| The suitability of forced air thin-layer dryer and fluidized-bed dryer for the dehydration of E. angustifolia roots was investigated by examining the drying characteristics of the roots, and evaluating the quality of dehydrated roots with echinacoside as a reference compound. Suitable storage conditions for preserving the echinacoside in ground dehydrated roots were also determined over a six-month storage study.;Two drying temperatures (50° and 30°C), air velocities (0.7 and 1.1 m/s for forced-air thin layer dryer, 3.3 and 4.8 m/s for fluidized bed dryer) and root sizes (small and medium) were examined in the drying experiments. Under similar drying conditions, the fluidized-bed dryer exhibited a higher drying rate than the thin-layer dryer at the initial drying stage. An extremely low drying rate was observed at the late stage of fluidized-bed drying, which might be attributed to the case hardening of the roots. Drying air temperature and root size were found to be important parameters affecting the drying rate in both thin-layer drying and fluidized-bed drying. Page equation appeared to fit the entire experimental data (R2 > 0.96). (Abstract shortened by UMI.)... |
