Evaluation of drying parameters and desorption isotherms of garden mint leaves (Mentha crispa L.)

Abstract

Mint has been used as a medicinal and aromatic plant since ancient times. Its leaves are used for flavoring, tea infusions and spicing. In addition, mint oil is used to treat several diseases. In order to preserve this seasonal plant, and make it available to consumers during the whole year, it undergoes specific technological treatments, such as drying. Here the desorption isotherms of mint leaves were determined at three temperatures. Experimental curves were fitted to three two-parameter equations, three three-parameter equations and one four-parameter equation. All BET, GAB, Oswin and Peleg models could be used to describe the mint desorption isotherms. Experimental data for the drying of mint was obtained at three different temperatures and two different air velocities. The drying process was interpreted through the diffusional model in order to obtain effective diffusivity values, which proved to range from 4.765×10−13 to 2.945×10−12m2/s. Activation energy was calculated as 82928.5 J/mol assuming an Arrhenius-type temperature reliance. The empirical Page model has shown a better fit to the experimental mint drying data as compared to Fick's model, except for the 50°C–1.0 m/s curve.