Thin-layer Drying of Cultivated Taxus Clippings

A promising cancer chemotherapeutic agent, taxol, is currently scheduled for full clinical development by the National Cancer Institute. The ornamental yew, Taxus x media Hicksii, has been identified as a renewable source of taxol. However, clippings from the plant must be properly and efficiently harvested, dried, and stored. Thin-layer drying studies of Taxus clippings, needles, and stems were conducted. Parameters for the thin-layer drying equation were successfully determined for drying temperatures of 30, 40, 50, and 60 C. The results showed that drying rates increased 28-, 15-, and 3-fold as drying temperatures increased from 30, 40, and 50 C to 60 C, respectively. Also, stems dried at a faster rate than needles and needles dried at a faster rate than whole clippings. Taxol yields (g/100 g, d.b.) from stems were nearly constant for the four temperatures tested. However, yields from needles increased linearly as drying temperatures increased from 30 to 60 C. The highest taxol yields were obtained from clippings. Nearly constant yields were obtained (~ 0.014 g/100 g, d.b.) for drying temperatures of 40, 50, and 60 C. The lowest yields for all three plant components occurred when the drying temperature was set at 30 C. The results suggest 60 C is the best temperature set point for drying Taxus x media Hicksii, but temperatures higher than 60 C should be evaluated.