Characteristic and antioxidant activity of retorted gelatin hydrolysates from cobia (Rachycentron canadum) skin.

Alkali-pretreated cobia (Rachycentron canadum) skin was extracted in a retort (121°C) for 30min to obtain a retorted skin gelatin hydrolysate (RSGH). The molecular mass distributions and antioxidant activities of cobia RSGH and enzyme-treated RSGHs (ET-RSGHs) derived from bromelain, papain, pancreatin, and trypsin digestion were then characterized. The molecular mass distribution of the RSGH ranged mainly between 20,000 and 700Da and those of ET-RSGHs ranged between 6500 and 700Da. The DPPH (α,α-diphenyl-β-picrylhydrazyl) radical scavenging effects (%) of 10mg/ml of RSGH and 10mg/ml of the four ET-RSGHs were 55% and 51-61%, respectively. The lipid peroxidation inhibition (%) of RSGH and ET-RSGHs (10mg/ml) were 58% and 60-71% on the fifth day in a linoleic acid model system, respectively. The 3Kd-ET-RSGHs, obtained by using a series of centrifugal ultrafiltration filters (molecular weight cut-offs of 10, 5, and 3kDa done sequentially with decreasing pore size), exhibited dramatically improved antioxidant activity, with most of the molecular mass ranging below 700Da. Compared to 10mg/ml of the RSGH, 10mg/ml of 3Kd-ET-RSGHs exhibited 45-65% more scavenging of DPPH radical and 24-38% more inhibition of lipid peroxidation. The peptides with molecular masses below 700Da in the ET-RSGHs or 3Kd-ET-RSGHs significantly affect the antioxidant properties. These peptides are composed of a small number of amino acids or free amino acids and have the potential to be added as antioxidants in foods.