Prebleaching of softwood and hardwood pulps by a high performance xylanase belonging to a novel clade of glycosyl hydrolase family 11

To discover and develop a xylanase enzyme that can significantly enhance wood pulp bleachability under typical kraft process conditions (high temperature and alkaline pH), close to 200 xylanases from diverse environments were discovered and screened using a 3-stage (XDEp) pulp biobleaching assay. Four xylanases belonging to a new clade of glycosyl hydrolase family 11 outperformed all other enzymes by reducing bleaching chemical consumption by 15–25% on softwood and hardwood pulps. During the screening process, many thermostable and alkali-tolerant family 10 xylanases were also identified, however, family 10 xylanases in general were not as effective as those from family 11 in enhancing wood pulp bleachability. The candidate selected for developing a prebleaching xylanase enzyme product, Xyn11a, retained 80% of its maximum activity after incubation at 65 °C for 30 min.