Development and validation of heat and mass transfer models for freeze-drying of vegetable slices

The objective of this work is to develop and validate mathematical models based on heat and mass transfer principles for freeze-drying of vegetable slices. Carrot samples of 1, 2 and 3 mm thickness were freeze dried to obtain drying curves. Developed mathematical models were tested against experimental data to establish that the freeze-drying process is mass transfer controlled. Average values of mass diffusivity were also obtained for samples of three different thicknesses. Capsicum was freeze-dried using two types of circular disk samples obtained from whole capsicum using a cork borer. In one set of samples the natural protective outer membrane was left as it is and in another set the layer was removed prior to freeze-drying. The resulting difference in drying behaviour was insignificant. The drying process was also found to be very slow for capsicum. Mushroom samples on the other hand showed a drying behaviour very similar to 2 mm thick carrot samples. (C) 2002 Elsevier Science Ltd. All rights reserved.