Thin-layer and vibrofluidized drying of basil leaves (Ocimum basilicum L.): analysis of drying homogeneity and influence of drying conditions on the composition of essential oil and leaf colour

Abstract

A study on hot-air drying basil (Ocimum basilicum) leaves was carried out by obtaining sorption isotherms, thin-layer drying kinetics and drying in vibrofluidized equipment under temperatures from 30 to 60 °C. Experimental data of sorption isotherms and moisture variations on thin-layer drying were fitted to empirical equations to predict the equilibrium moisture content and the drying kinetics. The moisture reduction and homogeneity in vibrofluidized drying were compared to data obtained in a conventional fluidized dryer. The application of mechanical vibration under an amplitude of 5 mm and a dimensionless vibration ratio equal to 1.0 produced leaves uniformly dried and with adequate moisture for storage. The volatile constituents of basil essential oil were well preserved after vibrofluidized drying and were not significantly affected by the air temperature. The effect of the drying temperature on most colour parameters was not significant, but the loss of the green colour was slightly smaller at 30 °C.