Anti-Listeria efficacy of peroxyacetic acid in bacterial buffered solution and on bell peppers

This study aims to 1) evaluate the efficacy of peroxyacetic acid (PAA) to inactivate Listeria monocytogenes in 0.1 % buffered-peptone-water; and 2) evaluate the reduction and mitigation of cross-contamination on peppers. In study-1, aliquots of 1.0-ml PAA solutions (133, 265, and 448 ppm) were added to the first 6 wells of 8-strip-deep well microplates. Then, 0.1 ml of serially diluted nalidixic-acid-resistant (NaL) L. monocytogenes was added and mixed immediately with a multichannel pipette. After exposure for 0, 5, 15, 30, and up to 120-s, 1 ml of 2 × D/E neutralized solution was added to terminate the reaction followed by spread-plating onto tryptic soy agar +200 ppm NaL and incubated at 35 °C for 48 h. In study-2, 5 inoculated red peppers were triple-washed with 15 uninoculated green peppers with 0, 23, 53, and 96 ppm of PAA and analyzed using MPN-method. L. monocytogenes counts were <0.3 log₁₀ CFU/ml after exposure to 133, 265, and 448 ppm of PAA for 120, 90 and 60 s, respectively and fit the Linear and Weibull Models. Applying 23–96 ppm of PAA reduced L. monocytogenes by 2.03–3.32 log₁₀MPN/g and transferred cross-contaminated cell counts by 2.36–3.17 log₁₀MPN/g, with no differences (P > 0.05) compared to the water only treatment. Results suggested that applying allowable concentrations (23–96 ppm) of PAA during triple-wash does not show promising anti-Listeria activity on peppers. Future studies are needed to determine the minimum concentrations of the PAA solution required to effectively reduce and mitigate microbial cross-contamination of Listeria monocytogenes on peppers.