Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 10, 2001
Publication Date: February 17, 2001
Citation: Friedman, M., Brandon, D.L. 2001. Nutritional and health benefits of soy proteins. Journal of Agricultural and Food Chemistry. 49(3):1069-1086. Interpretive Summary: In 1999, farmers planted soybeans on 72 million acres amounting to 27% of the total crop area in the U.S. The resulting harvest yielded 2.74 billion bushels valued at about 14 billion dollars. The consumption of soy foods (beverages, cereals, cheeses, salami, tofu, vegiburgers) is increasing because of reported beneficial effects in human nutrition. These effects include lowering of plasma cholesterol, prevention of cancer and diabetes, and protection against irritants of the digestive tract. This paper is based on an invited presentation at an American Chemical Society Symposium on "Biological Processes and Their Control" in honor of Professor Irvin E. Liener of the University of Minnesota. It (a) describes studies delineating the nutritional quality, safety, and health benefits of soy proteins; (b) discusses improved food processing techniques we have developed to inactivate soybean inhibitors of digestive enzymes; (c) outlines the application of immunoassays (ELISA's) we have developed to measure soybean inhibitors in processsed foods and in plant breeding programs; and (d) suggests further research needs in each of these areas. For instance, will soy protein protect against gastrointestinal inflammation (colitis) caused by human pathogens such as E. coli? A better understanding of the multifaceted aspects of soy protein nutrition should lead to better and safer foods and feeds and improved human health.
Technical Abstract: Soy protein comprises a major component of the diet of animals and is increasingly important in the human diet. However, soy protein is not an ideal protein since it is deficient in the essential amino acid methionine. The content of another essential amino acid, lysine, although higher than that of wheat protein is still lower than that of milk protein casein. Adverse nutritional and other effects following consumption of raw soybean meal have been attributed to the presence of inhibitors of digestive enzymes, lectins, and to poor digestibility. To improve the nutritional quality of soy foods, inhibitors and lectins are generally inactivated by heat treatment. Although lectins are heat-labile, the inhibitors are not. Most commercially heated meals retain up to 20% of the Bowman-Birk (BBI) inhibitor of chymotrypsin and trypsin and the Kunitz inhibitor of trypsin (KTI). To enhance the value of soybeans in human nutrition and health, a better understanding is needed of the factors that impact nutritional and health-promoting aspects of soy proteins. This paper discusses the composition in relation to nutritional properties of soy proteins and beneficial and adverse effects of soy-containing diets. The former include soy-induced lowering of cholesterol, anti-carcinogenic effects of BBI, and other benefits. The latter include poor digestibility and soy allergy. Approaches to reduce inhibitors by rearrangement of protein disulfide bonds, immunoassays of inhibitors in processed foods and soybean germplasm, and research needs in all of these areas are discussed.