Abstract:
Listeria monocytogenes has been referred to as a concern microorganism in cheese making due
to its ability to survive and grow in a wide range of environmental conditions, such as refrigeration
temperatures, low pH and high salt concentration at the end of the production process. Since cheese
may be a potential hazard for consumers, especially high-risk consumers (e.g., pregnant, young
children, the elderly, people with medical conditions), efforts of the dairy industry have been aimed at
investigating new conservation techniques based on natural additives to meet consumers’ demands
on less processed foods without compromising the food safety. Thus, the aim of this study was to
evaluate the efficacy of Myrtus communis L. (myrtle) and Rosmarinus officinalis L. (rosemary) essential
oils (EO) against Listeria monocytogenes ATCC 679 spiked in sheep cheese before ripening. After the
cheesemaking process, the samples were stored at 8 C for 2 h, 1 d, 3 d, 14 d and 28 d. The composition
of EO was identified by gas chromatography-mass spectrometry (GC-MS) analysis. Constituents
such as 1,8-cineole, limonene, methyl-eugenol, -pinene, -terpineol, -terpinolene and -pinene
were present in both EO, accounting for 44.61% and 39.76% from the total of chemical compounds
identified for myrtle and rosemary EO, respectively. According to the chemical classification, both
EO were mainly composed of monoterpenes. Minimum inhibitory concentration (MIC) against
L. monocytogenes was obtained at 31.25 L/mL to myrtle EO and at 0.40 L/mL to rosemary EO.
Then, cheeses were inoculated with L. monocytogenes (Ca. 6 log CFU/mL) and EO was added at
MIC value. The addition of rosemary and myrtle EO displayed lower counts of L. monocytogenes
(p < 0.01) (about 1–2 log CFU/g) during the ripening period compared to control samples. Ripening
only influences (p < 0.001) the growth of L. monocytogenes in control samples. Since rosemary and
myrtle EO do not exert any negative impact on the growth of native microflora (p > 0.05), their use
as natural antimicrobial additives in cheese demonstrated a potential for dairy processors to assure
safety against L. monocytogenes.
