Optimisation of hydrolysis of purple sea urchin (Strongylocentrotus nudus) gonad by response surface methodology and evaluation of in vitro antioxidant activity of the hydrolysate

BACKGROUND: Hydrolysates prepared from sea urchin (Strongylocentrotus nudus) gonad by enzymatic treatment showed strong 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity and reducing power. RESULTS: Hydrolysis of S. nudus gonad by the commercial protease papain was optimised for maximum degree of hydrolysis (DH) and trichloroacetic acid-soluble peptide index (TCA-SPI) using response surface methodology. Results showed that the optimal conditions were the following: temperature of 48.83 degrees C, pH of 6.92, enzyme-to-substrate ratio of 3143 U g(-1), and substrate concentration of 83.5 g L-1. Under these conditions, a DH of 27.96 +/- 0.54% and a TCA-SPI of 57.32 +/- 0.63% were obtained. The hydrolysate prepared in the optimal conditions was fractionated by an ultra-filtration system and the resultant fraction below 10 kDa was found to effectively scavenge hydroxyl radical (EC50 = 13.29 +/- 0.33 mg mL(-1)) and hydrogen peroxide (EC50 = 16.40 +/- 0.37 mg mL-1), inhibit lipid peroxidation (EC50 = 11.05 +/- 0.62 mg mL(-1)), chelate Fe2+ (EC50 = 7.26 +/- 0.44 mg mL(-1)), and protect mice macrophages against death induced by tert-butyl hydroperoxide. CONCLUSION: Hydrolysates prepared from S. nudus gonad have the potential to be applied as natural antioxidant agents. (C) 2012 Society of Chemical Industry