Drying of zucchini by using tray drying and microwave pretreatment

In this thesis, zucchini (Cucurbita pepo L. var cylindrica) slices were dried with and without microwave pretreatment in the tray dryer. Microwave pretreatment was applied for 7 minutes at three different microwave power levels (350, 490 and 700 W). Hot air drying was carried out at three different temperatures (40, 50 and 60°C) and two different air flow rates (1.0 and 1.2 m/s). Drying behaviors, bulk density and color changes of the dried zucchinis were examined. Increasing the temperature, microwave power and air flow rate reduced the drying time. The microwave pretreatment was led to a significant reduction in the drying time compared to the non-pretreated samples. The shortest drying time was observed in the zucchini at 60°C with an air flow rate of 1.2 m/s and 700 W. Effective moisture diffusivity values (Deff) were found as between 1.54*10-10 and 2.75*10-9 m2/s. The minimum activation energy was found as 20.51 kJ/mol for hot air drying at 1.2 m/s air flow rate, and maximum activation energy was found as 65.50 kJ/mol for microwave pretreatment at 700 W air flow rate of 1.2 m/s. For color values of L*, a*, b* and ΔE, there were significant change (p<0.05) between air flow rates and hot air temperatures. Minimum total color difference (ΔE) was found 10.60±2.30 during hot air temperature at 60°C and 1.0 m/s air flow rate and 700 W microwave pretreatment. Shrinkage values varied in between 0.75 and 0.80. Bulk density values were found between 0.21±0.02 and 0.41±0.01 g/mL. Keywords: Zucchini, Microwave, Drying, Diffusion, Color