Purification, characterization and in vitro antioxidant activity of a polysaccharide AAP–3–1 from Auricularia auricula

The objective was to investigate the in vitro antioxidant activity of a novel polysaccharide AAP–3–1 from Auricularia auricula. AAP–3–1 was isolated from the fruiting bodies of A. auricula by hot water extraction and ethanol precipitation and was purified by DEAE FF ion exchange chromatography and Superdex 200 gel filtration chromatography. The molecular weight and monosaccharide composition were determined by high performance gel permeation chromatography and high–performance liquid chromatography, respectively. Ultraviolet visible spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy were used for structural characterization. The results showed that AAP–3–1 is a heteropolysaccharide and is mainly composed of mannose and glucose in a molar ratio of 1.4:1 with a molecular weight of 320.9 kDa. AAP–3–1 exhibited antioxidant activity in a concentration–dependent manner and the scavenging rates at 1.6 mg/mL on superoxide anions and hydroxyl and 1,1–diphenyl–2–picrylhydrazyl radicals were 88.13%, 93.03% and 68.31%, respectively. AAP–3–1 effectively ameliorated 2,2′–azobis–2–methyl–propanimidamide–induced oxidative stress in HepG2 cells by inhibiting reactive oxygen species generation, decreasing the content of malondialdehyde, and increasing the activities of superoxide dismutase, glutathione peroxidase and catalase. The results indicated that the antioxidant mechanism of AAP–3–1 was associated with both non–enzymatic and enzymatic defense systems.