Ultrasonic pretreatment for preparation of antioxidant peptides from rice protein

In order to optimize enzymolysis technology for production of antioxidant peptides from rice protein using neutral protease, rice protein was pretreated by ultrasonic. Effects of ultrasonic power, time and initial temperature of ultrasonic treatment on the technology, in which scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical was taken as response value, were analyzed with response surface methodology. In addition, scavenging effects of antioxidant peptides of rice protein on superoxide anion radical, DPPH radical and hydroxyl radical, and their effects on chelation to ferrous ion and reduction ability were studied. The results showed that the optimum conditions of ultrasonic treatment were ultrasonic power 1500 W, ultrasonic pretreatment time 20 min and initial temperature of ultrasonic treatment 40℃. Under the opotimum conditions the antioxidant peptides(2.2057 g/L) that ultrasonic-treated rice protein was hydrolyzed with neutral protease were obtained, and their scavenging effect of DPPH radical increased to 74.8%, and their yield was 33.2%. Compared with the antioxidant peptides derived from untreated rice protein, the yield of antioxidant peptides derived from ultrasonic-treated rice protein increased by 43.7%, and their half inhibitory concentration (IC50) value decreased by 17.7%. Moreover, the result of antioxidation showed that the IC50 values of antioxidant peptides derived from ultrasonic-treated rice protein for scavenging superoxide anion, DPPH, and hydroxyl radicals were 0.0678, 0.9315 and 0.1173 g/L, respectively; and the corresponding IC50 values were 1.8, 175.8, and 1.4 times of that of ascorbic acid. Their IC50 value for chelation to ferrous ion was 42.2 times of that of ethylenediaminetetraacetic acid, and their reduction ability was 0.7 times of that of ascorbic acid.