Synergistic Inhibitory Effect of Clove Oil and Lauric Acid on Staphylococcus aureus
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Abstract:
The inhibitory effects of three plant essential oils, clove oil, thyme oil, peppermint oil, as well as medium-chain fatty acid, lauric acid, on Staphylococcus aureus were investigated. The combination of clove oil and lauric acid with a synergistic inhibitory effect on Staphylococcus aureus was selected. The effects of such a combination on the growth and cell membrane permeability of Staphylococcus aureus were studied. The combination was used to prepare an antimicrobial preservative solution, which was applied to preserve fresh rice noodles. The results showed that the minimum inhibitory concentrations of clove oil, peppermint oil, thyme oil and lauric acid against Staphylococcus aureus was 2.00 μg/mL, 4.00 μg/mL, 7.50 μg/mL and 9.00 μg/mL, respectively. The combined use of clove oil and lauric acid exhibited a synergistic antimicrobial effect when the concentration was 1/4 MIC clove oil + 1/4 MIC lauric acid, leading to a fractional inhibitory concentration index (FICI) of 0.50. The synergistic action of clove oil and lauric acid damaged the cell membrane of Staphylococcus aureus and increased the permeability. The antimicrobial preservative solution had inhibitory effects on the total plate counts and Staphylococcus aureus in the fresh rice noodles, and exerted a positive impact on maintaining the quality of fresh rice noodles. During the72-h storage, the treatment group had a lower initial total plate counts (by at least 1.50 lg CFU/g), smaller number of Staphylococcus aureus (by 1.65 lg CFU/g), lower acidity value (by at least 0.8 °T), compared with those of the control group; The sensory evaluation score of the treatment group was higher than that of the control group. The results showed that the antimicrobial preservative solution made by the combination of clove oil and lauric acid might be an alternative compound preservative solution for fresh rice noodles.
