Thin layer convective drying of mint leaves

Abstract

The drying kinetics of mint leaves (Mentha spicata L.) in terms of moisture content, moisture ratio, drying time and rate, and effective moisture diffusivity was investigated. A laboratory model tunnel dryer at a speed of 30 rpm was employed to study the drying behaviour at 45, 50, 55, 60 and 65°C. Mint leaves drying primarily occurred in falling rate period. The drying data were fitted to seven thin layer-drying models and the two-term model satisfactorily described the drying behaviour of mint leaves with highest r2 values. Effective moisture diffusivity (Deff) of mint leaves found to increase with the increase in drying air temperature and it ranged from 1.2325 × 10-10 to 2.6568 × 10-10 m2/s. The results of the study are very useful for commercial scale drying of mint leaves to optimize drying process and to achieve superior quality dried product. Key words: Drying, mint leaves, thin layer drying models, effective moisture diffusivity, tunnel dryer.