Environmental microbial risks associated with vented produce in distribution centers

The Food and Drug Administration’s (FDA) Preventive Controls for Human Food Rule (PCHFR) requires the establishment of environmental monitoring programs within FDA registered facilities, including in distribution centers (DCs) that receive, hold, and ship fresh produce. Generally, in the DC environment, product arrives fully packaged and is shipped in the same packaging, with minimal to no handling. However, FDA has determined that fresh produce entering these environments may be at risk for contamination due to the vented nature of the packaging materials used. Produce is typically shipped and stored in packaging that allows for dissipation of accumulated gas and moisture, which generates and continues after harvest. This vented packaging allows for sustained product quality throughout the supply chain. To date, no data has shown vented packaging is at high risk for product contamination. Additionally, little information exists on the likelihood of microbial contamination within the DC environment, such as the prevalence of Listeria species. This project will examine the risk of contamination in the DC environment by surveying DC managers and sampling their DCs, focusing on potentially high-risk areas, practices, or equipment within DCs. Knowledge gained from this project will assist DCs in evaluating the environmental microbial risks of vented produce, as well as eliminating high risk practices that may contribute to contamination events within DC environments.

Postharvest metabolic activity results in continued gas and vapor exchange between produce (fruits and vegetables) and the environment. Produce spoilage accelerates as heat and moisture accumulate, so produce is packed in bags, plastic tins, or boxes that are vented to accommodate gas exchange. The unsealed nature of this packaging has not been evaluated for its potential to allow pathogen transfer from the surrounding environment through the vents onto the product. Additionally, little research exists on the likelihood for microbial contamination of produce from the DC environment and/or the equipment found in the DC environment used to hold or distribute unsealed produce packages. The goal of this project is to assess microbial contamination risks within the DC environment. The proposed project aims to partner with >20 DCs to utilize expertise from industry (using surveys to collect management practices, such as current cleaning and sanitizing schedules) and environmental sampling data from storage and handing areas (using Listeria species as an indicator of microbial contamination). The primary expected outcome is to provide risk mitigation guidance for regulatory and industry partners addressing the likelihood of environmental contamination to vented produce in the DC environment, and potential risk mitigation procedures for identified hazards. Industry support has been offered to allow researchers access to DCs for performing surveys and environmental sampling. Along with support from DCs, support will also include advisory guidance to direct the research team and assist in result interpretation. The advisory board will be integral in communication between the research team and DC management by approving survey/sampling times to guarantee research efficiency and minimal disruption to DC operation. Three foreseeable outcomes could emerge based on findings from DC environmental sampling. Data may find insignificant levels of microbial contamination during environmental sampling across all DCs, indicating that vented products passing through these facilities may not be significantly vulnerable to contamination. Conversely, it may be determined that the DC environment, like many food manufacturing environments, has a low prevalence of environmental microbial contamination (using the indicator Listeria species). Finally, significant variability may exist in microbial contamination risk in the DC environment due to differences in company management; individual facility location; structural or equipment variability; regional differences; sanitation schedules; handling practices, among other factors. Data will be statistically analyzed to capture contamination risk due to these different factors. Findings will be analyzed to determine relative differences between practices or factors that may increase or decrease risk within DCs. These findings will be collated and submitted to the advisory board for review, then summarized for dissemination to the greater-industry, along with recommendations from the research team on appropriate environmental monitoring implementation for facilities that are considered at high risk for environmental contamination.

1. Collect current cleaning and sanitizing practices through a survey and on-site observations in parallel with microbial sampling within storage and handling areas in at least 30 distribution centers.

Although Listeria spp. were isolated within most distribution centers, the study did not confirm the presence of L. monocytogenes in order to facilitate company recruitment. However, as Listeria spp. are considered appropriate index organisms for L. monocytogenes, this work suggests the potential for contamination by L. monocytogenes within the distribution center environment. Knowing this, targeted, robust cleaning and sanitation regimes may be advisable to mitigate this potential hazard within the distribution center environment. Current cleaning programs may require remediation. For instance, the management survey indicated that floors are among the most frequently cleaned surfaces within the majority of distribution centers (Figure 6), yet they also most frequently yielded positive Listeria spp. samples (Figure 3). Therefore, more robust sanitation operation procedures may be advisable. Reliance on or integration of ATP within an environmental monitoring program may be necessary as the current data suggest a poor association between ATP and presence of Listeria spp. 

While ATP is a valuable resource to determine adequacy of cleaning activities, it should not be the primary component of an environmental monitoring program to the exclusion of microbial swabs. While the study indicates a likelihood for environmental contamination by L. monocytogenes, the study made no attempt to estimate the potential risk to fresh produce. First, thorough characterization of the Listeria spp. commonly isolated within distribution centers should ascertain if pathogenic species are present. Additionally, further work to determine the likelihood of pathogen ingress through vented packaging under conditions or situations simulating those within a distribution center may also be critical in determining the degree to which fresh produce is at risk in these environments.