Selenylation Modification of Degraded Polysaccharide from Enteromorpha prolifera and Its Biological Activities

Abstract

Polysaccharide extracted from Enteromorpha prolifera possessed excellent biological activities, but its molecular weight was greatly high which influenced the activity. Organic Se had higher biological activities and was safer than inorganic Se species. In the present study, Enteromorpha polysaccharide was degraded to low molecular weight by free-radical degradation method of H₂O₂ and ascorbic acid. By single factor and orthogonal experiments, the optimal degradation conditions were reaction time of 2 h, reaction temperature of 50°C, H₂O₂/ascorbic acid (n/n=1:1) concentration of 15 mmol L⁻¹, and solid-liquid ratio of 1:50 (g mL⁻¹). Then, the degraded polysaccharide was chemically modified to obtain its selenide derivatives by nitric acid-sodium selenite method. The selenium content was 1137.29 μg g⁻¹, while the content of sulfate radical had no change. IR spectra indicated that the selenite ester group was formed. Degraded polysaccharide selenide was characterized and evaluated for antioxidant, antifungal and antibacterial activities. The results showed that degraded polysaccharide selenide had strong capacity of scavenging DPPH and ·OH free radical. It had significant antibacterial properties for Escherichia coli, Bacillus subtilis and Salmonella spp., and it also had significant antifungal properties for Apple anthrax. The result ascertained degradation and selenylation modification did not change the main structure of polysaccharides. It was possible that free-radical degradation was an effective way for enhancing antioxidant activity to decrease molecular weight of polysaccharides.