Convective Drying Behavior of Tarhana Dough

In this study, convective air drying was applied to tarhana dough using an electric pilot oven. A three-stage drying process was recommended as a means of shortening the overall drying period. This consisted of the drying of one-side of a thin layer of tarhana dough, a subsequent drying of the reverse-side thin layer of tarhana dough, followed by that of flake drying, which is obtained after the flaking of the semi-dried thin layers. The moisture transfer behavior of the thin layers of tarhana dough and flakes was determined by observing the moisture content and drying rate (kg moisture/m2/s) profiles at air temperatures of 60, 80 and 100C, until the equilibrium of the final moisture content. The moisture diffusivities for each stage were predicted by the analytical solution of Fick's second law of diffusion. At each drying temperature, considerably higher effective diffusivity values were obtained for flake drying (16.3-36.4 x 10(-8) m(2)/s) as compared with thin layer dough drying (0.7-2.6 x 10(-8) m(2)/s; p < 0.05). The convective drying of tarhana in three stages was then simulated by an implicit finite difference numerical solution using the predicted effective moisture diffusivity values as input. A suitable agreement between the numerical and experimental moisture profiles was achieved. The volatile compounds of tarhana powders and their concentrations were determined by headspace solid-phase micro-extraction. A sharp reduction in the concentration of specific volatile compounds with applied air temperatures, which are equal to and higher than 80C, was observed.