BLEACH BOOSTING EFFECT OF CELLULASE-FREE XYLANASE OF STREPTOMYCES-THERMOVIOLACEUS AND ITS COMPARISON WITH 2 COMMERCIAL ENZYME PREPARATIONS ON BIRCHWOOD KRAFT PULP

Streptomyces thermoviolaceus extracellular xylanase preparations were used to treat birchwood Kraft pulp prior to chlorine bleaching. Xylana se concentrations in the range 5-100 IU g(-1) dry weight pulp released reducing sugars and chromophores that absorb at 280 nm. At enzyme dos es greater than or equal to 10 IU, further removal of chromophoric mat erial was not significant although reducing sugar yields probably from oligosaccharide hydrolysis continued to increase. Pulp Kappa number w as, educed by enzyme treatment with and without subsequent alkali extr action, and the pulp brightness after CEDED bleaching at 4% chlorine c harge was boosted without significant reductions in fiber strength or interfiber bonding. Scanning electron microscopy revealed marked disru ption and separation of pulp fibers even at low (5 IU g(-1) dry weight pulp) xylanase noses, and a 30-35% saving in the chlorine charge requ ired to obtain pulp brightness comparable to controls could be achieve d. Comparative and standardized treatments of pulp with the commercial bleach-boosting enzyme preparations Cartazyme and Pulpzyme demonstrat ed that the crude S. thermoviolaceus xylanase preparation was at least as effective in enhancing brightness with concomitant preservation of paper strength properties; however, S. thermoviolaceus xylanase does have the advantage of being active and stable at 65 degrees C and, lik e Pulpzyme but not Cartazyme, at neutral to alkaline pH values appropr iate for applications in paper pulp processing. (C) 1998 Elsevier Scie nce Inc.