Antioxidant and free radical-scavenging activities of smooth hound (Mustelus mustelus) muscle protein hydrolysates obtained by gastrointestinal proteases

We have investigated the antioxidative activity of five hydrolysates from smooth hound (Mustelus mustelus) meat obtained by various gastrointestinal proteases: crude enzyme extract, low molecular weight (LMW) alkaline protease and trypsin-like protease from M. mustelus intestine, pepsin from M. mustelus stomach, and bovine trypsin. The antioxidant activities of the different smooth hound protein hydrolysates (SHPHs) were evaluated using various in vitro antioxidant assays, such as 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity, reducing power, total antioxidant capacity, lipid peroxidation inhibition in rat liver homogenate and p-carotene bleaching assay. The five hydrolysates showed different degrees of hydrolysis and varying degrees of antioxidant activity. The hydrolysate produced by the LMW protease generally showed a greater antioxidative activity as indicated by all the methods considered. The IC50 values (the concentration of antioxidant substance removing 50% of DPPH radical) for DPPH and lipid peroxidation were found to be 0.6 +/- 0.01 and 1.1 +/- 0.06 mg/ml, respectively. Moreover, LMW protease hydrolysate exhibited notable reducing power and strong total antioxidant capacity. The protein hydrolysate produced by the LMW protease was then fractionated by size exclusion chromatography on a Sephadex G-25 into three major fractions (F-1-F-3). Fraction F-3, with molecular weight lower than 3500 Da, was found to display a high antioxidant activity than F-1 (12,200 Da) and F-2 (molecular weights between 6500 and 12,200 Da). The amino acid analysis by GC/MS showed that F-3 was rich in histidine, methionine. tyrosine, leucine, Isoleucine, glycine, and arginine. (C) 2008 Elsevier Ltd. All rights reserved.