A large number of soybean components have diverse biological activities. These include hormonal, immunological, bacteriological and digestive effects. The presently known allergens are listed. The divergence between chemical evaluation and biological value is highlighted. The following components are discussed: Kunitz inhibitor, Bowman-Birk inhibitor, saponins, soyacystatin, phytoestrogens (daidzein, glycitein, genistein), Maillard products, soybean hydrophobic protein, soy allergens, lecithin allergens, raffinose, stachyose, 2-pentyl pyridine. The studies describing the effects of the isolated components are reviewed.

Various animal models in farm and laboratory animals indicate the possible pathological effect of soybean feeding. Immunity and tolerance to oral soybean intake and a generalised meta-model of effects are discussed. It seems that FAO/WHO recommendations will have to be considered in assessing the biological value of soybean feed sources. Determination of hull content, antigenic potential, conglycinin and trypsin inhibitor content is warranted in view of the future component pricing of soybean meals.Key words: Soybean, villus height, antibody to soybean antigens, feed antigens, immune tolerance to feed, soybean pathology model, soybean allergy, component pricingIntestinal pathology in soybean fed animals McGuinnes et al. (1987) observed that rats fed on raw soybean meal developed enlarged pancreas and hyperplastic nodules which turned to adenomas and carcinoma. The effect was attributed to trypsin inhibitor effect, due to increased cholecystokinin plasma levels. According to Grant et al. (1987) the effect of pure soybean trypsin inhibitor on pancreas hypertrophy was less pronounced when it was fed in the form of soybean meal.Mice fed on raw soybeans survive only for weeks (Gee and Morgan, 1993). Feeding raw soybeans increases duodenal mucosa and smooth muscle layer thickness, but heat treatment significantly reduces this effect. Small intestinal weight is significantly increased in mice fed raw soybean meal (2.242 g vs. 1.410 g). A similar difference was observed in pancreas weight (0.547 g vs. 0.251 g). A similar effect was noted upon the administration of camostate (synthetic trypsin inhibitor), suggesting the role of trypsin inhibitors in the pancreas effect. However, small intestinal weight and structure are not influenced by camostate (unlike raw soybean meal), which suggests disparate effects on small intestine and pancreas. Pusztai et