Selecting a mathemathical model for drying kinetics of yoghurt in a microwave- vacuum dryer

In the present study, the drying kinetics of non-fat yoghurt with constant thickness of 2.2 mm) in a microwave–vacuum dryer to the power of (35, 130, and 260 W) as well as 5 absolute pressure levels (60, 200, 400, 600, and 800 mbar) were evaluated. To choose the best, also 12 experimental/ semi-theoretical and/or empirical thin-layer drying models were examined. Based on the findings of this study various ranges of microwave power affects drying time where by increasing the microwave power (from 35 to 260 W), drying time significantly decreases from 90 min to 15) which is (600%). However, no significant effects in drying time were observed when reduced the absolute pressure in the system. RMSE was picked to be the most suitable model when the comparison runs between Logistic, Middilli and coworkers models for it contained maximum R2 and minimum χ2 so it could satisfactorily describe the drying kinetics of non-fat yoghurt. The effective moisture diffusivity was increased by increasing the microwave power from 4.42×10-10 to 2.83×10-9 m2s-1 while the pressure had zero effect on this value. In addition, the activation energy was calculated using the modified Arrhenius equation method.