Optimization of ultrasound-assisted extraction of polyphenols from spruce wood bark

•Spruce bark (picea abies) is a rich source of phenolic compounds with antioxidant activity.•Non-toxic solvent was used (ethanol and water).•Effects of ultrasound-assisted extraction as influenced by time, temperature and ethanol concentration were evaluated.•Polyphenols extraction is improved by ultrasound assisted extraction with 70% ethanol.•The highest yield of total polyphenols obtained by ANOVA factorial was 13.232mgGAE/g spruce wood bark. Here we describe the ultrasound-assisted extraction of the phenolic compounds from spruce wood bark and present a straight-forward experimental planning method, allowing the optimisation of the process. The effect of ethanol concentration, temperature and extraction time were evaluated through a 32·2 experimental planning. The efficiency of the extraction process was appreciated based on factorial ANOVA results. The maximum extraction yield of total polyphenols (13.232mg gallic acid equivalents (GAE)/g of spruce bark tested) was obtained using a process time of 60min, an extraction temperature of 54°C and a concentration of ethanol of 70% respectively. These results indicate that an important quantity of bioactive compounds can be extracted from spruce wood bark by ultrasound assisted extraction technology.