Enhanced Efficacy of Peroxyacetic Acid Against Listeria monocytogenes on Fresh Apples at Elevated Temperature

Peroxyacetic acid (PAA) is the most commonly used antimicrobial in spray bar antimicrobial treatment during fresh apple packing and processing. However, there are limited data regarding its practical efficacy against Listeria monocytogenes on fresh apples. This study evaluated the antimicrobial activity of PM against L. monocytogenes on fresh apples applicable to current industry practice, and further examined practical parameters impacting its efficacy to maximize the biocidal effects. Apples were inoculated with a three-strain L. monocytogenes cocktail at similar to 6.0 Log(10) CFU/apple and then subjected to comparative antimicrobial treatments after 48 h post-inoculation. An 80 ppm PM treatment, at 30-s and 2-min exposure, reduced L. monocytogenes on fresh apples by similar to 1.3 or 1.7 Log(10) CFU/apple, respectively. The anti-Listeria efficacy of PM was not affected by the water hardness and pH of PM solution, while it improved dramatically when applied at elevated temperature. A 2-min exposure of 80 ppm PM at 43 and 46 degrees C resulted in a 2.3 and 2.6 Log(10) CFU/apple reduction, respectively. A 30-s contact time of 80 ppm PM at 43-46 degrees C reduced L. monocytogenes on apples by 2.2-2.4 Log(10) CFU/apple. Similarly, PAA intervention at elevated temperatures significantly strengthened its effectiveness against naturally occurring apple microbiota. PM treatment at 43-46 degrees C can provide a vital method to improve antimicrobial efficacy against both L. monocytogenes and indigenous microbiota on fresh apples. Our data provide valuable information and reference points for the apple industry to further validate or verify process controls.