Hypocholesterolemic effect of soybean protein in rats and mice after peptic digestion

Analyses of gastrointestinal contents of rats fed soybean protein isolate and casein showed that soybean protein was readily digested in the stomach but migrated slowly in the small intestine. The soluble fraction of the stomach contents of rats fed soybean protein was separated by gel-filtration on Sephadex G25 into large and small molecular fractions, the latter was not found in rats fed casein. The formation of low-molecular-weight peptides was pH dependent, and analogous peptides were produced by pepsin in vitro not only from soybean protein but also from casein. In rats the peptic digest of soybean protein was found to be as hypocholesterolemic as intact soybean protein. Meanwhile, the cholesterol-lowering action of the large molecular fraction of the peptic digest tended to be greater than that of the small molecular fraction in mice. These observations suggest a significant role of peptic digestion in the cholesterol-lowering action of soybean protein.