Fatty acids and their esters are major constituents of wood extractives and are known to cause a range of newsprint manufacturing problems including pitch deposition, poor paper machine runnability, low paper friction and strength. This study investigated the potential of using soybean lipoxygenase to degrade wood extractives present in thermomechanical pulp (TMP) samples. Lipoxygenase treatments of TMP resulted in a 15% reduction in total extractives. The enzyme showed a high specificity towards lipophilic extractives fractions, primarily consisting of fatty acids and their esters. After 2 h pulp treatments, the lipophilic extractives content was reduced by more than 25%, while there was little change in hydrophilic extractives. The activity of lipoxygenase towards individual wood extractives was determined by using a mixture extracted from TMP. It was found that several extractive compounds such as resin acids and lignans inhibited lipoxygenase catalyzed reactions with fatty acids. Transition metal ions present in the TMP contributed to further fragmentation of fatty acid hydroperoxides produced by lipoxygenase reaction with wood extractives. (c) 2006 Elsevier Inc. All rights reserved.