Biobleaching of wheat straw pulp with recombinant laccase from the hyperthermophilic Thermus thermophilus

The recombinant laccase from Thermus thermophilus was applied to the biobleaching of wheat straw pulp. The best bleaching effect was when the pulp was treated with 3 U laccase g(-1) dry pulp at 90 degrees C, pH 4.5, 8% consistency for 1.5 h. Under these conditions, the pulp brightness was increased by 3.3% ISO, and the pulp kappa number was decreased by 5.6 U. Enzymatic treatment improved the bleachability of wheat straw pulp but caused no damage to the pulp fibers. The use of enzyme-treated pulp saved 25% H2O2 consumption in subsequent peroxide bleaching without decreasing the final brightness. Pulp biobleaching in the presence of 5 mM ABTS further increased the pulp brightness by 1.5% ISO. This is the first report on the application of laccase from T. thermophilus in the pulp and paper sector.