APPLICATION OF THERMOSTABLE XYLANASE OF DICTYOGLOMUS SP IN ENZYMATIC TREATMENT OF KRAFT PULPS

Enzymatic treatment of pine and birch kraft pulps with a xylanase prep aration from a thermophilic anaerobic bacterium Dictyoglomus sp. strai n B1 was studied in order to improve pulp bleachability. Maximal solub ilization of pulp xylan was obtained at 90 degrees C and pH 6.0-7.0. T he enzyme was also active in the alkaline pH range; at pH 9.0 xylan hy drolysis was decreased by only 18% from the maximum at pH 7.0. The pos itive effect of xylanase pretreatment at 80 degrees C and pH 6.0 or 8. 0 on bleachability of pine kraft pulp was demonstrated. The brightness was increased by two ISO units in one-stage peroxide delignification, which corresponds well to values obtained with other enzymes at lower temperatures and pH values. Thus, the Dictyoglomus xylanase is well s uited for pulp treatments at elevated temperatures in neutral and alka line conditions.