Effects of air velocity and infrared radiation intensity on drying factors of lemon verbena (Lippia citriodora Kunth.)

To evaluate the effect of air velocity and infrared radiation intensity on drying time, essential oil content, and composition of Lemon Verbena (Lippia citriodora Kunth), a factorial experiment based on completely randomized design was carried out. The two main treatments were as follows: three air velocity levels (0.5, 1 & 1.5m/s) and three levels of infrared radiation intensities (0.2, 0.3 & 0.5W/cm2). After drying the samples, their essential oil was extracted by hydro-distillation method and compositions of essential oil were identified with capillary gas chromatography, using flame ionization and mass spectrometric detection. Results indicated that the various treatments had significant effects on drying time and essential oil content. With decreasing air velocity and increasing radiation intensity, drying time was reduced. Minimum drying time (35 minutes) was obtained at 0.5 m/s air velocity with the use of 0.5W/cm2 radiation intensity. In contrast, the maximum drying time (65 minutes) was revealed for the sample treated with 1.5 m/s air velocity, which received concomitantly 0.4W/cm2 radiation intensity. Increasing the intensity of infrared radiation in all air velocities had a significant effect on the essential oil content, so that the maximum essential oil content (1.1%) was obtained by application of 1 &1.5 m/s air velocity and the use of 0.5W/cm2 radiation intensity. The survey of essential oil components showed that the highest amount of oxygenated monoterpenes (73.3%), especially citral (61.3%) was measured from samples dried by 0.5 m/s air velocity and 0.2W/cm2 radiation intensity. According to these results, due to the decreased duration of drying time and desired essential oil content and composition, it seems that the use of infrared radiation in conventional dryers could lead to appropriate quality of essential oil.