Characterization of antioxidant and surface-active properties of gelatin hydrolysates obtained from croaker fish skin

In this study, antioxidant and surface-active properties of gelatin hydrolysates (GH) were mainly evaluated. Gelatin obtained from croaker fish (Johnius dussumieri) skin was hydrolysed by the application of visceral proteases extracted from gastrointestinal (GI) tract of two freshwater fish species rohu (Labeo rohita) and catla (Catla catla). The resultant GH was designated as 'gelatin hydrolysate-rohu protease' (GHRP) and 'gelatin hydrolysate-catla protease' (GH-CP). Surface-active properties (foaming and emulsion) of GH-RP were significantly higher than GH-CP at concentrations studied (P < 0.05). The GH obtained by enzymatic hydrolysis treatment was fractionated using ultrafiltration and a total number of five fractions were collected unfractionated (UNF), >10 kDa, 5-10 kDa, 3-5 kDa, 1-3 kDa and <1 kDa. The IC50 value of DPPH radical scavenging activity of fraction 1-3 kDa from GH-RP and fraction <1 kDa from GH-CP showed the value of 0.55 mg/ml and 0.56 mg/ml respectively. The ferric reducing power assay results indicate that fraction from <1 kDa from GH-RP and GH-CP showed a significantly higher value than the other fractions (P < 0.05). The fractions of 1-3 kDa from GH-RP and <1 kDa from GH-CP showed the highest ABTS radical scavenging activity of 594.84 and 558.46 Trolox mu M/mg respectively. Among all, the fractions <1 kDa from GH-RP and 3-5 kDa from GH-CP had shown higher antioxidant activity determined using beta-carotene - linoleic acid model system. The results of the present study indicate that the peptides have good antioxidant and functional properties.