Microwave-infrared combination drying of eggplants

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Food Engineering, Turkey

Approval Date: 2014




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 tray dryer at 50°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. In addition, increase in microwave and IR powers increased drying rates so decreased drying time. Effective diffusivity of hot air drying (5.07×10-10 m2/s) was found to be lower than that of microwave-IR drying (7.099×10-9-1.445×10-8 m2/s). Higher microwave and IR powers increased but osmotic pretreatment decreased effective diffusivity. 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. Decrease in IR power and increase in osmotic dehydration increased L* but decreased a* values. Eggplants dried in microwave-IR combination at 20% IR power and 50% microwave power without any pretreatment had higher rehydration ratio but lower shrinkage as compared to hot air dried ones.