Control of Listeria monocytogenes on apple through spray manifold-applied antimicrobial intervention

Listeria monocytogenes is listed by the Food and Drug Administration as a ‘pathogen of concern’ and has been singled out on both ready-to-wash and ready-to-eat produce due to its nature as a true evironmental species. The pacific apple industry, led by Washington, suffered a significant loss of income following the L. monocytogenes outbreak traced back to a California packer. The final FDA Produce Rule and Preventive Controls Rule are challenging apple packers and handlers to develop specific efficacy data for their process controls. The apple industry has an immediate need to begin the process of science-based improvements in Listeria control during packing and subsequent storage. The overall goal of the proposed studies is to comparatively assess and validate critical operating parameters for registered, commercially practical, and legally allowed sanitizer(s) against L. monocytogenes, and to further seek to verify their efficacy on multiple apple packing lines. The proposed project will develop information for apple producers about the practical efficacy of antimicrobial interventions under commercial packing conditions, resulting in tested and proven methods for spray bar intervention in fresh apples, which will fill critical gaps in the knowledge. It will be crucial for addressing L. monocytogenes safety in fresh apples.

The pacific apple industry, led by Washington State, suffered a significant loss of income following the Listeria monocytogenes outbreak traced back to a California packer. The final FDA Produce Rule and Preventive Controls Rule are challenging apple packers and handlers to develop specific efficacy data for their process controls. The apple industry has an immediate need to begin the process of science-based improvements in Listeria control during packing and subsequent storage. The overall goal of the proposed studies is to comparatively assess and validate critical operating parameters for registered, commercially practical, and legally allowed (Generally Recognized as Safe; GRAS) sanitizer(s) against L. monocytogenes, and to further verify their efficacy on multiple apple packing lines. We will pursue two specific objectives: 1) Validate the efficacy of selected sanitizers against L. monocytogenes on whole apple surfaces through laboratory testing; 2) Verify the selected sanitizer interventions in model/ pilot packing line and representative commercial apple packing lines in two states. The proposed project targets to identify effective intervention methods in substantially minimizing L. monocytogenes on a contaminated apple surface and preventing cross-contamination between non-contaminated fruit and fruit contact surfaces within the spray-bed operations and immediate down-stream handling surfaces; evaluate the fidelity of Enterococccus faecium NRRL B-2354 as a surrogate for L. monocytogenes in sanitizer inactivation validation in apple packing lines. The proposed studies will result in science-based data for apple producers about the practical efficacy of registered and economical antimicrobial interventions under commercial packing conditions, resulting in tested and proven methods for spray bar intervention in fresh apples. Knowledge obtained will be disseminated to the apple and tree fruit industries, generating immediately actionable information for the apple packers and handlers in Washington and California and other regions. Equally, there is a high potential for transferability to other tree fruit and fruit vegetable commodities with similar surface traits and postharvest handling systems.

1. Validate the efficacy of selected sanitizers against Listeria monocytogenes on whole apple surfaces. 

2. Verify the selected sanitizer interventions in the model/pilot packing line and representative commercial apple packing lines.

The chlorine-based sanitizers at 100 ppm free available chlorine level have limited efficacy against L. monocytogenes on apple surfaces. Compared with the chlorine-based sanitizers, PAA at practical concentration and contact time is more effective against L. monocytogenes on the surface of fresh apples. The anti-Listeria efficacy of PAA was not affected by the hardness of wash water or the pH of the PAA solution, and was improved dramatically when applied at elevated temperature. A 30-sec contact of 80 ppm PAA spray intervention at 43–45 °C can result in 1.4–2.3 log reduction of L. monocytogenes on fresh apples in commercial apple packing lines. It is important to point out that the tremendous variations in spray-bar brush-bed settings and nozzle alignments and parameters used will impact the practical efficacy of PAA. Therefore, the apple industry should take the unique settings of their packing lines into consideration before adopting the results of the current study. Data also indicate a need for further improvement in the efficacy of PAA or alternative sanitizers to control L. monocytogenes on apple surfaces.