Xylan purification

The ubiquity of lignin in plant tissue presents an obstacle to the removal and purification of xylan. Lignin retards or prevents the complete solution of xylan either because of mechanical obstruction or perhaps by reason of attachment through as yet unidentified covalent bonds. Furthermore, lignin is partially soluble in the various aqueous alkaline solutions used for dissolving xylan and, consequently, poses a purification problem in various subsequent steps designed to isolate the pure polysaccharide. 

Many substances besides xylan may be extracted from plant material and, hence, if this polysaccharide alone is desired one or preferably more purification steps must be employed. 

For further purification, the xylan can be dissolved in dilute alkali... 

Pure xylan is not employed in industry. but crude xylan or pentosans are of industrial importance. Xylan has been proposed as a textile size but is not employed as yet for this purpose.130 Perhaps the largest use of pentosans is in their conversion to furfural, which has many applications and serves as the source of other furan derivatives. At the present time, large quantities of furfural are used in the extractive purification of petroleum products, and recently a large plant has been constructed to convert furfural by a series of reactions to adipic acid and hexamethylene-diamine, basic ingredients in the synthesis of nylon. In commercial furfural manufacture, rough ground corn cobs are subjected to steam distillation in the presence of hydrochloric acid. As mentioned above, direct preferential hydrolysis of the pentosan in cobs or other pentosan-bearing products could be used for the commercial manufacture of D-xylose. 

Dupont, C., Daigneault, N., Shareck, F., Morosoli, R., and Kluepfel, D., Purification and characterization of an acetyl xylan esterase produced by Streptomyces lividans. Biochem J1996, 319 (Pt 3), 881-6. 

Ratanakhanokchai, K., Kyu, K. L., and Tanticharoen, M., Purification and properties of a xylan-binding endoxylanase from alkaliphilic bacillus sp. Strain K-l. Appl Environ Microbiol 1999, 65 (2), 694-7. 

Fehling solution forms insoluble complexes with some mannans and xylans, and has been used for their purification. Erskine and Jones have recommended the use of cupric acetate and ethanol for this purpose. Fruc-tans can be precipitated with calcium or barium hydroxide, and it has been shown that mannans with the 2,3-cfs- and galactans with the 3,4-cis-glycol grouping unsubstituted are almost completely precipitated by barium hydroxide. ... 

The (1 - 3)-/3-D-xylanase from Chaetomium globosum142 was purified by several fractionation steps employing ammonium sulfate and acetone, and the purified preparation resulting was shown to be free from a-amylase, cellulase, and (1 — 4)-/3-D-xylanase activities, and to have undergone a 106-fold purification. Whether this preparation was homogeneous was not indicated, but it has been used in study of mode of action on (1 — 3)-j8-D-xylan. 

For isolation of hardwood xylans by way of holocellulose, a choice has to be made between the different methods available, according to the objectives to be attained. If molecular properties are to be investigated, the modified chlorine-2-aminoethanol method and, possibly, also the method of Klauditz are suitable. For chemical studies, especially if the location of the 0-acetyl groups is to be established, only chlorine dioxide or chlorous acid can be used. The subsequent extraction of the holocellulose will also have to be adapted to the desired ends. For isolation of a pure (4-0-methylglucurono)xylan, aqueous potassium hydroxide is excellent, since it gives almost quantitative yields and seldom causes removal of the gluco-mannan. If necessary, further purification can be effected by precipitation with Fehling solution. - ... 

One of the first polymers to be obtained in the form of single crystals was a xylan from wood of white birch reported by Yundt in 1949. The crude xylan was purified by heating in boiling 0.2% oxalic acid solution, to give a highly swollen, water-insoluble fraction in a yield of 7.4% of the wood. Further purification was effected by autoclaving in water at 120° and... 

It is noteworthy that, in all those cases where L-arabinose residues have been reported to be few or absent, the yield of the xylan was only 1% or less (see Table XII). These preparations can scarcely be deemed representative of the entire xylan portion of the wood, but have to be regarded as fractions, modified to an unknown extent during lengthy processes of isolation and purification. Use of hydrochloric acid for destroying the... 

The glucomannans obtained in this way are usually pure enough for structural investigations. Minor proportions of a contaminating xylan are readily removed by one or two purifications by way of the insoluble complex of the glucomannan with barium hydroxide. The copper complex may also be used for this purpose. i - ... 

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