Parameters affecting microwave-assisted extraction of withanolides

Focused microwave-assisted extraction was applied to the extraction of thre e 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.