Abstract: In order to elucidate the kinetic characteristics of the enzymatic hydrolysis of whey protein that had been subjected to ultrasound-ionic liquid (UIL) treatment, the effects of initial substrate concentration, enzyme concentration and hydrolysis time on the degree of hydrolysis of whey protein were studied, and a kinetic model for the hydrolysis of whey protein by alcalase was established. In addition, the effect of UIL treatment was evaluated on antioxidant activities of whey protein hydrolysates such as 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, Fe2+ chelating activity and reducing power. Results showed that UIL treatment changed the kinetic model for enzymatic hydrolysis of whey protein. After UIL treatment, the critical enzyme concentration was decreased by 43.1%, suggesting that UIL treatment could promote the enzymatic hydrolysis of whey protein. Antioxidant assays showed that UIL treatment caused a 14.4% increase in the DPPH radical scavenging activity and a 28.4% increase in the Fe2+ chelating capacity of whey protein hydrolysate. Moreover, the reducing power was improved after UIL treatment. Size exclusion chromatography analysis showed that UIL treatment significantly increased the > 1-5 ku fraction from whey protein hydrolysate by 12.2% compared to untreated whey protein (P < 0.05).

Key words: whey protein, enzymatic hydrolysis, kinetics, ionic liquid, ultrasonic treatment