Determination of Optimum Conditions for Thin-Layer Drying of Lemon Balm Leaves (Melissa Officinalis L.)

Abstract

Drying kinetics of Melissa officinalis were investigated in a laboratory scale hot air dryer at an air velocity of 0.5, 0.75 and 1.00 m/s and temperature range of 30, 40 and 50°C to find out the optimum drying conditions in terms of drying rate.Drying rate increased significantly with the increase in air temperature. Drying rate increased with the increase of air velocity up to 1.0 m/s. Above this air velocity, drying rate became independent of air velocity. The optimum drying air conditions was the temperature of 50°C and air velocity of 1.0 m/s, when drying time was considered. The experimental data were fitted to determine the drying constant "k" for drying lemon balm in thin layer. Hence, optimum lemon balm in color may be dried at an air temperature of 40°C and air velocity of from 0.75 to 1.0 m/s and this is the maximum air temperature may be recommended to describe the thin layer drying of lemon balm. The effective moisture diffusivity was determined of lemon balm during drying. The effective moisture diffusivity of Melisa increased linearly from 9.2×10 -10 to 2.16 ×10 -9 m 2 /s as drying air temperature increased from 30 to 50°C. The activated energy of Melissa officinalis was calculated and found to be 24.62 kJ/mol.