Production, partial characterization and use of fungal cellulase-free xylanases in pulp bleaching

Seven fungal strains were screened for their ability to produce cellulase-f ree xylanases that could be used in pretreatment of sulphite pulp prior to bleaching. The potential xylanase producers were subjected to shake flask f ermentations using four different carbon sources: wheat bran, corn cobs, oa t spelts xylan and bleach plant effluent. When grown on corn cobs, Aspergil lus foetidus (ATCC 14916) produced significant levels of xylanase (547.4 U/ ml), accompanied however by 6.6 U/ml of cellulase activity. Two other strai ns, Aspergillus oryzae (NRRL 1808) and Gliocladium viride (CBS 658.70), pro duced high yields of cellulase-free xylanase on oat spelts xylan. The crude enzymes of these two isolates were characterized with respect to pH and te mperature optima and stability in order to standardize the optimum conditio ns for their use on pulp. Although the two xylanases differed in their abil ities to remove reducing sugars from pulp, their biobleaching abilities, wh en assessed in hydrogen peroxide delignification of pulp, were very similar : both of them increased brightness by 1.4 points and removed 7% of hemicel lulose from pulp. (C) 1999 Elsevier Science Ltd. All rights reserved.