Abstract: Casein hydrolysate with a hydrolysis degree of 10.9% and an ACE-inhibitory IC50 of 52.6 μg/mL was prepared by hydrolyzing casein with alcalase and then modified by alcalase-catalyzed plastein reaction. When the reaction time was fixed at 6 h, the optimal reaction conditions were achieved by response surface methodology to be enzyme dosage of 3.1 kU/g protein, reaction temperature of 25 ℃ and substrate concentration of 50 g/100 mL. Nine modified casein hydrolysates with different modification degrees were prepared. The results indicated that each modified casein hydrolysate had enhanced ACE-inhibitory activity. The IC50 of the modified hydrolysate with the highest activity was 14.9μg/mL. This modified hydrolysate was centrifuged into two fractions, a supernatant and a precipitation fraction. The supernatant and precipitation fractions revealed a reduced and enhanced ACE-inhibitory activity when compared with their suspension, suggesting that the precipitation fraction accounted mainly for the improved activity of the modified hydrolysate. Tricine-SDS-PAGE electrophoresis analysis also showed that some new peptides with higher molecular weights were generated in the modified hydrolysate and the precipitation faction. The further enzymatic hydrolysis of the supernatant and precipitation fractions could result in the impairment of ACE-inhibitory activity.

Key words: casein hydrolysate, alcalase, plastein reaction, ACE inhibitory activity