Enzymatic hydrolysis of Alaska pollack (Theragra chalcogramma) skin and antioxidant activity of the resulting hydrolysate

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BACKGROUND: Fish skin, a by-product of the food industry, contains a large amount of collagen. However, only a small proportion of fish skin is used in the production of leather materials and animal feedstuffs, most of it being discarded. The aims of this study were to prepare peptides from Alaska pollack (Theragra chalcogramma) skin by enzymatic hydrolysis and to evaluate the antioxidant activity of the resulting hydrolysate. RESULTS: Protamex was the most efficient enzyme for preparing antioxidant peptides from Alaska pollack skin. The optimal hydrolysis conditions were as follows: hydrolysis time 8 h; enzyme/substrate ratio 2:1000; skin/water ratio 1:6; temperature 55 degrees C; pH 6.0. Under these conditions the highest yield of peptides was 83.44%, with 85.95% of the hydrolysate being mainly composed of oligopeptides with molecular weights ranging from 180 to 1000 Da. The hydrolysate showed 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activity, with an IC(50) value of 2.5 mg mL(-1), and its reducing power was 0.14 at 1 mg mL(-1), 53.8% of that of reduced glutathione at the same concentration. CONCLUSION: This study demonstrated that the hydrolysate of Alaska pollack skin was mainly composed of oligopeptides with two to eight amino acid residues and possessed antioxidant activity.