Preparation and evaluation of antioxidant peptides from ethanol-soluble proteins hydrolysate of Sphyrna lewini muscle

To get high yield of ethanol-soluble proteins (EP) and the antioxidant peptides from Sphyrna lewini muscle, orthogonal experiments (L(9)(3)(4)) were applied to optimize the best extraction conditions and enzyme hydrolysis conditions. The yield of EP reached 5.903±0.053% under the optimum conditions of ethanol concentration 90%, solvent to material ratio 20:1, extraction temperature of 40°C and extraction time of 80min. The antioxidant SEPH (EP hydrolysate of S. lewini muscle) was prepared by using papain under the optimum conditions of enzymolysis time 2h, total enzyme dose 1.2%, enzymolysis temperature 50°C and pH 6, and its DPPH radical scavenging activity reached 21.76±0.42% at the concentration of 10mg/ml. Two peptides (F42-3 and F42-5) were isolated from SEPH by using ultrafiltration, anion-exchange chromatography, gel filtration chromatography and RP-HPLC. The structures of F42-3 and F42-5 were identified as Trp-Asp-Arg and Pro-Tyr-Phe-Asn-Lys with molecular weights of 475.50Da and 667.77Da, respectively. F42-3 and F42-5 exhibited good scavenging activity on hydroxyl radical (EC(50) 0.15mg/ml and 0.24mg/ml), ABTS radical (EC(50) 0.34mg/ml and 0.12mg/ml), and superoxide anion radical (EC(50) 0.09mg/ml and 0.11mg/ml), but moderate DPPH radical (EC(50) 3.63mg/ml and 4.11mg/ml). F42-3 and F42-5 were also effectively against lipid peroxidation in the model system and peroxyl free radical scavenging in β-carotene linoleic acid assay. Their high activities were due to the smaller size and the presence of antioxidative amino acids within the peptide sequences.