Optimization of antioxidants recovery from wild thyme (Thymus serpyllum L.) by ultrasound-assisted extraction: Multi-response approach

Abstract The main goal of this study was to valorize Thymus serpyllum L., the by-product of filter-tea production, for extraction of polyphenols with high antioxidant capacity by ultrasound-assisted extraction (UAE). Herbal dust is formed during the preparation of raw material for tea packaging, it is separated as a fraction which is unusable in the tea industry and distinguished as an industrial waste. In order to optimize the process, three levels, three variables, face-centered central composite experimental design within the response surface methodology (RSM) was applied. Temperature (50, 65 and 80 °C), extraction time (40, 55 and 70 min) and ethanol concentration (45, 60 and 75 %) were used as independent variables. Selected responses were total extraction yield (Y) and total phenols yield (TP), as well as antioxidant activity parameters obtained by DPPH, ABTS and FRAP assays. Results were fitted to a second-order polynomial model and goodness of fit was determined by regression analysis and analysis of variance (ANOVA). Good accordance between experimental and predicted values was achieved, which suggested that obtained models could be used for multi-response optimization in order to maximize yields of target responses and improve antioxidant potential of T. serpyllum liquid extracts. Furthermore, UAE provided advantages comparing to conventional solid-liquid extraction in terms of antioxidant activity and total extraction and total phenols yield. Therefore, it could be concluded that T. serpyllum herbal dust could be used as raw material for production of antioxidant-rich extracts.