In vitro antioxidant activity of acetylated derivatives of polysaccharide extracted from Ulva pertusa (Cholorophta)

Polysaccharides obtained from Ulva pertusa (Chlorophyta) contained a group of sulfated heteropolysaccharide referred to as ulvan in this paper. In this study, the acetylated ulvans with different substitution degree were prepared with acetic anhydride/ p-toluenesulfonyl chloride in N,N-dimethylacetamide, and their antioxidant activities were investigated including scavenging activity on superoxide, hydroxyl radicals and reducing power. The natural ulvan and its derivatives exhibited much higher scavenging activity on superoxide radical than vitamin C. Compared with natural ulvan, the acetylated ulvans exhibited stronger reducing power. The antioxidant activity of acetylated ulvans did not increase with increasing substitution degree. Interestingly, the ulvan (AU4) with highest degree of substitution showed weakest scavenging effect on hydroxyl radical.   Key words: Polysaccharides, Ulva pertusa, antioxidant activity, acetylated ulvans.