Abstract: Considering that soymilk is a complex system, this study designed three model systems (glucose + Bowman-Birk inhibitor (BBI), fructose + BBI, and soybean protein (SP) + BBI) to examine the contribution of reducing sugar, SP and heat treatment to BBI inactivation. Without heating, glucose could enhance the activity of BBI, but fructose could not. With heating, reducing sugar could obviously affect trypsin inhibitor activity (TIA) of BBI, but only slightly affect its chymotrypsin inhibitor activity (CIA); glucose affected BBI more obviously than did fructose. SP could affect CIA of BBI more obviously than its TIA; BBI could link to basic peptide chains of glycinin by disulfide bonding to form a dimer, and also could interact with SP to form a polymer by disulfide bonding; in addition, BBI could interact with itself to form a BBI dimer. Under the conditions of incubation in boiling water bath for 3 h, and BBI, glucose, fructose, and SP concentrations of 2 mg/mL, glucose made the greatest contribution to TIA inactivation, followed by heat-induced conformation change, fructose and SP, while SP made the greatest contribution to CIA inactivation, followed by heat-induced conformation change, and glucose/fructose.

Key words: Bowman-Birk inhibitor; glucose; fructose; soybean protein