Validation of sanitizer disinfection of wash water in dump tank operation of apple packing lines

The recent outbreak of Listeria monocytogenes linked to caramel apples and multiple L. monocytogenes recalls associated with fresh apples have brought the attention of the public to apple safety. In the production process, fresh apples are first handled by employing dump tank and flume systems to gently transfer apples from bins to the packing line. The dump tank water and flume system use massive volumes of water, which are commonly reused over several processing days. As a result, water in dump tanks is high in organic matter and can become a point of cross-contamination for foodborne pathogens including L. monocytogenes, causing a safety risk to consumers. Effective disinfection or antimicrobial intervention of the source water in the dump tank is vital to control and reduce the likelihood of L. monocytogenes contamination on apples. Disinfectants such as chlorine or peroxyacetic acid are extensively used in dump tanks and flumes during tree fruit packing. However, little is known about the practical efficacy of these compounds under industry-relevant conditions, leaving critical knowledge gaps. The overall goal of this study is to comparatively assess and validate critical operating parameters for commercially used sanitizers against L. monocytogenes in dump tank water thus cross-contamination, and to further seek effective intervention methods and verify their efficacies on multiple apple packing lines. We will pursue the following two specific objectives: 1) Assess efficacies of selected sanitizers to eliminate L. monocytogenes in wash water and cross-contamination in a simulated dump tank system; 2) Verify the selected sanitizer disinfections in representative commercial apple packing lines. The proposed studies will result in immediately actionable and science-based data about the practical efficacy of antimicrobial interventions in dump tanks for apple producers in Washington and other regions. Knowledge obtained would have high potential for transferability to other tree fruits and fruit vegetable commodities with similar surface traits and postharvest handling regimens. Outcomes of the proposed studies will help tree fruit packinghouses to further refine and substantiate critical control points utilized in their food safety plans.