Changes on antioxidant activity of microwave-treated protein hydrolysates after simulated gastrointestinal digestion: Purification and identification

Two samples of trout frame protein hydrolysates were prepared by Microwave Pretreatment followed by Conventional Enzymatic hydrolysis (MPCE) and Non-Pretreated followed by Microwave-assisted Enzymatic hydrolysis (NPME), respectively, were subjected to simulated gastrointestinal digestion. Changes on degree of hydrolysis, antioxidant activity, molecular weight, and amino acid composition between undigested and after gastrointestinal digestion of peptides were investigated. Comparing to undigested peptides, a breakdown of MPCE and NPME into smaller molecules was observed. Degree of hydrolysis, ABTS%+ radical scavenging activity and reducing power increased (P < 0.05) for both samples after gastrointestinal digestion. A purified peptide from GI-MPCE had two possible sequences, NGRLGYSEGVM or GNRLGYSWDD (1182.65 Da). Whereas GI-NPME had two peptides IRGPEEHMHR or RVAPEEHMHR (1261.77 Da) and SAGVPRHK or SARPRHK (962.63 Da). These results indicate that digested hydrolysates can be a rich source of antioxidants. Isolated peptides extracted from trout frame by-products could be new food ingredients used as natural antioxidants.