Mathematical Modelling and the Determination of Some Quality Parameters of Air-dried Bay Leaves

Bay leaves (Laurus nobilis L.) were dried at 40, 50 and 60°C air temperatures and 5, 10, 15% relative humidities and also under sun and shade in outdoor areas to see whether any significant difference of quality occurs in drying with hot air. During the drying tests with hot air, air flow velocity was held stable at 1·5 m s−1 and the samples were hung in the drying channels as the surface of the leaves were held parallel to the direction of air flow. To find out the moisture content changes of the samples, weight loss from the leaves were recorded at fixed intervals. Then, the data obtained from the drying tests were applied to various well-known semi-empirical mathematical models of drying. As part of this effort, five well-known models with drying rate constant as a function of air temperature and both temperature and relative humidity were tested for goodness of fit. Furthermore, to determine the effects of the drying conditions on the colour and the amount of essential oil of the bay leaves, fresh leaves and the leaves dried under different conditions were compared. Among all the drying models, the Page model was found to satisfactorily describe the kinetics of convection drying of bay leaves. It was concluded that no significant loss of quality occurs when drying bay leaves at 60°C air temperature.