Seasonal variation affects the composition and antibacterial and antioxidant activities of Thymus vulgaris

The chemical composition and pharmaceutical properties of thyme essential oil have been of great interest to researchers and food industries. The aim of the present study was to evaluate the effects of seasonal variation on the composition and antimicrobial and antioxidant activities of the essential oil of Thymus vulgaris, as well as to determine the activity of the main pure compounds. Composition of the essential oil was determined by GC/MS. Antioxidant activity of the essential oil and the pure compounds was tested by DPPH, ABTS, and FRAP methods. Antimicrobial activity of essential oil and pure compounds was evaluated by determination of minimum inhibitory concentration. The major compounds of all tested samples were thymol (38.99-52.92%), p-cymene (14.38-26.58%), γ-terpinene (10.43-19.09%), linalool (2.39-3.56%), and carvacrol (1.87-3.3%). The essential oil gathered in October/2012 showed the highest antioxidant activity and strongest antimicrobial activity against S. Aureus (MIC = 20 μg/mL), E. Coli (MIC = 50 μg/mL) and S. typhimurium (MIC = 500 μg/mL). Furthermore, the above sample contained the highest amount of thymol. Regarding the analyses of pure compounds, only thymol and carvacrol showed free radical scavenging capacity, and strong antimicrobial activity, while thymol was the most effective against S. Aureus (MIC = 250 μg/mL), E. Coli (MIC = 120 μg/mL) and S. typhimurium (MIC = 60 μg/mL). Data suggested the spring time (around 20 °C in Brazil) as the appropriate season to collect the essential oil from thyme.