Thermostable and alkali-tolerant xylanases for industrial applications
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Xylanase is the key enzyme to degrade xylan that is a major component of hemicellulose. The enzyme has potential industrial applications in the food, feed, paper and flax degumming industries. The use of xylanases becomes more and more important in the paper industry for bleaching purposes. Xylanases used in the pulp bleaching process should be stable and active at high temperature and alkaline pH. Thermophilic and alkalophilic xylanases could be obtained by screening the wild type xylanases or engineering the mesophilic and neutral enzymes. In this paper, we reviewed recent progress of screening of the thermophilic and alkalophilic xylanases, molecular mechanism of thermal and alkaline adaptation and molecular engineering. Future research prospective was also discussed.
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Xylan,a kind of poly-pentose,is one of the main compositions of hemicellulose.It exists in various plant resources widely.The present situations and the research advance in the induction of xylanase,the fermentation of xylanase,the properties of xylanase,the construction of xylanase,the determination methods of enzyme activity of xylanase and the gene engineering of xylanase were introduced in this paper.
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Thermostable cellulase and xylanase have potential applications in food, animal feed and chemical industries. A major endoglucanase (Endo-I), a major β-glucosidase (β-Glu-I), two major exoglucanases (Exo-HA and Exo-LA) and a major xylanase (Xln-I) were purified and characterised from the thermophilic fungus, Thermoascus aurantiacus. Endo-I, Exo-HA and Exo-LA were optimally active at 70°C, at pH 3.5 and between pH 4.4-5.2 respectively, whereas β-Glu-I and Xln-I showed optimal activity at 80°C and between pH 4.0-5.0. All five enzymes showed remarkable stability up to 60°C and between pH 4.0-6.0 for several hours. β-Glu-I was specific for β-linked glycosides, disaccharides and oligosaccharides. The Endo-I, Exo-HA and Exo-LA were specific for oligosaccharides and polysaccharides with β(1→4) glycosidic bonds. The Xln-I showed higher affinity towards substituted xylans and was active towards xylo-oligosaccharides (Xyln). β-Glu-I cleaved one glucose unit at a time from the non-reducing end of 4-nitrophenyl cello-oligosaccharides (4-NPGlcn). Endo-I hydrolysed Glcn, 4-methylumbelliferyl cello-oligosaccharides (MeUmbGlcn), carboxymethyl cellulose (CM-cellulose) and H3PO4-swollen cellulose in a random fashion. The Exo-HA and Exo-LA preferentially attacked the second glycosidic bond adjacent to 4-methylumbelliferone (MeUmb) of MeUmbGlcn. Xln-I cleaved xylans and Xyln in an endo-fashion. β-Glu-I and Xln-I from T. aurantiacus catalysed the synthesis of various alkyl- and aryl-glycosides. These results and the potential industrial applications of all five enzymes from T. aurantiacus are discussed.
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Xylanase(E.C.3.2.1.8) was related to a class of enzymes which breakdown the linear polysaccharide β-1,4-xylan into xylose,xylobiose,or xylotriose.To date,more and more studies focused on xylanases meeting industry application.Glycoside hydrolase families that contained xylanases were reviewed,as well as each member's characteristics of catalyzation.Also,the application of xylanase in baking industry was discussed.
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Xylan is one of the component of hemicellulose,exises in various plant resources. xylanase belongs to a hydrolytic enzyme of the xylan,application of the xylanase in the industry of the food ,feed and paper making are very wide. This paper is about the range, trait and principium of the application of the xylanase in food.
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Enzymatic Hydrolysis
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Xylanase enzyme is an extracellular enzyme that has the ability to hydrolyze xylan to xylose.Xylanase can be produced by thermophilic bacteria and is a natural xylanase that is active and stable at high temperatures and alkaline pH, so it has the potential to be used in industrial and biotechnology fields.One industry that utilizes xylanase enzymes is the pulp and paper industry.At present, the pulp bleaching process carried out in Indonesia consists of a bleaching process using chlorine or hydrogen peroxide.The substitution of the use of chlorine with xylanase enzymes is a worthy alternative to reduce the impact caused by the use of chlorine in the pulp bleaching process.This study aims to determine the potential of thermophilic bacterial xylanase enzymes on the brightness of the pulp, and determine the brightness of the pulp at variations in temperature and pH on pulp fermentation.The pulp is fermented with temperature variations (50ºC, 55ºC, 60ºC, 65ºC, 70ºC, 75ºC, 80ºC) and pH (7; 7.5; 8; 8.5; 9; 9.5; 10).The optimum temperature and pH that produces the lowest kappa number and highest enzyme activity is at 60ºC and pH 8.5.
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