Effects of thermo-vacuum treatment on antioxidant activity of the poplar wood extractives obtained by different techniques

Heat treatment has increased significantly in the last few years and is still growing as an industrial process to improve some wood properties. Nowadays, there is a renewed interest in producing of thermo-treated wood extractives and their potential application in chemical, pharmaceutical and food industries. Poplar (Populus spp.) is a deciduous tree belonging to the family of Salicaceae. It is one of the less expensive hardwoods. It's also fairly soft which makes it easy to work with. Poplar wood is quite white with some green or brown streaks in the heartwood and it's rarely used in the fine furniture. The aim of this study was to verify the influence of the heat treatment on the polyphenolic and flavonoid content and on the antioxidant activity. Poplar wood was treated at three different temperature, 180 degrees C, 200 degrees C and 220 degrees C in a thermovacuum system for 3 hours. Heat-treated and untreated boards samples (control) were reduced to small size and then particles with similar size were subjected to three different solid-liquid extraction techniques: maceration, ultrasound and accelerated solvent extraction (ASE). For each extractive technique, after the pre-treatment with n-hexane to remove the lipophilic components, the solid phase was extracted with an ethanol: water (70: 30 v/ v) mixture. All extracts were filtered and the solvent was removed by rotary evaporator at 37 degrees C. Dried extracts were kept at room temperature until the use. Total polyphenol, flavonoid and tannin content were evaluated by in vitro assays (Milella et al. 2011; Armentano et al. 2015). Antioxidant activity was evaluated by different assays, including DPPH (2,2-diphenyl-1-picrylhydrazyl) radical-scavenging method, FRAP (Ferric Reducing Ability Power) test and BCB (betaCarotene Bleaching) assay (Russo et al. 2015). Results in Figure (exemplified for ASE 100) reported the presence of polyphenol and flavonoid compounds. Tannins were detected in traces. The heat treatment influenced the content of these class of compounds and the highest content was observed in wood treated at 220 degrees C and 200 degrees C. The untreated wood, instead, showed higher amount of compounds than wood treated at 180 degrees C. Extractives obtained from the wood treated at the highest temperature (200 degrees C and 220 degrees C) reported also the highest antioxidant activity. According to the results of phenolic content, the antioxidant activity of poplar treated at 180 degrees C was less than the control. Extractive procedures showed slight differences in phenolic content and antioxidant activity, but poplar wood treated at 180 degrees C was less active in each of them.