The Antimicrobial Effect of Rosemary and Thyme Essential Oils Against Listeria Monocytogenes in Sous Vide Cook-chill Beef During Storage

Sous vide cook-chill (SVCC) is a technology characterized by vacuum-packaging of raw or partially prepared foods before pasteurization, followed by rapid chilling and storage below 3°C. The application of essential oils (EOs) is a strategy to control pathogens and to extend the shelf life of products by reducing microbial levels and oxidative processes. The aim of this study was to evaluate the efficacy of Rosmarinus officinalis L. (rosemary) Thymus vulgaris L. (thyme) EOs against L. monocytogenes ATCC 679, inoculated in beef processed by SVCC stored at 2°C and 8°C for 1, 2, 3, 7 and 14 days. Leaves were dried and hydrodistilled in a Clevenger. Determination of minimum inhibitory concentration (MIC) assay was performed. Beef samples of m. longissimus thoracis et lumborum were packaged in bags inoculated and added individually with one of each EO at MIC values. Bags were vacuum-sealed, and samples were processed at 55°C/65min (for 3-log10 reduction). L. monocytogenes enumeration was done according to ISO 11290-2. A reduction of the population of L. monocytogenes was observed in all samples at 2°C. At day 14, the population of L. monocytogenes was similar in thyme and control at 2°C and 8°C. Inversely, rosemary at both temperatures show an added reduction of about 2-log10, comparatively to control. These results support the possibility of using rosemary as natural preservative to contribute in the reduction of L. monocytogenes and confirm the importance of using adequate chilling storage for maintain this pathogen at acceptable levels in view to prevent the risk for consumers.