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The Packinghouse: Safety and Uses of Process-Water


(This is Part 1B of a five-part series on produce safety by Roy E. Costa, R.S., M.S., a registered professional sanitarian and founder/owner of Environ Health Associates Inc. Part 1A was posted here on Feb. 25, 2015, and the series introduction was posted here on Feb. 10, 2015.)

Packinghouse operations use process-water to cool and clean produce and also as a means of moving products via flumes. The commingling of products and reuse of water generally increase risk, especially if the process-water becomes contaminated. A flume is an example of a circulated water process where commingling of products occurs, being a trough of moving water that is circulated, or “re-circulated,” using a pump.

http://www.dreamstime.com/royalty-free-stock-images-red-bell-pepper-water-image22806049Some operations provide a cooling step prior to packing using what is known a “hydro-cooler.” Hydro-coolers also commingle product and use circulated water. Due to high operating expenses involved in operating these units, the chilled water is often used for days at a time. Hydro-coolers can be standalone structures or cabinet-like pieces of equipment that use a refrigerated, circulated water bath to remove field heat (from products such as cantaloupe), increasing the “shelf life” of such products. Some temperature-sensitive products may also need ice (top ice, or injected) to ensure adequate cooling and cold storage.

Buyers often require washing of produce before packing to remove soil and to improve its appearance and marketability. Washing may be performed in a “dump tank” or by spraying water onto the products as they pass by on the conveyor belt. Washing may clean the product, but as in other water applications, washing also increases risk. Large volumes of process-water can also create wet environments, creating conditions conducive to colonization by microbes. The proper drainage and disposal of wastewater is another poorly addressed design feature in many facilities.

The guidance from FDA on the use of “post-harvest” process-water requires that all such uses utilize potable water. A potable source of water is therefore required, and it needs to be maintained as such. Where municipal water supplies are available, the risk from a contaminated source is greatly reduced, but not entirely; CDC advises that waterborne illnesses are still reported from federally regulated Public Drinking Water Systems (PDWS). The risk varies by area and greatly increases in locations where water treatment is unreliable.

Wells are very often used as the source of water in packinghouse operations, especially in more rural facilities where PDWS are not available. Microbial standards for post-harvest use of water are more stringent then those for irrigation water and must meet the definitions in EPA’s Safe Drinking Water Act (SDWA). The implementation of SDWA has been the responsibility of each state department of health; however, authority for agricultural operations is not specifically covered in the federal rule and, as a result, there has been little public health oversight over packinghouse water supplies in many jurisdictions. Such wells are often treated as “agricultural,” with such wells resembling irrigation wells in their construction and operation. Currently, third-party standards simply ask for microbial tests as a means of establishing a potable supply when much more is actually required for safe operation. Even when tests are used as the primary indicator of acceptability, third-party standards do not typically reference a need for compliance with the full EPA requirements for public drinking water.

Maintaining the potability of water in circulated systems is commonly done through the addition of antimicrobials, including chlorine, peracetic acid, chlorine dioxide and ozone. All such compounds must carry EPA and FDA approvals for use as disinfectants in potable water and must be Generally Recognized As Safe (GRAS); virtually all commercially available disinfection formulations carry such approvals.

USDA has not to this point in time provided guidance on the application of antimicrobials to whole produce as a means of reducing contamination. FDA has not provided such antimicrobial registrations for whole fruits and vegetables either, as this is the traditional domain of USDA (FDA registrations do not apply until such products are processed).  Given the dearth of legal requirements and lack of registrations, the produce industry lacks a uniform and verifiable means of assuring that any antimicrobial treatment is effective to sufficiently reduce microbial contamination on fruits and vegetables. The current voluntary standards most often applied to this area of water use are ambiguous as a result. The Global Food Safety Initiative (GFSI) standards rely on a risk assessment to determine where controls are needed. While such standards do not specifically require that whole fresh produce be washed or in any way treated with an antimicrobial, a risk assessment might result in a perceived need for it. However, there does not appear to be a legal or scientifically validated basis, as yet, for such requirements.

The scientific literature available on the subject of produce decontamination is substantial, but often conflicting, and the reported methods suffer from a lack of specificity and uniformity. Some studies show efficacy in some applications of antimicrobials, such as with electrolysis-derived hypochlorous acid, while others do not show much of a reduction of harmful microbes, such treatment being about equivalent to washing in plain water. The reason for the difficulty is attributed to the fact that bacterial pathogens, in particular Salmonella, Listeria monocytogenes and the several strains of pathogenic E. coli, are capable of invading plant material, which provides a complex substrate for attachment and allows microbes to resist inactivation. FDA advises that washing may reduce contaminants; however, the guidance is cautionary owing to the ambiguity of the scientific findings.

In spite of the many millions of dollars spent on antimicrobial treatments, the produce industry does not have complete assurance that washing produce makes it safe. While hard surface sanitizers and process-water disinfection chemicals have the benefit of EPA or FDA registration, probably the most important aspect of produce safety remains without a legal and scientific basis for efficacy.

In any event, water quality parameters must be maintained to reduce the potential for the water itself to become a means of spreading pathogens. Chemicals used for this purpose must usually be diluted to safe operating limits but still maintain efficacy in process water, and often there is a just a small window for safe, yet effective, concentrations (for example, 5.0 ppm to 10.0 ppm chlorine dioxide).

Knowledgeable and well-trained personnel are needed to operate chemical feeders, antimicrobial solution test kits, and Oxidization Reduction Potentiometers (ORP-meters), for example. Failure to correctly operate systems leads to ineffective water treatment and potential occupational exposures if off-gassing occurs (such as with hypochlorite). Given that personnel must be knowledgeable about water chemistry in sufficient detail to manage large volumes of treated water under various organic loads, the industry is in dire need of qualified operators. The Cooperative Extension programs at land grant universities are active in the training of agricultural personnel and offer training to satisfy EPA’s requirements for Worker Protection and Safety (WPS), but there are no specific food safety training courses for operators of water systems in produce packing facilities. Too often, personnel are trained on the job and shifted from duties such as shipping or receiving to operate complicated antimicrobial addition systems. More effort is needed to better qualify key personnel, especially in facilities using process-water treatments.

Testing and sampling

Third-party food safety standards for packinghouses usually have a provision for microbial testing of the equipment and environment. This is a useful tool when sampling methods are controlled for bias and results are properly interpreted. As in the case of employees overseeing water process control, competent employees are needed when tasked with microbial sampling. They must have familiarity with the reservoirs of microbiological agents when collecting samples and accurately interpret the findings. Some buyers have specified a particular set of microbial standards for the industry to follow when interpreting such results, but there are no specific industry-wide requirements for approved sampling methods, or for the acceptable levels of microbial indicator organisms on working surfaces. Without reliable sampling methods and references, operators might find it difficult to intelligently interpret environmental test results.

Routine microbial product testing is not commonly done by packinghouses, although at least one major buyer requires a “test and hold” procedure for high-risk items. It is interesting to note that investigations of outbreaks of produce-borne infection often reveal the agent on suspect products. It appears, therefore, that product testing is a useful prevention tool, but given the vast assortment of fresh fruits and vegetables in countless varieties, developing a universally effective microbial screening procedure might seem impractical. Fortunately, new microbial-assay methods that utilize rapid molecular testing are paving the way for advancements in this critical area.

Other controls

Temperature controls are often in place to preserve fresh produce, some of which is highly perishable with a few degrees sacrificing a week or more of shelf life. Therefore, the packing industry is keenly aware of the need to cool and maintain temperature-sensitive products from receipt through to shipping. Such handling may also influence the safety of the products as well, but at this time there is no definitive guidance on temperature control for safety (TCS) in whole, fresh produce. Many items do not actually require temperature control for preservation, but even with credible evidence that certain whole fruits and vegetables can act as hosts for harmful bacteria, such an effort to classify the safe temperatures ranges for a huge potential assortment of such commodities is a daunting task.

FDA has approved irradiation for many commodities, and the technology is used primarily for phytosanitary purposes. While there is controversy about the safety of such treatments, many experts believe the application of this technology would be beneficial for public health. Irradiation will be discussed further in “Processing Operations.”

Applicability of Hazard Analysis and Critical Control Points (HACCP)

With the success of HACCP in reducing the risks of foodborne illness in several commodities, such as red meat and juice, regulators have turned to HACCP in fresh produce. The produce industry must become familiar with the application of HACCP, as the FSMA now imposes a legal requirement that post-harvest produce operations implement Hazard Analysis and Risk-Based Preventive Controls (HARPC).

As in the classic NACMCF HACCP model, the HARPC concept requires a thorough description of products, the distribution and users of the product, a detailed flow chart of processes, and then, a hazard analysis to determine the operational risk-based controls needed. The difference between the two methodologies appears to be at the setting of Critical Control Points (CCP). Whereas HACCP “critical” controls are found in regulations for red meat, poultry, fisheries and juice, there are no regulatory mandated critical controls currently in place under HARPC guidelines. A commonly accepted definition of CCP is a step in a process where contamination must be reduced to safe levels, prevented or eliminated.

Operators of produce packinghouses can rely on guidance documents for GMP and GAP, but have difficulty when it comes to setting critical controls. Where microbial contamination is concerned, the wash step, when it is correctly performed, has the potential to meet this definition. The problem with selecting this step as a CCP, as previously explained, is one of validity. The answer to this problem is to conduct a challenge study that is reliable under operating conditions for each product and each process. Unfortunately, this is an expensive and major scientific undertaking, and it may be economically out of reach for even a large firm.

Another commonly accepted definition of a CCP is a step in a process where the loss of control results in an unacceptable level of risk. Clearly, water-processes that commingle products or that utilize circulated water meet this definition.

The best answer to the CCP question may be that when products are commingled in a common water application, or when water is reused, water treatment is critical to keep cross-contamination from occurring. Critical controls now become practical. The critical operating limits become the process-water quality parameters set by FDA and EPA to maintain potable water and the antimicrobial treatment needed to reduce the amount of harmful organisms to safe levels. The science is particularly strong in the area of water disinfection, with numerous studies indicating that EPA-registered process-water chemical treatments are effective for this purpose.

While we do not have a readily available “kill step” in the fresh produce industry, HACCP adds a needed backbone to process-water control. The attention paid to monitoring critical limits and taking corrective actions, along with the attendant documentation, provides a verifiable means of reducing risk in water applications.

Summary and conclusions

Investigators have identified packinghouse operations in foodborne illness outbreaks as the source of pathogens, but given the huge amounts of products flowing through these operations, the risk for contamination appears to be low. However, contamination events, when occurring at the packinghouse, can result in the exposures of large volumes of products, which can then be distributed throughout the supply chain and result in massive recalls and foodborne illness.

The low risk of contamination events occurring at the packinghouse may be due to the sporadic and low-level incidence of human pathogens in the primary production environment when GAP are used. The safety of produce is highly dependent on the safety of each link of the supply chain working together to minimize the risks to consumers, as this series will further explain.

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