Exopolysaccharides from Pleurotus pulmonarius: Fermentation Optimization, Characterization and Antioxidant Activity

Culture conditions for exopolysaccharide (EPS) production by Pleurotus pulmonarius in submerged culture are optimized. The suggested medium composition was as follows: 60 g/L of xylose, 6 g/L of soy extract, 5 mM of KH2PO4 and 5 mM of MgSO4. Under the optimized culture conditions in a 5-litre stirred tank fermentor, the maximum concentration of EPS was 6.36 g/L. Furthermore, the morphological parameters (i.e. average diameter, circularity, roughness and compactness) of the pellets and the broth viscosity are characterized. It has been proven that mycelial morphology and broth viscosity may be the critical parameters affecting the EPS yield. After deproteinization using Sevag method, a group of EPS (designated as fraction) was obtained from the culture filtrates by gel filtration chromatography. FT-IR analysis of the purified EPS revealed prominent characteristic groups corresponding to polyhydric alcohols. GC analysis showed that the purified EPS were mainly composed of galactose and glucose. Furthermore, thermogravimetric analysis indicated that the degradation temperature of the purified EPS was 217 °C. Finally, the antioxidant activity of the EPS fraction was investigated and the relationship with molecular properties was discussed as well.