Effect of Pepsin–Trypsin In Vitro Gastro-Intestinal Digestion on the Antioxidant Capacities of Ultra-Filtrated Rice Bran Protein Hydrolysates (Molecular Weight > 10 kDa; 3–10 kDa, and < 3 kDa)

Abstract

The antioxidant capacities of rice bran protein hydrolysates (RBPH) obtained by in vitro gastro-intestinal (GI) digestion by pepsin–trypsin (P–T) system were investigated. The hydrolysates were separated by ultrafiltration into three fractions (FI: molecular weight (MW) > 10 kDa, FII: MW 3–10 kDa, and FIII: MW < 3 kDa). Furthermore, the protein content and free amino acids of hydrolysates were studied. The results showed that fraction FII with MW 3–10 kDa had the highest antioxidant activity: DPPH of 28.34 ± 0.16%, ABTS of 30.66 ± 0.29%, and metal chelating activity of 61.04 ± 0.38%, and was further purified by RP-HPLC. Four sub-peptide fractions (F1, F2, F3, and F4) were collected and their antioxidant activities were assessed. The results displayed that F2 sub-peptide fraction owned a higher metal chelating activity (72.09 ± 0.32%) than other sub-peptide fractions. The amino acids composition of the purified peptide (F2) was evaluated, which could play an essential role in its antioxidant activity. The results indicated that rice bran proteins are rich in antioxidant peptides which can be employed as a potential source of natural bioactive compounds. The peptides produced can resist physiological digestion in the GI tract.