Produce Degradation Pathways and Prevention

572 Produce Degradation: Reaction Pathways and their Prevention

19.2.3 HEMICELLULOSE, PECTIN, AND OTHER INTERACTING CELL

WALL POLYMERS

Primary cell walls in plants are complex matrices where fibers are interconnected
to other polysaccharide components such as hemicellulose and pectin. The
microfibrils are usually embedded in a matrix of hemicellulose and lignin. Hemi-
cellulose is an abundant, heterogeneous group of branched polysaccharides that are
tightly bonded to the surface of cellulose microfibrils as well as to each other via
hydrogen bonding. The type of hemicelluloses present in the cell wall varies con-
siderably depending on the botanical origin and the stage of the growth cycle. All
hemicelluloses have a 14-linked linear backbone of one sugar from which short side

FIGURE 19.9Cellulose degradation model showing how cellobiohydrolases, endogluca-
nases, and β-glucosidases function together. Glucose residues are indicated by hexagons;
reducing ends are shown in black. (From Béguin, P. and Aubert, J.-P., Cellulases, in Ency-
clopedia of Microbiology, Lederberg, J., Ed., Academic Press, New York, 1992, pp. 467–477.
With permission.)