Coupled Extraction and Dynamic Headspace Techniques for the Characterization of Essential Oil and Aroma Fingerprint of Thymus Species

Natural essential oils and extracts were obtained from three different Thymus species (T. zygis subsp. gracilis (Boiss.) Morales, T. x citriodorus (Pers.) Schreb. and T. fontqueri (Jalas) Molero e Rovira) using hydrodistillation and supercritical fluid CO2 extraction techniques, respectively. Furthermore, the aroma fingerprint of the plant materials was also characterized by collecting the volatiles through dynamic headspace-thermal desorption technique. In order to achieve that goal, the odor space was characterized by calculating odor values and by using an olfactory family model previously validated for both quantification and classification of volatile odorants. The obtained oils were characterized in terms of their organoleptic qualities as well as their chemical composition by gas chromatography coupled with mass spectrometry. A comparison amidst different species indicates that T. zygis and T. fontqueri show a phenolic type, mainly from high thymol and carvacrol content, respectively, while T. x citriodorus was richest in geraniol and citral. Furthermore, their organoleptic qualities also revealed odor similarities between T. zygis and T. fontqueri, both exhibiting a light herbaceous odor, in opposition to a strong lemon-herbaceous scent for T. x citriodorus. Hydrodistillation extraction yields ranged between 0.67% (w/w) for both T. zygis and T. fontqueri and 1.26% (w/w) for T. x citriodorus. In comparison, extraction yields for supercritical CO2 samples were lower for T. x citriodorus and T. fontqueri (