Microwave-assisted extraction of flavonoids from Radix Astragali

Microwave-assisted extraction (MAE) technique was developed for the fast extraction of flavonoids from Radix Astragali. Several influential parameters of the MAE procedure (microwave power, extraction cycles, ethanol concentration, extraction temperature, irradiation time, and solvent to material ratio) were studied for the optimization of the extraction protocol. The maximum yield of flavonoids with MAE was obtained by dual extraction with 90% ethanol 25ml/g material at 110 degrees C for 25 min. No degradation of the flavonoids was observed using the developed extraction protocol. The optimal yield with MAE 1.190 +/- 0.042 mg/g were close to that of Soxhlet extracted with methanol for 4 h (1.292 +/- 0.033 mg/g) and higher than that of ultrasound assisted extraction with methanol for 2 x 30 min and heat reflux extraction with 90% ethanol for 2 x 2 h. (c) 2008 Elsevier B.V. All rights reserved.