EFFECT OF HEAT, AMYLASE, AND DISULFIDE BOND-CLEAVAGE ON INVITRO DIGESTIBILITY OF SOYBEAN PROTEINS

Various protein fractions were prepared from defatted soybean flour based on solubility differences and size on Sephadex G-200. The in vitro digestibility of these fractions by trypsin and by successive pepsin-trypsin treatment was affected by the presence of trypsin inhibitors, native structure of the proteins, and the presence of starch (present in soybeans). The trypsin inhibitors were destroyed by heating at 100.degree. C for 30 min at pH 1 but not at neutrality. The native structure of the proteins could be destroyed by heating, particularly at low pH, digestion with pepsin at pH 1, or by cleavage of the disulfide bonds. Cleavage of disulfide bonds increased the in vitro digestibility of the proteins. Prior amylase treatment increased the trypsin digestibility of most of the protein fractions.