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The foodborne illnesses associated with poultry meat due to Salmonella are a major concern in the United States. In this study, the antimicrobial efficacy of carvacrol, eugenol, thyme essential oil, and trans-cinnamaldehyde was determined against different Salmonella serotypes in vitro and on turkey breast cutlets. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of antimicrobial agents were determined using a microdilution colorimetric assay. Carvacrol was the most effective antimicrobial agent since it exhibited the lowest MIC and MBC (0.313 μL/mL, respectively) in culture media against Salmonella. Turkey breast cutlets inoculated with Salmonella Enteritidis, Salmonella Heidelberg, and Salmonella Typhimurium were dip treated with different concentrations (0.5, 1, 2, and 5% vol/vol) of carvacrol, eugenol, thyme essential oil, and trans-cinnamaldehyde for 2 min. Samples were analyzed after 24-h storage at 4°C for recovery of Salmonella. Significant reductions of Salmonella (p≤0.05) on turkey breast cutlets were obtained with 1, 2, and 5% treatments. These compounds exhibited a concentration-dependent response on turkey breast cutlets against Salmonella. For example, 1% carvacrol resulted in 1.0 log colony-forming units (CFU)/g reduction of Salmonella whereas 5% carvacrol caused 2.6 log CFU/g reduction. Based on its efficacy in the 2-min dip study, carvacrol was selected for 30-s and 60-s dip treatments of Salmonella-inoculated turkey breast cutlets. Dipping turkey breast cutlets in 5% carvacrol for 30 s and 60 s resulted in 1.0 and 1.8 log reductions of Salmonella (p≤0.05), respectively. None of the antimicrobial agents caused any changes in the meat pH (p>0.05). In conclusion, this study revealed that plant-derived compounds such as carvacrol can reduce Salmonella on turkey breast cutlets without changing the pH of meat.

Sodium metasilicate (SMS) is an alkaline antimicrobial approved by the U.S. Department of Agriculture for use in poultry processing and ready-to-eat poultry products. The objectives of this study were to determine the effectiveness of SMS against Salmonella enterica serovar Typhimurium in suspension and to elucidate the antimicrobial mechanism of action of SMS. Salmonella Typhimurium (ATCC 14028) was exposed to 0 (positive control), 0.5%, 1%, 2% (wt/vol) SMS and 0.1 N NaOH (high pH) solutions for 1, 10, and 30 min. The viability of Salmonella Typhimurium cells treated with different SMS concentrations and high pH was determined on selective and nonselective media and by staining with fluorescent propidium iodide (PI) and SYTO9 nucleic acid stains in combination with flow cytometry. Transmission electron microscopy of Salmonella Typhimurium cells was performed to observe the changes at the cellular level following exposure to SMS and high pH treatments. Treating Salmonella Typhimurium cells with SMS (as low as 0.5%) resulted in immediate inactivation of Salmonella with no detectable survivors. The breakage in membrane integrity and loss of cell viability was observed by PI uptake by cells treated with SMS with subsequent flow cytometry. Salmonella Typhimurium cells exposed to SMS and high pH appeared wrinkled, vacuolated, and lysed with their cytoplasmic material leaking into extracellular matrix on transmission electron micrographs. The findings from this study indicate that SMS acts on the cytoplasmic membrane and causes lysis of the cells and leakage of intracellular contents.

Sodium metasilicate (SMS) is a U.S. Department of Agriculture-approved antimicrobial for use in meat and poultry processing and has been known to be effective against various foodborne pathogens. However, its antimicrobial mechanism has not yet been revealed. In this study, we attempted to elucidate the mechanism by which SMS inactivates Listeria monocytogenes, a Gram-positive bacterial pathogen encountered commonly in ready-to-eat meat and poultry products. L. monocytogenes (Scott A) cells were treated with different concentrations of SMS (1.0, 2.0, 3.0, 4.0, 5.0, and 6.0% [wt/vol]) and compared with high pH treatment (0.1, 0.2, and 0.3N NaOH solutions) for 1, 10, and 30 min. SMS exhibited concentration and time effects on inactivation of L. monocytogenes. The effect of SMS on the membrane integrity and viability of L. monocytogenes was determined by use of propidium iodide (PI) and SYTO9 nucleic acid stains with subsequent flow cytometry. The breakage in membrane integrity was observed by uptake of PI by cells treated with SMS with subsequent flow cytometry. Ultrastructural changes from corresponding transmission electron micrographs further revealed the disruption in the cytoplasmic membrane and changes in the morphology of the cells treated with SMS and high pH. The results from flow cytometry experiment and transmission electron microscopy study indicated that following SMS treatment, the membrane integrity of L. monocytogenes was compromised leading to leakage of intracellular contents and subsequent cell death.