Fractionation and antioxidant properties of rice bran protein hydrolysates stimulated by in vitro gastrointestinal digestion

•In vitro GI digestion influenced antioxidant activities of rice bran protein.•Metal chelator peptide could be separated by membrane ultrafiltration.•Peptides with MW <3 kDa possessed the highest free radicals scavenging activity.•Anti-free radicals activity was strongly related to Tyr and Phe contents.

Rice bran was used as a starting material to prepare protein concentrate through enzyme-assisted extraction. The hydrolysis of protein concentrate under in vitro gastrointestinal digestion (pepsin-trypsin system) greatly improved the antioxidant properties. Rice bran protein hydrolysate was further fractionated by membrane ultrafiltration (UF, F1: molecular weight (MW) <3 kDa, F2: MW 3-5 kDa, and F3: MW 5-10 kDa). Peptides with smaller MW possessed higher antioxidant activities (P < 0.05). UF showed a great efficacy to selectively separate the metal-chelating peptides. Tyrosine and phenylalanine had positive correlations with their DPPH & ABTS radicals scavenging activities and ferric reducing antioxidant power (r > 0.831). A major peptide fragment was detected at m/z 1088 by a MALDI-TOF mass spectrometry. There is high potential that antioxidative peptides from rice bran might also be produced in the gastrointestinal tract of the human body.