Ultrasound pre-treatment prior to unripe banana air-drying: effect of the ultrasonic volumetric power on the kinetic parameters.

Abstract

Aiming to decrease the water content during the air-drying process of unripe banana slices, ultrasound (US) pre-treatments (25°C) for 20 and 25min at 9.38 and 25.63W/L ultrasonic volumetric power were evaluated. Air-drying was performed at 50 and 60°C for 360min. Unripe banana slices pretreated at 25.63W/L did not improve water migration, under either air-drying temperature, while slices pretreated at 9.38W/L resulted in an increase in water effective diffusivity of 4.8 and 13.7% at 20min US + air-drying at 50°C and 25min US + air-drying at 60°C, respectively. The drying time saving of 7% and 9%, respectively, was achieved, showing that these treatments were alternative for processing unripe banana slices. Thus, ultrasound and air-drying operational parameters required accurately defined to achieve desirable results. Experimental data were adjusted to four models and the Midilli model resulted in the best experimental data fit, with r 2 > 0.9988, RMSE < 0.0873 and χ2 < 0.00996.