Resumen

The antimicrobial activity of thyme essential oil against pathogenic microorganisms has been extensively studied in many in-vitro studies, however not many in-vivo studies have been reported, especially related to its application on fresh cheese. The aim of this study was to determine the effect of thyme essential oil against the growth of Escherichia coli and Listeria monocytogenes, which are amongst the most important foodborne pathogenic microorganisms, in fresh cheese; it is important to note that several foodborne outbreaks produced by these microorganisms from cheese consumption have been reported. Different concentrations of thyme essential oil, applied by direct contact, were evaluated in in-vitro systems (tryptic soy agar plates) inoculated with E. coli and L. monocytogenes for studying the possible antibacterial effect and obtain the minimal inhibitory concentration (MIC) of this essential oil against these microorganisms. Afterwards, the effect of MIC and 2MIC in fresh cheese (stored at 10°C for 14 days) inoculated with E. coli and L. monocytogenes, was studied. Results show that the growth of E. coli in fresh cheese, stored at 10°C was effectively inhibited by applying thyme essential oil at a concentration of 0.22 μl thyme essential oil/g cheese. On the other hand, the growth of L. monocytogenes was also inhibited in an in-vitro system, stored at 10°C, by applying thyme essential oil at a concentration of at least 0.14 μl thyme essential oil/g cheese. However, in fresh cheese not even a concentration of 0.44 μl thyme essential oil/g cheese attained the inhibition of growth of L. monocytogenes; this microorganism has a great resistance to thyme essential oil when applied to a food system that provides a favorable environment for its growth.

Thus, thyme essential oil can be a viable alternative to use as antimicrobial agent against the growth of E. coli in fresh cheese since the required concentration is low, so it is unlikely that it will affect sensory attributes. Regarding its use as an antimicrobial against L. monocytogenes, definitive conclusions cannot yet be made, because although it seems that thyme essential oil does have an effect on L. monocytogenes growth, additional tests are required to observe if at higher concentrations than the ones tested, the essential oil manages to inhibit its growth in fresh cheese, while determining that this concentration does not affect fresh cheese sensory characteristics.

Key words: Thyme essential oil, Escherichia coli, Listeria monocytogenes, antimicrobial, minimal inhibitory concentration.

Palabras clave: Thyme essential oil, Escherichia coli, Listeria monocytogenes, antimicrobial, minimal inhibitory concentration..

Table of content

Portada (archivo pdf, 167 kb)

Agradecimientos (archivo pdf, 286 kb)

Índices (archivo pdf, 235 kb)

Capítulo 1. Introduction (archivo pdf, 290 kb)

Capítulo 2. Materials and Methods (archivo pdf, 505 kb)

Capítulo 3. Results and Discussion (archivo pdf, 493 kb)

Capítulo 4. Conclusions and Recommendations (archivo pdf, 440 kb)

Referencias (archivo pdf, 264 kb)

Tecuanhuey López, M. d. 2017. Response of Listeria monocytogenes and Escherichia coli inoculated in Fresh Cheese exposed to thyme essential oil by direct contact. Tesis Licenciatura. Ingeniería de Alimentos. Departamento de Ingeniería Química, Alimentos y Ambiental, Escuela de Ingeniería, Universidad de las Américas Puebla. Diciembre. Derechos Reservados © 2017.