Antioxidant and antimicrobial activities of fennel, ginger, oregano and thyme essential oils

In this study, the aim was to evaluate the antimicrobial and antioxidant activities of thyme (Thymus vulgaris), oregano (Origanum vulgare), ginger (Zingiber officinale) and fennel (Foeniculum vulgare) essential oils in addition to their chemical compositions. Based on the results of gas chromatography-mass spectrometry (GC—MS) analysis, major components were thymol and p-cymene in thyme, carvacrol, and p-cymene in oregano, α-zingiberene and ar-curcumene in ginger and (E)-anethole in fennel essential oils. Essential oils were investigated for their antimicrobial activities by agar well diffusion and broth microdilution methods against Campylobacter jejuni and Campylobacter coli. The inhibition zone diameters varied from 9.2 ± 0.7 to 28.7 ± 2.1 mm for C. jejuni and 14.7 ± 2.0 to 27.8 ± 2.8 mm for C. coli. While the minimum inhibitory concentrations (MICs) were lower for thyme and oregano EOs (5.65–43.20 μg/ml), the highest MIC value was obtained in fennel EO against C. jejuni (28530 μg/ml). Total phenolic contents and antioxidant activities of these essential oils were evaluated by using Folin Ciocalteu, 1,1-diphenyl-2-picrylhydrazyl (DPPH), Cupric Reducing Antioxidant Capacity (CUPRAC) and 2, 2-azinobis(3-ethylbenzo-thiazoline)-6-sulphonic acid (ABTS) methods. The total phenolic content of the essential oils ranged between 7.72 (ginger) to 193 (thyme) mg GAE/L. Antioxidant activities of thyme and oregano were found to be the highest according to the ABTS method, whereas thyme was found to be the highest by the CUPRAC method and ginger by the DPPH method.