Abstract: During the enzyme-assisted aqueous extraction of oil from extruded soybean, soybean protein hydrolysates (SPHs) with strong antioxidant capacity are produced by enzymatic hydrolysis (alcalase and flavourzyme). Thus, it is necessary to study the effect of simulated gastrointestinal (GI) digestion on antioxidant properties of SPHs. In this study, the alcalase and flavourzyme hydrolysates were subjected to simulated GI digestion. The degree of hydrolysis (DH) during digestion, amino acid composition, and molecular mass distribution were determined. Antioxidant properties were evaluated by oxidative radical absorption capacity (ORAC), 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and 2,2’-azinobis- (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS) cation radical scavenging assays. The results showed that the alcalase hydrolysate had higher antioxidant activity compared with the flavourzyme hydrolysate, while the opposite was observed when we compared their digests. The antioxidant activity of the digest of the flavourzyme hydrolysate was determined to be 69.15 μmol/mg, 27.29% and 56.21% in the ORAC, DPPH and ABTS cation radical scavenging assays, respectively, and it had a higher peptide content of 75.86%. Moreover, the peptides had higher levels of amino acids with antioxidant activity and fractions with a molecular mass of less than 1 kDa were the most dominant, accounting for 17.35% of the total peptides.

Key words: enzyme-assisted aqueous extraction, protein hydrolysates, antioxidant activity, simulated gastrointestinal digestion