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

Abstract

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 ± 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 (μg/mg in the rice protein hydrolysate), respectively.