| Abstrakt: |
Natural antimicrobials such as plant essential oils (EOs) may be useful for controlling pathogenic bacteria on fresh-cut vegetables. The antilisterial properties of EOs (thyme, oregano, and rosemary), in combination with different storage atmospheres (air, 5% CO2–2% O2–93% N2, and 20% CO2–1% O2–79% N2) and temperatures (4 and 8°C), were examined using a gas flow-through system combined with a vegetable agar model. The antimicrobial effects of the EOs varied depending on the oil, the Listeriastrain and species, the method of application, and the storage conditions tested. Using the disk diffusion assay, the antilisterial effectiveness of the oils was in the following order: thyme EO > oregano EO > rosemary EO. Volatiles released from the EOs resulted in very small antilisterial effects, indicating that the oils needed to be in direct contact with cultures in order to be effective. There were strain and species effects, with L. innocuaNCTC 11288 exhibiting the strongest resistance to EOs, and L. monocytogenesNCTC 7973 being the most sensitive strain. In addition, the effectiveness of the EOs was influenced by storage atmosphere and temperature. Use of EOs in combination with a gas atmosphere of 20% CO2–1% O2–79% N2had the greatest antilisterial effect, suggesting that high CO2atmospheres enhanced the antilisterial properties of EOs. Lowering the storage temperature from 8 to 4°C improved the antilisterial activity of thyme oil. It is concluded that thyme and oregano EOs display strong inhibitory effects against Listeriaand that increasing CO2levels and lowering storage temperatures further enhance these antilisterial effects. |
