High level expression of a recombinant xylanase by Pichia pastoris NC38 in a 5 L fermenter and its efficiency in biobleaching of bagasse pulp

A genetically modified XynA gene from Thermomyces lanuginosus was expressed in Pichia pastoris under the control of GAP promoter. P. pastoris expressed greater levels of xylanase (160 IU ml−1) on BMGY medium without zeocin after 56 h. The xylanase production by recombinant P. pastoris was scaled up in a 5 L fermenter containing 1% glycerol and the highest xylanase production of 139 IU ml−1 was observed after 72 h. Further studies carried out in fermenter under controlled pH (5.5) yielded a maximum xylanase production of 177 IU ml−1 after 72 h. The biobleaching efficacy of crude xylanase was also evaluated on bagasse pulp and a brightness of 47.4% was observed with 50 IU of crude xylanase used per gram of pulp, which was 2.1 points higher in brightness than the untreated samples. Reducing sugars (24.8 mg g−1) and UV absorbing lignin-derived compounds values were considerably higher with xylanase treated samples.