Abstract: Purpose: To investigate the antioxidant and antibacterial activities of polysaccharides from Chinese surf clam (Mactra chinensis). Methods: Polysaccharides from the whole viscera of the shellfish were extracted by alkaline extraction and alcohol precipitation and deproteinized by Sevag,s method. The purified extract was determined for its polysaccharide content, hydroxyl and superoxide anion free radical scavenging activity and antibacterial activity. A high extraction efficiency of polysaccharides from dried powdered material was obtained by using alkaline extraction, reaching 15.45%. Polysaccharides extracted from Chinese surf clam had strong antioxidant properties and the scavenging rates against superoxide anion and hydroxyl free radicals at 0.8 mg/mL were 86.49% and 49.31%, respectively. These polysaccharides had different antibacterial activity against Staphylococcus aureus, Bacillus subtilis and Escherichia coli. The antibacterial activity against Staphylococcus aureus was the strongest, followed by Bacillus subtilis; they had the weakest antibacterial activity against Escherichia coli. The corresponding minimum inhibitory concentrations were 12.5, 25 mg/mL and 25 mg/mL. Conclusions: Polysaccharides from Chinese surf clam have scavenging activity against superoxide anion and hydroxyl free radicals in a concentration-dependent way in a certain range of concentrations and show stronger antimicrobial activity against Gram-positive bacteria than Gram-negative bacteria.

Key words: Mactra chinensis, polysaccharide, antioxidant activity, antibacterial activity