Recycling of filter tea industry by-products: Application of subcritical water extraction for recovery of bioactive compounds from A. uva-ursi herbal dust

Abstract

In this study, classical extraction (CE) and subcritical water extraction (SWE) of polyphenolic compounds from A. uva-ursi herbal dust (a by-product of a filter tea factory) were performed. The extraction yields obtained through the application of these two extraction techniques were comparable, but higher a concentration of polyphenolic compounds (total phenols (TP) from 7.3088 to 10.6441g GAE/100g, and total flavonoids (TF) from 1.0344 to 1.8638g CE/100g) were recovered using SWE during a significantly shorter extraction time. SWE, as the more appropriate extraction technique, was further optimized by simultaneous maximization of total phenols (TP), total flavonoids (TF) yields and antioxidant activity. In order to optimize the SWE process, a Box-Behnken three level three variables experimental design was used. Temperature (T, 120–220°C), extraction time (t, 10–30min) and hydrochloride concentration (c, 0–1.5%) were independent variables. The experimentally obtained values were fitted to a second-order polynomial model. Multiple regression analysis and an analysis of variance (ANOVA) were used to determine model fitness and optimal conditions. The optimal SWE conditions were determined to be a temperature of 151.2°C, an extraction time of 10min and an addition of 1.5% HCl. The predicted values of targeted responses under these conditions were: 9.8431g GAE/100g, 1.7558g CE/100g, 5.02μg/ml and 27.60μg/ml for TP, TF, IC50 and EC50, respectively. Results suggested that A. uva-ursi herbal dust could potentially be utilized as raw material for the extraction of polyphenolic compounds, and that SWE instead of CE should be applied for this purpose.