Influence of Microwave Osmotic Dehydration Pre-Treatment on the Second Stage of Air-Drying Kinetics of Apples

The effect of microwave-osmotic dehydration pre-treatment under continuous flow medium spray (MWODS) conditions on the second stage air-drying kinetics of apple (Red Gala) cylinders was evaluated. MWODS pre-treatment was carried out using a response surface methodology involving 5-levels of sucrose concentration (33-66.8 degrees B), temperature (33-66.8 degrees C) and contact time (5-55 min). Drying time and coefficient of moisture diffusion (Dm) and coefficient of moisture infusion (I(m)) during rehydration were evaluated as responses and the results were compared with their air-dried (AD) (worst scenario) and freeze-dried (FD) (best scenario) counterparts without the osmotic treatments. The diffusion and infusion coefficients were based on the solution of Fick's diffusion model. Empirical models developed for all response variables were significant (P <= 0.001) and the lack of fit was not significant (P > 0.05). MWODS pre-treatments significantly influenced the Dm values and reduced the air-drying time of apples by 30-65 percent in comparison with untreated apple thereby providing opportunity for better energy savings. On the other hand, the values of Im during the rehydration process were highest for the freeze-dried samples followed by apples air-dried after MWODS treatment, and the least for the untreated air-dried samples.