Characterization of a cellulase-free, neutral xylanase from Thermomyces lanuginosus CBS 288.54 and its biobleaching effect on wheat straw pulp

Abstract

A xylanase purified from the thermophilic fungus Thermomyces lanuginosus CBS 288.54 was characterized and its potential application in wheat straw pulp biobleaching was evaluated. Xylanase was purified 33.6-fold to homogeneity with a recovery yield of 21.5%. It appeared as a single protein band on SDS-PAGE gel with a molecular mass of approx. 26.2 kDa. The purified xylanase had a neutral optimum pH ranging from pH 7.0 to pH 7.5, and it was also stable over pH 6.5–10.0. The optimal temperature of the xylanase was 70–75 °C and it was stable up to 65 °C. The purified xylanase was found to be not glycosylated. The xylanase was highly specific towards xylan, but did not exhibit other enzyme activity. Apparent K m values of the xylanase for birchwood, beechwood, soluble oat-spelt and insoluble oat-spelt xylans were 4.0, 4.7, 2.0 and 23.4 mg ml −1, respectively. The potential application of the xylanase was further evaluated in biobleaching of wheat straw pulp. The brightness of bleached pulps from the xylanase pretreated wheat straw pulp was 1.8–7.79% ISO higher than that of the control, and showed slightly lower tensile index and breaking length than the control. Although chlorine consumption was reduced by 28.3% during bleaching, the xylanase pretreated pulp (15 U g −1 pulp) still maintained its brightness at the control level. Besides, pretreatment of pulp with the xylanase was also effective at an alkaline pH as high as pH 10.0.