Application of intermittent microwave - convective hot air technique on quality and nutritional characteristics of dried kiwi slices

For producing a product with better quality and nutritional characteristics, we can use a combination of hot air and microwave oven and take the advantage of both methods. In this study the effects of three drying methods (oven (40, 50 and 60 °C), microwave (90, 180 and 360 W) and the combination of microwave, oven) were investigated on fresh kiwi fruit (Hayward variety) in terms of quality properties (rehydration capacity, shrinkage and color) and nutritional properties (phenolic compounds and vitamin C). The results showed that drying of kiwi sheets using microwave, shortens drying time, although the increasing of power could adversely affects the product quality. The maximum rehydration capacity was observed in the oven method, the lowest rate of shrinkage in combined method, the lowest color changes in the microwave method, the highest phenolic compounds in combined and oven methods and highest vitamin C content in the microwave method. At the end on the basis of optimal properties, Design Expert software chose the optimum methods of kiwi drying: microwave method applying power of 90 and 360 watts, oven method applying temperature of 40 °C and combination of microwave and oven with power of 90 watts and temperature of 40 °C.