Inactivation Kinetics of Listeria monocytogenes on Hard-Cooked Eggs Treated with Organic Acids

Peeled hard-cooked eggs (HCEs) are a popular and convenient choice for consumers and food servicers. A recent outbreak and several recalls of HCEs have highlighted their susceptibility to contamination with <i>Listeria monocytogenes</i>. HCEs are generally treated with antimicrobials, such as citric acid, to enhance the safety and quality of the product. A 2019 multistate outbreak linked to consumption of contaminated HCEs in the U.S. prompted research on the effectiveness of citric acid, and other organic acids, to control <i>L. monocytogenes</i> on this food product. This study therefore assessed the use of organic acids as antimicrobials against <i>L. monocytogenes</i> on HCEs. HCEs were dip-inoculated with <i>L. monocytogenes,</i> resulting in an initial concentration of ca. 8 log CFU/HCE. Following air-drying for 10 min, HCEs were treated at 5 or 25 °C with water, 0.3 or 2% citric acid, or 2% acetic, lactic, or malic acid for up to 24 h to determine reductions in <i>L. monocytogenes</i> populations. After 24 h of treatment, 0.3% citric acid treatment resulted in population reductions of <1.24 log CFU/HCE regardless of treatment temperature, while 2% organic acids resulted in statistically significant reductions of 2.88-4.78 log CFU/HCE at 5 °C and 2.35-5.10 log CFU/HCE at 25 °C. The highest <i>L. monocytogenes</i> reductions on HCEs resulted from the 2% malic acid treatment at 5 °C and the 2% acetic acid treatment at 25 °C. Primary modeling was used to determine the inactivation kinetics and model fit with the Weibull and log-linear models, both estimating the rapid rates of inactivation when using the 2% malic and lactic acid treatments at 25 °C. The results of this study suggest that 2% acetic, lactic, and malic acids may be effective treatments for the control of <i>L. monocytogenes</i> on HCEs.