Determination of Kinetic and Thermodynamic Properties of Dill Leaves during Convective Drying

The design of drying equipment and plants requires the knowledge of accurate kinetic and thermodynamic properties of agricultural products. Furthermore, these properties are important for the calculation of energy requirements in drying process, the properties of adsorbed water, evaluate the microstructure of foodstuff and to study the physical phenomenon that occurs on the food surface. Since there is no report on the thermodynamic properties of dill leaves, the aim of this study was to obtain the drying curves of dill leaves, determination of the activation energy and the thermodynamic properties under different drying temperature. Color characteristic was evaluated as one important indicator of food quality and marketability. Dill leaves were dried in a hot air dryer at four temperatures (50, 60, 70,80° C) from an initial moisture content 6.185 (kg water/kg dry matter) to the moisture content 0.075 (kg water/kg dry matter). Midilli model was chosenasthe best model to describe the drying process of dill leaves. The effective diffusion coefficient of dill leaves increased with increasing drying temperature.The activation energy for leaves drying for liquid diffusion was obtained 42.29 kJmol−1. The enthalpy and entropy decreased with increasing temperature, while Gibbs free energy increased. Their values ranged between 39.35 and 39.60 kJ mol−1, between −0.3079 and −0.2927 kJ mol−1 K−1 and between 138.96 and 143.46 kJ mol−1for enthalpy, entropy and Gibbs free energy, respectively. Results of color parameters showed that drying caused a decrease in brightness, yellowness and greenness and the lowest loss of color was observed in 60°C.