Antioxidant activity of Scots pine heartwood and knot extractives and implications for resistance to brown rot

Brown rot (BR) fungi are highly destructive wood decaying organisms that utilise free radicals in the initial stages of decay. Although many wood extractives have been shown to have antioxidant (AO) activity, their ability to protect wood from radical-based degradation has received little attention. The present paper reports on the ability of Scots pine heartwood (hW) and knotwood (knW) extractives to inhibit radical-based degradation, with a focus on the Fenton reaction. AO assays showed that extract solutions and pure pinosylvins had good radical scavenging activity and weak to moderate ferrous iron binding and ferric iron reducing activities. AO assays were repeated with wood powders and showed that extractives were also active in wood: hW and knW had significantly higher activities than their extracted counterparts or sapwood. However, when wood powders were subjected to degradation by Fenton reagent, only knW showed reduced mass loss. Based on the activity profiles of knW and hW, it appears that the radical scavenging activity of pine extractives is more important than their interaction with iron. The results suggest that the AO activity of extractives may play a role in inhibiting BR, but its importance relative to the other biological activities of extractives is unknown.