Combined microwave (MW)/vacuum drying of fruit materials has a promising potential for high-quality dehydrated products. A better knowledge of the drying kinetics of fruit products could improve the design and operation of efficient dehydration systems.
A laboratory MW/vacuum drier was used for drying kinetics experiments with model fruit gels, simulating orange juice concentrate. The system was operated in the vacuum range of 30–50 mbar and MW power of 640–710 W. The distribution of the electromagnetic field in the cavity of the oven was determined from the drying rate of samples, placed at 5 different locations.
The drying rate was determined by periodic weighing of the sample. The rate constant (K) of the single-layer model of drying was estimated by regression analysis of the experimental data. An empirical model is proposed for estimating the drying constant (K) as a function of the absolute pressure and the MW power of the system.