Minimizing Microbiological Risks in Multiple-Use Containers

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Table 1: Example of interim guidance for ATP and aerobic plate count outcomes of harvest and shipping container microbiological swab-analysis.

For growers, handlers, and shippers that use RPC, for direct field-pack or packaging after post-cooling, washing, and grading steps, there has always been an inherent understanding and expectation that these pool-system units would be delivered between each use in a clean and sanitary condition. Whether using pool RPC by preference or conforming to customers’ requests and requirements, suppliers have pointed to a lack of control and knowledge of the cleaning and sanitizing practices by the central RPC provider. Produce quality and safety specifications derived primarily from buyer mandated criteria have expanded, especially over the past five years, to include all forms of packaging and packing materials. Although there’s been a level of grumbling over the years about where the RPC was last in non-produce uses, both food and non-food shipping, it wasn’t until the recent release of a “RPC cleanliness” study report by Keith Warriner, PhD, professor of food science at the University of Guelph, that the issue heated up. In response to that media-based communication, multiple concerns from grower/shippers and produce handlers were shared anew in the U.S. Issues raised related to foreign objects, impacted soil, decaying organic matter, presumptive excess cleaner residues, excess free water, and multiple adherent stickers and sticker-adhesives made it apparent that the concerns raised by the Guelph report were not likely regionally-limited issues.

The issue of excess free water, alone, within a folded RPC arriving for packing fresh produce is significant for many packers, as any water in contact with the dry surface of produce such as dry onions, garlic, and items with a tender calyx (stem-cap), such as many types of eggplant, will likely stimulate decay microbes to infect. In some areas, this moisture will evaporate quickly if erected (unfolded and locked) RPC sit out in the field for even a short time, but this is not always the case in high humidity field environments or in many packing facility rooms. Packers have commented that they assign crews to hand wipe RPC prior to use to remove pooled water.

Since the initial Guelph study, my colleagues at the University of California, Davis (UCD) and I conducted a similar microbiological survey in California over a six-week period and Dr. Warriner conducted a second, expanded study. These collective outcomes uniformly point to an inconsistency of microbiological cleanliness, which would be prudent to address among RPC providers. While our study did not specifically address the issue of actual pathogen detection, by design, the relatively high numbers of viable bacteria on the interior surface of the swabbed RPC strongly indicate that current cleaning and sanitation practices lack the rigor needed or expected by their customers. In the UCD survey, while many individual RPC were below the limit of detection, (less than 0.9 colony-forming unit (CFU)/swab) and would be classified as “clean” (less than 60 CFU/centimeter2), individual RPC across pallets and sampling dates exceeded log 5 CFU/swab nine of 24 times or 37.5 percent and the range of outcomes exceed log 6 CFU/swab two times or 8.3 percent. Details of the methods used and study outcomes are contained within the current report. To expedite availability to the industry, a more lay-technical presentation was released; a more formal journal manuscript is being developed with additional evaluations and reported data.

Current Actions and Corrective Measures

Fortunately, a major RPC provider has been taking steps to improve handling at its central depots and to stabilize confidence in pool system contribution to supply chain food safety.