BIOBLEACHING OF OXYGEN DELIGNIFIED KRAFT PULP BY SEVERAL WHITE-ROT FUNGAL STRAINS

Twenty-five white rot fungal strains were tested for their ability to bleach Eucalyptus globulus oxygen delignified kraft pulp (OKP). Under nitrogen-limited culture conditions, eight outstanding biobleaching st rains were identified that increased the brightness of OKP by more tha n 10 ISO units compared to pulp incubated in sterile control medium. T he highest brightness gain of approximately 13 ISO units was obtained with Bjerkandera sp. strain BOS55, providing a high final brightness o f 82% ISO. This strain also caused the greatest level of delignificati on, decreasing the kappa number of OKP by 29%. When the white rot fung al strains were tested in nitrogen-sufficient medium, the extracellula r activities of laccase and peroxidases increased in many strains; non etheless, the pulp handsheets were either destroyed or brightness gain s were lower than those obtained under nitrogen-limitation. The titer of ligninolytic enzymes was not found to be indicative of biobleaching potential. However, the best biobleaching strains were generally char acterized by a predominance of manganese dependent peroxidase (MnP) ac tivity compared to other ligninolytic enzymes and by a high decolorizi ng activity towards the polyanthraquinone ligninolytic indicator dye, Poly R-478. (C) 1997 Elsevier Science B.V.