Hemicelluloses glucomannan

In this study, thus, we selected sugi as softwood and buna as hardwood species. Just for comparison, cellulose and hemicellulose (glucomannan, xylan) and lignin (milled wood lignin) were also studied for their reaction in supercritical water. 

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]. 

The end group which is produced contains a carboxylic acid functionality which has an influence on the anionicity of pulp fibres (Chapter 6) but, in this form, it is resistant to further alkaline degradation. The hemicelluloses are also able to undergo the same type of peeling reaction but at different rates from each other and from cellulose. The /3-1,4-xylans, for example, are more stable to alkaline degradation than the glucomannans. 

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... 

Cellulose is the main component of the cell-wall which forms the insoluble skeletal framework of all higher plants. This polymer is associated with other polysaccharides, chiefly xylan, pectin, glucomannan, and hemicelluloses. 

Hansson, J.-A. (1970). Sorption of hemicelluloses on cellulose fibres, Part 3. The temperature dependence on sorption of birch xylan and pine glucomannan at kraft pulping conditions. Sven. Papperstidn. 73,49-53. 

Closely associated with cellulose in the wood structure and paper products are other polysaccharides called hemicelluloses, which often have been labeled as the matrix material of wood. In hardwoods the primary hemi-cellulose is a xylan (polymer of xylose), whereas in softwoods the primary hemi-cellulose is a glucomannan, although both of these polysaccharides occur to some extent in both types of wood. The DP of the hemicelluloses is much less than that of cellulose, in the range of 100-200. 

Glucomannan, on the other hand, is biosynthesized from GDP-o-mannose and GDP-o-glucose. It is important to note that the activities of hemicellulose synthetases are controlled depending on the stage of cell wall formation. 

Glucomannan is a minor fraction of hardwood hemicelluloses (about 3-5%), and is a P-(l-4)-linked linear copolymer of glucose and mannose at the ratio of 1 1-2. 

The predominant hemicelluloses in secondary cell walls of both monocotyledons and dicotyledons are xylans. These polysaccharides have a xylan main chain that is decorated with 4-0-methyl-D-glucopyranosyluronic acid, D-glucopyranosyluronic acid, L-arabinofuranosyl, and/or L-arabinopyranosyl units. These related polysaccharides are usually acetylated to various degrees. Gymnosperms contain glucomannans, also acetylated, as the principal secondary cell-wall hemicellulose [26]. 

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