Structural characterization of a polysaccharide and a β-glucan isolated from the edible mushroom Flammulina velutipes

Two polysaccharides were isolated from the basidiomycete Flammulina velutipes, via successive hot extraction with water, 2% and 25% aq. KOH, and then submitted to freeze-drying. The precipitate formed by repeated freeze-thawing from the 2% aq. KOH extraction PK2 was analyzed by determination of its monosaccharide composition, as well as by methylation analyses using GC-MS, mono- (C-13, H-1 NMR) and bidimensional (H-1 (obs.), C-13 HMQC) spectroscopy, and controlled Smith degradations. It was established to be a branched beta-glucan, with a main chain of (1 -> 3)-linked-Glcp residues, substituted at O-6 by single-unit beta-Glcp side chains. The precipitate formed by repeated freeze-thawing from the 25% KOH extraction PK25 contained Xyl, Man, and Glc and was heterogeneous by HSPEC and extraction with DMSO gave a soluble xylomannan (XM). It was homogeneous with a molar mass 30.8 x 10(4) g/Mol (dn/dc = 0.186). Using the above chemical analyses, it was a xylomannan with Man and Xyl in a 3:2 molar ratio. Its main chain consisted of (1 -> 3)linked alpha-Manp units, mainly substituted at O-4 by beta-Xylp units or with some beta-Xylp-(1 -> 3)-beta-Xylp groups. (c) 2006 Elsevier Ltd. All rights reserved.