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    Product Testing, Part 8: Sampling is a Challenge

    Tuesday, February 15th, 2011


    Julia Stewart:
    Hello, this is PMA PR Director Julia Stewart, and welcome back to our “Ask Dr. Bob” audio blog series on product testing, “with PMA’s Chief Science and Technology Officer Dr. Bob Whitaker. This post is part of a series we’ve been doing on the topic of product testing. Bob, in several posts now you have indicated that sampling is actually a more significant challenge than actual testing…Tell us more.

    Bob:
    Julia, as we’ve talked about earlier in this series, the specificity and selectivity of pathogen tests is only half the equation – the other half is your sampling program or the method you use to collect fruit and vegetable material to be tested. From our previous posts, I think you can all see there are many challenges and benefits associated with the actual pathogen tests. Yet in many ways developing a sampling methodology that can achieve statistically significant confidence levels is more troublesome.

    So, let’s start with what we know … Based on the millions of pounds of produce harvested, shipped and consumed each day by millions of people throughout the country without illness, we know that the frequency of pathogen contamination is low. We also know from data shared at the Center for Produce Safety’s Research Symposium in June 2010 that pathogens do not survive well in production environments.  Indeed, two days after purposely spraying attenuated E. coli O157:H7 on leafy greens crops, researchers could only recover it by using enrichment techniques.  (By the way, “attenuated” means the pathogen’s disease-causing gene has been deactivated so the bacteria can be used in testing without risking making anyone sick.)

    So, because we face both low-frequency contamination and low pathogen survivability, it’s crucial for our sampling methods to be constructed so we can detect even sporadic, low levels of key pathogens. Further, contamination – when it does occur – it is not uniform. When contamination is found in a field, it tends to be random and isolated. That in turn can make follow-up testing a big challenge. Leafy greens growers commonly report following up on confirmed positive tests with extensive field or finished product-level sampling only to find that the  initial positive test results are seldom repeated.  The key to understanding sampling issues in produce is to understand the size of typical production lots or finished product production runs. 

    Just think about a single production block of fresh spinach. Let’s say the block is 10 acres in size; that’s about a day’s harvest for a small to medium size producer.  Planted at a density of about 4 million plants to the acre, our production block has approximately 40 million plants in it.  Each spinach plant at the time of harvest has 4-6 leaves, so choosing the middle of that range, that makes the total number of leaves in our production block around 200 million. 

    Today, sampling programs generally follow a “Z” pattern originally developed for pesticide residue sampling, which is a much different sampling challenge than microorganisms.  Along the “Z” pattern, the sampler chooses 15 points and collects 4 samples from each point for a total of 60 samples per block.  The size of the sample generally ranges from 25 grams to 100 grams per sample point or about 50 to 200 leaves.  That means a maximum number of 12,000 leaves are collected in any given field sample of 60 points.  These are generally mixed in a sample bag to form a composite sample.  From this composite, 50 to 200 leaves are selected to create a test sample.  So, in our block of 200 million potential leaves, our test comes down to evaluating 50 to 200 leaves. 

    Another way of looking at this is a commercial spinach field has an average yield of 12,000 pounds.  In our 10-acre block, that’s 120,000 pounds of harvested product.  Using the sampling program currently employed by many in our industry, we are attempting to represent that 120,000 pounds of product by sampling about three pounds of product, and then selecting a quarter of a pound of leaves from that to actually test. 

    Talk about finding a needle in a haystack!

    Julia:
    So why not just test more material then, Bob?

    Bob:
    To be sure, there many variations on the “Z”-pattern test just described.  Some are doing a “Z”-pattern test on each acre within a production block.  In the example above that would be a factor of 10 greater than just doing a single “Z” pattern on the whole 10 acres.  Others are using other patterns designed to pick up border areas as well as the center regions of a field, known as “box” or “box-X” patterns.  So while your statistics may improve by a factor of 10 or so, unfortunately you’re still in the needle in a haystack territory.  

    Remember, these contamination events are random, low frequency, and isolated. You could take a thousand samples from that same production block and only minimally increase the relative amount of product tested – and just as easily still fail to sample the exact location where the potential contamination resides. 

    And, by the way, the same sampling issues arise if you’re talking about testing finished product. Let’s say you are packing 60 to 100 bags per minute, which is standard for some products.  Simply removing five or 10 bags of product every hour or so and then making a composite sample gives you very similar statistics compared to in-field testing.

    Julia:
    So how exactly do you sample effectively to detect contamination?

    Bob:
    Well, with today’s technology, there’s really no satisfactory answer to that question.  There are new innovations on the horizon, such as environmental vacuums and other technologies that are being adapted from the Department of Defense, where screening vast areas for weaponized microorganisms has been a priority for several years.   However, given the state of sampling technology, it’s important to understand what sampling and testing can – and can’t – do. 

    Right now, the only contamination events we can feel reasonably sure to detect would be massive breakdowns in our food safety programs.  For example, if a pesticide applicator used a grossly contaminated water source to mix pesticides and then applied them to edible portions of the product, or an animal intrusion event where the animals were indeed infected with a human pathogen. Typical sampling programs might well detect this contamination, but these types of massive breakdowns have been well managed by Good Agricultural Practice programs and so have only rarely been associated with foodborne illnesses.  In other words, if a massive breakdown occurs, there are food safety programs in place to identify these issues outside of testing, and generally producers do not harvest the crop.   

    I always get back to risk-based testing. If a producer knows a risk event may have occurred like an animal intrusion, or if environmental conditions known to support pathogen survival might have been in place during production, one might increase sampling in specific locations.  Likewise, if you are producing in a field where previous potential positive samples were detected in past seasons, it may make sense to screen these fields more intensely.  It comes down to evaluating the risks associated with each production block or product run and then using the context of the physical evidence, observations, and other food safety data to better target sampling.  It means taking an active role in the sampling program and not simply putting the execution of the program on auto-pilot.

    Julia:
    Wow, Bob, good points to consider! Next time, we’ll explore the critical issue of raw versus finished product testing.  This is a central issue for our industry with important ramifications for supply chain logistics.

    Thank you, listeners, for joining us!

    The Truth About Pesticides, Part 2: What Are They Afraid Of?

    Thursday, October 14th, 2010

    From Bryan Silbermann, PMA president & CEO
     
    Last month, Ask Dr. Bob introduced you to a new campaign from our colleagues at the Alliance for Food and Farming called “The Truth About Pesticides”. The alliance’s Marilyn Dolan joined him for that post. You’ll recall that the alliance commissioned a blue-ribbon panel of experts from different scientific disciplines to review claims being made that pesticide residues on produce are unsafe.
     
    In a nutshell, that panel found Dirty Dozen-type claims to be groundless and without scientific basis. There is simply no documented scientifically-validated evidence that the very trace amounts of residues that might be found on fresh produce can cause health problems. The panel’s findings were unveiled to industry, the media and consumers back in July. 
     
    PMA is proud to have supported this campaign since its inception, including funding development of the consumer website, www.safefruitsandveggies.com. Simply put, our industry must act to counter the negative effects such claims have on our consumers. This summer, 29% of consumers The Hartman Group surveyed for PMA told us that they are avoiding eating fresh produce because of concerns about pesticide residues. The alliance is now working to get the word out about what the panel had to say – and in the process encourage consumption of all fresh produce, conventional and organic.
     
    The environmental community’s response has been, let’s just say, strong. We’ve clearly hit a nerve.  The Alliance’s intent in commissioning a review of these claims was to start a conversation on the subject. Unfortunately, the reaction of several activist groups – including the folks behind the Dirty Dozen list – has been the exact opposite. Rather than considering what we have to say, they appear to be actively working to squelch this new information. Their tactics so far have included trying to position the producer-backed alliance as a store front for the chemical industry, and trying to pressure state government officials into revoking grant funding the Alliance received to help it get the word out about the science report.
     
    PMA and our colleagues at the Alliance are hopeful that at the end of the day, facts and reason will prevail – and consumers will eat more fresh produce, not less because they’ve been frightened. We invite you to help us get the word out to consumers and consumer media about www.safefruitsandveggies.com. For more information on what you can do, contact the Alliance for Food and Farming.
     
    Unfortunately, not everyone is interested in advancing the consumer’s right to know.  Recently, we learned just how strongly entrenched one television show host’s opinions are.  In September, the Alliance, PMA and several other organizations contacted Dr. Mehmet Oz after he aired a particularly egregious segment.  Alas, even this doctor by training wasn’t interested in the facts if it gets in the way of good theater. That gives you an idea of the long, uphill climb we have ahead of us. But at the end of the day, climbing that hill is what’s best for our consumers, for public health – and yes, for our industry, too.

    Why Small Grower Food Safety Matters

    Tuesday, October 12th, 2010

    Julia Stewart:
    Hello, this is PMA PR Director Julia Stewart, and welcome back to PMA’s audio blog, “Ask Dr. Bob”.  Today I’d like to welcome PMA’s Director of Food Safety and Technology, Johnna Hepner, to talk about the intersection of two very hot topics.  Johnna, small family farms are the life’s blood of our industry and with the buy local trend many small growers are getting a renewed shot in the arm. However, as we’ve seen increasing focus on produce food safety, many small growers feel they’re being pressed to do something that is overwhelming.

    Johnna:
    Yes Julia, that’s right. The focus on local sourcing is definitely shining a spotlight on smaller growers — and with that spotlight has come discussion over whether they should be required to comply with federal food safety measures.

    Julia:
    So Johnna, are food safety and small grower two mutually exclusive terms?

    Johnna:
    Some might think so, Julia. In fact, it has been suggested that small farms should be exempted from some of the food safety legislation currently being debated by Congress. But that’s not in anyone’s best interest, and especially not that of the small grower. Small growers as well as large ones all have sound reasons for ensuring they have the most up-to-date food safety practices.

    Julia:
    Well, why should the food safety rules have to apply to small growers?

    Johnna:
    First of all, we can’t say that small growers don’t cause foodborne illness outbreaks. The identified causes of produce-related outbreaks, like field-level contamination or contaminated inputs like water, don’t discriminate between small or large producers. And even now, smaller outbreaks could be slipping under the radar, since it typically takes a critical mass of illnesses to catch the public health community’s eye.  Currently about 70 percent of reported foodborne illnesses are never linked to a specific source.

    Julia:
    And where are buyers on this?

    Johnna :
    The reality is that the market is another real driver for this. Most buyers already require their produce suppliers to have food safety programs, and to be audited. If you want to sell your goods to the retail or foodservice market, you will be required to address food safety – buyers won’t risk anything less. So if small growers don’t comply with all the accepted standards, it could actually result in potential business being closed to them.

    Julia:
    So, small growers should be included. But how do they get started, if they haven’t started already?

    Johnna:
    It starts with the risk assessment and risk management process, Dr. Bob has spoken extensively about this in previous posts. Since the food safety net can’t have any holes in it and nobody wants to risk their farm or harm consumers, all producers must use baseline standards to conduct risk assessments – and then minimize the risks those assessments expose.

    The good news is that food safety programs and costs are scalable. As a small grower, you’ll probably face lower food safety costs than a larger grower. For example, you likely have fewer water sources, less acreage, fewer products produced – and fewer buyers requiring audits.

    Julia:
    Where can they get help if they need it?

    Johnna:
    You can start right here with this blog, which contains a wealth of information on understanding and implementing food safety. And PMA members have access to our food safety staff, which include top-level subject matter experts who understand our industry and can really help deliver real-world solutions. We’re accessible to you.  And finally, the PMA-founded Center for Produce Safety is a tremendous source of ongoing food safety research and information. Their website is cps.ucdavis.edu.

    Last but not least is the local grower food safety workshop series that PMA is putting on with Sysco Corporation, I discussed this in a previous post.

    I think we all agree that our first commitment must always be to protect consumers. PMA is committed to working with our industry’s small and local growers to ensure that you too can thrive and grow in this new reality.

    Julia:
    Absolutely! Thank you Johnna.

    Listeners, you can learn more about food safety topics at AskDrBob.pma.com. Thanks for joining us!

     
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