INFLUENCE OF DRYING METHOD ON THE REHYDRATION PROPERTIES OF APRICOT AND APPLE

This study aims to determine the influence of microwave drying coupled with air drying of apricot and apple in terms of the rehydration rate and capacity of dried samples. The microwave power level was 0.4 W/g for apricot and 0.5 W/g for apple samples. The effect of air temperature (50 and 30C) and vacuum impregnation pretreatment (with a commercial isotonic juice) was examined. The sample mass change, water gain and soluble solids loss, were obtained before sample rehydration (in distilled water at 20C for 8 h). Peleg's model was used to assess the effect of process conditions on rehydration kinetics, with a good fit of the experimental data. Taking into account the lower values for Peleg's constants of k1(i) and k2(i), the vacuum impregnation pretreatment and microwave application to air drying allow us to obtain a dried product with a better rehydration capacity, promoting the rate and capacity of water gain and solute loss, although the structure of product remains with a lower liquid phase retention capacity. A less relevant influence of air temperature on water gain kinetics was observed, improving the rehydration ratio only for nonvacuum-impregnated samples.