Hemicelluloses from natural sources

As I have already indicated, the polymeric carbohydrate materials available from natural sources include gums, starch and dextrins, cellulose, hemicellulose, chitin, and bacterial polysaccharides. 

NATURAL SOURCES Wood (coniferous, deciduous), bamboo, cotton, hemp, straw, jute, flax, reed, sisal. Cellulose is isolated from the plant cell walls and is never in a pure form in nature. Always associated with lignin and hemicellulose. ... 

Specifically, some hemicelluloses from plants and higher plants are a potential source of industrial polysaccharides. The pharmaceutical industry has benefitted from such diversity of biomaterials and has exploited the use of natural products as sources of both drugs and excipients. One example of a promising biomaterial for pharmaceutical use is xylan, a hemicellulose largely found in nature and considered the second most abundant polysaccharide after cellulose [41, 43]. Melo et al. [31] have reported research on the activity of antioxidant, antimicroba, and anticoagulant from corn cobs xylan. 

Cellulose is found in nature in combination with various other substances, the nature and composition of which depend on the source and previous history of the sample. In most plants, there are three major components cellulose, hemicelluloses, and lignin. Efficient utilization of all three components would greatly help the economics of any scheme to obtain fuel from biomass. Hemicelluloses, lignocellulose and lignin remaining after enzymatic degradation of the cellulose in wood would require chemical or thermal treatment - as distinct from biochemical - to produce a liquid fuel. 

Cellulosic materials are quite variable from source to source, not only in cellulose, hemicellulose, and lignin content but also in the crystallinity of the cellulose. As a consequence, each natural substrate would be expected to have its own unique set of process conditions to optimize glucose yield and minimize secondary product contamination. The next section on kinetics of acid hydrolysis will examine this point. 

This chapter gives a general introduction to the book and describes briefly the context for which the editors established its contents and explains why certain topics were excluded from it. It covers the main raw materials based on vegetable resources, namely (i) wood and its main components cellulose, lignin, hemicelluloses, tannins, rosins and terpenes, as well as species-speciflc constituents, like natural rubber and suberin and (ii) annual plants as sources of starch, vegetable oils, hemicelluloses, mono and disaccharides and algae. Then, the main animal biomass constituents are briefly described, with particular emphasis on chitin, chitosan, proteins and cellulose whiskers from molluscs. Finally, bacterial polymers such as poly(hydroxyalkanoates) and bacterial cellulose are evoked. For each relevant renewable source, this survey alerts the reader to the corresponding chapter in the book. 

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