Xylan occurrence

Occurrence. D-Xylose (10) is present in widely abundant polysaccharides of plant tissues. Xylan is the main carbohydrate found in the hemicellulosic fraction, and accounts for one third of all renewable organic carbon available on earth. The structure and composition of xylans are variable, from linear (3-(l->4)-linked xylose chains to highly branched heteropolysaccharides. The branches may involve short oligosaccharides, usually of L-arabinofuranosyl units. Xyloglucans are also important hemicellulose polysaccharides consisting of a backbone of ( I — 4)-(i-D-glucopyranosyl residues heavily substituted with a-D-Xylp. Other monosaccharides may also be present.44... 

In summary, there seems to be little doubt that the major proportion of the D-xylose residues in the wood of gymnosperms originates from an arabino-(4-0-methylglucurono)xylan. The simultaneous occurrence of a minor proportion of (4-0-methylglucurono)xylan, albeit not very likely, cannot at present be entirely discounted. 

The data presented in this work regarding xylanase production by B. circulans D1 point out the presence of a constitutive xylanase, produced in media with different carbon sources, besides xylan. In many of the reports regarding xylanase production, there is the occurrence of constitutive enzymes [23-26],... 

In recent ten years, xylans and mannans have been studied as potential raw materials for biodegradable films. Sometimes they are blended with other polymers or mixed with nanoparticles to achieve enhanced properties. This chapter covers the occurrence, structure and properties of xylans and mannans as well as recent smdies on xylan- and mannan-based blends, composites, and nanocomposites. 

M. A. Coimbra, N.M. Rigby, R.R. Selvendran, K.W. Waldron. Investigation of the occurrence of xylan-xyloglucan complexes in the cell walls of Olive pulp Olea ewopaea). Carhohydr Polymers, 1995, 27, 277-284... 

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