Hemi-celluloses

The filaments of all plant fibers consist of several cells. These cells form crystalline microfibrils (cellulose), which are connected together into a complete layer by amorphous lignin and hemi-cellulose. Multiple layers stick together to form multiple layer composites, filaments. A single cell is subdivided into several concentric layers, one primary and three secondary layers. Figure 5 shows a jute cell. The cell walls differ in their composition and in the orientation of the cellulose microfibrils whereby the characteristic values change from one natural fiber to another. 

Lappalainen A, Tenkanen M, Pere J (2004) In Gatenholm P, Tenkanen M (eds) Hemi-celluloses Science and Technology. ACS Symposium Series 864, p. 140... 

The thermo-gravimetric (TG) and differential thermo-gravimetric (DTG) curves of the gingko nut shell are shown in Fig. 2 where the moisture losses take place up to 200°C followed by the pyrolysis reaction. Then, the major weight loss due to the main degradation occurs at around 360°C. This zone is referred to as the active pyrolysis zone where the evolution of volatile compounds occurs during decomposition of the primary hemi-cellulose and cellulose [5]. 

Unlimited food supply (hemi-cellulose chains and other nutrients). 

It has been reported by Granichstadten and Percival189 that 3,4,6-trimethyl-D-glucose is one of the components of the mixture of methylated monosaccharides produced by methylation and hydrolysis of the hemi-cellulose fraction of Iceland moss. 

Cellu- 14.2g lose, per day hemi-cellulose or pectin Zn Lowered balances with hemicellulose (31)... 

Cellu- 10 or 20g ulose, per day hemi- cellulose or wheat bran Zn Increased fecal losses of zinc (32)... 

Lignocellulose biomass is a mixture of phenolic lignin and carbohydrates -cellulose and hemi-cellulose. It grows abundantly on earth and is largely available as agricultural and forestry residues. Lignocellulose can be converted via four major routes pyrolysis, gasification, hydrolysis and fermentation. 

Biocatalytic conversion of lignocellulose into bioethanol, which requires upgrading of existing processes of fermenting sugars by using enzymatic-enhanced pretreatment of (hemi)cellulose. New, improved biocatalysts are needed for this route. 

Table II. Monosaccharide Composition of Pectic Polysaccharides and Hemi-cellulose Obtained from Different Cell Wall Preparations...

Lymphocyte stimulation. Bran fiber hemi-cellulose, administered to rats at a dose of 10% of the diet, produced weak activity on sperm cells° . 

However, oral administration of these polysaccharides had no effect. Hemi-celluloses from different higher plants caused regression of solid Sarkoma 180 in mice but not of ascites tumor. Arabinoglucuronoxylan isolated from wheat-straw hemicellulose was completely devoid of activity, whereas arabinoglucoxylan was highly active (Nakahara 31)). 

Classically, wall polysaccharides have been separated into three fractions the pectic polysaccharides, which are extracted by hot water, ammonium oxalate solution, weak acids, or chelating agents the hemi-celluloses, which can be extracted by relatively strong alkali and the residue remaining, which is composed mainly of cellulose. Although these extraction techniques suffer from incomplete and overlapping extraction of the polymers, they are still widely used. 

Kauss (39) has shown that the esterification of the carboxyl groups in the D-galacturonic acid chain takes place by a transfer of the methyl groups from S-adenosyl-L-methionine, analogous to the case in which the 4-methyl ether groups are transferred to D-glucuronic acid of hemi-cellulose (40). 

The other carbohydrates in cane juice are the soluble polysaccharides vaguely classified under the terms "hemi-celluloses, soluble gums and pectins. It is possible that some of these polysaccharides may enter the juice during the milling of the cane as the plant cell structure is destroyed. A gummy product has been isolated from cane fiber by alkali extraction followed by alcohol precipitation. Acid hydrolysis of this substance yielded crystalline D-xylose and L-arabinose.10 Such gums in Trinidad cane juices were isolated by alcohol precipitation at suitable hydrogen ion concentration and assayed for pentose content by the Tollens 2-fural-dehyde assay the results showed an apparent pentosan content of 0.04-0.07%u of the Brix solids. 

Among the plant polysaccharides there may be mentioned the hemi-celluloses the most common of these contain 4-O-methyl-D-glucuronic acid as branch units linked to a /3-D-xylan backbone.110 The commercially important gum arabic, a soluble polysaccharide produced by Acacia trees and widely used in foods and pharmaceuticals, also contains glucuronic units.111 D-Glucuronic acid has been found in sulfated complex polysaccharides from brown algae.112... 

Organic C inputs to soils mainly consist of plant residues that all contain the same classes of organic compounds such as cellulose, hemi-cellulose, starch, proteins,... 

Di-0-methyl-D-xylose-(3 — 1) 2,3,4-tri-O-methyl-D-glucosid- Wheat-straw hemi-cellulose B a 70... 

On the basis of these approaches, the following biphasic equation can be applied to describe the amount of xylan left in the solid phase for hemi-cellulose hydrolysis ... 

All processes used for pulping have the same goal, and that is the release the fibrous cellulose from its surrounding lignin while keeping the hemi-celluloses and celluloses intact, thereby increasing the yield of useful fibers. The fibers thus obtained are naturally colored and must be bleached before they can be used for paper. 

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