Heat Inactivation of Protease Inhibitors in a Soybean Line Lacking the Kunitz Trypsin Inhibitor

The effect of heat treatment (autoclaving at 121°C, 15 psi for various periods of time) on the trypsin‐ and chymotrypsin‐inhibitor activities of a soybean line lacking the Kunitz trypsin inhibitor (SBTI) was compared to that of commercial untoasted soy flour. The trypsin‐ and chymotrypsin‐inhibitor activites of the SBTI‐free soybeans were approximately one‐half and three‐fourths that of the soy flour, respectively. Less heat treatment was required to produce a given level of destruction of these inhibitor activities in the case of the SBTI‐free soybeans than with the soy flour. The effect of heat on the ratio of chymotrypsin‐ to trypsin‐inhibitor activities was notably different between the two soybean samples and presumably reflects differences in the amounts and thermal stability of the various protease inhibitors known to be present in soybeans. The nutritional implications of these findings are discussed.