Chemical and cellular antioxidative properties of threadfin bream (Nemipterus spp.) surimi byproduct hydrolysates fractionated by ultrafiltration

Protein hydrolysate from frame, bone and skin (FBSH) of threadfin bream was prepared using Virgibacillus sp. SK33 proteinase and fractionated using sequential ultrafiltration membranes with molecular weight cut-offs (MWCO) of 30, 5 and 1 kDa, respectively. Four fractions, namely FBSH-I (>30 kDa), FBSH-II (5–30 kDa), FBSH-III (1–5 kDa), and FBSH-IV (<1 kDa), were obtained. All fractions were rich in Lys, Glu/Gln, Gly, Pro, Ala, Asp/Asn, and Arg. FBSH-III and FBSH-IV showed the highest surface hydrophobicity measured by 8-anilino-1-naphthalenesulfonic acid (ANS) probe (p < 0.05). FBSH-III showed the highest antioxidant activity and cytoprotective effects against tert-butyl hydroperoxide (TBHP)-induced cytotoxicity of Caco-2 cells. In addition, FBSH-III inhibited lactate dehydrogenase (LDH) leakage and intracellular reactive species (ROS) production in a dose-dependent manner. FBSH-III retained antioxidant activity and cytoprotective capacity after in vitro simulated gastrointestinal digestion. These results suggested that FBSH-III might potentially be nutraceutical peptides with antioxidative properties.