Laccase from Trametes versicolor -: Stability at temperature and alkaline conditions and ifs effect on biobleaching of hardwood kraft pulp

The enzyme laccase was produced by the white-rot fungus Trametes versicolor in repeated batches cultures with immobilized mycelium. Two different culture conditions were used. Enzymes produced were evaluated regarding their stability at high temperatures (55 degrees C and 65 degrees C) and at alkaline conditions (pH 7.0 and pH 8.0) having in view the application of these enzymes in biobleaching of hardwood Kraft pulp. Biobleaching experiments were divided in two parts, enzymatic prebleaching followed by chemical bleaching. In the enzymatic prebleaching the enzyme laccase was used at two conditions of pH and temperature, whereas the reaction time was fixed at 1 h in all pretreatments. In the chemical bleaching the DEDED and DEpDED sequences were used. The enzyme action was evaluated by Kappa number, viscosity, and bright ness at the end of bleaching sequences. There were obtained values of Kappa numbers lower than control assays, viscosities compatible with industrial pulps, and brightness higher than controls, when pulps were pretreated for 1 h with laccase at pH 8.0 and 55 degrees C.