Analysis of conditions for microwave-assisted extraction of total water-soluble flavonoids from Perilla Frutescens leaves

Perilla Frutescens is a traditional Chinese medicinal herb. Microwave-assisted extraction (MAE) technique was developed for the fast extraction of flavonoids from Perilla Frutescens leaves. Several influential parameters of the MAE procedure (microwave power, extraction cycles, solvent to material ratio, irradiation time and pH value) were investigated for the optimization of the extraction using single factor and Box-Behnken experimental design. Response surface methodology analysis showed good correspondence between experimental and predicted values. It was found that the most effective parameter was solvent to material ratio, which was in good agreement with the experimental value. The adjusted coefficient of determination (R (adj) (2) ) for the model was 93.45%. Probability value (P < 0.001) demonstrated a very high significance for the regression model. The maximum yield of flavonoids with MAE was obtained by dual extraction with solvent to material ratio of 1: 16.5, irradiation time of 23 min, and pH value of 8.4 at microwave power of 600 W. The optimal yield with MAE 6.07 mg/g were slightly lower than that of Soxhlet extracted and higher than that of heat reflux extraction with water. The extracts exhibited high scavenging effects on DPPH radical. With increasing concentration between 0.10 and 0.80 mg/mL, the scavenging rate achieved 62.3%.