Minimizing Microbiological Risks in Multiple-Use Containers

In addition to direct FCS interactions with fresh produce, there is the likely potential for indirect transference of contamination from external container surfaces during stacking and palletizing but more broadly by water transport. Soil, non-product organic matter (e.g. leaf matter, non-crop vegetation, decayed or damaged crop), and other foreign objects may be introduced into water dumps and flumes in recirculating wash or cooling systems, onto dump tables and spray-brush beds, and onto conveyors during harvest container inversion.

Image Credit: PrimusLabs.
Decomposing plant residues attached to RPC ­delivered from a central depot, signified as cleaned and sanitized, represented 48 % of the units swabbed For Cause due to a visual ­“cleanliness” defect in the six-week UCD study.

In some systems, the reusable harvest container, which may be wood or plastic, is introduced into a flotation tank or pool to gently release the produce to a water conveyance system to minimize bruising and other forms of injury. These container-adherent potential sources of contamination are often acquired in the produce field or orchard. Adhering soil and some of the non-product organic matter is impacted onto multiple crevices on the footings, corners, bottoms, and sides of containers, most pronounced with RPC, if placed directly on the soil of row crops on the orchard floor. In water-based postharvest handling systems, there is the high risk potential for any microbiological contamination to be broadly spread among multiple containers in a single lot and among multiple lots if the water quality is not maintained under high-process control standards.

In a closed-loop system, these containers are typically cycled back into harvest operations, which may involve a single grower or farm location or be co-mingled and distributed to multiple farm locations and among multiple growers. Invariably, these are dedicated-use containers that only hold produce. In pool-system RPC use, these containers are shipped to a processor or retail distribution center and ultimately consolidated and shipped back to the RPC-owner depot for distribution back directly to a grower’s harvest location, shipping yard, or a secondary container distributor. Regionally, these may be commonly used or reserved for produce packing but many pool-RPC pass through many non-produce operations or uses as well.

Cleaning and Sanitizing

For growers and produce handlers with a closed-loop RPC system for harvest and wash-cooling operations, it is fair to expect that full responsibility for meeting expectations for FCS cleanliness between cycles-of-use resides with that company. In this regard, many of the questions that arrive at my desk are seeking best practice guidance for sanitizing of harvest totes and bins and appropriate schedules for routine and deep cleaning. This is not a new subject matter for the produce industry, especially in the tree fruit category, as problems arising from cross-contamination with postharvest decay microbes, primarily fungal pathogens, has been a longstanding issue. As with more recent concerns for human pathogen transference, this carryover contamination is generally an implementation barrier rather than a lack of evidence and protocols for proper cleaning and sanitation or disinfection with available chemistries. For the purpose of this article, the focus will be on plastic/polymer containers, intentionally avoiding the issue of wood bins and wire-bound wood crates that become multiple-use packing and shipping units. There are few current studies that provide cleaning and sanitization validation data and address the establishment of a Master Sanitation Schedule for multiple-use plastic containers with much more than a finger-in-the-wind best guess. Naturally, in the absence of hard data that covers a multitude of conditions and practical logistics and harvest/shipping unit availability, there’s a wide range of management schemes that are rigorously or more loosely followed within each company. In many operations, practical inabilities to allow adequate time for complete drying post-washing, originally essential for minimizing the issues of fungal decay spore germination during refilling with produce, are causing packers to eliminate washing altogether. The standard practice is a simple bin or tote inversion to clear most adhering soil and leaf trash. More recently this practice has been retained or adopted in produce operations meant to remain dry due to concerns for residual moisture, elevating the risk of survival and growth of pathogens. In these cases, cleaning and sanitation is typically conducted between seasons. In both wet and dry applications it’s common, but not uniform, that single-use polymer liners are placed inside of multiple-use harvest and shipping containers to alleviate the concern for incomplete or inadequate sanitation options.