Thermostable and alkaline-tolerant microbial cellulase-free xylanases produced from agricultural wastes and the properties required for use in pulp bleaching bioprocesses: a review

The number of possible applications of microbial xylanases in the pulp and paper industry is gradually increasing and several are approaching commercial use. However, the properties of commercial xylanases make them unsuitable for the real process of pulp bleaching. This industry needs xylanases which are free of cellulase, function for a long time, at least 3 h, at temperatures over 70 degreesC and which are active at a pH higher than 8.0. Newly isolated microbes, which produce cellulase-free xylanases and are easily grown using a low-cost agricultural waste substrate were investigated. The properties of cellulase-free xylanases from Streptomyces sp. Ab106 produced from a simplified low-cost substrate of cane bagasse matched the following industrial requirements: active and stable at temperatures of 50-80 degreesC, active at alkaline pH (pH 7-9), half-life at 70 degreesC, pH 9.0 of 5 h. (C) 2003 Elsevier Science Ltd. All rights reserved.