Antimicrobial mechanism of trans-cinnamaldehyde and other essential oil compounds in Listeria monocytogenes

Natural antimicrobials enjoy an increasing interest in view of the trend towards healthy, minimally processed food that has a natural image and a conveniently long shelf life. They can be integrated in a hurdle concept of multiple mild food preservation strategies, which address the challenges of this trend in terms of microbiological stability and safety. Studies on natural food preservatives have so far been mainly descriptive, reporting the antimicrobial activity of different extracts and compounds against a range of food spoilage bacteria and pathogens in pure culture and in foods, sometimes in combination with other (natural) antimicrobials or processing and preservation methods. Studies on the mode of action of these compounds are however scarce. Yet, this knowledge is important to understand why some combinations of hurdles are more effective than others and it thus forms the rational basis for the development of more effective hurdle applications. Therefore, the objective of this work was to investigate the mode of action of trans-cinnamaldehyde and allyl isothiocyanate, which were previously shown to synergistically reinforce bacterial inactivation by high pressure treatment in our laboratory. Listeria monocytogenes was chosen as a model organism for this work, since it is one of the most important food-borne pathogens in minimally treated, refrigerated ready-to-eat foods.