Enzymes Produced during Brightening of Pulp by White-Rot Fungi

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Biobleaching of hardwood unbleached kraft pulp (LUKP) by Phanerochaete chrysosporium and Trametes versicolor was studied in the solid-state fermentation system. When brightness increase and cumulative activities of oxidizing enzymes, manganese peroxidase (MnP), lignin peroxidase, and laccase, were determined, a linear relationship between brightness increse and cumulative MnP activity was found in this system with both P.chrysosporium and T.versicolor. This result suggests that MnP is involved in brightening and deligni-fication of LUKP by white-rot fungi.On the other hand, the cumulative reducing enzyme activity rather related to the degradation of cellulose than to that of lignin.In vitro, biobleaching of unbleached kraft pulps was performed with partial purified MnP from P.chrysosporium. When the LUKP (kappa number : 15.5) and two of softwood unbleached kraft pulp (NUKPs), normal NUKP (NUKP-N,kappa number : 28.4) and low-lignin-content NUKP (NUKP-L,kappa number : 18.3), were repeatedly treated three times with MnP,kappa number of each pulp decreased by 60.6,67.6, and 71.4%, respectively. As the result, the biobleaching process combined with MnP treatment and chemical bleaching (C/D-E-D) could reduce the amount of effective chlorine to obtain a pulp with 85% brightness by 69.0,51.0, and 66.2% compared with conventional bleaching process (C/D-E-D-E-D) for LUKP,NUKP-N,and L,respectively. This indicates that MnP treatment is effective in reducing the use of chloring-based chemicals in pulp bleaching.