A comparative study of microwave-assisted air drying of potato slices

Potato slices were dried in a tunnel dryer, a conventional fluidised bed dryer and a fluidised bed dryer with the application of microwaves. A multifactorial experimental design (3 x 2 2) was applied to analyse the effects of type of dryer, temperature, and air speed in studies of drying kinetics, until a final moisture content of 12 +/- 1.5% (wet basis) was reached. Some quality parameters of the dried potato slices for combinations of the process variables are also compared. The type of dryer and the drying temperature had a strong effect on drying rate and on the colour and porosity of the dried potato slices, while rehydration capacity and maximum penetration force were not affected. The statistical analysis showed a marked lowering of drying time when microwaves were applied to a fluidised bed, in agreement with observations reported in the literature. Around a 70% decrease in drying time was observed when the tunnel dryer was replaced by the fluidised bed dryer. Drying time was further reduced to half of that time when microwaves were applied to the fluidised bed, resulting in an 85% drying time reduction in total. The variable diffusivity model, the modified quasi-stationary model and Page's equation were used to fit the experimental drying kinetics, and Page's equation gave the best fit with a root-mean-square error in the range of 1.6-9.1%. Additionally, the effective diffusivity values determined in this work were similar to those reported in the literature. (C) 2007 IAgrE. Published by Elsevier Ltd. All rights reserved.