Hemicelluloses

Literature References: Large group of polysaccharides found, in association with lignin, in the primary and secondary cell walls of all plants and of some seaweeds. Whether lignin and hemicellulose are chemically bonded or lignin mechanically entraps hemicellulose molecules is still unknown. There are variations in the hemicellulosic composition of plants and even between the organs of the same plant. Hemicellulosic composition of plants changes with growth and maturation and is influenced also by environmental factors during growth. Principal sugar residues present in hemicellulose are: D-xylose, D-glucose, D-galactose, D-mannose, L-arabinose, D-glucuronic acid, D-galacturonic acid, 4-O-methyl-D-glucuronic acid, L-rhamnose and L-fucose. The most ubiquitous and abundant hemicelluloses are the xylans which are composed of linear and/or branched chains of b-(1®4) linked D-xylopyranosyl units. Hemicelluloses from woods: T. E. Timell, Adv. Carbohydr. Chem. 19, 247 (1964); idem, ibid. 20, 409 (1965). Hemicelluloses from grasses and cereals: K. C. B. Wilke, ibid. 36, 215 (1979).