Antimicrobial properties of essential oils and flavour compounds.

The antimicrobial effects of many herbs and spices have been well known for centuries and are used to increase the shelf-life of foods. These antimicr obial properties are attributed to the essential oil fraction. Essentials o ils have a broad spectrum of activity, with inhibition observed against bac teria, yeasts and fungi. As natural products already used as food flavours, essentials oils are currently being studied to acquire a better understand ing of their natural food preservative potential. The methods for testing t he antimicrobial properties of essential oils and aroma compounds are revie wed, with a focus on micro-atmosphere, and direct contact in liquid or soli d media. Hydrophobic compound dispersion is the main problem encountered by authors, although the use of colloidal agar-agar mixtures seems to offer a valuable solution. Essential oils and aroma compounds have a negative effe ct on the growth (8.0. Escherichia coli 0157:H7, Listeria monocytogenes), s porulation (e.g. Clostridium botulinum) and toxinogenesis (e.g. Staphylococ cus aureus) of bacteria. Concerning yeasts, the compounds show some influen ce on growth and pseudomycelium production. In fungi, spore germination may be inhibited, as well as mycelium elongation (8.0. Aspergillus flavus), sp orulation and toxinogenesis (8.0. Aspergillus ochraceus). Usually, the resu lts obtained on synthetic culture media are confirmed in food assays, but o nly if a higher amount of essential oil is added, leading to concern over p otential alteration of the organoleptic quality of foods.