Hemicelluloses glucuronoxylan

Glucuronoxylan Even if hemicelluloses in various hardwood species differ from each other both quantitatively and qualitatively, the major component is an 0-acetyl-4-0-methylglucuronoi3-D-xylan, sometimes called glucuronoxylan. Often the xylose-based hemicelluloses in both softwoods and hardwoods are termed simply xylans. 

Figure 18 O-Acetyl-4-O-methyl-D-glucuronoxylan, a type of hemicellulose, structure from angiosperms (Dekker, 1985) (reproduced by permission of Academic Press from Biosynthesis and Biodegradation of...

Glucuronoxylan (15-30%) is the major hemicellulose of hardwoods such as birch, eucalyptus and poplar/aspen. It is similar to grass xylan, but lacks the arabinofuranosyl decoration (Figure 4.44). 

Xylan is the main component of hardwood (HW) hemicelluloses (10-35% of the wood). In contrast to softwood Xylans, hardwood xylans do not contain a-D-arabinofuranosyl units and, therefore, they are glucuronoxylans. The content of 4-0-methyl-a-D-glucuronic acid moieties in HW xylans is lower than in the softwood ones, about 1 unit per 10 xylopyranosyl units [1-3]. In addition, xylopyranosyl units in HWs are partially acetylated at the C-2 and/or C-3 position with total amounts of 3.5-7 acetyl groups per 10 xylopyranosyl units [13]. 

Hemicelluloses, Polysaccharides, Xylan, Glucuronoxylan, Arabinoxylan, Mannan, Glucomannan and galactoglucomannan. Polymer, Bios3uithesis, Biodegradation, Properties, Applications... 

The glucuronoxylans are composed of linear chains of p-(l->4) xylopyranosyl residues branched with a-(l->2)-linked 4-0-methylglucuronopyranosyl residues (4-0-MeGlcA). The 4-0-MeGlcA-to-xylose ratio is -1 6 for softwood and -1 10 for hardwood xylans. (7-acetyl-(4-D-methylglucurono)-xylan is the major hemicellulose present in hardwood, whereas arabino-(4-6>-methylglucurono)-xylan is present in softwood. 

Figure 3.8 Principal structure of the main softwood hemicellulose type, galactoglucomannan, and of the main hardwood hemicellulose type, 4-Omethyl glucuronoxylan.

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