Investigation of ultrasound pretreatment time and microwave power level on drying and rehydration kinetics of green olives

Abstract In this study, the effect of ultrasound (US) combined microwave (MW) drying of green olive slices was studied. Olive samples were exposed to ultrasound (5 and 10 minutes; 32 KHz) at room temperature before dried at microwave at 3 different power level (180W, 450 W and 800 W). The drying and rehydration characteristics and quality parameters of olives were determined by comparing with obtained by non-ultrasound pretreated MW dried samples. Midilli et al and Diffusion models were the most suitable models for US-MW drying with the highest R2, and lowest RMSE and chi square values. Total phenolic compounds (TPC) of olive slices reduced during drying in all treatments, however TPC of ultrasound pretreated samples were relatively higher those non treated samples dried at same microwave. Increasing of microwave level and ultrasound time decreased the total drying time up to B.5. This study showed that US-MW can be a useful combine drying method for olive slices which decreased the drying time and improved the qualitative properties of olives.