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    Product Testing, Part 9: In-field Raw Product Testing

    Julia Stewart:
    Hello, this is Julia Stewart, and welcome back to PMA’s audio blog, “Ask Dr. Bob” with PMA’s Chief Science & Technology Officer Dr. Bob Whitaker. This post is part of a continuing series we’ve been doing on product testing. In the last post we talked about the challenges of product sampling.  Today, we want to go back and look at sampling from an operational perspective.  Where and when you take samples can have very real impact on our bottom line. Previously, we’ve talked about the perishable nature of our products and the time it takes to perform testing; Bob, are there any options that might buy us some time?

    Well, Julia, as the industry has looked for ways to resolve the supply chain logistics issues versus the timing it takes to test products, some have implemented in-field or pre-harvest testing programs rather than testing and holding finished product.  This can be advantageous because the testing is done before harvest and before the shelf life “clock” starts ticking. Typically, these testing programs rely on field sampling 2 to 7 days prior to harvest. This permits enough time to sample the field, test the product, and get the results back from the lab so that a “negative” result can essentially “clear” the field for the scheduled harvest date.

    For many commodities this is a better alternative than trying to hold harvested or even finished processed product. If testing does reveal a “positive” there is time to perform confirmation tests – then if these also come out positive, the affected product is not harvested and public health is not compromised in any way.  As a side benefit, since the contaminated product remains in the field, the event can be studied and perhaps the cause of contamination can be determined.  Recent work of this nature performed by Dr. Trevor Suslow and his team at University of California-Davis, with funding from the Center for Produce Safety and others, has shown some very interesting preliminary results regarding the importance of sample sizes, the presence of multiple pathogenic strains in a single contamination event, and the importance of temperature and rainfall for pathogen survivability. 

    In-field testing also has the benefit of helping to manage costs.  Although growing costs are effectively committed just prior to harvest, in-field raw product testing permits evaluation prior to harvest so that harvest costs can be avoided if positive tests are uncovered.

    So what are its challenges?

    Well, although it generally avoids some of the issues we discussed in previous posts on perishability and test and hold practices, field-level raw product testing can still be highly disruptive to the supply chain. Harvest windows are often narrow due to rapidly changing market opportunities. Delaying harvest to permit product testing may impact a grower’s flexibility to hit a specific harvest window in a tight market.  In-field testing also leaves open a potential window of vulnerability. For example, if the raw product is tested in the field 2 to 7 days prior to harvest, any contamination occurring after sampling but before harvest could go undetected.  Indeed, data shared at the CPS Research Symposium in June 2010, indicated that attenuated E. coli O157:H7 purposely sprayed directly onto spinach or Romaine lettuce died off quickly, so that within two days, the attenuated strain could only be detected using enrichment procedures.  (I mentioned that research in a previous post in this series.) This may indicate that contamination events occurring within a few days of harvest may be more problematic than those occurring further away from the harvest date.  

    There are also challenges in implementing raw product testing, whether it is implemented broadly across the produce industry, or even just targeted to “high risk commodities.” Aside from technical issues that may exist with the test itself and field sampling issues, pre-harvest or raw product testing requires active and complete communication between growers, shippers and processors. Test results obtained by any party sourcing raw products from common fields or lots must be shared in a timely fashion prior to harvest. This can be quite difficult to do in practice.

    For example, a particular field could test positive by one shipper and would not be harvested by that company. However, a second company sourcing raw product from that same field might not have a field level testing program or if they do, their sampling scheme may not yield a positive result. That second company could then unknowingly harvest and ship the product only to find out later, if at all, that the field had potential contamination issues.  This lack of communication could easily translate into the second company having to perform a product recall with all the corresponding costs and damage to brands that encompasses.

    So, while raw-product testing has some advantages over finished product testing from the perspective of perishability, it’s not without potential problems that could prove difficult to overcome if broadly implemented.     

    Thanks Bob. We’ve now talked about the issues of perishability, typical tests currently in use, product sampling issues, and raw versus finished product testing.  Next time I know you want to look at the significance of these testing programs and cover some additional thoughts on how all this data can be used.

    (laughing) OK.  I’ll be ready.  I look forward to it. 

    So will we, Bob.

    Remember listeners, if you’d like to send Dr. Bob any comments or questions about product testing you can email him at AskDrBob@pma.com. In addition to listening to these and other Ask Dr. Bob blog posts, we invite PMA members to visit our new online Food Safety Resource Center on PMA.com and check out the lab testing white paper in the Education section. Until next time!

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