Production Optimization, Molecular Characterization and Biological Activities of Exopolysaccharides from Xylaria nigripes

Y. P. Ma, D. B. Mao, L. J. Geng, W. Y. Zhang, Z. Wang and C. P. Xu

Abstract
The optimal culture conditions of exopolysaccharides (EPS) production in submerged culture medium by Xylaria nigripes were determined using orthogonal matrix method. The optimal medium (per liter) EPS was 60.0 g L–1 maltose, 1.0 g L–1 peptone, 5 mmol L–1 KH2PO4, and initial pH 7.0 at 28 oC. In the optimal culture medium, the maximum EPS production was 11.967 g L–1 in shake flask. Two groups of EPSs (designated as Fr-I and Fr-II) were obtained from the culture filtrates by size exclusion chromatography (SEC), and their molecular characteristics were examined by a multiangle laser-light scattering (MALLS) and refractive index (RI) detector system. The weight-average molar masses of Fr-I and Fr-II of EPS were determined to be 6.327x104 and 1.478x104 g mol–1, respectively. The SEC/MALLS analysis revealed that the molecular formation of Fr-I is of nearly globular shape. Furthermore, the experiments in vitro indicated that X. nigripes EPS exhibited high antioxidative effects though its antitumour activity was limited.

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Keywords
optimisation, exopolysaccharides, Xylaria nigripes, molecular characterization, antioxidant, antitumour