Hemicelluloses galactoglucomannan

Glucomannans (GM) and galactoglucomannans (GGM), common constituents of plant cell walls, are the major hemicellulosic components of the secondary cell walls of softwoods, whereas in the secondary cell walls of hardwoods they occur in minor amounts. They are suggested to be present together with xylan and fucogalactoxyloglucan in the primary cell walls of higher plants [192]. These polysaccharides were extensively studied in the 1960s [6,193]. 

Shimizu, K., Teratini, F., Hashi, M. and Miyazaki, K. (1972). Effect of the thermal treatment on wood hemicelluloses. VI. Studies on the thermal analysis of arabinogalactan, and O-acetyl and deacetylated-galactoglucomannans. Mokuzai Gakkaishi, 18(2), 79-84. 

Cell walls of woods contain other subgroups of hemicelluloses, in particular those composed primarily of D-mannopyranosyl or D-galactopyranosyl units. Glucomannans [11078-31-2] comprise 3—5% of the wood of angiosperms and 3—12% of the wood of gymnosperms. Galactoglucomannans... 

Whatever the role of the 0-acetyl groups in wood, their presence seems to be of some importance to the tree, since the preponderant hemicellulose carries these groups, both in the gymnosperms and in the (botanically much younger) angiosperms— in the former, the galactoglucomannans, and in the latter, the xylan. 

The strainTFfects due to dehydration are nowhere better illustrated than in the precautions that must be taken to dry and season wood before its use. This problem relates to water removal from capillaries but certainly the dehydration of the hemicelluloses which are in a paracrystal1ine order at the surface of the microfibrils ( ) must play a role. Xylan (4) in hardwoods and galactoglucomannans (IJ ) in softwoods have the characteristics of columnar and sheet hydration, respectively. 

As will be discussed later (see p. 473), the alkali-soluble glucomannans in softwoods have now been shown to be partially 0-acetylated in their native state. If the 0-acetyl groups in softwoods are associated only with the D-mannose-containing hemicelluloses, experimental data indicate that the galactoglucomannans must also carry 0-acetyl groups. This conclusion is strengthened by the fact that the extracellular galactoglucomannans are partly 0-acetylated. 

All of the major polysaccharides in softwoods are now known these are cellulose, galactoglucomannans, arabino-(4-0-methylglucurono)xylan, ara-binogalactan, galactan, pectic material, and starch. It is clear, however, that other minor polysaccharide constituents, still unknown, must also be present. These polysaccharides have not yet been isolated, but their presence may be inferred from the formation of di- and tri-saccharides of unknown origin on partial hydrolysis of wood or crude hemicellulose preparations. 

Other hemicelluloses, composed mainly of hydrocolloids, are used primarily as an extracellular energy, raw materials storage system, and as a water retention mechanism in seeds. Galactoglucomannans, glucomannans, galactomannans, and h-glucans tend to be heavily hydrated and have fewer, if any, ester-linked side chains [57]. 

The whole pectin fraction usually contains one or both types of pectinic acid and arabinogalactans. Hemicellulose is a complex mixture of arabino-galactan, xylans, sometimes some glucomannan or galactoglucomannan, and callose. Its composition is variable with the source. The cellulose fraction, not only contains p-l,4-glucan, but almost always has small amounts of inseparable glucomannan. The primary cell wall is relatively richer in hemicellulose than the secondary wall, while the latter contains a good deal of cellulose. Pectins are found in primary walls and probably comprise much of the middle lamella. 

Hartman, J., Albertsson, A.-C., Sjoberg, J. Surface- and bulk-modified galactoglucomannan hemicellulose films and film laminates for versatile oxygen barriers. Biomacromolecules 7, 1983-1989 (2006)... 

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

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