|Minor, James - USDA FOREST SERVICE|
Submitted to: Polymeric Materials Encyclopedia
Publication Type: Book / Chapter
Publication Acceptance Date: August 15, 1995
Publication Date: N/A
Technical Abstract: Hemicelluloses are a diverse class of plant polysaccharides found in close physical association with cellulose, but unrelated chemically to cellulose. The name was originally proposed for those polysaccharides which could be extracted from plants with aqueous alkali, but now includes all non-cellulosic cell wall structural polysaccharides of land plants. Understanding compositional and structural features of individual polysaccharides provides more information on physical and chemical properties and a more refined classification scheme that may be exploited for specific product needs. Plant biosynthesis of structural polysaccharides is a complex metabolic process that cannot be economically duplicated in the laboratory. The more complicated the polysaccharide (types of monosaccharides or linkages), the more complex the biosynthetic apparatus within the plant. Utilization of these complex polysaccharides requires extraction from plant walls followed by fractionation into functionally similar groups. Wall preparation methods must have common features of inactivation of hydrolytic enzymes, particle size reduction, and removal of cytoplasmic contaminants. Major uses of hemicelluloses include feedstocks for the production of sugars which can then be converted to other products (e.g., xylitol, fuel alcohol from fermentable sugars), food additives, and sustained release compositions for delivery of specific molecules (pharmaceutical tablets). Oxidation products of hemicelluloses may be used as additives to surface active detergents or cleaning agents. New uses are being developed as methods for isolation and fractionation improve to give more refined compositional groups that would have more uniform properties.