Antioxidant activity of bigeye tuna (Thunnus obesus) head protein hydrolysate prepared with Alcalase

The antioxidant activities of tuna head protein hydrolysate (THPH) prepared with Alcalase were evaluated. THPH showed evident radical scavenging activity in a dose-dependent manner with the IC50 values for 1,1-diphenyl-2-pycrylhydrazyl (DPPH), superoxide and hydroxyl radicals being 1.34, 1.20 and 2.84 mg mL-1, respectively, and its reducing power was 0.948 at 12.5 mg mL-1. THPH showed good inhibitory activity in soybean oil peroxidation after accelerated oxidation at 60 degrees C, and the oils with 0.01%, 0.05% and 0.1% THPH had significantly (P < 0.05) lower peroxide values than the control, after storage at 60 degrees C. Moreover, the inhibited oxidation effect of 0.1% THPH was similar to that of 0.01% butylated hydroxytoluene (BHT). The molecular weight distribution of THPH revealed that 70.5% of the total amount was peptides with molecular weight lower than 5000 Da, composing mostly of low molecular weight peptides located at 10202585 Da (30.78%) and 2411020 Da (37.15%).