Drying kinetics and thermodynamic properties of patawa pulp (Oenocarpus bataua Mart.)

Abstract The patawa is an Amazonian fruit that, due to its sensory and nutritional properties, has aroused the interest of the scientific community. However, its high moisture content confers high perishability to the fresh product. Thus the convective drying kinetics were studied and the thermodynamic properties of the patawa pulp determined. Drying was carried out at different temperatures (40, 50 and 60 °C) and layer thicknesses (0.3 and 0.6 cm), with a constant air velocity of 1.8 m s-1. Different thin layer drying models were adjusted to the experimental data. Increasing the air temperature and decreasing the layer thickness increased the moisture removal rate and thus reduced the overall process time. Based on the statistical parameters, the Midilli model was the one that best described the drying kinetics of the samples under all conditions evaluated. The effective diffusion coefficients increased with increase in air temperature, showing magnitudes to the order of 10-10 m2 s-1, and its temperature dependence was represented by the Arrhenius equation, with the activation energy (Ea) from 32.41 and 40.10 kJ mol-1 for the thicknesses of 0.6 and 0.3 cm, respectively. The variations in enthalpy (ΔH) and entropy (ΔS) decreased with increasing drying temperature, being lowest in the sample dehydrated in a 0.6 cm layer, while the variation in Gibbs free energy (ΔG) increased with the increase in temperature, being higher when dried in a 0.3 cm layer.