title: Bleach boosting effect of xylanase A from Bacillus halodurans C-125 in ECF bleaching of wheat straw pulp.
abstract: Past studies have revealed major difficulties in applications of xylanase in the pulp and paper industry as enzymes isolated from many different species could not tolerate high temperatures or highly alkaline conditions. The thermostable xylanase A from Bacillus halodurans C-125 (C-125 xylanase A) was successfully cloned and expressed in Pichia pastoris with a yield as high as 3361 U/mL in a 2 L reactor. Its thermophilic and basophilic properties (optimal activity at 70 °C and pH 9.0), together with the fact it is cellulase-free, render this enzyme attractive for compatible applications in the pulp and paper industry. The pretreatment of wheat straw pulp with C-125 xylanase A at pH 9.0 and 70 °C for 90 min induced the release of both chromophores (Ab(237), Ab(254), Ab(280)) and hydrophobic compounds (Ab(465)) into the filtrate as well as sugar degradation. Moreover, the addition of 10 U xylanase to 1 g wheat straw pulp (dry weight) as pretreatment improved brightness by 5.2% ISO and decreased the kappa number by 5.0% when followed by hydrogen peroxide bleaching. In addition, compared with two commercial enzymes, Pulpzyme HC and AU-PE89, which are normally incorporated in ECF bleaching of wheat straw pulp, C-125 xylanase A proved to be more effective in enhancing brightness as well as preserving paper strength properties. When evaluating the physical properties of pulp samples, such as tensile index, tearing index, bursting index, and post-color (PC) number, the enzymes involved in pretreating pulps exhibited better or the same performances as chemical treatment. Compared with chemical bleaching, chlorine consumption can be significantly reduced by 10% for xylanase-pretreated wheat straw pulp while maintaining the brightness together with the kappa number at the same level. Scanning electron microscopy revealed significant surface modification of enzyme-pretreated pulp fibers with no marked fiber disruptions.
authors.affiliation: Guangdong Key Laboratory of Fermentation and Enzyme Engineering, School of Bioscience and Bioengineering, South China University of Technology, Guangzhou 510006, PR China.
authors.forename: Xiao-qiong
authors.initials: XQ
authors.lastname: Lin
authors.forename: Shuang-yan
authors.initials: SY
authors.lastname: Han
authors.forename: Na
authors.initials: N
authors.lastname: Zhang
authors.forename: Hui
authors.initials: H
authors.lastname: Hu
authors.forename: Sui-ping
authors.initials: SP
authors.lastname: Zheng
authors.forename: Yan-rui
authors.initials: YR
authors.lastname: Ye
authors.forename: Ying
authors.initials: Y
authors.lastname: Lin
mesh_terms: D001407:Bacillus / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D019149:Bioreactors; D057886:Bleaching Agents / Q000494:pharmacology*; D003001:Cloning, Molecular; D003116:Color; D043364:Endo-1,4-beta Xylanases / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008855:Microscopy, Electron, Scanning; D010209:Paper; D010843:Pichia; D018547:Plant Stems / Q000187:drug effects* / Q000648:ultrastructure; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D013718:Tensile Strength; D014908:Triticum
chemical_list: D001426:Bacterial Proteins; D057886:Bleaching Agents; D011994:Recombinant Proteins; D006861:Hydrogen Peroxide; D043364:Endo-1,4-beta Xylanases