Published in Scientific Bulletin. Series F. Biotechnologies, Vol. XX
Written by Aglaia BURLACU, Călina Petruța CORNEA, Florentina ISRAEL-ROMING
Xylan is the major constituent of hemicellulose, the second most abundant natural polymer on earth. There are four main categories of xylans: arabinoxylans, glucuronoxylans, glucurono arabinoxylans and galacto glucurono arabinoxylans. The side chains of each xylan are being responsible for the solubility, physical conformation and reactivity of the xylan molecule with other components of the hemicellulose and therefore, influencing the mode and extent of enzymatic cleavage. Xylanases, as glycoside hydrolase members, are able to catalyse the hydrolysis of xylan, by breaking the β-1,4-glycoside linkages, in order to produce simpler compounds such as xylose. Because of the heterogeneity and complex chemical nature of xylan, the complete breakdown requires the action of several hydrolytic enzymes that are different considering their structure, the substrate specificities, their mode of action or biochemical properties. Many degrading microorganisms produce xylanases such as fungi (Aspergillus spp., Trichoderma spp.), bacteria (Bacillus spp., Streptomyces spp.), yeast (Cryptococcus spp.), marine algae etc. Depending on the source, microbial xylanases have different characteristics, that makes them useful for an application or another. Worldwide, the market of xylanases has expanded rapidly because of its potential in industrial use, especially in the biotechnological applications. In this review, are presented the significant aspects concerning the complete hydrolysis of xylan, and therefore of hemicellulose.
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