Microwaves phenomena during drying of apple cylinders

Dehydration of apple cylinders applying microwaves (3 and 10 W/g initial incident microwave power) combined with forced air (40 °C air temperature) was performed. Drying rate and sample temperature and volume were recorded in order to analyse the coupling of heat and mass transfer mechanisms and deformation–relaxation phenomena in line with the sample dehydration. Experimental results showed the effect of temperature raise on internal evaporation phenomena producing both plasticization of sample matrix and an increase of internal pressure. As a consequence changes in sample temperature and volume, as well as the drying rate and dissipated power showed a common pathway. A general description has been developed to explain the behaviour of apple tissue under microwave drying.