Saccharides hemicellulose

Dietary fibre consists of all components of plant cell walls not digested by human alimentary enzymes. Chemically, fibre is a mixture of cellulose, lignin, heteropoly-saccharides (hemicelluloses), acidic polysaccharides and pectin. In the colon, bacteria hydrolyse up to 15% of cellulose and 70-95% of other polysaccharides giving rise to volatile gases and low molecular weight fatty acids (acetic, butyric etc.) which have weak laxative activity. In addition the cellulosic and non-cellulosic polysaccharides are hydrophilic and absorb large amounts of fluid from the gut lumen, increasing in bulk as they do so. This is exactly the... 

In a typical hemicellulose isolation process, finely ground plant material (200 g) is treated with 5-10% sodium hydroxide in oxygen-free water at 25°C for 18-24 h (Whistler and Feather, 1965). The water-insoluble fraction, containing two subfractions differentiated by density, is extractable with higher rather than lower NaOH concentrations progressively higher concentrations of alkali extract progressively more of the dense saccharides. 

Saccharides and polysaccharides — starch and cellulose (Bqczkowicz et al., 1991), pectins (Sikora etal., 1998), and hemicelluloses (Tomasik and Zawadzki, 1998) — heated with amino acids develop scents specific for polysaccharide, amino acid, and reaction conditions. Thus, supplementation of saccharides and polysaccharides with amino acids and proteins, as well as supplementation of protein-containing products with saccharide, can be useful in generation, modification, and enrichment of flavor and aroma of foodstuffs and tobacco. 

The term lignocellulose, often used for description of plant materials, does not properly describe their main components. Besides cellulose and lignin, the third main component, as indicated above, is hemicellulose, or, more correctly, hemicel-lulosics. The plural form here reflects a set of various heteropolymeric saccharides, the so-called matrix plant polysaccharides. These hemicellulosics mainly form... 

All of the major polysaccharides in softwoods are now known these are cellulose, galactoglucomannans, arabino-(4-0-methylglucurono)xylan, ara-binogalactan, galactan, pectic material, and starch. It is clear, however, that other minor polysaccharide constituents, still unknown, must also be present. These polysaccharides have not yet been isolated, but their presence may be inferred from the formation of di- and tri-saccharides of unknown origin on partial hydrolysis of wood or crude hemicellulose preparations. 

Altered Chemicals, Hedges et al. (4) used a more refined analysis for the altered chemicals present. They analyzed for individual saccharides of the three polysaccharides (cellulose, pectin, and hemicellulose) and for the... 

The molecular structures of water-soluble and -insoluble hemicelluloses from bamboo leaves, and of a hemicellulosic D-xylan of the former, have been examined. Attached to the main D-xylan chain of all the polysaccharides are the side-chains (7)—(10) and single residues of L-arabinofuranose and D-glucopyranosyluronic acid and its 4-0-methyl ether. The polysaccharides differ in the degree of substitution of the main D-xylan chain by these mono-, di-, and tri-saccharides. 

Typical wood samples contain approximately 40 X> cellulose, and cotton is nearly 90%. Cellulose has a pseudocrystalline structure in the form of fibrils that are bonded together by the lignin and hemicellulose. Flemicellulose is also a saccharide-based biopolymer composed of subunits of glucose, galactose, mannose, and xylose, to name a few. The most coirunon subunit is the xylans, as shown in Figure 13.17. Hemicelluloses constitute approximately 25% of wood... 

Hemicellulose A saccharide-based biopolymer composed of subunits of glucose, galactose, mannose, and xylose. 

Japanese beech wood Temperature 170-290°C Residence time 30 min Pressure 20 MPa In both batch and semi-batch conversions, saccharides yield obtained from cellulose and hemicelluloses was maximum. Lu and Saka, 2010... 

The molar mass of natural cellulose is about 1.5 to 2.0 x lO g moP. The treatments performed during its extraction appreciably reduce this value. In pure cellulose, the molecular stmcture is almost perfectly regular and the percentage of irregular units is about 0.1%. In the original state, cellulose is mixed with hemicelluloses that are branched polysaccharides with saccharide units possessing various molecular structures. 

Figure 6 Structure of cellulose/consisting of glucose monomers regularly linked by 3-1,4 -glycosidic bonds. (In contrast, hemicellulose consists of varying types of saccharide monomers and has a branched structure overall see Ref. 171.)...

---