Enhanced production of a thermostable xylanase from Streptomyces sp. QG-11-3 and its application in biobleaching of eucalyptus kraft pulp

• Published in: Enzyme and microbial technology 2000-10, Vol.27 (7), p.459-466
• Main Authors: Beg, Qasim Khalil, Bhushan, Bharat, Kapoor, Mukesh, Hoondal, G.S.
• Format: Article
• Language: English
• Subjects: Biobleaching; Biological and medical sciences; Biotechnology; Bleaching; Enzyme engineering; Fermentation; Fundamental and applied biological sciences. Psychology; Immobilization; Kraft pulp; Methods. Procedures. Technologies; Production of selected enzymes; Solid-state fermentation; Streptomyces; Streptomyces sp; Substrates; Thermodynamic stability; Xylanase
• ISSN: 0141-0229; 1879-0909
• DOI: 10.1016/S0141-0229(00)00231-3

A thermostable and cellulase-free xylanase has been produced from Streptomyces sp. QG-11-3 in solid substrate fermentation using wheat bran and eucalyptus kraft pulp as the prime solid substrates. The maximum xylanase yield obtained using these two substrates were 2360 U/g and 1200 U/g dry solid substrate at substrate:moisture ratios of 1:3 and 1:2.5, respectively. In immobilized cell system using polyurethane foam (PUF) and three nonwoven fabrics, namely, polyester, silk, and cotton, the xylanase yields were enhanced by 2.5-fold (203 U/ml), 1.91-fold (155 U/ml), 1.54-fold (125 U/ml), and 1.47-fold (119 U/ml), respectively, compared to the xylanase yield in liquid-batch fermentation (81 U/ml). In the biobleaching experiments, the xylanase dose of 3.5 U/g moisture free pulp exhibited the optimum bleach boosting of eucalyptus kraft pulp at pH 8.5 and 50°C after 2 h of treatment. When xylanase treated pulp was subsequently treated with 4.5% chlorine, it resulted in reduction of kappa number by 25%, enhanced the brightness (%ISO) by 20% and improved the pulp properties such as tensile strength and burst factor by up to 63% and 8%, respectively.