Abstract
Grass carp (Ctenopharyngodon idellus) is one of the three most cultivated freshwater fish around the world, but it is mainly consumed afresh, so only a small part of them are processed into salted fish or snack food. This research was performed to prepare and screen antioxidant peptides from grass carp muscle to promote its high-value utilization. The parameters of double-enzyme two-step hydrolysis were optimized, the peptides with the highest ABTS.+ scavenging ability were enriched and identified by Sephadex G-25 and LC-Q-Orbitrap-MS/MS. The synergistic-antagonistic effect among identified peptides was also investigated. The optimized conditions were hydrolyzed with protamex (10,000 U/g) at pH 8.0, 50°C for 3 h, followed by hydrolysis with alcalase (6,000 U/g) at pH 9.0, 50 °C for 2 h, and the protein-liquid ratio was 4%. The hydrolysates were further fractionated to obtain five fractions, in which fraction 3 (F3) exhibited the strongest ABTS.+ and O⋅−2O2·-<math><msubsup><mi>O</mi> <mn>2</mn> <mrow><mo>·</mo> <mo>-</mo></mrow> </msubsup> </math> scavenging ability with the IC50 values of 0.11 and 0.47 mg/ml, respectively. Twelve novel antioxidant peptides were identified, in which VAGW possessed the highest activity (139.77 μmol GSH/g). Significantly synergistic effects were observed on the two and three peptides' combination among VAGW, APPAMW, LFGY, FYYGK, and LLLYK, while the C-terminal tryptophan (Trp) played an important role in the synergism. This study found that grass carp muscle hydrolysates can be potential natural antioxidants in functional products. The synergistic effects among peptides may provide a perspective for the combined application of peptides.