Polysaccharides hemicelluloses

Smaller amounts of other hemicellulose polysaccharides are also found in softwoods. In particular, larch contains an unusually large amount of arabinogalactan, which is usually only a minor components of other wood species. 

While the hemicelluloses obtained from the germ, aleuron, and caryopsis coat cell walls all showed a similar monosaccharide composition, this was not the case for the endosperm tissue. Thus, a major difference in the structure of hemicellulosic polysaccharides exists between the preparations obtained from the endosperm cell walls and those from the cell walls of the other parts of the grain, i.e., rice bran. (Rice bran consists of the caryopsis coat, aleuron layer and germ.) Comparison of the detailed structural features of the hemicellulosic polysaccharides of endosperm and bran cell walls will be discussed in the following sections. 

Figure 3 shows the structure of the hemicellulosic polysaccharides obtained from the bran cell wall preparations. These structures were deduced from the results of the methylation analysis of purified fractions (13). In contrast to the endosperm cell wall, no / -l,3-,l,4-glucan was obtained from... 

Figure 2. Structure of hemicellulosic polysaccharides obtained from the rice endosperm cell wall, (a) From ref. 12 (b) and (c), deduced from the results described in ref. 11.

Classic methods in use to fractionate plant cell wall polysaccharides are mainly based upon the differential solubilities of various cell wall polysaccharide constituents (32). To solubilize pectic polysaccharides, the cell wall material is extracted with water, ammonium oxalate or disodium EDTA. The solubilization of pectic polysaccharides could then be followed by solubilization of hemicelluloses, i.e., polysaccharides rich in D-glucuronic acid 4-0-methyl-D-glucuronic acid, D-xylose and D-glucose residues. The solubilization of hemicellulosic polysaccharides is accomplished by treatment of water, ammonium oxalate or EDTA insoluble material with a strong alkali. 

Hemicellulose Polysaccharides with a random, amorphous structure that are components of plant cell walls. Umelated to cellulose structurally, they are composed of a variety of monosaccharides, including some acidic sugars, with xylose being the most prevalent. 

Occurrence. D-Xylose (10) is present in widely abundant polysaccharides of plant tissues. Xylan is the main carbohydrate found in the hemicellulosic fraction, and accounts for one third of all renewable organic carbon available on earth. The structure and composition of xylans are variable, from linear (3-(l->4)-linked xylose chains to highly branched heteropolysaccharides. The branches may involve short oligosaccharides, usually of L-arabinofuranosyl units. Xyloglucans are also important hemicellulose polysaccharides consisting of a backbone of ( I — 4)-(i-D-glucopyranosyl residues heavily substituted with a-D-Xylp. Other monosaccharides may also be present.44... 

Hemicelluloses are non-cellulosic low molecular weight polysaccharides that are found together with cellulose in plant tissues 1311. In the cell walls of land plants, xylan is the most common hemicellulosic polysaccharide, representing more than 30% of the dry weight 1321. Most xylans are heteropolysaccharides which are composed of 1,4-linked (3-D-xylopyranosyl residues 133, 134, 135). This backbone chain is substituted with acetyl, arabinosyl, and glucuronosyl residues 133. Homoxylans, on the other hand, consist of xylosyl residues exclusively and have been isolated from esparto grass 136, tobacco stalks 137, and guar seed husk 138. ... 

Hemicelluloses (polysaccharides composed primarily of xylose and mannose) are much shorter in length than cellulose and are extensively branched these species may act to cross-link cellulose and other polymers, and also form the amorphous matrix of the interfibrillar space, in which cellulose microfibrils are embedded. Pectins are jelly-like, acidic polymers composed... 

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

Cross-linking between polymers is the main reason for the limited accessibility of polysaccharides, while lignin replaces water, thereby increasing the occurrence of hydrogen bonds between hemicelluloses, polysaccharides, and cellulosic microfibrils (Donaldson, 2001). 

Yapo, B. M. and Koffi, K. L. (2008). The polysaccharide composition of yellow passion fruit cell wall Chemical and macromolecular features of extractable pectins and hemicellulosic polysaccharides. Journal of the Science of Food and Agriculture 88, 2125-2133. 

The hemicelluloses are a heterogeneous group of polysaccharides that vary from plant to plant and from one plant part to another. There are four basic types of hemicellulose polysaccharides D-xyloglucans, composed of D-xylopyranose attached to a cellulose chain D-xylans, composed of D-xylose D-mannans, composed of D-mannose and D-galactans, composed of D-galactose. These polysaccharides are similar to cellulose in having their main chains linked p-1 -> 4. Most of the hemicelluloses are, however, heteropolysaccharides with one to three monosaccharides units linked to the main monosaccharide chains. 

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