Endoxylanase action towards the improvement of recycled fibre properties

The nature of recycled paper fibres varies widely. Those fibres contain high amounts of heteroxylans and lignin besides cellulose. In order to study the potential effect of xylanases on the quality of recycled fibres, chemithermomechanical pulp fibres (CTMP) are used as model substrates owing to their high content in non-cellulosic components. It has been found that the morphology of CTMP fibres changes by means of xylanase treatment. Treatments of CTMP fibres with an endoxylanase result in an improved surface area of the fibres by fibrillation, without shortening the fibres. The chemical composition of the surfaces of the fibres changes and an augment in surface hydrophilicity as a result of the removal of lignin and extractives associated to the xylan backbones is observed. Experimental results are in agreement with the findings when studying the chemical composition of the fibres’ surfaces: the xylan backbone is removed by the action of the endoxylanase, resulting in fibre fibrillation; further hydrolysis of released xylan chains proceeds in the bulk down to the monomer xylose.     

Specificity and mode of action of a thermostable xylanase from bacillus amyloliquefaciens on-line monitoring of hydrolysis products

A thermostable xylanase purified from a strain of Bacillus amyloliquefaciens MIR 32 was characterized with respect to its substrate specificity and mode of hydrolytic action. The enzyme was highly specific for xylans as substrate and displayed no activity toward other polysaccharides, including cellulose. The enzyme exhibited K_m and V_max of 4.5 mg/mL and 0.58 mmol/min/mg, respectively, with birchwood xylan as the substrate. Microdialysis sampling with anion exchange chromatography and integrated pulsed electrochemical detection were used for rapid on-line monitoring of products during hydrolysis of oat spelt and bagasse xylan, and xylooligosaccharides. Xylobiose and xylotriose were the main end products. Xylotetraose was the smallest oligosaccharide to be acted on by the xylanase. The product pattern confirmed that the enzyme was an endoxylanase.     

Extraction and characterization of native heteroxylans from delignified corn stover and aspen

Dimethylsulfoxide-solubilized polysaccharides from delignified corn stover and aspen were characterized. The biomass was delignified by two different techniques; a standard acid chlorite and a pulp and paper QPD technique comprising chelation (Q), peroxide (P), and acid-chlorite (D). Major polysaccharides in all fractions were diversely substituted xylan. Xylan acetylation was intact after chlorite delignification and, as expected, xylan from QPD-delignified fraction was de-acetylated by the alkaline peroxide step. The study of DMSO-extractable xylans from chlorite-delignified biomass revealed major differences in native acetylation patterns between corn stover and aspen xylan. Xylan from cell walls of corn stover contains 2-O- and 3-O-mono-acetylated xylan and [MeGlcA-α-(1 → 2)][3-OAc]-xylp units. In addition, aspen xylan also contains 2,3-di-O-acetylated xylose. 1,4-β-d-xylp residues substituted with MeGlcA at O-2 position are absent in chlorite-delignified aspen xylan. Sugar composition in accord with NMR-spectroscopic data indicated that corn stover xylan is arabinosylated while aspen xylan is not. We have shown that corn stover xylan has similar structure with xylans from other plants of Poales order. No evidence was found to indicate the presence of 1,4-β-d-[MeGlcA-α-(1 → 2)][Ara-α-(1 → 3)]-xylp in corn stover xylan fractions.