Efficacy of plant essential oils as antimicrobial agents against Listeria monocytogenes in hotdogs

The purpose of this study was to evaluate the antimicrobial activity of different plant essential oils against Listeria monocytogenes, both in vitro and in a food system. Essential oils of thyme, clove, and pimenta were found to be most effective, based on disc diffusion experiments. Thyme and clove proved to be highly effective against L. monocytogenes in peptone water (I g/l) and reduced the bacterial population below detection limits at concentrations of 1 ml/l. Experiments were also carried out in hotdogs of different fat content (zero-, low-, and full-fat) to evaluate the antimicrobial activity of essential oils against L. monocytogenes. Thyme essential oil reduced bacterial populations significantly (P less than or equal to 0.05) at 1 ml/l level in zero- and low-fat hotdogs, but not in full-fat hotdogs. At 10 ml/l level it reduced the bacterial population > 1.3 log(10)cfu/g in zero-fat hotdogs, but was less effective in low- and full-fat hotdogs. Clove essential oil also exhibited antimicrobial activity at I ml/l in all hotdogs, and was more effective than thyme at 5 ml/l. However, increasing concentration to 10 ml/l did not result in significant (Pless than or equal to0.05) reduction of bacterial population. It is concluded that efficacy of essential oils was reduced in a food system due to interaction with food components. (C) 2003 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.