Modeling the dehydration and analysis of dielectric properties of ultrasound and microwave combined vacuum frying apple slices

In this study, dehydration kinetics of ultrasound and microwave combined vacuum frying (UMVF) of apple slices was investigated and the most suited model predicting the drying kinetics was determined. The variation in dielectric properties (DPs) during frying of apple slices was determined to understand the heating behavior in microwave electric fields. In addition, oil uptake, texture properties and color parameters were also measured and analyzed. Two microwave (MW) power levels (800 and 1000 W) were used at a constant ultrasound power and frequency of 600 W and 28 kHz, respectively. The experimental frying data of apple slices were used to fit ten different mathematical models and non-linear regression analysis was used to determine model parameters. The goodness of fit was determined using the coefficient of determination (R-2), reduced chi-square (sigma(2)), root mean square error (RMSE). The Logarithmic model was found to be the most suitable for describing the frying process. By increasing MW power, the effective moisture diffusivity values increased from 1.7791 to 2.2761 x 10(-9) m(2)/s. The results have shown that the dielectric constant (e ') and loss factor (e '') of the apple slices decreased significantly with increasing frying time and the combination of ultrasound in both MW power levels. The combination of ultrasound with microwave significantly increased the penetration depth compared to when microwave vacuum frying (MVF) was used. The oil uptake of fried apple slices was reduced in UMVF compared to MVF. At the same time textural crispiness and color perimeters significantly improve in UMVF process. UMVF had greater advantages on moisture evaporation rate and uniform heating compared to MVF and it can be confidently used to produce crispy, desirable texture, healthier, and visually appealing fried foods in short time.