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
Fig. 3 shows how the drying rate of apple samples was
changed with increased drying time under various drying conditions.
The drying rates increased with the increasing microwave
power levels. The maximum drying rates were
approximately 0.382, 0.898 and 2.299 kg [H2O]/kg dry mater/
min, when the microwave powers of 200, 400 and 600 W were
applied, respectively. The moisture content of the material was
very high during the initial phase of the drying which resulted
in a higher absorption of microwave power and higher drying
rates due to the higher moisture diffusion. As the drying progressed,
the loss of moisture in the product caused a decrease