4. Conclusion
Characteristics of the microwave drying of apple (about
54 ± 0.5 g with 5 mm of sample thickness) were determined.
Microwave drying period of samples lasted between 25 and
4.25 min at the microwave powers at 200 and 600 W, respectively.
This study indicated that based on non-linear regression
analysis, the Midilli et al. model gave excellent fitting to the
drying experimental data of apple slices. The drying time of
apple slices decreases and the effective diffusivity increases as
the microwave output power increases. The values of effective
diffusivity for microwave drying of apple ranged from
3.93 · 107 to 2.27 · 106 m2
/s and activation energy was
found to be 12.15 W/g. The changes of moisture content have
been described by using the Midilli et al. model. We concluded
that 600 W is the optimum microwave power level in the
microwave drying of apple with respect to drying time and energy
efficiency. The models and parameters found in this study
can be applied to industrial designs and operational guides for
the microwave drying of apple slices.