Cell wall constituents digestibility

An understanding of relationships between cell wall constituents and wall biodegradation is of particular importance to the economics of animal production since low digestibility of forages is associated with reduced intake. Such an understanding is also important in elucidating the role of fiber in human nutrition and of the decomposition of organic matter in soil. 

Table II. Digestibility of Cell Wall Constituents in Various Plant Materials...

When relationships could be determined, components of nutritional value, such as the in vivo digestibility of the organic matter, were calculated by regression so that they corresponded with the average values of chemical characteristics given in the table. Many of these equations use cell wall constituents (crude fibre, NDF, ADF or ADL) as predictors, but other parameters were... 

For pigs, ruminants, rabbits and horses, the prediction of the digestibility of energy (Ed) or organic matter (OMd) is, in most cases, based on the cell wall constituents. The relationships obtained for each species differ, as illustrated in figure 2. Therefore, it was necessary to develop specific tables. 

Although man has long known about some of the beneficial and harmful effects of roughage in the digestive tract, evidence which suggests that there may be other important physiological actions of cell wall constituents has been found recently. It has even been suggested that fiber may soon be classified as an essential nutrient. Discussions of some of these effects follow. 

Buxton DR, Russell JR. 1988. Lignin constituents and cell wall digestibility of grass and legume stems. Crop Sci 28 553-558. 

Cell walls are biochemically rather inert with reduced digestibility to many organisms because of their complex cellulose, pectin, and lignin molecules. Callose and lignin are often accumulated at the site of infection or wounding (6,7) and form a penetration barrier. Synthesis of inhibitory proteins (e.g., lectins, protease inhibitors) or enzymes (e.g., chitinase, lysozyme, hydrolases, nucleases) that could degrade microbial cell walls or other microbial constituents would be protective, as well as synthesis of peroxidase and phe-nolase, which could help inactivate phytotoxins produced by many bacteria and fungi. These proteins are either stored in the vacuole... 

Non-starch polysaccharides (NSP) Plant cell-wall NSP Other NSP Many different types of polysaccharides Main constituents arabinose, xylose, mannose, galactose, glucose, uronic acids Many types of constituents Escape digestion in the small intestine and are fermented to different extents Encapsulate and slow absorption of nutrients. Good marker for naturally fiber-rich diets for which health benefits have been shown Food additives. Minor components of the human diet. The amounts added to foods are known and regulated... 

Cellulose is the main constituent of plant cell walls, where it usually occurs together with hemi-celluloses, pectin and lignin. Since cellulase enzymes are absent in the human digestive tract, cellulose, together with some other inert polysaccharides, constitute the indigestible carbohydrate of plant food (vegetables, fruits or cereals), referred to as dietary fiber. Cellulases are also absent in the digestive tract of animals, but herbivorous an-... 

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