Modeling kinetics of convective drying of Curcuma longa L. ¹

Modelagem e cinética de secagem da Curcuma longa L. sob convecção

ABSTRACT

This study aimed to determine drying curves of land saffron (Curcuma longa L.) rhizomes at different temperatures and ventilation conditions to adjust non-linear regression models, and to calculate effective diffusion coefficients and activation energies. Saffron rhizomes were randomly collected in natura with a hoe from the soil in Rio Verde, Goiás, Brazil. They were subsequently sized, sanitized, and sliced into 2.63 ± 0.1 mm thick sections. Rhizomes were dried in an oven with forced air ventilation at 45, 55, 65 and 75 °C for 18, 14, 10 and 9 hours, respectively. As the temperature increased, drying time was reduced. Consequently, moisture content also decreased, facilitating the drying process by decreasing the energy required to remove water molecules. Among the analyzed models, the Midilli model was best adjusted to the data under different drying air conditions. Effective diffusion coefficients (D) were 9.17 × 10^-11, 13.33 × 10^-11, 20.09 × 10^-11, and 35.89 × 10^-11 m² s^-1 at 45, 55, 65 and 75 °C, respectively, increasing with higher temperatures. Activation energy for liquid diffusion during drying was 21.186 kJ mol^-1.

Key words:
land saffron; drying curves; effective diffusion coefficient; Midilli model