Trypsin inhibitor activity (TIA) is an important antinutritional factor in soymilk. In this study, the effects
of NaCl preaddition on TIA and the heat-induced TIA inactivation mechanisms were examined. The
results showed that Kunitz trypsin inhibitor (KTI) and Bowman-Birk inhibitor (BBI) contributed 74%
and 26% to raw soymilk TIA, respectively. The heat-induced quick KTI incorporation into protein aggregates
was the reason for its quick TIA inactivation. The heat-induced slow cleavage of one BBI peptide
bond was the reason for its slow TIA inactivation. Heat-induced protein aggregate formation had little
effect on BBI inactivation owing to the fact that BBI and its degradation product tended to remain in
the supernatant (197,000g, 1 h) in all conditions used in this study. NaCl could accelerate the KTI incorporation
into protein aggregates and the cleavage of one BBI peptide bond, which supplied a simple and
quick method for low TIA soymilk processing.