Isolation and characterization of polysaccharides of "Kikurage", fruit body of Auricularia auricula-judae.

Abstract

Two kinds of β-D-glucans and an acidic heteropolysaccharide were isolated from the fruit body of Auricularia auricula-judae, and their structural features were elucidated. A water soluble glucan ([α]D -10°) consists of a backbone chain of β-(1→3)-linked D-glucose residues, two out of three glucose residues being substituted at the C-6 positions with single glucose units. The other glucan, which was obtained as the hot alkali insoluble residue, is also β-(1→3)-glucan with single branches at C-6 positions, but it has an extremely highly branched struc-ture; a small proportion of (1→6)-internal linkages may be situated in the side chains. An acidic heteropolysaccharide ([α]D -20°), isolated from the hot water extract through insoluble complex formation with cetylpyridinium chloride, contains D-xylose, D-mannose, D-glucose and D-glucuronic acid (molar ratio, 1.0:4.1:1.3:1.3). Methylation followed by acid hydrolysis of the polysaccharide yielded 2, 3, 4, 6-tetra-O-methyl-D-mannose(glucose), 2, 3, 4-tri-O-methyl-D-xylose, 2, 4, 6-tri-, 4, 6-di-, and 2, 4-di-O-methyl-D-mannose, 2, 4-di-O-methyl-D-glucose, together with 2, 3, 4-tri-O-methyl-D-glucuronic acid, suggesting that it consists of a backbone chain of (1→3)-linked mannose residues, which are attached with D-xylose, D-mannose and D-glucuronic acid residues at the C-2 or C-6 positions. On the basis of these findings, the constitution of the A. auricula judae was compared with that of Tremella fuciformis.