The aim of this study was to optimize the antimicrobial efficacy of plant essential oils (EOs) for control of
Listeria monocytogenes (L. monocytogenes) serovar 4b CECT 935 using laboratory media and minced beef
stored at 5 1 C. Commercial EOs obtained from leave parts of Mediterranean Pistacia lentiscus
(P. lentiscus) and Satureja montana (S. montana) were analyzed by gas chromatographyemass spectrometry
(GCeMS). The main components of EOs obtained were b-myrcene (15.18%) and carvacrol
(29.19%), respectively for P. lentiscus and S. montana. The in vitro antimicrobial activity of both EOs was
evaluated against L. monocytogenes using the agar diffusion technique, the minimum inhibitory
concentrations (MIC) were also determined against the same microorganism using the broth microdilution
method. According to the diameters of inhibition, S. montana EO had more antibacterial effects
than that from P. lentiscus. MICs showed a range of 0.03 and 0.10% (vol/vol) respectively for S. montana
and P. lentiscus. S. montana and P. lentiscus EOs were added respectively in minced beef (twofold MIC
values) at 0.06 and 0.20%, experimentally inoculated with L. monocytogenes at a level of 3 105 CFU/g
and stored at 5 1 C during one week. S. montana EO was the more effective (P < 0.05) against target
bacteria. P. lentiscus EO also demonstrated antibacterial effect against the same bacterium. EO combinations
were also investigated in minced beef and P. lentiscus combined with S. montana had synergistic
effects. This work shows that the combined EOs might be more effective against L. monocytogenes when
applied to minced beef at the ratio of 1/1 to 2/2 according to the MIC values. Sensory evaluation revealed
that minced beef treated with EOs was acceptable by panelists at the levels used.