Hemicellulose
From Wikipedia, the free encyclopedia
A hemicellulose can be any of several heteropolymers (matrix polysaccharides) present in almost all plant cell walls along with cellulose. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength. It is easily hydrolyzed by dilute acid or base as well as myriad hemicellulase enzymes.
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[edit] Composition
Hemicellulose contains many different sugar monomers. In contrast, cellulose contains only anhydrous glucose. For instance, besides glucose, sugar monomers in hemicellulose can include xylose, mannose, galactose, rhamnose, and arabinose. Hemicelluloses contain most of the D-pentose sugars, and occasionally small amounts of L-sugars as well. Xylose is always the sugar monomer present in the largest amount, but mannuronic acid and galacturonic acid also tend to be present.
[edit] Structural comparison to cellulose
Unlike cellulose, hemicellulose (also a polysaccharide) consists of shorter chains - 500-3000 sugar units as opposed to 7,000 - 15,000 glucose molecules per polymer seen in cellulose. In addition, hemicellulose is a branched polymer, while cellulose is unbranched.
[edit] Native structure
Hemicelluloses are embedded in the cell walls of plants, sometimes in chains that form a 'ground' - they bind with pectin to cellulose to form a network of cross-linked fibres.
[edit] Applications
As percent content of hemicellulose increases in animal feed, the voluntary feed intake decreases.
Hemicelluloses include xylan, glucuronoxylan, arabinoxylan, glucomannan, and xyloglucan.
Hemicellulose is represented by the difference between neutral detergent fiber (NDF) and acid detergent fiber (ADF).
[edit] Functions
Microfibrils are cross-linked together by Hemicellulose homopolymers. Lignins assist and strengthen the attachment of Hemicelluloses to microfibrils.
