Effects of Microwave-Infrared Combination Drying on Quality of Eggplants

The objective of this study was to investigate the effects of hot-air drying and microwave-infrared combination drying on drying characteristics and quality parameters of eggplants. Eggplant slices were dried by using microwave-infrared combination oven at different microwave powers (30, 40, and 50 %) and different infrared (IR) powers (10, 20, and 30 %). Hot-air drying was performed in a tray dryer at 50 A degrees C with an air velocity of 1.5 m/s. As quality parameters, color, rehydration ratio, shrinkage, microstructure, and pore size distribution of dried eggplants were chosen. Microwave-IR combination provided significantly shorter drying time than hot-air drying. Osmotic dehydration also reduced drying time in microwave-IR combination oven. Effective diffusivity of moisture in hot-air drying (5.070 x 10(-10) m(2)/s) was found to be lower than that observed in microwave-IR drying (7.100 x 10(-9)-1.445 x 10(-8) m(2)/s). Higher microwave and IR powers increased but osmotic pretreatment decreased effective diffusivity. Decrease in IR power and osmotic dehydration treatment increased L* but decreased a* values of dried eggplants. Microwave-IR-dried eggplants had more porous structure than hot-air-dried ones. Therefore, these eggplants had lower shrinkage and higher rehydration ratio than hot-air-dried ones. Osmotically dehydrated eggplants had higher shrinkage and lower rehydration ratio than untreated ones.