Convective air drying of apples as affected by blanching and calcium impregnation

The effect of previous blanching and calcium impregnation at atmospheric pressure (AI) or in vacuum (VI) on the rate of moisture movement during the first falling rate period of air drying of apples at 60 degrees C was studied. It was found that the effective diffusion coefficient of water(D-ef) calculated with Fick's second law was strongly affected by heat pretreatment. With the exception of non-blanched tissues subjected to VI or VI followed by AI for 1.5 h, calcium uptake during impregnation step appeared to modify the matrix resistance to water flux only when tissue was previously heated. Light microscopy studies of apple tissues allowed explaining the observed drying behaviour. (c) 2007 Elsevier Ltd. All rights reserved.