Fractionation and characterization of antioxidant peptides from rice bran protein hydrolysates stimulated by in vitro gastrointestinal digestion

Abstract Background and objective Rice bran protein concentrate was prepared and hydrolyzed by using pepsin–pancreatin. The obtained result was further filtered through 5‐kDa membranes. A permeate was collected and sequentially fractionated by different chromatographic techniques. The peptide fractions were determined for the antioxidant activities. Findings Three peptide fractions were derived after separating the crude protein hydrolysates by anion‐exchange chromatography. Due to its highest ABTS radical scavenging and metal chelating activities (p < .05), fraction F2‐A was pooled and separated further by size‐exclusion chromatography (SEC). Among the SEC fractions, F1‐S showed strongest antioxidant activities; thus, it was collected for reverse‐phase HPLC purification. Subsequently, the peptide fractions were successfully separated and F4‐H had the greatest ABTS‐scavenging activities (214.61 µmol Trolox/g sample, respectively). In addition, it displayed the strongest ability to reduce ferric to ferrous ions (104.80 µmol FeSO4/g sample) (p < .05), while F1‐H showed the highest ability to chelate metal ions (266.40 µmol EDTA/g sample) (p < .05). Conclusion These results demonstrate that hydrophobic amino acids play a major role in scavenging free radicals, whereas polar amino acids are responsible for reducing and chelating metal ions. Significance and novelty Rice bran protein composes of high ratio of hydrophobic amino acid. It is a suitable source of antioxidant peptides that might be produced during gastrointestinal digestion. Separation and purification using chromatographic techniques showed promising results for selectively fractionate antioxidant peptides with specific activity.