Anti-oxidation Activities of Rice-Derived Peptides and Their Inhibitory Effects on Dipeptidylpeptidase-IV

In this study, anti-diabetic and anti-oxidation activities of the rice-derived peptides, obtained from sake lees and rice bran using a commercial protease from Aspergillus oryzae, were evaluated. Rice and rice bran peptides showed moderate anti-oxidation activities that were determined using the hydrophilic oxygen radical absorbance capacity assay. However, the hydrolysates from rice and rice bran exhibited no inhibitory activity against human maltase-glucoamylase. On the contrary, the rice protein hydrolysate showed an inhibitory activity (IC50 = 1.45 +/- A 0.13 mg/mL) toward dipeptidylpeptidase-IV (EC 3.4.14.5, DPP-IV) that metabolizes the insulinotropic hormone, glucagon-like peptide-1, in the same manner as the rice bran protein hydrolysate. The sake lees hydrolysate showed lowest bioactivity among the other rice-derived hydrolysates. Further, we identified that the dipeptides Ile-Pro, Met-Pro, Val-Pro, and Leu-Pro from the rice protein hydrolysate are involved in the inhibitory activity against DPP-IV. The concentrations of Ile-Pro, Met-Pro, Val-Pro, and Leu-Pro dipeptides were 1.22, 0.23, 1.59, and 1.94 (mu g/mg in the rice protein hydrolysate), respectively.