High concentrations of fatty acids affect the lipase treatment of softwood thermomechanical pulps

Triglycerides, a major class of wood extractives, contribute to the colloidal pitch that initiates pitch deposits. Because industrial or pilot-scale treatments with lipolytic enzymes to reduce triglyceride concentrations in pulp have not been successful in North America, we investigated such treatments at a laboratory scale. Different batches of industrial softwood chemithermomechanical pulps (CTMP) were treated with a range of concentrations of two commercial lipases: Resinase A 2X (Novo Nordisk AG) and Lipidase 10 000 (American Laboratories Inc.). A pilot-scale thermomechanical pulp (TMP) made from the same wood as the CTMP, but without the sodium hydrosulfite used in the CTMP, was also treated with the lipases. While triglycerides decreased in all the pulp treatments, the extent of their hydrolysis varied according to the ratio of triglyceride to the fatty/resin acid fraction. As this ratio can vary significantly in softwood TMP and CTMP, the success of industrial treatments of softwood mechanical pulps by commercial lipases may be related to variations in this ratio. Supporting this, adding linoleic acid to an extractives-free pulp that was spiked with olive oil reduced lipase activity by up to 55%. Received: 7 August 1997 / Received last revision: 8 December 1997 / Accepted: 14 December 1997