Oregano essential oil: influence of the chemical composition on the inhibitory activity against Salmonella Enteritidis

This study evaluated the influence of the origin and content of phenolic compounds in five Oregano Essential Oil (OEO) brands, from different part of the world, on the inhibitory activity against Salmonella Enteritidis (SE). The composition of each OEO was determined by gas chromatography coupled to mass spectrometry (GC-MS-IE). The inhibitory activity on SE was evaluated by the agar well diffusion test using alcoholic solutions at 0.1, 0.2, 0.5, 1.0, or 2.0%, observing the formation of inhibition halos after 24 hours of incubation at 30 C. Using a GC-MS-IE seventeen volatile components were identified. Carvacrol was the major component of all OEO samples. They were active against SE in all tested concentrations. The differences in the inhibitory activity presented by the five brands were not significant (p > 0.05), but the OEO from the Mediterranean, which contained p-cymene and gamma-terpinene besides carvacrol, resulted in larger inhibition halos than the other OEO. It was concluded that the in vitro growth of Salmonella Enteritidis can be inhibited by OEO, regardless the region in which oregano is produced. However, the essential oils that contain carvacrol, p- cymene, and gamma-terpinene may present a more effective antimicrobial effect.