Isolation and characterization of the exopolysaccharide produced by Daedalea quercina

The production of exopolysaccharide (EPS) by a strain of the basidiomycete Daedalea quercina was investigated. Of seven different carbon sources, glucose and dextrins gave the highest crude polysaccharide yield (4.7-5 g 1-1, 55-60% carbohydrate content) in shake-flask cultures, at 14 days of fermentation. Experiments carried out in a 101 fermenter, at two different agitation speeds, gave the best results at 300 rpm, resulting in 12-14 g 1-1 of crude exopolysaccharide in 9-11 days. Fractionation of the EPS samples, carried out by tangential flow ultrafiltration, evidenced a single EPS fraction (MW > 30 000 Da) in samples from glucose, while two fractions (MW > 30 000 Da and 30 000 > MW > 10 000 Da) were present in samples from dextrins. Fractions characterization by HPLC and proton NMR spectroscopy revealed diversity in composition and structure in the obtained EPS: from glucose mainly an α-linked mannan, and from dextrins mainly an α- and β-linked glucan.