ARABINOSE-CONTAINING OLIGOSACCHARIDES FROM TAMARIND XYLOGLUCAN

Oligosaccharide mixtures were obtained by enzymatic degradation of tam arind xyloglucan from the seeds of Tamarindus indica by commercial Asp ergillus niger endo-(1-->4)-beta-D-glucanase, and their composition an alyzed by HPAE-PAD liquid chromatography revealing two major groups of oligosaccharides. The first group contained oligomers of DP 7, 8 and 9, while the second group consisted of a large variety of oligomers of DP 12 to 18. After purification by SEC and HPLC in semi-preparative s cale, single oligomers were characterized by glycosyl-residue composit ion, glycosyl-linkage analysis and plas ma desorption mass spectrometr y. Beside beta-D-glucosyl, beta-D-galactosyl and alpha-D-xylosyl units , some higher oligomers contained beta-D-galactosyl-(1-->5)-alpha-L-ar abinosyl units, linked to 0-6 in the glucosyl units of the (1-->4)-bet a-D-glucan backbone. Other L-arabinosyl residues were located in termi nal positions of alpha-D-xylosyl side chains. The variety of isolated oligomers reflected a complicated random distribution of side chains i n tamarind xyloglucan. Based on the characteristics of the oligomers, four structure forming units for the polysaccharide are proposed.