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.