Evaluation of qualitative characteristics of hyssop (Hyssopus officinalis L.) in infrared drying

In order to investigate the effects of infrared radiation intensity and air velocity on some of the qualitative characteristics of hyssop (Hyssopus officinalis L.) during the drying process, a factorial experiment was conducted in a completely randomized design with three replications. The infrared radiation intensity was investigated at three levels of 0.2, 0.3 and 0.5 W/cm2 and the air flow velocity at 0.5, 1 and 1.5 m/s, and traits such as color parameters, essential oil content and composition were evaluated. The results showed a significant effect of treatments on all studied traits. In the radiation intensity of 0.3 W/cm2, with increasing air flow velocity, there was a significant increase in the desired color parameters such as brightness index (L), green color (a) and color purity (chroma). Generally, the color of samples was better maintained at lower radiation intensities. The essential oil content of dried samples in the intensity of 0.2 and 0.3 W/cm2 was about 0.2% higher than the radiation intensity of 0.5 W/cm2. Increasing the air flow velocity at low radiation intensities reduced the essential oil percentage, but in 0.5 W/cm2, the essential oil content increased by 0.17% with increasing the air flow velocity. The amount of cis-Pinocamphone in the essential oil of treated samples with a low-intensity infrared radiation was higher than the high-intensity treated ones, so that the amount of this component in 0.2 W/cm2 was 3.5 to 18.9% more than 0.5 W/cm2. Overall, the results of this study showed that the use of low infrared radiation intensity in drying process of hyssop could preserve leaves color parameters along with the essential oil content and its main components.