Abstract

This thesis focuses on discovering new enzymes for applications in the control of extractives in pulp and paper manufacturing and high efficiency biobleaching. The goal was to better understand the potential of soybean lipoxygenase for removal of detrimental pulp extractives from thermomechanical pulp (TMP). Lipoxygenase treatment at both a 1% and 12% pulp consistency resulted in a 15% reduction in total extractives. The enzyme showed a high specificity towards lipophilic fractions primarily consisting of fatty acids and their esters. Several extractive compounds such as resin acids and lignans inhibited lipoxygenase-catalyzed reactions with fatty acids. In proving the concept of lipoxygenase for extractives degradation, a 96-well UV microplate assay was developed to screen enzymes from fungal species with high reduction oxidases. A second contribution from this thesis was to determine the potential of accessory enzymes in pulp bleaching. A commercial lipase, lipase A "Amano" 12® was used since it exhibited high levels of accessory enzymes. Enzymatic treatment of hardwood and softwood kraft pulps resulted in a notable reduction of kappa number and hexenuronic acid contents. Two enzyme fractions containing high accessory enzyme activities were obtained. There fractions exhibited high bleaching efficiency and a high selectivity as was demonstrated which led to a notable reduction in the amount of sugar released compared to present enzyme bleaching with the commercial xylanase produced by Iogen.