Enhanced inhibition of Listeria monocytogenes and Salmonella enterica serovar Enteritidis in ready-to-eat meat by lactate and diacetate

The antimicrobial activities of salts of organic acids such as lactate and diacetate are well documented, but there is limited information on their combined effect on the survival and growth of Listeria monocytogenes and Salmonella spp. in ready-to-eat (RTE) meat. In the present study, 2.5% sodium lactate and 0.2% sodium diacetate were found to effectively control growth of the pathogens. Enhanced inhibitory effect was observed in the salt combination treatment, being synergistic in Listeria at both 5 and 10°C for up to 60 days. An additive effect was generally observed in Salmonella in an RTE meat model system. The effective inhibitory concentrations of lactate and diacetate were tested in beef bologna, a commercial RTE meat product. Enhanced pathogen inhibition was also observed.; The automated optical procedure and the standard procedure for cell enumeration were used to determine the behavior of Listeria in RTE meat, and to test the efficacy of the antimicrobials. A high negative correlation (r), ranging from 0.92 to 0.99, was obtained between the detection time (DT) recorded by the optic procedure (BioSys Instrument) and cell numbers determined by the standard procedure. The rapid (<24 h) optic procedure was reliable in assessing the efficacy of the antimicrobials and in the rapid detection of low levels of listeriae that were undetectable by direct plating procedure.; An investigation into the effect of the stress resistance of L. monocytogenes to the salts of lactate and diacetate at pH 6.3 using a proteomic approach showed that the sodium diacetate treatment produced the highest changes in total number of proteins (198 vs. 131 in control and 150 in lactate treatment), highest unmatched proteins (124 vs. 53 in lactate), highest increase in expression (20 vs. 5 in lactate), and highest number of novel proteins (90 vs. 45 in lactate). The highest number of repressed proteins was observed in the combination treatment (41 vs. ∼30 in the single salt treatment). No difference showed in the expression level of prfA protein, the regulator of virulence genes of the pathogen, using Western blot analysis. The study suggests that the ability of L. monocytogenes to survive in the presence of lactate and diactetate is similar to survival mechanisms during NaCl or acid stress conditions, and that the expression of virulence proteins may not be affected by these salt treatments.