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 (D_eff) 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.