Biological and physiological factors in soybeans.

There are limitations to which one is justified in drawing broad generalizations concerning the diverse biological and physiological effects of soy protein products. Nevertheless, there appear to be two distinct situations: (A.) Proper heat treatment exerts a beneficial effect upon the nutritive value of whole soybeans, full-fat and defatted meal. Associated with proper heating is inactivation of trypsin inhibitor and other heat-labile factors and conversion of raw refractory proteins to forms that are more readily digested. (B.) Moist heat also has a beneficial effect upon the nutritive value of soy protein isolates. However, a deficiency of certain essential nutrients and the interaction of phytic acid with protein, vitamins, and minerals during processing are the primary factors responsible for the poor nutritive value of soy isolates. Occasionally mineral deficiency symptoms do occur in animals fed soybean meal. It is a Inisnomer to refer to the growth-inhibiting and pancreatic hypertrophic properties as a "toxic" effect since both properties are reversible. Modern analytical techniques should be used to reinvestigate the relationship between phytic acid and availability of Ininerals and vitaInins in soy protein isolate diets. Research also is needed to determine more accurately vitaInin and Inineral contents of soy protein isolates and the availability of vitamins and minerals in soy protein concentrates. Breeding soybean varieties genetically deficient in antinutritional and nonflatulent factors does not appear promising. More research is needed to deterniine whether fermentation and enzyme processes can be used to prepare flatulent-free soy products. Minor factors to be considered in assessing the nutritive value of soy products include a weak goitrogen present in soybeans, and a very low estrogenic activity.