Ions and low molecular weight components in sulfite pulp mills strongly reduce or boost lipases activity on lipophilic wood extractives

Lipophilic wood extractives (LWEs), including triterpenes, fatty acids, resin acids, waxes, alcohols, sterols, sterol esters, and glycerides, pose significant challenges for pulp and paper mills. Microbial triacylglycerol lipases (EC 3.1.1.3), stable at high temperatures and pH, offer a solution by hydrolyzing detrimental triglycerides into free fatty acids, which can be solubilized in alkaline environments. However, inconsistent performance and limited understanding of process dynamics under industrial conditions have hindered their application. This study evaluated the effects of phenols, salts, and organic acids on lipase activity using a p-nitrophenyl butyrate assay. Additionally, the influence of pulp and process waters was assessed using a self-established assay designed to mimic process conditions and analyze complex matrices. Among five tested microbial lipases, those from Burkholderia cepacia and Thermomyces lanuginosus exhibited up to a 220 % increase in activity at 150 mM sodium-sulfate, as well as enhanced activity with higher acetate concentrations. In contrast lipases from Candida rugosa, Candida antarctica, and Rhizopus oryzae did not respond to kosmotropic ions (Mg²⁺ and SO₄^2-). Most lipases benefitted from lignin-derived phenolic compounds containing syringol moieties. Notably, lipase from Burkholderia cepacia exhibited a 230 % activity increase with 1 mM syringic alcohol. Conversely, linoleic acid above its critical micelle concentration and abietic acid inhibited all enzymes except the lipase from Candida rugosa. Magnesium ions mitigated linoleic acid's inhibitory effect through charge neutralization, enabling maximum activity. The addition of 10 mM Mg²⁺ ions decreased the zeta potential of a lipid emulsion composed of triolein and linoleic acid from -55 mV to -10 mV, and increased triglyceride conversion with Thermomyces lanuginosus lipase from 0 to -72 %. This study identifies key factors influencing enzymatic hydrolysis of triglycerides and elucidates interactions with compounds common in pulp mills, advancing the development of efficient enzymatic treatments.