Summary
The recent listeriosis outbreak linked to apples highlights the importance of controlling Listeria monocytogenes in fresh apples. During commercial processing, apples are first soaked in a dump tank and flume water system, with its water commonly reused over several processing days. This creates a potential hazard for foodborne pathogen cross-contamination between water and incoming fruits. Thus, it is vital to properly manage the sanitation of tank and flume water. Despite that disinfectants such as chlorine or peroxyacetic acid are extensively used in dump tank water, the practical antimicrobial efficacy of these sanitizers used in dump tanks has not been directly assessed and there is inadequate science-based data available, 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. 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 process water disinfection, which will be crucial for addressing Listeria safety in fresh apples.
Technical Abstract
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.
Research Objectives
1. Assess the efficacies of selected sanitizers to eliminate Listeria 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.
Findings & Recommendations
The study revealed that L. monocytogenes can be easily spread from contaminated apples to wash water and uninoculated apples, and from contaminated process water to apples. The use of PAA and chlorine in process water can reduce L. monocytogenes in wash water and on apple surfaces and limit bacterial transfer but they cannot eliminate cross-contamination. Chlorine efficacy was highly dependent on levels of organic matter. In addition, the effectiveness of chlorine or PAA against the Listeria surrogate in commercial dump tanks varied among different facilities. While application of chlorine at 50 ppm FC and 60 ppm PAA in commercial dump tanks resulted in reductions of 1.4-1.6 log and 1.6-1.7 log of the Listeria surrogate on inoculated fruits, respectively, there was still a 2.3-2.6 log and 2.3-2.5 log bacterial transfer to uninoculated fruits, respectively. Moreover, all dump tank water treated with 50 ppm FC or 60 ppm PAA were positive for the Listeria surrogate. Based on the findings, the apple industry is recommended to treat dump tank water with sanitizers and regularly monitor sanitizer concentrations and COD levels during packing to reduce the risk of L. monocytogenes contamination. However, the unique settings of each packing line should be taken into consideration before adopting the results of the study. It is important to implement multiple interventions to reduce the risk of L. monocytogenes contamination and ensure the safety of fresh apples.