Due to small occurrence of Thymus carnosus Boiss. in wild, it is considered a near threatened species. Apart from some individuals growing in botanical gardens, it can only be found in Portuguese south and southwest shore, and in Huelva, Spain. Only the essential oils of this species were analysed in previous works, with borneol being the main component, followed by camphene and terpinen-4-ol. The polyphenolic composition is still unknown, being the purpose of this work to identify and quantify the polyphenols in this thyme.
Plants were harvested in UTAD botanical garden, in flowering stage, lyophilised and grounded. Then, two extraction methods were chosen: decoction, and repeated hydroethanolic extraction (HE), aiming to extract all extractable polyphenols. Extracts were frozen and lyophilised. Extract yield was higher in HE (24.67±0.58%) than in decoction (21.24±1.57%). Total phenols, flavonoids and ortho-diphenols were quantified. Although there were no significant differences in total phenols, the flavonoids and ortho-diphenols content was higher in HE than in decoctions.
The extracts were analysed by HPLC-DAD and HPLC-ESI-MSn to assess their polyphenolic composition. Phenolic acids, as rosmarinic and caffeic acids, and derivatives of some flavonoids, as eriodyctiol, quercetin, luteolin and apigenin, were found in both extracts and are commonly found in Thymus genus. The three main components of the extracts were rosmarinic acid, a salvianolic acid A isomer and salvianolic acid K, these two salvianolic acids are rarely described in thyme species. Salvianolic acid A, ursolic acid and salvianic acid A were also identified but are present in lower concentrations. Their quantification revealed significant differences between extraction methods, with HE as the best method, extracting the highest amount of polyphenols.
Keywords: Thymus carnosus Boiss., phenolic profile, antiradical activity
Acknowledgements to: UTAD Botanical Garden, FCT (grant to M.T.; PD/BD/52563/2014); INTERACT-project–NORTE-01-0145-FEDER-000017, in its research line entitled ISAC, co-financed by ERDF through NORTE2020.