Purification, composition analysis and antioxidant activity of a polysaccharide from the fruiting bodies of Ganoderma atrum

A water-soluble protein-bound polysaccharide was extracted from the fruiting bodies of Ganoderma atrum and isolated by gel-filtration chromatography. Its primary structural features and molecular weight were characterized by infrared spectrometry, gas chromatography, size exclusion chromatography, amino acid analyzer and high-performance liquid chromatography (HPLC). The data obtained indicated that the glycoprotein contains 10.1% of protein and 17 general amino acids and it is rich in glutamic acid, asparagic acid, alanine, glycine, threonine, and serine. It was mainly composed of mannose, galactose and glucose in a molar ratio of 1:1.28:4.91, with an average molecular weight of about 1013 kDa. The existence of an O-glycosidic linkage in PSG-1 (polysaccharide1) was demonstrated by a β-elimination reaction. The antioxidant activity of the purified polysaccharides was evaluated in vitro by 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging assay, self-oxidation of 1,2,3-phentriol assay. Those various antioxidant activities were compared to standard antioxidants vitamin C and BHT. It was found that the scavenging effects of the purified polysaccharides increased with measuring concentration. The results indicated that the purified polysaccharides showed strong DPPH free radical and superoxide anion radical scavenging activities. This study suggested that the purified polysaccharides could potentially be used as natural antioxidants.