CINÉTICA DE SECAGEM E PROPRIEDADES TERMODINÂMICAS DE FOLHAS DE BOLDO (Plectranthus bardatus Andrews)

Abstract

The leaves of Plectranthus Bardatus are used as medicinal plants by the Brazilian population. Among many factors that contribute to the proper storage of these products, drying is a fundamental process to reduce the moisture content, in order to maintain its herbal qualities. Different works involving the drying of leaves were carried out in the last years. However, there is no information related to the drying process related to boldo leaves. The objective of this study was to evaluate the drying kinetics at temperatures of 20, 40 and 60°C and determine its thermodynamic properties: enthalpy, entropy and Gibbs free energy. Were used for forced ventilation ovens drying process leaves thin layer. The leaves, cut evenly rectangular, were weighed periodically until reaching a constant weight. Many mathematical models were fitted to experimental data to characterize the drying processes using statistical criteria: coefficient determination (R²), estimated mean error (SE), chi-square (c²) and the distribution of residuals. According to the criteria used, Modified Henderson & Pabis was the model that best represented the drying kinetics of boldo leaves. The activation energy for the drying of the boldo leaf was 17.969 kJ mol-1. Both enthalpy and entropy decreased with increasing temperature and Gibbs free energy increased.