Structural elucidation of a soluble polysaccharide XYLP-II from the fruiting body of Xylaria sp. L1 and its antibacterial and antioxidant activity.

Xylaria can be used as food and medicine for its inflammatory and hepatoprotective effects. Of them, polysaccharide is a major bioactive ingredient. To explore the function of a novel polysaccharide (XYLP-II) purified from the fruiting body of Xylaria sp. L1, the structure, antibacterial and antioxidant activities, and its protective ability in the primary mouse jejunum mucosal epithelial cells of XYLP-II were extensively studied. The structural analysis of XYLP-II showed that monosaccharide composition of XYLP-II was only glucose, had a molecular weight of 345.43 kDa. Combined with FT-IR, methylation, and NMR analysis, it was preliminarily concluded that the main chain of XYLP-II was composed by →4)-α-D-Glcp-(1 → 2)-α-D-Glcp-(1→, and the branch structure α-D-Glcp-(1 → 6)-α-D-Glcp-(1 → connected to the O6 position of the main chain. Meanwhile, the antibacterial activity of XYLP-II on gram-positive bacteria was stronger and it increased cell permeability by destroying bacterial cell wall and cell membrane. In vitro experiments indicated XYLP-II effectively protected against oxidative damage in the mouse jejunum mucosal epithelial cells by increasing the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-PX) and inhibiting the activity of malondialdehyde (MDA). Collectively, these results provide theoretical basis of Xylaria sp. L1 for its use in food additives and antioxidant therapeutics in medicine.