The investigation and modelling of drying kinetic, colour change kinetic and porosity analysis of okra and spinach undergoing microwave

Utilizing a variety of food by drying has been a process being applied for centuries. The process, being achieved simply in early times, has a place in the food industry and a lot of new ones, high efficient, low cost and high quality in final products, have been developed in time. The method widely used for drying in an agriculture country, Turkey, is solar drying. However, solar drying is not a preferred method due to some disadvantages such as dusting, long period of drying, low efficiency and insufficient exposure to solar beam every time. In this stage, microwave drying has gained a great importance and alternative way due to rapid involving in food technologies. In this study, the effect of microwave drying technique on drying characteristics, color change kinetics, rehydration kinetics, Vitamin C loss and porosity of both okra and spinach have been examined. It has been observed that drying time has decreased by increasing the microwave output power or decreasing the sample amount. Although, the color of okra samples changed obviously, the color of spinach samples did not change significantly. Rehydration characteristics was also investigated.. Finally, the porosity analysis was done. But, during drying, the pores of okra samples were not observed while the pores of spinach samples were increased with the increase in microwave output power or decrease in sample amount. Mathematical modelling was done for drying, color change and rehydration kinetics and observed that Page model was fitted to drying kinetic, zero and first order kinetic model were fitted to color change kinetic and Peleg model was fitted to rehydration kinetic. Therefore, the activation energies for all kinetic parameters were calculated by using an exponential expression based on Arrhenius equation. Keywords: Okra, Spinach, Microwave, Drying time, Colour change, Rehydration, Vitamin C, Mathematical modelling, Activation energy