Parameters affecting microwave-assisted extraction of withanolides

Focused microwave-assisted extraction was applied to the extraction of three main withanolides from air-dried leaves of Iochroma gesnerioides, namely, withaferin A, iochromolide and withacnistin. Six extraction variables, i.e. nature and volume of extracting solvent, sample moisture, extraction time, power of irradiation and particle size, were investigated with respect to the recovery of withanolides. The most favourable conditions were obtained by using powdered plant material (< 220 mum), previously impregnated with water for 15 min, and extracted with methanol for 40 s at 25 W. The results obtained using the optimised method were compared to those achievable with Soxhlet extraction. Copyright (C) 2001 John Wiley & Sons, Ltd.