Evaluation of drying parameters and sorption isotherms of mint leaves (M. pulegium)

This paper deals with sorption isotherms and drying kinetics of mint leaves (M. pulegium). The sorption isotherms have been determined using a static gravimetric method and then fitted by GAB, equation at 30, 40 and 50 °C over a range of relative humidity from 0.05 to 0.9. Experimental data for the drying of mint was obtained at four temperatures and two flow rate. The increase in air temperature significantly reduced the drying time of the mint leaves. Drying data of this material were analysed to obtain diffusivity values from the falling rate-drying period. In this period, moisture transfer from mint leaves was described by applying the Fick’s diffusion model. Effective diffusivity varied from 1.9871 × 10-11 to 1.4221 × 10-10 m2/s and increased with the air temperature. An Arrhenius relation with an activation energy value of 57.12 kJ/mol expressed effect of temperature on the diffusivity. The expression of the drying rate is determined empirically from the characteristic curve of drying. The logarithmic model was found to satisfactorily describe the kinetics of air-drying of mint leaves.