KINETICS OF DRYING AND REHYDRATION OF APPLE SLICES

The apple is a fruit much appreciated for its crunchy texture, sweet taste, juicy Pulp, and a considerable amount of vitamins, minerals, and antioxidants. Considering the high losses in harvesting and post-harvesting of fruits and that their moisture is a preponderant factor in the matter, drying represents an alternative for reducing waste and increasing shelf life. Many dry products are rehydrated after their final use, making it possible to assess the structural damage suffered during drying through this operation. This work aimed at drying and rehydrating 1 cm thick apple slices. Fruit slices were dehydrated to equilibrium at temperatures of 50 and 70 °C and, after drying, they were rehydrated to equilibrium at 2 °C and 25 °C. Kinetics were monitored by periodic weighing. The experimental data were adjusted to Fick's Law for flat plates, allowing the effective water diffusion coefficient calculation, and to twelve empirical/semi-empirical models. Fruit drying resulted in foods with a low water activity (<0.6), ensuring their microbiological safety; while the rehydration of dry samples was able to recover moisture from fresh fruits in a short period. The influence of temperature on operations was verified, with higher rates being observed for higher temperatures. Evidence of greater cellular damage was observed when drying was carried out at higher temperatures. Fick's law satisfactorily represented the experimental data on the dehydration of apples (R²>0.82), but not their rehydration (R²<0.7). For apples dehydrated at 50 °C, the Diffusion Approximation model was the one that best represented the experimental data of rehydration at both temperatures, and the Page model was the one that best represented the rehydration of samples dehydrated at 70 °C at both temperatures.