Effects of Lignification, Cellulose Crystallinity and Enzyme Accessible Space on the Digestibility of Plant Cell Wall Carbohydrates by the Ruminant

Intrinsic characteristics of plant cell walls limiting susceptibility of structural carbohydrates to microbial attack in the ruminant's gastrointestinal tract are lignification of the cell wall, covalent bonding of phenolic acids to cell wall polysaccharides, the crystalline structure of cellulose and li mited fibrolytic enzyme accessible space. The exact mechanism by which or degree to which each of these characteristics affect rate and/or extent of cell wall polysaccharide hydrolysis by gastrointestinal tract microbes is not well unders tood. Lignification and limited e n zyme accessible space probably affect the extent of cell wall degradation by preventing contact between microbial enzymes and cell wall polysaccharides. Phenolic acids may limit cell wall carbohydrate degradation by s teric hindrance of the fihrolytic e n zyme, which could affect both rate and extent of degradation, and by their potentially toxic effects on microbes. Crystalline cellulose, occurring in secondary cell walls, may be degraded at a slower rate than amorphous cellulose . Further research is needed to gain a better understanding of the mechanisms by which these characteristics limit structural polysaccharide degradation by gastrointes tinal tract microbes and to determine to what degree each contributes to limiting digestibility of cell wall carbohydrates by ruminants . Initial paper received May 25, 1987 Manuscript received February 01, 1988 Direct inquiries to M.S. Kerley Telephone number: 314 882 0834