Abstract

Hemicellulose, a poorly utilized component of arborescent plants, is a complex mixture of polysaccharides, each exhibiting polydispersity, polymolecularity, and polydiversity to varying extents. Hemicellulose is defined in this article as the noncellulosic polysaccharides that make up the cell wall structure of vegetable material, but other definitions based on solvent behavior also occur in the literature. The most common polysaccharides included in all definitions are xylans, arabinogalactans, and pectic materials of varying compositions found in gymnosperms and angiosperms, glucomannans found in gymnosperms and dicotyledons but seldom, if at all in monocotyledons, and -D-glucans found only in monocotyledons. Xylans and glucomannans are the primary hemicellulose components of fibers and tracheids of arborescent plants, but other unique hemicellulose components may occur in significant quantities in other parts of the plant. The intimate association of hemicellulose with lignin and cellulose makes it difficult to isolate without unwanted degradation. Some mixtures of hemicellulose components cannot be separated in a quantitative manner. The utilization of hemicellulose components is complicated by their complexity and because of the transformations that they have undergone in many manufactured products. They affect the products in which they are present, being harmful in dissolving pulps and a mixed blessing in paper products, and are generally a beneficial components of foods.