Isolation and characterisation of five novel antioxidant peptides from ethanol-soluble proteins hydrolysate of spotless smoothhound (Mustelus griseus) muscle

Ethanol-soluble proteins (EP) were obtained from spotless smoothhound (Mustelus griseus) muscle, and the EP antioxidant hydrolysates (E-AMH) were prepared using papain. Five antioxidant peptides were isolated from the E-AMH using ultrafiltration and consecutive chromatographic methods including ion-exchange chromatography, gel filtration chromatography, and RP-HPLC, and their sequences were identified as Gly-Ala-Ala (217.3 Da), Gly-Phe-Val-Gly (378.5 Da), Gly-Ile-Ile-Ser-His-Arg (682.0 Da), Glu-Leu-Leu-Ile (486.7 Da), and Lys-Phe-Pro-Glu (519.6 Da). All of these purified peptides exhibited high scavenging activity on hydroxyl radical (IC50 1.6337 mg/ml, 0.8944 mg/ml, 0.0769 mg/ml, 0.1173 mg/ml, and 0.1510 mg/ml, respectively), ABTS radical (IC50 1.7541 mg/ml, 1.3055 mg/ml, 0.3493 mg/ml, 0.3274 mg/ml and 0.4645 mg/ml, respectively), and superoxide radical (IC50 0.6714 mg/ml, 0.3082 mg/ml, 0.1508 mg/ml, 0.1851 mg/ml, and 0.2053 mg/ml, respectively). These five purified peptides also effectively inhibited the autooxidation in linoleic acid model system. The antioxidant activities of these purified peptides were attributed to their amino acid compositions, sequences, and hydrophobicities. These results suggested that these five peptides isolated from the E-AMH of spotless smoothhound muscle were potent antioxidants and might be effectively used as food additives and pharmaceutical agents.