Characterization and optimization of hydrothermal extraction of quercetin from Quercus leaves using response surface methodology

Abstract

AbstractA hydrothermal process using subcritical water and ethanol as an extraction solvent has been studied to extract high‐value flavonoid compounds from Quercus leaves. The univariate analysis showed that the maximum quercetin yield was 34.6 mg/g obtained at the liquid–solid ratio of 30:1 ml/g, concentration of ethanol 60% (V/V), extraction temperature of 180°C, and extraction duration of 5 h. Based on the Box–Behnken experiment design, the response surface methodology (RSM) was used to optimize the liquid‐to‐solid ratio, extraction time, extraction temperature, ethanol concentration, and other operating conditions of hydrothermal extraction of quercetin. The regression equation showed that the maximum yield of quercetin was 36.1 mg/g under the conditions of solvent ethanol concentration of 65% (V/V), liquid–solid ratio of 40:1 ml/g, extraction temperature of 189°C, and extraction duration of 5.5 h. The quercetin yield of 36.1 mg/g obtained by the hydrothermal method was 5.6 times the 6.4 mg/g obtained by the traditional ethanol reflux extraction at the same concentration of ethanol 65% (V/V), liquid–solid ratio of 40:1 ml/g, and extraction duration of 5.5 h, but at the boiling point of the solvent.