Antioxidant Peptides Prepared by Enzymatic Hydrolysis of Whey Soy Proteins and Their Antioxidative Activities in Vitro

To improve the application value of whey soy proteins (WSP) in soy whey wastewater, they were used to prepare antioxidant peptides by enzymatic hydrolysis in a self-made ultrasound-thermostatic reaction system. Using sing-factor tests and response surface methodology, the technology for enzymatic hydrolysis of WSP was optimized with total reducing force, scavenging rate of DPPH radical and scavenging rate of hydroxyl radical as indicators. Then, ultrafiltration with a molecular weight cut-off of 30 kDa was adopted to separate antioxidant peptides from the hydrolysates and ascorbic acid as a reference to evaluate their antioxidant activities in vitro. The results showed that neutral protease and pepsin were the most suitable for the hydrolysis of WSP. On this basis, the optimal technological conditions were determined as enzyme-substrate ratio 5000 U/g WSP, hydrolysis time 6 h and WSP concentration 9.0 mg/mL. Under these conditions, the scavenging rate of DPPH of WSP hydrolysates reached 62.3%±1.1%. The antioxidant peptides isolated from the above hydrolysates had IC50 values for total reducing force, scavenging rate of DPPH radical and scavenging rate of hydroxyl radical of 0.128, 0.221 and 0.185 mg/mL, respectively. These corresponding IC50 values were 2.56, 40.76 and 1.47 times of those of ascorbic acid, respectively. It was indicated that the antioxidant peptides had slightly lower activity than ascorbic acid. Therefore, WSP is a suitable source of antioxidant peptides with high activities