Antioxidant activity of sulphated polysaccharide conjugates from abalone (Haliotis discus hannai Ino)

The water-soluble sulphated polysaccharide conjugates were obtained from abalone viscera (Haliotis discus hannai Ino) by alkaline protease extraction followed by ethanol precipitation. Their antioxidant activities were evaluated in vitro by hydroxyl radicals scavenging activity, reducing power and metal chelating activity. Those various antioxidant activities were compared to standard antioxidants ascorbic acid and EDTA. The experimental results indicated that the crude extract having notable hydroxyl free radicals scavenging activity and moderate reducing power and chelating potency. The crude sulphated polysaccharide conjugates was enzymatically hydrolyzed by five commercially available proteases (trypsin, vernase, neutrase, pepsin and papain), and the resultant digests were tested for their antioxidant activities. Those proteolytic hydrolysates, although improving the hydroxyl radical scavenging activity in all cases except one, had lower reducing power and 3–15 times lower chelating ability than the native extract. Product derived from pepsin hydrolysate was fractionated by gel-filtration chromatography with sephadex G-100, giving two fractions containing sulphated polysaccharide conjugates termed ACP I and ACP II. The neutral monosaccharide composition of ACP I is rhamnose, fucose, xylose, mannose, galactose and glucose in a molar ratio of 1.00:45.14:4.00:5.36:33.18:2.15, with an average molecular weight of about 271 kDa. The neutral monosaccharide composition of ACP II is rhamnose, fucose, xylose, mannose, galactose and glucose in a molar ratio of 1.00:12.51:1.33:4.98:16.08:1.46, with an average molecular weight of about 6 kDa.