Drying of American ginseng (Panax quinquefolium) roots by microwave hot air combination

American ginseng (panax quinquefolium) roots were dried, respectively, with hot air and combined microwave-hot air methods in a modified experimental microwave oven. For hot air drying, the lending size, drying temperature and air flow rate were 100 g, 40 degrees C and 60 l/min, respectively. For combined microwave-hot air drying the additional microwave power of 60 W was used. Drying time to achieve the desired moisture level (10%) in the final product, and the colour of the product, were used to evaluate the combined microwave-hot air drying and the conventional hot nil drying methods. Combined microwave-hot air drying resulted in a substantial decrease (28.7-55.2%) in the drying time and had little influence on the colour of the final product. (C) 1998 Elsevier Science Limited. All rights reserved.