Optimization of various extraction methods for quercetin from onion skin using response surface methodology

Quercertin and typical flavonoids present in onion skin draw interest due to bioactive properties. For utilizing quercetin from onion skin, conventional solvent extraction (CSE), microwave assisted extraction (MAE), and ultrasound assisted extraction (UAE) were employed. Statistic models of each method were proposed to estimate the best possible yield of quercertin employing response surface methodology (RSM). The effects of several independent variables including concentration of ethanol, provided power or the temperature, and reaction time were investigated. From 1 g sample of dried onion skin, the highest yield of each method could be achieved at 16.5 min of process time under 59.2°C for CSE with 59.3% ethanol, 117 s for MAE with 69.7% ethanol, and 21.7 min for UAE using power of 606.4 W with 43.8% ethanol. The most productive method was MAE, whose maximum yield was 20.3 and 30.8% higher than UAE and CSE, respectively.