Fresh Focus: Pathogen Testing for Safety

Since the E. coli outbreak on spinach last fall, there has been a lot of discussion about raw and finished product testing for leafy greens and other commodities. This is a timely subject that needs to be considered carefully to understand what testing can accomplish. Can product testing assure safety?

The new California Leafy Greens Handler Marketing Agreement only talks about product testing as part of the remediation of contaminated water. Apparently, the scientific community that participated in the development of the document decided they should focus their initial efforts on prevention, not product testing. Further recommendations may come in future iterations of the agreement because growers want to assure product safety and buyers want verification.

With produce, there are many unanswered questions about what to test for, what testing protocol is best and when products should be tested. The subject is rife with unknowns. Before embarking on aggressive product testing, consider the following points to make sure you know how to shape your own program.

Supplier Verification

In planning for pathogen testing for a processor, the first step is to consider raw product. Water, soil and compost tests are conducted regularly. Because of customer requirements, some companies test lettuce commodities for pathogens several days before harvest. With a proper holding time for results, decisions can be made about harvesting or taking remedial steps if there are positive results.

Testing is a verification step, so use results to verify that proper food safety procedures are in place. But testing should not be relied on as the only way to verify food safety procedures:

-Training must occur for employees to know proper procedures

-Record keeping becomes a verifiable paper trail detailing execution of proper procedures

-Internal auditing on a regular basis by management confirms that employees know what to do and records are correct

-Third-party auditing confirms that management knows what procedures to have in place

If these steps are in place, then testing can provide further evidence that the product was grown under safe conditions.

Testing Procedures

Once you decide to conduct microbiological testing on raw products from the field, procedures are needed. First, you need to define a “product lot” so that a representative sample is taken from the “lot.” One must take a large enough sample from a defined section of a field to provide statistically valid results.

For example, consider an acre as a “lot” and draw an imaginary line in the ground. Grab samples of product from a cross-section of the lot to provide a variety of plants from a known area. This becomes a composite sample to be run in the lab for a pathogen or a pesticide residue screen.

Don’t forget to use sanitary procedures when taking the product samples to prevent unnecessary contamination. There are several companies experienced in field testing procedures, such as Davis Fresh Technology, Primus Labs and Scientific Certification Systems.

For lab tests, it is important to verify the lab’s quality assurance procedures for handling samples. Also, it is important that they are using AOAC-approved or FDA-approved methods for the pathogen sampling. Rapid methods are desirable to speed up the process since produce is so perishable, but make sure the methods are approved or in the process of being approved.

Processing Conditions

Once the product is cleared for harvest and shipping to the processing plant, the focus must be on contamination prevention. That means monitoring the processing conditions to make sure no other source of pathogens has been introduced. There are several monitoring steps that can provide assurance that contamination is absent.

One use of microbiological testing should be focused on the environment of the processing plant. During the week, swab samples should be taken in various spots around the plant – walls, floors, drains, doors, etc. These tests should consist of Total Plate Counts (TPC) to monitor the actual cleaning procedures. Another recommended test is for listeria, a pathogen capable of surviving within the processing environment.

These swab tests can be taken after cleaning to verify the cleaning procedures are working. Swabs can also be taken during production to verify that listeria is not present during production. When embarking on an environmental pathogen testing plan, consideration should be given to procedures for handling positive results.

Finished Products

There are many food safety procedures that need to be verified along the production route to finished product. In addition to in-field Good Agricultural Practices (GAP) and environmental plant sanitation, other important procedures are associated with the processing plant.

HACCP, employee hygiene, Good Manufacturing Practices (GMP), pest control and record keeping procedures are just some of the critical food safety processes that must be in control in the processing plant to produce a product free of pathogens.

But what steps can be taken to verify safety? As discussed earlier, training, record keeping, internal auditing and third-party auditing can provide assurance that correct procedures are being followed. If all these processes are working, then finished product testing can provide further evidence that the product was produced under safe conditions – but testing alone cannot assure safety.

If considering finished product testing, work with your lab and your customers to settle on a definition of a “lot” so tests can be economical and conducted with statistical assurance. Again, make sure you have considered follow-up procedures for positive results. Millions of dollars worth of product and consumer health will depend on accurate and consistent testing procedures.

Product testing by itself cannot assure safety, because you cannot test every leaf. But pathogen testing, along with other monitoring steps, can provide verification to assure safety in produce.

Edith Garrett & Associates is a consulting firm specializing in helping the produce industry with third-party food safety audit preparation, fresh-cut product development, market research, marketing strategies and advertising plans. For more information, call 828-684-3686 or visit www.edithgarrett.com.



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