BLEACHING OF HARDWOOD KRAFT PULP WITH MANGANESE PEROXIDASE FROM PHANEROCHAETE SORDIDA YK-624 WITHOUT ADDITION OF MNSO4

In vitro bleaching of an unbleached hardwood kraft pulp was performed with partially purified manganese peroxidase (MnP) from the fungus Pha nerochaete sordida YK-624 without the addition of MnSO4 in the presenc e of oxalate, malonate, or gluconate as manganese chelator. When the p ulp was treated without the addition of MnSO4 the pulp brightness incr eased by about 10 points in the presence of 2 mM oxalate, but the brig htness did not significantly increase in the presence of 50 mM malonat e, a good manganese chelator. Residual MnP activity decreased faster d uring the bleaching with MnP without MnSO4 in the presence of malonate than in the presence of oxalate. Oxalate reduced MnO2 which already e xisted in the pulp or was produced from Mn2+ by oxidation with MnP and thus supplied Mn2+ to the MRP system. The presence of gluconate, prod uced by the H2O2-generating enzyme glucose oxidase, also improved the pulp brightness without the addition of MnSO4, although treatment with gluconate was inferior to that with oxalate with regard to increase o f brightness. It can be concluded that bleaching of hardwood kraft pul p with MnP, using manganese originally existing in the pulp, is possib le in the presence of oxalate, a good manganese chelator and reducing reagent.