Characterization of some Italian ornamental thyme by their aroma

Abstract

The aromatic profiles of five commercial thyme cultivars (T. vulgaris 'Silver Poise', T. vulgaris 'Erectus', T. vulgaris 'Faustini', T. x citriodorus 'Anderson's Gold', and T. x citriodorus 'Silver Queen'), cultivated in Italy, were defined both by their static headspaces (HS) and essential oils (EOs). In addition, a botanical garden sample of T. vulgaris was considered as reference material to evaluate the morphological and phytochemical differences from the selected market samples. Extractions of the volatile constituents of the different plant material were carried out by SPME (static headspace, HS) and hydrodistillation (HD) processes. GC-MS analysis provided the separation and identification of approximately 70 components in the HS samples and 50 in the hydrodistilled essential oils, accounting for more than 95% of the total. The typical main constituents of T. vulgaris were detected in all the EO samples, although qualitative and quantitative differences were found among the selected ornamental Thymus varieties. Thymol (50-55%) was the marker constituent for the three T. vulgaris cultivars, while geraniol (61-67%) characterized the essential oils of the two T. x citriodorus varieties. In all the analyzed essential oils, non-oxygenated (16-79%) and oxygenated (5-26%) monoterpenes were the typical volatile constituents. Specific target compounds (thymol, geraniol and 6-methyl-5-hepten-2-one) were selected to characterize the five thyme cultivars that are considered at present only as ornamental plants. A comparative evaluation of their EO quality was carried out in order to propose them as alternative sources of Italian raw plant material for industrial production.