Abstract: Antioxidant peptides were purified from millet protein hydrolysate by sequential column chromatographies on Sephadex G-25 and DEAE-32. Cellulose acetate electrophoresis was used to determine the purity of the purified peptides. The antioxidant effect was investigated by detecting radical scavenging activity against superoxide anion, hydroxyl and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals. In order to investigate the protective effect of the antioxidant peptides on islet cells, an INS-1 cell model of oxidative stress induced by H2O2 was used. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl- 2-H-tetrazolium bromide method was applied to detect the cell viability, flow cytometry was used to detect the cell apoptosis, and real-time polymerase chain reaction was employed to analyze the gene expression of antioxidant enzymes. The results showed that the peptides were purified to electrophoretic homogeneity. The percentage scavenging of superoxide anion, hydroxyl and DPPH radicals by the peptides were (62.71 ± 3.86)%, (73.56 ± 4.51)% and (82.62 ± 5.25)%, respectively. The peptides could significantly promote cell viability, reduce the level of cellular reactive oxygen species, and inhibit cell apoptosis (P < 0.05). The mechanism may be related to the up-regulated expression of antioxidant enzymes including superoxide dismutase 1, catalase enzymes, glutathione S-transferases, and quinone oxidoreductase 1. This study conclusively demonstrated that the antioxidant peptides from millet showed a significant protection against oxidative stress induced by H2O2 in INS-1 cells.

Key words: antioxidant peptides from millet, oxidative stress, islet cell, apoptosis