Study of Thin-Layer Drying Kinetics of Fermented Cocoa Beans (Theobroma Cacao L) Using Semi-Empirical Models: Determination of Effective Moisture Diffusivity and Activation Energy

Abstract

This study is all about of cocoa beans moisture content behavior and prediction, during drying and experimental determination of effective moisture diffusivity and activation energy of thin-layer. Experiments were carried out on fermented cocoa beans using an oven at 40, 45, 50, 55 and 60°C. Seven semi-empirical models based on the drying kinetics were used for the modeling. This work determined the effective moisture diffusivities and activation energy of cocoa beans using respectively a variable diffusivity model based on Fick's second diffusion law and Arrhenius standard equation. The aim was to obtain the evolution of moisture content in cocoa beans considering temperature, moisture content ratio and time. The results revealed and demonstrated the reliability of some theoretical models with natural drying for temperatures below 45 °C and others with convective hot-air drying for temperatures above 50°C. All of these models seemed to be the most appropriate for describing the type of drying of cocoa beans. Values of the apparent diffusion coefficient are between 2.33275 x 10^-11 m²/s and 2.8561 x 10^-11 m²/s. The effective moisture diffusivity increases as a function of the drying temperature and decreases as a function of the decrease in moisture content of the product. Values of Do and Ea were estimated respectively as 1.23 10^-6 m²/s and 43.56 kJ/mol respectively, in accordance with material and literature. It was observed that, pH values of different cocoa beans samples were between 4.82±0.26 and 5.43±0.41.