Chemical composition, antioxidant and antimicrobial activity of the essential oil of the thyme and rosemary

Abstract

The present study was conducted to evaluate the in vitro antimicrobial and antioxidant properties of thyme and rosemary essential oils. The chemical compositions of hydro distilled essential oils were analyzed by GC/MS system. A total of 30 constituents representing of thyme oil were identified: thymol (39.44%), P-cymene (23.6%), γterpinene (12.51%), ledol (2.24%) and Aromadenrrene (2.12%) were the main components comprising 79.91% of the oil. While 37 constituents representing of rosemary oil were identified: borneol (24.13%), α – pinene (9.72%), αcaryophyllene (8.35%), ledol (6.42%), eucalyptol (5.11%), camphor (5.01%), γ – terpinene (5.005), Dverbenone (4.17%), limonene (2.29%) and methyl jasmonate (2.24) were the main components comprising 72.445 % of the oil. Antioxidant effects of essential oils from thyme and rosemary were determined on flaxseed and sesame oils. These essential oils were added to the oils at concentrations of 0.25% and 0.5%, besides the control groups for comparison. The samples were stored 65° C in darkness for 14 days. The antioxidant activity of the essential oils was determined by measuring peroxide values (meq O2/kg oil). On the basis of peroxide value assay, the essential oils showed stronger antioxidant effect when compared to control groups. Amongst the investigated essential oils, the thyme oil was the most effective on retarding lipid oxidation of crude oils, which was followed by rosemary oil. On the other hand in the present investigation antimicrobial activity of two essential oils has been evaluated. After bioassays, most of the essential oils were found susceptible to Gram-positive bacteria such as Staphylococcus aureus, Bacillus subtilis, and didn't showed any activity against Gram-negative bacteria Pseudomonas aueginosa, Escherichia coli. For screening of antimicrobial susceptibility in each essential oil, both positive and negative controls were set to determine growth inhibition zone diameters and MIC (minimum inhibitory concentration).Among two essential oils thyme oil was found to be highly antimicrobial, as it has shown high growth inhibition zone diameter in comparison to rosemary oil except against Aspergillus niger.