Extraction of thymol from different varieties of thyme plants using green solvents

[Background]: Thymol (2-isopropyl-5-methylphenol) is the main monoterpene phenol found in thyme essential oil. This compound has revealed several biological properties, including antibacterial, anti-inflammatory and antioxidant activities. In this work, a comparison was made between the performance of different green solvents (ethanol, limonene and ethyl lactate), by pressurized liquid extraction (PLE) and supercritical fluid extraction (SFE) at different conditions, to extract thymol from three different varieties of thyme (Thymus vulgaris, Thymus zygis and Thymus citriodorus). Additionally, new solubility data of thymol in limonene and ethanol at ambient pressure and temperatures in the range 30-43 °C are reported. [Results]: The highest thymol recoveries were attained with T. vulgaris (7-11 mg g-1). No thymol could be quantified in the PLE samples of T. citriodorus. The highest concentrations of thymol in the extracts were obtained with limonene. Thymol is very soluble in both solvents, particularly in ethanol (~900 mg g-1 at ~40 °C), and is the main compound (in terms of peak area) present in the essential oil extracts obtained. [Conclusion]: The three solvents show good capacity to extract thymol from T. vulgaris and T. zygis by PLE. Although PLE proved to be a suitable technology to extract thymol from thyme plants, the highest concentrations of thymol were obtained by SFE with supercritical CO2.The authors gratefully acknowledge the financial support from Ministerio de Ciencia e Innovación (project 25506 FUN-C-FOOD ) and Comunidad Autónoma de Madrid (ALIBIRD- CM, project S2013/ABI-2728). DVB thanks Consejo Superior de Investigaciones Científicas (CSIC) of Spain for a JAE-pre fellowship.Peer Reviewe