Changes in Effective Moisture Diffusivity and Activation Energy During the Drying of Apple Fruit (Yellow Delicious) with Microwave and Oven

In this study,the effective moisture diffusivity and activation energy of apples with %84 w.b moisture during one- and two-stage drying were investigated. The blanching was done at 5 minutes in 1% ascorbic acid to browning inhibition. The un-blanched samples were controlled. Drying ran with four methods. Two methods consist of oven drying through one stage at 50, 60, and 70 ℃, two-stage at (50-60, 50-70, 60-70 ℃), and microwave drying with one stage (90, 180, and 360 W) and two-stage in (90-180, 90-360, 180-360 W) treatments. the equilibrium moisture was 20%. In two-stage drying, when the moisture of samples reached %50 on initial moisture, the temperature or power changed to next. The effective moisture diffusivity and activation energy were calculated as results. Results show when the microwave power increases, the drying rate and thus the effective moisture diffusivity increase. The moisture removal is better in two-stage drying. The blanching has a lower effect on effective moisture diffusivity inhot air drying. The temperature had no significant effect on effective moisture diffusivity during two-stage drying. During drying with microwave, increasing power reduced the needed energy for removing the moisture from the apple surface which shows the activation energy. Without considering the blanching process in two-stage dried samples, the best power of microwave was 90 W and then 360 W. in this power, the low initial energy for drying and low activation energy are the important benefits of drying. Blanching can reduce the amount of needed energy for starting the evaporation of water. In two-stage drying, increasing the power leads to decreasing the activation energy, without considering the blanching process. Finally, drying of samples with oven and microwave in two stages caused better emission of moisture and reduction of the required energy for starting moisture evaporation in apple sheets.