Hemicelluloses from

The rheological behavior of xylans has rarely been investigated [4,114,115]. The water-insoluble hemicellulose from the viscose process (containing > 85% xylan) was reported to form thixotropic aqueous dispersions of high... 

The number of reports about hemicelluloses that have been covered by this review indicates the significantly increased importance of all types of hemicelluloses as plant constituents and isolated polymers during the last decade. Attention has been paid not only to known hemicelluloses but also to the primary structure, physicochemical, physical, and various functional properties of hemicelluloses isolated from hitherto uninvestigated plants. The efforts to exploit a variety of plant as potential sources of hemicelluloses were pointed out particularly for agricultural crops, wood wastes, as well as for by-products of pulp and rayon fiber technologies. Many studies were devoted to characterize seed-storage hemicelluloses from plants that have been traditionally applied in food and medicine of many underdeveloped countries to find substitutes for imported commercial food giuns. 

Little information is available on the enzymatic hydrolysis of xylan. The kinetics of breakdown of xylan are reported.128 Hemicellulose from linden wood is said to be extensively hydrolyzed124 by the digestive juices of Helix pomatia. Xylanase128 of Aspergillus niger, while active on xylan between pH 2-8, has its optimum at pH 4.0. 

Unfortunately, pure xylan is an expensive carbon source for commercial-scale xylanase production. Therefore, several groups have tried to develop xylanase production on cheaper xylan-rich materials. The best candidates for the purpose appear to be water-soluble hemicellulose from steam-treated wood (63,69) and residues of annual plants like wheat bran (70). 

Pleurotus sajor-caju utilizes polysaccharides (cellulose and hemicelluloses) from various agricultural residues to produce mushrooms for human consumption throughout the world (5). It is also known to degrade lignin (6,7). 

The second area of application involves the use of cellulase-free xylanases for removal of hemicellulose from pulps (10-20) and plant fibres (21). It is essential that these xylanase preparations are free of contaminating cellulase activity or damage to the cellulose fibres and consequently the product quality will result. 

The role of LCC s in living plant tissues is presumed to be related to the prevention of water-soluble hemicelluloses from dissolving out of the cell wall by the formation of micelles or aggregates that immobilize sugar chains, and the solubilization of water-insoluble material such as lignin, thereby enabling it to move to any place in the cell. 

The steam explosion process is a recent development in wood processing (1,2). Much attention has been paid to this process from the viewpoint of total wood utilization. Cellulose and hemicellulose from this process can be converted into sugars of commercial value by enzymatic methods (3). However, the conversion of lignin from this process (steam explosion lignin) into useful materials continues to present difficulties. Preparation of adhesives from it is considered to be a feasible way to solve this problem. 

Processes need to be developed to expose LHC for effective penetration of chemicals that promote separation of LHC or which render cellulose accessible by swelling. These processes can have many objectives (1) to get at cellulose (2) to remove hemicellulose from the reaction site before cellulose hydrolysis (3) to remove lignin from the site and (4) to bring penetrating or hydrolysis agents into effective contact with cellulose. 

Furoic acid (furan-2-carboxylic acid, or pyromucic acid) is used as a bactericide, and the furoate esters are used as flavoring agents, as antibiotic and corticosteroid intermediates. It is obtained by the enzymatic or chemical/catalytic aerobial oxidation of furfural (2-furalaldehyde) the latter is the only unsaturated large-volume organic chemical prepared from carbohydrates today. D-Xylose and L-ara-binose, the pentoses contained in the xylan-rich portion of hemicelluloses from agricultural and forestry wastes, under the conditions used for hydrolysis undergo dehydration to furfural. 

The hemicellulose from the pulping of trees is an underused resource. A small amount is currently being hydrolyzed to xylose for hydrogenation to the sweetener xylitol. A good use could be as a substrate for fermentation. 

Christov and Prior (10) used a crude xylanase preparation from Aurebasidium pullulans to remove hemicellulose from unbleached sulfite pulp in which the pulp was pretreated with 0.03 g of NaOH 1 h of pulp at 80°C for 1 h and with 2.5% pulp consistency. After 24 h of incubation, 12.8 mg of reducing sugar 1 g of pulp was produced, fivefold lower than the value achieved in the present work (63.4 mg of xylose 1 g of dried corncob), although different pretreatment conditions had been employed. 

As shown on Table III, the subjects fed 20 g of hemicellulose from purified psyllium fiber excreted significantly more manganese in the feces than when they were fed bread without the hemicellulose supplement. Unlike wheat bran, purified psyllium fiber (sold commercially as a bulk laxative) contains no manganese or phytates hence, any change in fecal manganese excretion when psyllium fiber is added to human diets can probably be credited to the mixture of hemicellulose comprising this product. 

Carbohydrate polymers are available in large quantities from both plant and animal sources. These include cellulose and hemicellulose from woody plants,... 

As used in this Chapter, the term non-endospermic hemicellulose refers to hemicelluloses from aerial tissues and organs (bran, cob, hull, husk, leaves, stems, and other parts), but excludes those from root tissues. The hemicelluloses associated with cereal starches and flours are collectively termed endospermic hemicelluloses. 

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