Abstract
The atmospheric freeze drying (AFD) constitutes an interesting alternative to vacuum freeze drying providing products with
similar quality at lowest cost. However, the long process time needed represent an important drawback. In this sense, the
application of high intensity ultrasound can enhance heat and mass transfer and intensify the operation. In hot air drying
operation, the ultrasonic effects are dependent on the process variables such as air velocity, internal sample structure or ultrasonic
power applied. However, in AFD processes, the internal structure of material or the air velocity has not significant influence on
the magnitude of ultrasonic effects. The aim of this work was to determine the influence on drying kinetics of the ultrasonic
power applied during the AFD of apple. For that purpose, AFD experiments (-10ºC, 2 m/s and 15% relative humidity) of apple
slabs (cv. Granny Smith, 30 x 30 x 10 mm) were carried out with ultrasound application (21 kHz) at different power levels (0,
10.3, 20.5 and 30.8 kW/m3). The drying kinetics was obtained from the initial moisture content and the weight evolution of
samples during drying. Experimental results showed a significant (p<0.05) influence of the ultrasound application on drying.
Thus, drying time was shorter as higher the ultrasonic power applied. From modeling, it was observed that the effective diffusion
coefficient identified was 4.8 times higher when ultrasound was applied at the lowest power tested (10.3 kW/m3) that illustrated
the high intensification potential of ultrasound application in the AFD.
