Antimicrobial potential of origanum vulgare hydrolate on fresh produce. Effect on rocket salad spiked with Listeria monocytogenes

Introduction: Fresh-cut salads are increasingly recognized as possible carriers of foodborne pathogens, including Listeria monocytogenes (L. monocytogenes). As interest in their consumption rises, maintaining their microbiological safety is crucial. To this effort, this study aimed to evaluate Origanum vulgare (O. vulgare) subsp. Hirtum hydrolate as an antimicrobial washing solution for rocket salad spiked with the pathogen L. monocytogenes. Material and methods: First, in vitro investigations were performed to assess the Minimum Inhibitory Concentration (MIC) of the hydrolate against three L. monocytogenes strains and analyze their growth potential at incremental hydrolate concentrations. Subsequently, the hydrolate was applied as a dipping solution to rocket salad (500 μL mL−1, 5 min) that was then stored at 4 °C for 48 h. Enumeration of the inoculated L. monocytogenes, as well as of the rocket salad microbiota, were performed. Physical–chemical (pH, aw, and color) and sensory characteristics were also evaluated. Results: The treated samples showed a reduction of L. monocytogenes load (about 1.0 log CFU/g) and a modest effect on total mesophilic and psychrophilic counts, Bacillus spp., and lactic acid bacteria, compared with control samples washed with Phosphate-Buffered Saline solution (PBS). As a positive result, the treatment did not affect significantly the physical–chemical and sensory characteristics of the rocket salad during storage. Discussion: The treatment demonstrated the antimicrobial potential of O. vulgare against L. monocytogenes while preserving product quality; however, further optimization is required to enhance effectiveness, particularly against contaminant microbiota.