Structural Characterization of Extracellular Polysaccharides Produced by the Marine Fungus Epicoccum nigrum JJY-40 and Their Antioxidant Activities

Two extracellular polysaccharides, ENP1 and ENP2, were isolated from the fermentation liquid of the marine fungus Epicoccum nigrum JJY-40 by anion-exchange chromatography and gel-filtration chromatography, and their structures were investigated using chemical and spectroscopic methods including methylation analysis and NMR spectroscopy. The results demonstrated that ENP1 was composed of mannose, glucose, and galactose in the molar ratio of 5.0:2.1:1.0, and the main chain of the polysaccharide consisted of (1 -> aEuro parts per thousand 2)-linked mannose, (1 -> aEuro parts per thousand 3)-linked mannose, terminal mannose, (1 -> aEuro parts per thousand 6)-linked glucose, (1 -> aEuro parts per thousand 4)-linked glucose, and (1 -> aEuro parts per thousand 4)-linked galactose. ENP2 was composed of mannose, galactose, glucose, and glucuronic acid in a molar ratio of 12.4:11.2:8.3:1.0, and its glycosidic linkage patterns included terminal mannose, (1 -> aEuro parts per thousand 6)-linked glucose, (1 -> aEuro parts per thousand 4)-linked galactose, and (1 -> aEuro parts per thousand 3)-linked mannose. The two polysaccharides had a partially branched structure with branch point located at C-3 position of (1 -> aEuro parts per thousand 6)-linked glucose residue. The molecular weights of ENP1 and ENP2 were 19.2 kDa and 32.7 kDa, respectively. Antioxidant properties of the two polysaccharides were evaluated with hydroxyl, superoxide, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities and lipid peroxidation inhibition in vitro, and results showed that ENP2 and ENP1 had good antioxidant activities, especially ENP2. ENP2 could be effective as a potential antioxidant.