly used for the production of isolated soy protein, concentrated protein and structural protein. These proteins are added to various foods in the food-processing industry for the production of soybean protein-rich foods. For instance, wheat flour is supplemented with a certain amount of soybean protein for the production of bread and cake. Soybean protein supplementation improves the water absorption of meat and the palatability of sausages. Soybean protein can be used to process protein fibre, which can be blended with cotton, wool or chemical fibres. The texture of the resulting fabric is soft and of high quality.
Many soybean food products, including the traditional non-fermented soybean products such as bean curd, soybean milk and bean curd stick, can be processed by using soybean as a raw material. In China, soybean is used to produce Bei bean curd (the coagulating agent is MgCl2), Nan bean curd (the coagulating agent is CaCl2), lactone bean curd (the coagulating agent is gluconolactone) and others through soaking, grinding, boiling and adding different coagulating agents. The fermented soybean products are soy paste, fermented soybeans, soybean cheese, soybean sauce and others. Small seed soybean sprouts are used for making dishes or soup. Soybean sprout soup is common in Korea, while soybean sauce soup is often eaten in Japan.
Along with the depth of research on the nutritional elements of soybean, soybean functional foods such as soy peptide, isoflavones, saponins, phosphatides, sterol, oligosaccharide and edible fibre have been developed. Lactoserum waste water is produced during the processing of bean curd and other products and 2-5 t of lactoserum waste water can be produced from 1 t of soybean. Soybean protein content in lactoserum is 8.2%. Through filtration of lactoserum waste water by using dynamic membranes, 85-93% of the protein can be recovered. The lactoserum protein is a natural surface active agent and can be used for cosmetics. Lactoserum protein is easily digested and assimilated and has a high metabolic rate and biological value. Lactoserum waste water can be used for the extraction of oligosaccharides, which can promote intestinal peristaltics and ease constipation. It also promotes the growth of Bifidobacterium and improves the structure of the intestinal bacterial flora.
Isoflavones also can be extracted from lactoserum waste water. Soybean isoflavone consists of flavone glycoside (97-98%) and aglycones (2-3%). Agly-cones have biological activity. Isoflavone glycoside is separated from agly-cones by the actions of different isoflavone-glucosidases, and the genistein with biological activity is then released. Genistein can attenuate postmeno-pausal osteoporosis in humans. Isoflavones have inhibitory effects on the early transformation and proliferation of cancer cells. They can effectively inhibit the angiogenesis of a cancer structure and thus block the supply of nutrients to cancer cells. Therefore, isoflavone is of therapeutic use in breast cancer, colon cancer, lung cancer, prostate cancer, leukaemia and others.
Phosphatide, sterone and vitamin E can be extracted from the residues that remain after soybean extraction. The main contents of soybean phosphatide are phosphatidylcholine, phosphatidylethanolamine, phosphati-dylinositol, phosphatidylserine and phosphatidic acid. Soybean phosphatide is a natural emulsifier and can be used to supplement the nutrient requirements of the human body; therefore, it is used extensively in the production of candies, biscuits, chocolate, artificial cream and other food products. Soybean phosphatide is a by-product of oil extraction, but as its source is rich and the price is cheap, it has broad prospects for applications in food, medicine and animal production.
Soybean polypeptide is a hydrolyzed product of protein through special treatment. Generally, it consists of peptides of 3-6 amino acids. Soybean polypeptide has a high nutritional value, high digestibility coefficient and low antigenicity, and the results of experiments show that its digestibility coefficient is much better than that of protein or amino acids. Soybean poly-peptide can be used as a raw material for or additive to health foods. It has a therapeutic effect on high blood pressure and cardiovascular and cerebro-vascular diseases, and is safe and reliable. Soybean polypeptide also decreases the deposition of subcutaneous fat and increases fat burning and it is, therefore, a safe food for people who want to lose weight. Soybean polypeptide also has an antioxidant effect, and it has been claimed that the muscle cells of athletes recover faster when they imbibe a polypeptide-containing drink (Wang et al., 2004).
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