Chemical Structure in the Hemicellulose Group

The polysaccharides that accompany cellulose in the plant cell wall consist mainly of xylans, glucomannans, arabogalactans and related polymers containing residues of L-rhamnose. The xylans are of various types, all of which have as a common feature chains of ß-1,4′-linked xylopyranose residues. To these are attached as side-chains various residues including, amongst others, L-arabofuranose, D-glucuronic acid, 4-0-methyl-D-glucuronic acid, 2-(ß-D-xylopyranosyl)-L-arabofuranose, D-galactose, L-galactose. The xylans differ amongst themselves in the nature of the side chains and in their relative proportions. From the marine algae, another type of xylan has been isolated having both βI,3′- and βl,4′-linked xylose residues in the main chain. Consideration is given also to the main structural features of some galactomannans, glucomannans and arabogalactans that accompany xylans in many groups of cell wall polysaccharides.