Novel isolation of water-soluble polysaccharides from the fruiting bodies of Pleurotus ostreatus mushrooms

Novel water-soluble polysaccharides have been isolated from the fruiting bodies of the edible mushroom Pleurotus ostreatus. Three polysaccharide fractions were obtained by ethanol precipitation from cold water, hot water and hot aqueous NaOH extracts. The fractions were purified by size exclusion chromatography showing a unique carbohydrate occurring in each fraction: PC from the cold fraction, PH from the hot fraction and PB from the hot aqueous NaOH fraction. The analysis of the methylated alditol acetates and the NMR studies revealed that all the polysaccharides displayed a linear backbone. PC was formed by α-(1→3),(1→6)-linked galactopyranosyl residues whereas PH and PB consisted of glucose-linked units. PH was exclusively composed of glucopyranosyl units bound by α-(1→4) linkages whereas PB was a β-linked glucan showing (1→3) and (1→6) glycosidic bonds. The analysis of molecular arrangement by complexation with Congo red showed that only the β-linked polysaccharide (PB) displayed a triple helix conformation.

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► Fruiting bodies of Pleurotus ostreatus were used for isolation of polysaccharides.
► Three fractions were obtained by cold water, hot water and hot NaOH extractions.
► PC, PH and PB were α-(1-3),(1-6)-galactan, α-(1-4)-glucan and β-(1-3),(1-6)-glucan.
► Their molecular masses were 10 kDa (PC), 140 kDa (PH) and 30 kDa (PB).
► All the polysaccharides displayed a linear backbone.