Glucomannans and Galactoglucomannans

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]. 

Glcp residues, what differs from previous investigations. Based on C-NMR spectroscopy, the sequences of Glcp and Manp were estimated and a model structure for the GM was proposed. 

In a recent paper [213], various GM-rich hemicellulose fractions containing 26-64% mannose and 1.4-2.2% galactose were isolated from ramie (Boehmeria nivea), which is a perennial grass. This is unexpected, because hemicelluloses of grasses contain predominantly xylans [4]. 

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In describing and interpreting some of the more important properties of plant galactomannans, comparisons will be made with structurally similar polysaccharides, including the closely related glucomannans and galactoglucomannans, and those based on (1 — 4)-/3-D-xylan main-chains (for example, the arabinoxylans) and (1 — 4)-/3-D-glucan main-chains [for example, the amyloids and sodium 0-(carboxymethyl)cellulose]. 

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

Similar structural problems exist for the distribution of side chains in galactoglucomannans, xyloglucans, arabinoxylans, and 4-0-methylglucuronoxylans, and even for the distribution of acetyl groups in glucomannans and for related features in many other polysaccharides. 

Obviously, Meier s results may equally well be interpreted in terms of a triheteropolymer galactoglucomannan. Glucomannans are well known for their insolubility in water and their limited solubility in certain aqueous alkalis, whereas galactomannans are water-soluble. A glucomannan and a galactomannan, if really present, should be separable. It also appears... 

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. 

CeU waUs of woods contain other subgroups of hemiceUuloses, 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 [9040-29-3] are also common. 

Alkali-induced deacetylation and hydrolysis of the uronic acid group of xylans proceed readily under alkaline pulping conditions and contribute significantly to xylan redeposition onto the fibers. The galactose side chain in galactoglucomannans is fairly resistant to alkaline hydrolysis (Table 2). Wood xylans are much more stable than glucomannans under alkaline conditions [34]. 

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