Synergistic Antimicrobial Effect of Sodium Chloride and Essential Oil Components

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Abstract
The antimicrobial effect of a variety of essential oil components was examined in the presence of various concentrations of NaCl, using air-borne microorganisms and purely cultured fungi. Even at a NaCl concentration of 15%, various kinds of microorganisms grew in 7 to 10 days of incubation at 27°C. All the essential oil components examined, at a concentration of as high as 1 mM, allowed the growth of various microorganisms within a few days of incubation at 27°C when the NaCl concentration of culture media was less than 3%. However, in the presence of 7 to 10% NaCl, cinnamaldehyde, perillaldehyde, citral (α,β-unsaturated aliphatic aldehydes), citronellol, perillalcohol and geraniol (primary alcohols) all exhibited a potent antimicrobial effect at a concentration of less than 1 mM. Cuminaldehyde and eugenol were also potent in the respect. L-Menthol at 1 mM was only modest, but at 2 mM was potent in this effect. Citronellal, D-carvone, vanillin, and linalool were only modestly effective, and 1,8-cineole, anethole, and safrole were almost ineffective even at a concentration of 2mM. Hydrocarbons (α-pinene, β-pinene, camphene, β-myrcene, β-caryophyllene, and ρ-cymene) even at a concentration of 2 mM were all ineffective under the same condition. These results suggest that certain essential oil components are applicable to effectively preserve foods containing more than 7% NaCl.