MODELLING OF THIN LAYER DRYING KINETICS OF COCOA BEANS IN A MICROWAVE OVEN AND SUN

Abstract

The purpose of this work was to make a drying experiment of fermented cocoa beans concomitantly in the sunlight (using the experimental tray as a recommended device) and in a microwave oven (MO) to simulate the process by empirical models. The gradient method was used to estimate the coefficient of empirical models used in the study. The experimental data were adjusted from eleven equations published in the literature. The best suitable model was evaluated using the coefficient of determination (R²), reduced chi square (χ²), the Root Mean Square Error (RMSE), the Sum Square Error (SSE) and the Mean Relative Deviation (MRD) in percentage (%) between the experimental and predicted values. The diffusion approach model was selected for the solar drying because this model presents the best statistics characteristics (0.991; 2.49 E-04; 0.036; 0.037 and 3.401%). For the microwave oven drying, high R² values (higher than 0.95), low values of χ², RMSE, SSE and the MRD  values below 10% are given by the Page and Newton models proposed: 0.981; 0.002; 0.080; 0.080; 3.718% for the device MO 2400W; 0.974; 0.003; 0.096; 0.067; 7.708% for the MO 2800W and 0.982; 0.002; 0.069; 0.107; 8.496% for MO 3200W.