Air-borne ultrasound application in the convective drying of strawberry

The use of non-thermal technologies, such as power ultrasound, is mostly suitable for the drying of thermolabile food materials. Thereby, the air-borne ultrasonic application as a means of improving the convective drying of strawberry has been explored in this work. Experiments were conducted by setting the acoustic power applied (0, 30 and 60 W) and the air temperature (40, 50, 60 and 70 degrees C). The desorption isotherms and the shrinkage pattern were also experimentally determined. In order to describe the drying kinetics, a diffusion model considering both convective transport and shrinkage was used. The increase in both the applied acoustic power and temperature gave rise to a significant reduction of drying time (13-44%). The application of power ultrasound involved a significant (p < 0.05) improvement in the effective moisture diffusivity and the mass transfer coefficient, the effect being less intense at high temperatures. The results reported here highlight the fact that ultrasonic application during convective drying is a promising supporting technology with which to reduce the drying time needed for heat sensitive products, such as strawberry. (C) 2014 Elsevier Ltd. All rights reserved.