Effect of ultrasound pre-treatment on the kinetics and thermodynamic properties of guava slices drying process

Abstract

The present work aims to evaluate the influence of sonication pre-treatment on the drying kinetics of guava circular slices in electric oven. Circular guava slices with 6.0 mm thickness were pre-treated with ultrasound for 0 min, 10 min, and 20 min, respectively. Drying kinetics experiments were performed at the temperatures of 50, 70, and 90 °C using an electric oven at 1200 W. Drying kinetics experimental data were fitted using empirical models and a diffusive model with third type boundary conditions. Process activation energy and thermodynamic properties were also determined. Drying of pre-treated samples revealed higher drying rates and less process time. Both Page and the diffusion models were adequate to describe the drying phenomena presenting coefficients of determination higher than 0.99 and low chi-squared values. Results also revealed that sonication times increased moisture transport rates with uniform distribution along with the interior of the slices during drying. The activation energy and enthalpy presented negative values and a positive correlation with the sonication time, while entropy and Gibb's free energy presented positive values and a negative correlation to the sonication time.