Microwave Drying of Green Bean Slices: Drying Kinetics and Physical Quality

Several microwave power settings were applied to green beans in order to determine the effect on the drying kinetics along with the rehydration ratio and colour values. In the experiments, several microwave power settings were studied as 180, 360, 600, and 800 W. From the results, it is seen that the level of microwave power affected the drying kinetics, rehydration ratio, and colour of the beans slightly. The nine best known thin-layer drying models that were used in literature were applied to the experimental data and the results showed that Midilli et al. model best fits the experimental data for the drying kinetics of green bean slices. Effective moisture diffusivity was found to be between 1.387 x 10(-8) and 3.724 x 10(-8) m(2)/s. Using modified Arrhenius type equation the activation energy was found as 19.185 kW/kg. The rehydration ratio of samples dried at 800 W was higher than those of samples at other power settings. It was observed that an increase in the microwave power increased the brightness and yellowness, on the contrary, it decreased the greenness of the dried samples.