ANALYSIS OF THERMODYNAMIC PROPERTIES OF COFFEE BERRIES DURING DRYING

Drying process is an important post harvest procedure, which grants the possibility to prevent or minimize the quantity and quality losses of agricultural products. This process decreases the water activity of the product, which is the main factor that affects the respiration rate of the product, fermentation processes and plague attack. Drying procedure is affected by several parameters, in which thermodynamic parameters have been recently investigated. The correct knowledge of the thermodynamic properties of the drying process of agricultural products is an important attribute in order to design drying equipments, calculate the energy required to do so, to study the properties of adsorbed water, evaluate the microstructure of foodstuff and to study the physical phenomenon that occurs on the food surface. Thus, the aim of the present work was to evaluate and obtain thermodynamic parameters of the drying process of coffee grain (Coffea arabica L.), cv. Catuai Amarelo. The dynamic method was employed to obtain the equilibrium moisture content. Entropy, enthalpy and Gibbs free energy were investigated in the present research. Three conditions of temperature and relative humidity were used (35 oC and 32.1 %; 45 oC and 15.7 % and; 55 oC and 10.2 %). Coffee berries were manually harvested with initial moisture content of 1.25 dry basis (d.b.), being submitted to the drying process until an average moisture content of 0.13 (d.b.). Enthalpy and entropy increased with the decrease of the drying air temperature. Gibbs free energy had an increment behavior with the increase of temperature.