Anti-listerial activity of ethanolic extracts of medicinal plants, Eremophila alternifolia and Eremophila duttonii, in food homogenates and milk

Listeria monocytogenes is a foodborne pathogen responsible for the disease listeriosis. Ethanolic extracts from two native Australian traditional medicinal plants, Eremophila alternifolia and Eremophila duttonii, have been found to inhibit the growth of L. monocytogenes. These plants were investigated for their ability to control the growth of L. monocytogenes in full cream milk and skim milk and in diluted homogenates of salami, pâté and brie cheese. Time-kill experiments indicated that the extracts were able to inhibit the growth of L. monocytogenes in food at 4 °C and 37 °C. However, components in the food appeared to inhibit the anti-listerial activity of the extracts, necessitating higher concentrations to control microbial growth relative to those used in laboratory media. Preliminary investigations suggested that the active components responsible for the antimicrobial activity of each extract are most likely to be terpenes or sterols. Our study suggests that natural products derived from medicinal plants have the potential to be used as food preservatives.