Cell walls, biodegradability

The relationship between the amount of phenolics released by NaOH and cell wall biodegradability measured by a cellulase technique has been examined with maize stem. The walls were treated. .for varying periods of time to release different... 

Lewis NG, Paice MG. Plant Cell Wall Polymers, Biogenesis and Biodegradation, American Chemical Society, Washington, DC, 1989. 

HUl, C.A.S., Forster, S., Farahani, M.R.M., Hale, M.D.C. and Williams, G. (2005). An investigation of cell wall micropore blocking as a possible mechanism for the decay resistance of anhydride modified wood. International Bio deterioration and Biodegradation, 55(1), 69-76. 

Poutanen, K. Puls, J. In Biogenesis and Biodegradation of Plant Cell Wall Polymers, Lewis, G. Paice, M., Eds. American Chemical Society Washington, D.C., 1989 pp 630-640. 

To use organic molecules as a food source, microorganisms have to be able to take up the substance and metabolize it within their cells. A prerequisite is that the molecules are water-soluble and that they are small enough to pass through the cell walls and membranes of the microorganism. Polymers are typically not water-soluble and, by definition, are not small molecules [4]. Therefore, the biodegradation of polymers typically needs to follow four distinct steps. 

Plant cell walls are complex, heterogeneous structures composed mainly of polymers, such as cellulose, hemicelluloses, and lignins. In spite of several decades of research, cell wall assembly and the biosynthesis and ultimate biodegradative pathways of individual polymers are still far from being fully understood. One simple example will suffice Even today, no enzyme capable of catalyzing cellulose formation in vitro has been obtained. 

The nature and amounts of low molecular weight phenolic constituents in cell walls of graminaceous plants (grasses and cereals) are reviewed and relationships discussed between these constituents and wall biodegradability. The formation in cell walls of 4,4 -dihydroxy-truxillic acid and other cyclodimers of p-coumaric and ferulic acid is suggested as an important mechanism for limiting the biodegradability of wall polysaccharides. 

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. 

In recent years, positive relationships have been found between phenolic constituents of cell walls liberated by alkali and biodegradability of the... 

For example, when cell walls of maize stem were treated with sodium hydroxide (0.1M) at 20°C for various times to release different amounts of phenolics, a highly significant correlation (r = 0.98) was found between the amount of phenolics released and wall biodegradability (measured by cellulase ) (5). It is of interest to note that alkali treatment of poor quality graminaceous forages (e.g., cereal straw) is used commercially to increase their biodegradability, and thus their feed value for the animal (1). 

It has been proposed that dehydrodiferulic acid units are formed by enzymic dehydrogenation of two ferulic acid units ester-linked to the cell wall (15). As can be seen from Table I, only very small amounts of the acid were found in cell walls it seems unlikely that such amounts are sufficient to have a large effect on limiting the biodegradation of the walls. 

Saka, S. Goring, D. A. I. Localization of Lignins in Wood Cell Walls In Biosynthesis and Biodegradation of Wood Components Higuchi, T., Ed. Academic Press New York, 1985 pp. 51-62. 

Plant polymers—Synthesis—Congresses. 2. Plant polymers—Biodegradation—Congresses. 3. Plant Cell Walls—Congresses. 

Hartley, R. D., Morrison, W. H., Bomeman, W. S., Rigsby, L. L., O Neill, M., Hanna, W. W., and Akin, D. E., 1992, Phenolic constituents of cell wall types of normal and brown midrib mutants of pearl millet (Pennisetum glaucum (L.) R. Br.) in relation to wall biodegradability,... 

There is also US research interest in using pectin in polymer applications. Pectin is a complex plant cell wall heteropolysaccharide (based on galactose, rhamnose, arabinose and xylose) that can be blended with synthetic polyvinyl alcohol (PVA) to produce biodegradable polymers with a wider range of properties than those of starch-based polymers alone. The new pectin/PVA biodegradable polymer should be capable of replacing conventional PVA applications in blow-moulded, extruded, film and injection-moulded applications. 

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