Purification and structural characterisation of (1 → 3;1 → 6)-β-D-glucans (botryosphaerans) from Botryosphaeria rhodina grown on sucrose and fructose as carbon sources : a comparative study

Abstract Two botryosphaerans, exopolysaccharides (EPS) secreted by the ascomyceteous fungus Botryosphaeria rhodina , when grown on sucrose and fructose as sole carbon sources, were structurally compared after their isolation from the culture medium. Both EPS were submitted to trypsin digestion, and eluted as a single peak on gel filtration. Total acid hydrolysis yielded only glucose, and data from methylation analysis and Smith degradation indicated that both EPS constituted a main chain of glucopyranosyl β(1→3) linkages substituted at O-6. The products obtained after partial acid hydrolysis demonstrated side chains consisting of glucosyl- and gentiobiosyl- linked β(1→6) residues. 13 C-NMR spectroscopy studies showed that all glucosidic linkages were of the β-configuration. The carbon source affected the side chain structures of botryosphaeran but not the main chain makeup. Sucrose produced less branching (21%) than fructose (31%).