Expression of the changes in essential oil components of Shirazi thyme (Zataria multiflora Boiss.) as affected by various drying methods

Abstract

The purpose of this research was to investigate the impact of various drying techniques on the quality characteristics of Shirazi thyme (Zataria multiflora Boiss.) using a completely randomized design with three replications. The treatments included fresh samples, shade-drying (SHD), sun-drying (SD), oven and vacuum-drying (OD and VD) each at three different temperatures (45, 55, and 65 °C), and microwave-drying (MD) at three different power levels (200, 400, and 600 W). The results indicated that vacuum and oven-drying at 45 °C were effective in preserving valuable secondary metabolites compared to traditional drying methods. The essential oil (EO) content was lowest in the microwave-drying at 600 W (1.3 %), and highest in vacuum-drying at 45 °C (2.99 %). Vacuum-drying at 45 °C also produced the highest levels of carvacrol (72.5 %) and thymol (7.21 %) content, while the lowest levels were found in fresh samples. The main components in the EO were monoterpene hydrocarbons (11.47–27.33 %), oxygenated monoterpenes (74.81–86.9 %), and oxygenated sesquiterpenes (76.50–86.50 %). The results showed that the amount of sesquiterpene hydrocarbons and oxygenated monoterpenes were higher at low temperatures. Furthermore, the color parameters showed changes based on the drying methods, with vacuum-drying at 45 °C increasing the L* parameter (lightness), vacuum-drying at 65 °C increasing the a* parameter)brightness(, and oven-drying at 45 °C increasing the b* parameter)greenness). Understanding the different methods and operations of drying Shirazi thyme can provide valuable insight for its professional application and development in food and pharmaceutical industries.