New Insight and Evaluation of the Extractives from Thermo-Treated Woods

Several studies reported changes in physical and mechanical wood characteristics due to thermotreatment but the information on the considerable significance and industrial potential of the role of extractives are underevaluted. The heat treatment modifies the chemical composition of the wood organic compounds and consequently its secondary metabolites content. The differences of the chemical composition and the antioxidant activity of the native extracts of a species and the extracts obtained from thermo-treated wood is poorly investigated. In this preliminary study the extraction of secondary metabolites from thermo-treated (at temperature between 170-220 °C for 3 hours) and untreated wood of several species was carried out and the content of polyphenols, tannins and flavonoids and the antioxidant activity of the extractives were also evaluated. The heat treatment clearly increased the extract yield in some investigated wood species, whereas in others the extractive yields were almost unchanged. The content of polyphenols, tannins and flavonoids was also higher in some species after the thermal treatment compared with other species. All samples, heat treated and untreated, exhibited antioxidant activity by DPPH assay. This activity increases with the content of secondary metabolites of the extracts, but not always the highest activity was exhibited by the heat treated extract. These differences were originated from intrinsic properties of lignin and other wood components and they are specific for each species. Further investigations will be focused on the identification of the compounds in untreated and heat treated samples and to deepen the biological activity of the extracts.