Microwave/vacuum drying of model fruit gels

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. (C) 1999 Elsevier Science Ltd. All rights reserved.