Cellulose lignin digests

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... 

Cellulose is the most abundant polymer constituting the cell walls of all plants. Oven-dried cotton consists of lignin and polysaccharides in addition to 90% cellulose. On digesting it under pressure and a temperature of 130-180°C in 5-10% NaOH solution, all impurities are removed. The residual a-cellulose has the following structure ... 

Historically, dietary fiber referred to iasoluble plant cell wall material, primarily polysaccharides, not digested by the endogenous enzymes of the human digestive tract. This definition has been extended to iaclude other nondigestible polysaccharides, from plants and other sources, that are iacorporated iato processed foods. Cellulose [9004-34-6] (qv) is fibrous however, lignin [9005-53-2] (qv) and many other polysaccharides ia food do not have fiberlike stmctures (see also Carbohydrates). 

Consid - the Kraft pulping process shown in Fig. 8.8 (Dunn and El-Halwa, 1993). The first step in the process is digestion in which wood chips, containing primarily lignin, cellulose, and hemicellulose, are cooked" in white liquor (NaOH, Na2S, Na2C03 and... 

Climatic conditions, age, and the digestion process influence not only the structure of fibers but also the chemical composition. Mean values of components of plant fibers are shown in Table 4. With the exception of cotton, the components of natural fibers are cellulose, hemi-cellu-lose, lignin, pectin, waxes, and water-soluble substances. 

Fourth lesson - combination of different compounds in unique macrostructure provides unique performance properties. Starch is used extensively in nature to store carbon and energy. Starch is readily digested and must be protected from degradation by a resistant coating, for example, a seed (e.g. com, wheat or rice) or a skin (e.g. potato). Woody materials such as trees, soft plants and grasses are composed of a complex combination of aliphatic and aromatic compounds (cellulose, hemicellulose and lignin). 

The cellulosic residue used in these experiments is advantageous for acid hydrolysis compared to untreated wood. The cellulosic residue is finely divided, and of higher density than wood chips, 0.5 g/ml compared to 0.36, and has a very low lignin content. As a result, the output of fermentable sugars for a given size of digester will be about twice that obtainable with chips. 

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