Thin layer drying models and characteristics of scent leaves (Ocimum gratissimum) and lemon basil leaves (Ocimum africanum)

Abstract

The effect of air temperature on the drying kinetics and characteristics of scent and lemon basil leaves were investigated using a vacuum oven dryer at 30 °C, 40 °C, 50 °C, 60 °C and 70 °C. Suitable drying models were obtained to describe the drying process. Falling rate drying phenomenon was observed for both leaves. Six thin layer drying models namely: Lewis model, Page model, Modified Page model, Logarithmic model, Two term model and Midilli model were fitted to the moisture ratio data for both scent and lemon basil leaves. Highest coefficient of determination (R2), and least sum of square error (SSE) and root mean square error (RMSE) values were determined for the Logarithmic model for scent leaf as 0.9998, 0.0002, 0.0081, and 0.9961, 0.0034 and 0.0222 for lemon basil leaf. The Two term model showed the same values for scent leaf as the Logarithmic model and 0.9967, 0.0024 and 0.0185 for lemon basil leaf. They were the best fit models for all the drying temperatures. The results showed that scent and lemon basil leaves can best be dried at 70 °C and 60 °C, respectively. The specific energy consumption and the effective moisture diffusivities (Deff) of scent and lemon basil leaves were determined at different drying air temperatures. Deffranged from 4.76×10−13to 1.47×10−12m2/s and 4.80×10−13 to 2.06×10−12 m2/s for scent and lemon basil leaves respectively, as temperature increased. Using the Arrhenius equation, the activation energy (Ea) and pre-exponential factor (Do) were determined as 25.01 kJ/mol and 8.19×10−9 m2/s for scent leaf and 32.35 kJ/mol and 1.49×10−7 for lemon basil leaves. Therefore, the Logarithmic and Two term models are recommended as the best models for the drying kinetics of scent and lemon basil leaves from the experiment.