Hemicellulose enzymic degradation

The plant cell wall is a polymeric mesh consisting of cellulose, hemicellulose, pectin and protein. Cellulose and hemicellulose are integral components of the cell wall, but pectic substances are located mainly in the outer wall regions within the middle lamella (McNeil et ai, 1984). Pectic substances are more susceptible to enzymatic degradation, because they are more exposed than other cell wall components. Therefore, pectin-degrading enzymes may play a central role in the penetration of plant tissue by bacteria. 

Further research is directed to the determination of the fine-structure of the pectins and hemicelluloses isolated from soy meal, using chromatography and degradation with specific enzymes. With these results a model of the polysaccharides present in the cell wall of soy will be formulated. Furthermore, application directed experiments will be performed to obtain information about structure-function relationships. 

Enzymes should be added to the feed together with the pre-mix. Granulated enzyme products may readily be mixed with feed components, as they are based on normal feed components such as wheat or soy grits. A wide range of enzyme products are available. Enzyme products should contain specific enzyme activities necessary to degrade specific substances such as glucans, starch, protein, pectin-like polysaccharides, phytic acid, raffinose, stachyose, hemicellulose, and cellulose. 

The foregoing observations confirm the conclusions derived from former experiments with beechwood holocellulose (10) (1) A partial degradation of the hemicelluloses is imperative before the cellulose fibrils can be attacked. (2) The hemicelluloses seem to be deposited between the cellulose fibrils or even to be encrusting them. (3) The enzymatic hydrolysis of the cellulose is governed by the porosity of the tissue (enzyme diffusion), the impediment of the hemicelluloses, and the properties of the cellulose (e.g., crystallinity). 

The hemicellulose-degrading enzymes (Ultraflo L) and the cellulases (Celluclast 1.5L) were kindly donated by Novozymes A/S. Celluclast 1.5L had a filter paper activity of 80 filter paper units/mL, determined according to the procedure of Mandels (8-9). For the present study the most important side activities of Ultraflo L were endo-l,4-P-xylanase, P-xylo-sidase, and a-arabinofuranosidase (10). 

The complete degradation of hemicellulose becomes more complex than that of cellulase, since substituent-hydrolyzing activities are also necessary. With heteroxylans, apart from endo-l,4- 3-xylanase, which catalyzes the hydrolysis of internal 3-l,4-xylan links and P-xylosidase, which catalyzes the hydrolysis of xylooligossacharides, mainly xylobiose into xylose, other enzymes must act to accomplish complete hydrolysis, such as acetyl xylan esterase, a-glucuronidase, and a-L-arabinofuranosidase (1). 

Lignin is the third most abundant structural polymeric material found in plant cell walls typically comprising up to 20-30% of woody biomass, from which most lignin is sourced as a by-product of papermaking. Lignin binds hemicellulose and cellulose together in plant cell walls and shields them from enzymic and chemical degradation. 

---