Subcritical water extraction of sage (Salvia officinalis L.) by-products—Process optimization by response surface methodology

Abstract

In this work, subcritical water extraction (SWE) of polyphenols from sage (Salvia officinalis L.) herbal dust was optimized by simultaneous maximization of total phenols (TP) and total flavonoids (TF) yields, as well as maximized antioxidant activity, determined by DPPH, ABTS and reducing power assay. Sage herbal dust, discarded as by-product from filter tea factory, was used as raw material for extraction. Three level, three variables, Box-Behnken experimental design (BBD) with response surface methodology (RSM) was used for optimization of SWE. Temperature (X1: 120–220°C), extraction time (X2: 10–30min) and HCl concentration in extraction solvent (X3: 0–1.5%) were investigated as independent variables. Experimentally obtained values were fitted to a second-order polynomial model, and multiple regression analysis and analysis of variance (ANOVA) were used to determine model fitness and optimal conditions. The optimal SWE conditions for simultaneous maximization of TP, TF and antioxidant activity were temperature of 201.5°C, extraction time of 15.8min and pure water as extraction solvent, while predicted values of TP, TF, IC50, TEAC and EC50 at this experimental point were 7.98g GAE/100g DW, 4.93g CE/100g DW, 13.38μg/mL, 38.34mM Trolox/100g DW and 41.66μg/mL, respectively. Results suggested that SWE provided significant advantages in terms of polyphenols yield, comparing to maceration, and that herbal dust from filter tea factory could be potentially utilized as good raw material for extraction of valuable bioactive compounds.