Hemicelluloses components

Derivatives of hemicellulose components have properties similar to the ceUulosic equivalents but modified by the effects of thek lower molecular weight, more extensive branching, labile constituents, and more heterogeneous nature. Acetates, ethers, carboxymethylxylan (184), and xylan—poly(sodium acrylate) (185) have been prepared. 

Xylan-type polysaccharides are the main hemicellulose components of secondary cell walls constituting about 20-30% of the biomass of dicotyl plants (hardwoods and herbaceous plants). In some tissues of monocotyl plants (grasses and cereals) xylans occur up to 50% [6j. Xylans are thus available in huge and replenishable amoimts as by-products from forestry, the agriculture, wood, and pulp and paper industries. Nowadays, xylans of some seaweed represent a novel biopolymer resource [4j. The diversity and complexity of xylans suggest that many useful by-products can be potentially produced and, therefore, these polysaccharides are considered as possible biopolymer raw materials for various exploitations. As a renewable resource, xylans are... 

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 surface wettability of heat-treated wood decreases due to a reduction in the hydroxyl content of the modified wood (Pdtrissans etal., 2003). There is a reduction in the water-sorption capacity, which is related to a reduction in the number of primary sorption sites (OH groups) within the wood cell wall, largely as a result of the removal/degradation of the hemicellulosic component. As remarked upon earlier, hygroscopic properties are strongly influenced by the treatment method employed. Podgorski etal. (2000) heated... 

Hardwood xylans and xylans of annual plants may contain up to 7% O-bound acetyl groups. Seven out of ten xylose residues in native hardwood xylan are acetylated on C-2 and/or C-3 (10). Because of the possible migration of O-acetyl groups between 2- and 3-positions during and after isolation of hemicellulose components, it is difficult to determine their original distribution in nature (11). The ratios reported for 2-, 3-, and 2,3-positions of acetyl groups in birch xylan have been 2 4 1 (3) and 2 2 1 (10) and in bracatinga xylan 3 3 1 (12). 

The common hemicellulose components of arborescent plants are listed in Table I. 

Since dilute-acid hydrolysis mainly solubilizes the hemicellulose components, the changes in solid yield (a measure of dry weight loss) are useful for monitoring the progress of the treatment. Table 1 shows the yield and... 

One strategy to minimize ethanol production cost is to run simultaneous saccharification and fermentation, or SSF, which would utilize ethanologens engineered to operate in high-temperature environments. Also, the fermentation organism s ability to utilize C5 sugars derived from the hemicellulose component, and have acceptable productivities in the presence of numerous byproducts of the... 

Ester groups in wood polysaccharides are for the most part acetyl substituents on the hemicellulose components. In the presence of... 

Dilute hydrochloric acid is as effective in the hydrolysis of the hemicellulose components of lignocellulosic biomass as sulfuric acid but it is more corrosive to equipment. Other acids such as dilute phosphoric acid have been used to hydrolyze sugar cane bagasse hemicellulose [52]. 

Krishnan et al. [121] pretreated corn fiber with dilute hydrochloric acid (0.5 wt%) at 120°C for 45 min to hydrolyze starch and hemicellulose components prior to SSF with Saccharomyces 1400 (pLNH33) as the biocatalyst. Over 40 g/1 ethanol was produced after 48 h of incubation (Fig. 11). 

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