Phenolic Acids and Free Radical Scavenging Activity of Endemic Thymus Species

The present study aimed to examine phenolic acid profiles and free radical scavenging activity of four endemic Thymus species: T. perinicus (Velen.) Jalas (Bulgarian endemic), T. longedentatus (Degen & Urum.) Ronniger , T. comptus Friv. (Balkan endemics) and T. atticus Čelak (sub-endemic). Phenolic acids of the species were characterized in their three forms: free (identified in methanolic extracts), esterified (identified in methanolic extracts after alkaline hydrolysis) and methanol insoluble bound (identified after alkaline hydrolysis of residue material after methanol extraction). Extracts and fractions of the studied species were analysed by GC/MS. Free radical scavenging activity and total phenolic content of methanolic extracts were determined by the DPPH method and Folin – Ciocalteu reagent, respectively. 4(p)-Hydroxybenzoic, vanillic, hydroxycinnamic, protocatechuic, syringic, caffeic, ferulic, chlorogenic and rosmarinic acids were identified in the free form in the methanolic extracts. Mentioned above compounds, except dimeric phenolic acids and cinnamic acid, were found as methanolic soluble alkaline hydrolysable phenolic acids. Salicylic and sinapic acids were established as methanolic unsoluble bound phenolic acids additional. Differences in quality and especially in the quantitative composition of phenolic acids between different species were established. High free radical scavenging activity (IC 50 around 50 µg/mL) was established for all studied extracts. The study presents new data about four endemic species’ phenolic acid composition and antioxidant capacity.