Study on alkaline protease hydrolysis of soy protein isolate and its antioxidant activity.

The factorial level design of Plackett-Burman was used to study soybean peptides obtained through hydrolyzing soybean isolated proteins by Alcalase,and then the antioxidant activities of soy isolate protein hydrolyzate was studied.The antioxidant activity of hydrolysate was detected by measuring its ferrous iron's reducing capacity,and the optimal hydrolysis conditions were as followings: reaction temperature of 72 ℃,substrate concentration of 9%,enzyme concentration of(E/S) 1%,pH 7.0,hydrolysis time 5 h.The hydrolysis degree obtained under the optimum hydrolysis conditions was 19.78 %,and the reducing capacity of ferrous iron in prepared hydrolysate was 987.13 μmol·L-1.The study also detected the activity of hydrolyzate in terms of inhibiting overoxidation of lipid peroxidation(TBARS),and eliminated the DPPH free radical.The study showed that hydrolysate had a higher antioxidant activity which could inhibit overoxidation of lipid peroxidation and eliminate the DPPH free radical.Although the antioxidant capacity of hydrolysate was lower than that of chemical synthesized antioxidant,apparently higher than that of unhydrolyzed proteins.