Passivation of trypsin inhibitors in soybean protein concentrate modulates the structural and functional properties of the soya proteins.

Soybean protein concentrate (SPC) was extracted from defatted soybean meal via alcohol extraction, and the activity of soybean trypsin inhibitor (STI) in SPC was determined to be 28,836.67 U/g using the BAPNA method. The optimal treatment conditions for chemical modification of STI were comprehensively analyzed by employing sodium metabisulfite (SMB) as a reducing agent, with trypsin inhibitor activity (TIA) and protein content as evaluation indices. Under the optimized conditions (60 °C, 0.3 % SMB), the TIA was significantly reduced to 1894 U/g, achieving a passivation rate of 93.43 %. Notably, the residual sulfur dioxide content in the system was extremely low (<30 mg/kg), complying with national food safety standards. Compared to untreated SPC, the low-STI SPC exhibited reduced solubility but enhanced surface hydrophobicity, foaming capacity, emulsifying activity, and free sulfhydryl content, ultimately forming a more robust gel network structure. These modifications suggest that SMB-mediated STI passivation is an effective strategy to simultaneously improve nutritional quality and functional properties of soy protein for food applications.