Drying and Extraction Kinetics of Rosemary Leaves: Experiments and Modeling

Abstract

The purpose of this study is to determine and model the drying and extraction kinetics of rosemary leaves, to evaluate the influence of drying on yield and quality of essential oil of rosemary ( Rosemarinus officinalis L.). The drying was carried out in a convection oven (40, 50 and 60°C) and at ambient air drying (21°C), by using five models reported in the literature and from the statistical view, the Page model fits well the results for oven drying and the Fick model for the ambient air drying. Apparent moisture diffusivity ranged between 0.2×10−12 and 9.4×10−12 m2/s and increases with the air temperature, and an Arrhenius relation with an activation energy value of 66.3 kJ/mol expressed effect of temperature on the diffusivity. The fresh and dried leaves of rosemary were subjected to steam distillation. Higher drying temperature decreased the essential oil content (% w/w), from 1.3% (ambient air) to 0.9% (40°C) to 0.4% (50°C) and 0.2% (60°C). The dried leaves at ambient temperature showed the highest oil contents and an extraction rate of essential oil significant. In addition, the Fick's model describes correctly the extraction of essential oil of rosemary leaves with a range of apparent diffusivity varying from 9.8×10−13 to 1.4×10−12 m2/s and decreases when the temperature of drying increases. The analysis of the oils by GC-MS revealed a total of 28 compounds in essential oils obtained from dried leaves at ambient temperature. The major components were camphor (25.5%), α-pinene (17.9%), camphene (10.3%), ortho-cymene (8.6%) and borneol (4.0%). The composition of the oil of this rosemary selection (old age) is different to other rosemary oils, o-cymene was found to be the characteristic constituent of the oil of the new Algerian selection.