Microwave Drying of Black Olive Slices : Effects on Total Phenolic Contents and Colour

In this study, the drying behaviour of black olive slices using microwave was investigated and the effects of microwave power on total phenolic content and colour were determined. Black olive slices were dried at different power levels (180, 360, and 540 W) using a microwave cabin. The results showed that the drying time of the olive slices decreased considerably as the microwave power increased. The total phenolic content of the product dried at 540 W was found to be significantly lower than those dried at 180 or 360 W. For the microwave power range studied, the use of an irreversible first-order model adequately described the decrease in the total phenolic content. The effects of microwave power level on changes of the surface temperatures and weight loss ratios of the olive slices were also determined. The temperature increase and the weight loss were the highest at 540 W during drying. Changes in the colour values (L*, a*, and b*) of the black olive slices during drying were statistically different ( P<0.05 ) for each microwave power level and the maximum colour change in brightness occurred drying at 360 W. It is thought that results obtained in this study will provide valuable data for the design of microwave drying systems used for drying of olive slices in pilot or industrial scales.