Resumo

The use of xylanolytic enzymes as bleaching agents of cellulose pulps has been considered one of the main industrial applications of these enzymes and many studies have demonstrated the pre-treatment of pulps with xylanases can reduce the use of chemical agents in subsequent bleaching stages. Bacterial xylanases are more commonly evaluated as they usually are active in more alkaline pH, although many fungal xylanases have also being evaluated. An oxygen pre-bleached ,Eucalyptus spp pulp was treated with P. janczewskii crude extract obtained under previously optimized conditions for xylanase production (Vogel liquid medium with 1% w/v xylan from oat spelts pH 6.5, 30°C, 7 days cultivation). Although other xylanolytic enzymes are present in the crude extract, enzymatic treatments were based only on the charges of xylanase into this extract corresponding to 2, 4, 8, 18 and 32 U/g oven-dried pulp. The experiments were carried out in polyethylene plastic bags at a consistency of 10%, pH 5.5, incubation at 50°C during 1 and 2 h. After the treatment, the pulp was filtered in a Büchner funnel, washed with 200 ml distilled water and used for determination of kappa number and viscosity parameters, according to a standard methodology. Controls were prepared with distilled water instead of enzyme. Treatments of pulp with 2 and 4 U/g pulp for 1h promoted reduction of 3 and 3.3 units in kappa number, respectively. With higher enzyme concentration only small reduction on kappa number was observed. The same reduction pattern was observed in 2h treatments, and kappa number values were only slightly lower than those observed in 1h treatments. These results indicated that after more extended treatment periods no additional benefits in terms of the kappa number reduction is achieved. This study demonstrates that the use of P. janczewskii xylanases in this process is quite promisor. The pulp viscosity was not altered, confirming the maintenance of the pulp characteristics due to the absence of cellulolytic enzyme in the crude extracellular extract produced by this fungus.