DRYING OF THYME (THYMUS VULGARIS L.) AND SELECTION OF A SUITABLE THIN-LAYER DRYING MODEL

The air drying characteristics of thyme was investigated at a temperature range of 40-60C and at an air velocity of 2.0 m/s. The drying time varied from 120 to 495 min. Increase in air temperature significantly reduced the drying time of the thyme. Effective moisture diffusivity was estimated using the analytical solution of Fick's law of diffusion. It was found to be in the range of 1.097-5.991 x 10(-9) m(2)/s in the temperature range. The temperature dependence of the effective moisture diffusivity was described by the Arrhenius relationship with activation energy of 73.84 kJ/mol. Twelve mathematical models were evaluated by using the coefficient of determination (R-2), mean relative percent error (P), reduced chi-square (chi(2)) and root mean square error. The drying characteristics of thyme were well predicted by the Midilli et al. model within the limits of the experiment. Rehydration behaviors were affected by the drying temperature and were found to increase with drying temperature. PRACTICAL APPLICATIONS Thyme is an aromatic herb that is used extensively to add a distinctive aroma and flavor to food. Moreover, it is also used as a herbal tea. Thyme is highly perishable, because of its high moisture content, and needs drying. Unfortunately, there has been no study ever carried out explaining the drying characteristics of thyme in literature. This research is useful for producers of not only dry thyme, but also aromatic herbs.