Sources and Structure of Hemicellulose

Hemicellulose is a group of polysaccharides that can be found in the plant s cell wall that surrounds the cellulose, protein, lignin, and other materials that covalently bonded, hydrogen bonds, ionic bonds and interactions hydrophoby [35]. In plants, hemicellulose is a second polymer after cellulose that abundance in wood and cereals. It consists of approximately one-quarter to one-third of the plant material. This amount varies according to the type of plants, such as corn steins [28.0%], wheat straw [38.8%), rice straw [35.8%), and rye straw [36.9%). Hemicellulose serves as a supporter to cell wall and as an adhesive between single cells In plants [10]. 

These polysaccharides are one of the renewable resources that are most widely found in nature. These polymers present in plants together with cellulose and lignin. Hemicellulose is different from other celluloses in terms of the monomer composition, and has a long chain and molecular chain branching. The content of these compounds differ from species to species [9,10]. 

Chemical and thermal stability of hemicellulose is generally lower than other celluloses, due to the lack of crystallinity and the lower degree of polymerization. This compound is very easily hydrolyzed, especially in the presence of hydroxyl groups on each unit of the chain. The results of hydrolysis include glucose, xylose, mannose, galactose, arabinose, glucuronic acid, and mannuronic acid in different amounts [9]. 

Hemicelluloses are heteropolysaccharides. Their structure and polymeric properties vary depending on the origin, i.e., plant species, industrial processing, isolation and purification procedure. They are a heterogeneous group of polysaccharides. The term was coined at a time when the structures were not well understood and biosynthesis was completely unknown [6]. 

Hemicelluloses have relatively low molar mass compared with other wood polymers. The degree of polymerization of hemicelluloses is around 80-200. The general units of hemicelluloses are pentosans and hexosans. Their general formulas are (CsHgOJn and [CgHioOsin, respectively. Hemicellulose does not have a repeated structure. There are many variations in the structure that are not well known. The detailed structure of the hemicelluloses and their abundance vary. 

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