Research Article Impact of Moderate Heat, Carvacrol, and Thymol Treatments on the Viability, Injury, and Stress Response of Listeria monocytogenes L. Guevara, 1 V. Antolinos, 1 A. Palop, 1,2 and P. M. Periago 1,2 1 Departamento de Ingenier´ ıa de Alimentos y del Equipamiento Agr´ ıcola, Campus de Excelencia Internacional Regional “Campus Mare Nostrum”, Escuela T´ ecnica Superior de Ingenier´ ıa Agron´ omica, Universidad Polit´ ecnica de Cartagena, Paseo Alfonso XIII 48, Cartagena, 30203 Murcia, Spain 2 Instituto de Biotecnolog´ ıa Vegetal, Campus de Excelencia Internacional Regional “Campus Mare Nostrum”, Universidad Polit´ ecnica de Cartagena, Edifcio I+D+I, Muralla del Mar, Cartagena, 30202 Murcia, Spain Correspondence should be addressed to P. M. Periago; paula.periago@upct.es Received 22 April 2015; Accepted 11 June 2015 Academic Editor: Avelino Alvarez-Ord´ o˜ nez Copyright © 2015 L. Guevara et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te microbial safety and stability of minimally processed foods are based on the application of combined preservative factors. Since microorganisms are able to develop adaptive networks to survive under conditions of stress, food safety may be afected, and therefore understanding of stress adaptive mechanisms plays a key role in designing safe food processing conditions. In the present study, the viability and the sublethal injury of Listeria monocytogenes exposed to moderate heat (55 ∘ C) and/or essential oil compounds (carvacrol and thymol, 0.3mM) treatments were studied. Synergistic efects were obtained when combining mild heat (55 ∘ C) with one or both essential oil compounds, leading to inactivation kinetics values three to four times lower than when using heat alone. All the treatments applied caused some injury in the population. Te injury levels ranged from around 20% of the surviving population under the mildest conditions to more than 99.99% under the most stringent conditions. Protein extracts of cells exposed to these treatments were analysed by two-dimensional gel electrophoresis. Te results obtained revealed that stressed cells exhibited diferential protein expression to control cells. Te proteins upregulated under these stressing conditions were implicated, among other functions, in stress response, metabolism, and protein refolding. 1. Introduction Listeria monocytogenes is a Gram-positive foodborne path- ogen microorganism. Tis microorganism causes a disease called listeriosis, which has been associated with outbreaks by ingestion of milk, cheese, vegetables, salads, and meat [1, 2]. Te pervasiveness of this microorganism is due, in part, to its ability to tolerate extreme environment conditions (high salt concentration, wide range of pH and temperature, and low water availability) [3]. Food manufactures and consumers demand additive- free, fresher, and full tasting food products while maintaining high standards of microbiological safety. Te use of natu- ral antimicrobial systems for preservation of foods could accomplish this demand. Although essential oil components are used as favourings in the food industry, nowadays they represent a highly interesting source of natural antimicrobials for food preservation due to their antimicrobial and antiox- idative activity [4]. Carvacrol and thymol are natural phenolic compounds present in the essential oil fraction of Origanum and Tymus plants [5, 6] and have long been used in foods as favour enhancers. Both compounds of essential oils (car- vacrol and thymol) have been shown to exhibit antibacterial and antifungal activity including food pathogens [5–10]. A synergistic efect of nisin, carvacrol, and thymol [9, 11] or thymol and cymene [7, 12] against vegetative cells of B. cereus has been observed. When a mild thermal treatment was applied prior to the growth in presence of antimicrobials, the sensitivity to antimicrobials was increased [8, 11]. Likewise, a synergistic efect of carvacrol and cymene [13] or nisin Hindawi Publishing Corporation BioMed Research International Volume 2015, Article ID 548930, 10 pages http://dx.doi.org/10.1155/2015/548930