Influence of the Applied Acoustic Energy on the Drying of Carrots and Lemon Peel

Abstract

The application of power ultrasound could constitute a way of improving traditional convective drying systems. The different effects produced by the application of power ultrasound may influence the drying rate without provoking any significant increase in product temperature. Due to the fact that the effect of power ultrasound is product dependent, the aim of this work was to address the influence of the applied acoustic energy on the convective drying of carrot and lemon peel.

Convective drying kinetics of carrot cubes (side 8.5 mm) and lemon peel slabs (thickness 7 mm) were carried out at 40°C and 1 m/s by applying different levels of acoustic power density: 0, 4, 8, 12, 16, 21, 25, 29, 33, and 37 (kW/m³). The application of power ultrasound during drying was carried out using an airborne ultrasonic transducer (21.7 kHz). Drying kinetics were described considering a diffusion model.

In both products, the application of power ultrasound improved the effective moisture diffusivity (D_e ). The improvement was linearly proportional to the applied acoustic power density. In the case of lemon peel, the effects of power ultrasound were found over all the range tested (0–37 kW/m³), whereas in the case of carrot, it was necessary to apply an acoustic power density of over 8–12 kW/m³ to be able to observe the influence. The more intense effect of acoustic energy in lemon peel drying may be explained by the fact that lemon peel is a more porous product than carrot.

Keywords:

• Drying
• Modeling
• Porosity
• Power ultrasound

ACKNOWLEDGEMENTS

The authors acknowledge the Ministerio de Educación y Ciencia for the financial support of Project AGL2006-14146-C02-01/ALI.

Notes

^a,b,c,d Homogeneous groups established from LSD intervals (p < 0.05).

^a,b,c,d,e Homogeneous groups established from LSD intervals (p < 0.05).