Preparation and antioxidant activities of a sulfated derivative of exopolysaccharide from Escherichia coli K5

Escherichia coli K5 strain was cultivated by fermentation, the supernatant was treated by ultrafiltration, exopolysaccharide (EPS) was extracted by ethanol precipitation, and then purified by Sevage method, dialysis, freeze-dried, DEAE-Sepharose and Sephadex G-75 column, finally high-purity K5 polysaccharide (K5) was obtained. N site of the K5 polysaccharide was chemically sulfated by Sulfur trioxide pyridine complex, NS-K5 polysaccharide (NS-K5) was prepared, and disaccharide analysis revealed that N-sulfation rate was up to 57%. The antioxidant capacity of K5 polysaccharideand N-sulfated K5 polysaccharide was investigated, the results showed that:within a certain concentration range, the reducing activity of NS-K5 was powerful over K5, when the concentration of K5 and NS-K5 was up to 1mg/mL, the hydroxyl radical scavenging rates were 17.7%, 25.6%, and DPPH radical scavenging rates were 26.1%, 45%, respectively. The result indicated that NS-K5 showed stronger antioxidant activity than K5.