PMA: Research on produce safety priorities

Bob Whitaker, Ph.D., chief science and technology officer for Produce Marketing Association (PMA), writes that because it provides inherently healthy, nutritious foods, the fresh produce industry is uniquely positioned to help solve the nation’s obesity epidemic. To do so, consumers must have confidence in the safety of the fresh fruits, vegetables, and nuts they eat and feed their families.

A green row celery field is watered and sprayed by irrigation equipment in the Salinas Valley, California USA

Following a large and deadly outbreak of foodborne illness linked to fresh spinach in 2006, the U.S. produce industry couldn’t wait for government or other direction. After finding significant knowledge gaps and a lack of data needed to build risk- and science-based produce safety programs, the industry created the Center for Produce Safety (CPS) in 2007.

CPS works to identify produce safety hazards, then funds research that develops that data as well as potential science-based solutions that the produce supply chain can use to manage those hazards. While two foodborne illness outbreaks in the first half of 2018 associated with leafy greens demonstrate the industry still has challenges to meet, CPS has grown into a unique public-private partnership that moves most of the research it funds from concept to real-world answers in about a year.

Each June, CPS hosts a symposium to report its latest research results to industry, policy makers, regulators, academia, and other produce safety stakeholders. Key learnings from the 2017 symposium have just been released on topics including water quality, cross-contamination, and prevention. A few highlights from those key learnings are summarized here, and for the full details, you can download the Key Learnings report from CPS’s website.

Know Your Water (we were doing that in 2002, long before youtube existed)
Irrigation water is a potentially significant contamination hazard for fresh produce while it is still in the field. While CPS research has revealed many learnings about agricultural water safety in its 10 years, many questions still remain. Meanwhile, the U.S. Food and Drug Administration (FDA)’s proposed Food Safety Modernization Act (FSMA) water testing requirements—which offers some challenges for producers in specific production regions—recently raised even more questions.

New CPS research illustrates the risks of irrigating with “tail water” from runoff collection ponds. With water becoming a precious resource in drought-stricken areas, the objective was to learn if tail water might be recovered and used for irrigation.  We learned that differences among pond sites—for example, water sources, climate, ag management practices—can strongly influence the chemistry and microbiology of the water. Further, water pH can influence disinfection treatment strategies.[1]

CPS research continues to investigate tools for irrigation water testing, looking specifically at sample volumes,[2] and searching for better water quality indicators and indexing organisms including harnessing next-generation DNA sequencing.[3] Following a CPS-organized colloquium on ag water testing in late 2017, FDA subsequently announced it would revisit FSMA’s ag water requirements, and postponed compliance.

Bottom line, CPS research demonstrates that growers must thoroughly understand their irrigation water before they can accurately assess cross-contamination risk. CPS’s findings clearly point to the need to take a systems approach, to understand and control the entire water system to help achieve produce safety. Long term, this may mean prioritizing research into ag water disinfection systems to better manage contamination hazards that can also operate at rates needed for field production.
Cross-Contamination Can Happen across the Supply Chain
While conceptually and anecdotally the fresh produce industry knows that food safety is a supply chain responsibility, research is needed that documents the role of the entire supply chain to keep fresh produce clean and safe from field to fork. At the 2017 CPS Research Symposium, research reports were presented focusing on cross-contamination risks from the packinghouse to retail store display.

In the packinghouse, CPS-funded research found that wash systems can effectively control cross-contamination on fruit, when proper system practices are implemented.[4] Post-wash, CPS research involving fresh-cut mangos also demonstrated that maintaining the cold chain is critical to controlling pathogen populations.[5] Across the cantaloupe supply chain, CPS studies show food contact surfaces—for example, foam padding—are potential points of cross-contamination.[6] See the full 2017 Key Learnings report for details, as these brief descriptions only scratch the surface of this research.

CPS studies clearly demonstrate that food safety is a supply chain responsibility—a message that must be internalized from growers and packers to transporters, storages, and retailers to commercial, institutional, and home kitchens. While translating this research into reality will present engineering and operational challenges, our new understanding of produce safety demands it.
Verifying Preventive Controls
The produce industry must know that its preventive controls are in fact effective. That said, validation can be tricky. If validation research doesn’t mimic the real world, industry ends up fooling itself about whether its food safety processes work—and the human consequences are real.

Numerous scientists presented research at the 2017 CPS Research Symposium that validates various preventive controls, from heat treating poultry litter[7] to pasteurizing pistachios[8] to validating chlorine levels in wash water systems.[9] Some researchers effectively used nonpathogenic bacteria as a surrogate in their validation studies, while another is working to develop an avirulent salmonella surrogate, and another. Wang used actual Escherichia coliO157:H7 (albeit in a laboratory).

Importantly, CPS research finds that the physiological state of a pathogen or surrogate, and pathogen growth conditions themselves, are critically important to validation studies.[10] Meanwhile, suitable surrogates have been identified for some applications, the search continues for many others.

The research findings described here are just some of the real world-applicable results to emerge from CPS’s research program. To learn more, download the 2017 and other annual Key Learnings reports from the CPS website > Resources > Key Learnings page at

We were doing these videos in the early 2000s, long before existed, and weren’t quite sure what to do with them. But we had fun.


Yup, they get into produce seeds, especially sprouts: Salmonella and E. coli internalization

Vegetable seeds contaminated with bacterial pathogens have been linked to fresh-produce-associated outbreaks of gastrointestinal infections. This study was undertaken to observe the physiological behavior of Salmonella enterica and enterohemorrhagic Escherichia coli (EHEC) cells artificially internalized into vegetable seeds during the germination process.

Surface-decontaminated seeds of alfalfa, fenugreek, lettuce, and tomato were vacuum-infiltrated with four individual strains of Salmonella or EHEC. Contaminated seeds were germinated at 25°C for 9 days, and different sprout/seedling tissues were microbiologically analyzed every other day. The internalization of Salmonella and EHEC cells into vegetable seeds was confirmed by the absence of pathogens in seed-rinsing water and the presence of pathogens in seed homogenates after post-internalization seed surface decontamination.

Results show that 317 (62%) and 343 (67%) of the 512 collected sprout/seedling tissue samples were positive for Salmonella and EHEC, respectively. The average Salmonella populations were significantly larger (P < 0.05) than the EHEC populations. Significantly larger Salmonella populations were recovered from the cotyledon and seed coat tissues, followed by the root tissues, but the mean EHEC populations from all sampled tissue sections were statistically similar, except in pre-germinated seeds. Three Salmonella and two EHEC strains had significantly larger cell populations on sprout/seedling tissues than other strains used in the study.

Salmonella and EHEC populations from fenugreek and alfalfa tissues were significantly larger than those from tomato and lettuce tissues. The study showed the fate of internalized human pathogens on germinating vegetable seeds and sprout/seedling tissues and emphasized the importance of using pathogen-free seeds for sprout production.

Fate of Salmonella enterica and Enterohemorrhagic Escherichia coli cells artificially internalized into vegetable seeds during germination

Appl. Environ. Microbiol. January 2018 84:e01888-17; Accepted manuscript posted online 27 October 2017, doi:10.1128/AEM.01888-17

Da Liu, Yue Cui, Ronald Walcott and Jinru Chen



Maybe? USDA says antimicrobial wash reduces health risks in fresh produce

An Agricultural Research Service (ARS) scientist in Wyndmoor, Pennsylvania, and his collaborators have developed an antimicrobial wash that reduces the risk of foodborne pathogens contaminating fresh produce.

usda.produce.washJoshua Gurtler and scientists at NatureSeal Inc. have found that a combination of lactic acid, fruit acids, and hydrogen peroxide can be used in a produce rinse for commercial food distributors. NatureSeal, based in Westport, Connecticut, already markets an anti-browning wash developed by another ARS team in the 1990’s for sliced apples and 18 other types of produce.

E. coli, Listeria, Salmonella and other foodborne pathogens sicken approximately 1 in 6 Americans (48 million people) each year. A recent U.S. outbreak of Salmonella associated with cucumbers sickened over 765 people in 36 states and killed 4.

First Step+ 10 is designed to reduce those numbers, and is expected to be used in the commercial flumes and rinse tanks that wash fresh produce, Gurtler says.

The ingredients are all classified as Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration (FDA). The wash also has been approved for use in Canada; is U.S. Department of Agriculture (USDA) certified organic; is biodegradable; and does not affect the taste, texture, smell, or appearance of produce.

To save water, some food processors reuse wash water, a practice that can contaminate produce in subsequent washes. Along with reducing the risk of contamination, the new rinse will cut back on waste water because processors won’t have to replace water in their tanks as frequently.

To test First Step+ 10, Gurtler inoculated fresh cut apples, baby spinach, cantaloupe rind, and cherry tomatoes with highly resistant outbreak strains of E. coli O157:H7, Listeria, and Salmonella. He soaked them in the wash for 5 minutes and then measured pathogen levels in the wash water and on the produce. The antimicrobial wash reduced pathogen levels on the produce by 99.99 percent. It also rid the wash water of 100 percent of pathogens, making it safer to reuse.

Along with securing FDA approval, Gurtler and his collaborators at NatureSeal have filed a patent application and presented findings at scientific meetings.

ARS is USDA’s chief intramural scientific research agency.

Read more about this work in the January 2016 issue of AgResearch.

E. coli and Salmonella in tomatoes

Salmonella serovars have been associated with the majority of foodborne illness outbreaks involving tomatoes, and E. coli O157:H7 has caused outbreaks involving other fresh produce.

tomatoContamination by both pathogens has been thought to originate from all points of the growing and distribution process. To determine if Salmonella serovar Typhimurium and E. coli O157:H7 could move to the mature tomato fruit of different tomato cultivars following contamination, three different contamination scenarios (seed, leaf, and soil) were examined. Following contamination, each cultivar appeared to respond differently to the presence of the pathogens, with most producing few fruit and having overall poor health.

The Micro-Tom cultivar, however, produced relatively more fruit and E. coli O157:H7 was detected in the ripe tomatoes for both the seed- and leaf- contaminated plants, but not following soil contamination. The Roma cultivar produced fewer fruit, but was the only cultivar in which E. coli O157:H7 was detected via all three routes of contamination. Only two of the five cultivars produced tomatoes following seed-, leaf-, and soil- contamination with Salmonella Typhimurium, and no Salmonella was found in any of the tomatoes. Together these results show that different tomato cultivars respond differently to the presence of a human pathogen, and for E. coli O157:H7, in particular, tomato plants that are either contaminated as seeds or have a natural opening or a wound, that allows bacteria to enter the leaves can result in plants that have the potential to produce tomatoes that harbor internalized pathogenic bacteria.

 Movement of Salmonella serovar Typhimurium and E. coli O157:H7 to ripe tomato fruit following various routes of contamination

Microorganisms 2015, 3(4), 809-825

Deering, A.J.; Jack, D.R.; Pruitt, R.E.; Mauer, L.J.

Poop in the field

Two new studies assess the risk of various manures in broccoli and spinach respectively.

cow.poop2In 2011 and 2012, trials consisting of experimental plots were carried out to evaluate the presence of pathogenic (Listeria monocytogenes, Salmonella) and prevalence of indicator (Escherichia coli) microorganisms in broccoli fertilized with liquid hog manure or mineral fertilizers and irrigated zero, one, or two times with E. coli–contaminated water.

In 2011, results showed that E. coli contamination in broccoli heads was affected by the interval between irrigation and sampling (P = 0.0236), with a significant decrease between the first and third day following irrigation (P = 0.0064). In 2012, irrigation frequency significantly increased E. coli prevalence in broccoli samples (P = 0.0499). In 2012, E. coli counts in the soil were significantly influenced by the type of fertilizer applied, as plots receiving liquid hog manure showed higher bacterial counts (P = 0.0006). L. monocytogenes was recovered in one broccoli sample, but geno-serogrouping differentiated the isolate from those recovered in manure and irrigation water. The L. monocytogenes serogroup IIA, pulsotype 188 strain was found in six soil samples and in irrigation water applied 5 days before soil sampling.

This study highlights the link between E. coli levels in irrigation water, irrigation frequency, and interval between irrigation and harvest on produce contamination. It also demonstrates that L. monocytogenes introduced into the soil following irrigation can persist for up to 5 days.

In the second study, the authors write that concerns about the microbiological safety of fresh produce have attracted attention in the past three decades due to multiple foodborne outbreaks. Animal manure contaminated with enteric pathogens has been identified as an important preharvest pathogen source.

This study investigated the survival of Salmonella enterica in dust particles of dehydrated turkey manure and how association with manure dust may enhance the survival of salmonellae on leafy greens in the field. The survival of a cocktail of multiple Salmonella serotypes in the dried fecal material of various particle sizes (125 to 500 μm) was examined at varying moisture contents (5, 10, and 15%). Survival times of the pathogen were inversely related to moisture content and particle size of manure dust, with viable Salmonella still detectable for up to 291 days in the smallest particle size (125 μm) with 5% moisture. Association with manure dust particles increased the survival of Salmonella when subjected to UV light both under laboratory conditions and on the surface of spinach leaves in a greenhouse setting.

poop ice creamThe results of this study suggest that aerosolized manure particles could be a potential vehicle for Salmonella dispersal to leafy greens if the microorganism is present in the dry manure.



Persistence of indicator and pathogenic microorganisms in broccoli following manure spreading and irrigation with fecally contaminated water: field experiment

Journal of Food Protection®, Number 10, October 2015, pp. 1776-1924, pp. 1776-1784(9)

Généreux, Mylène; Breton, Marie Jo; Fairbrother, John Morris; Fravalo, Philippe; Côté, Caroline


Survival of Salmonella Enterica in dried turkey manure and persistence on spinach leaves

Journal of Food Protection®, Number 10, October 2015, pp. 1776-1924, pp. 1791-1799(9)

Oni, Ruth A.; Sharma, Manan; Buchanan, Robert L


Leafy greens carry risks; at-home rinsing of pre-washed salad mix isn’t doing much

In the quest to get healthier, including losing weight and reducing my body fat percentage, I’ve been paying particular attention to my eating habits and eating a bunch more vegetables.

I’ve become increasingly fond of the convenience of pre-washed, bagged, fresh whatever. A staple of my weekly meals is 4oz of steak, a crumble of blue cheese, grilled mushrooms, sliced pear, a few walnuts all over a bed of 50/50 mix of pre-washed baby spinach and and mesclun mix.img86l

I just open the bag and throw it on the plate. Because there’s not much I can do, safety-wise, to it once it’s in my home. If there’s pathogenic E. coli, Listeria or Salmonella there (or others) I’m stuck with it. I’m following recommendations from a bunch of my food safety friends who reviewed the literature on cut, bagged, washed, ready-to-eat leafy greens from a few years ago. In the abstract, they write:

The panel concluded that leafy green salad in sealed bags labeled “washed” or “ready-to-eat” that are produced in a facility inspected by a regulatory authority and operated under cGMPs, does not need additional washing at the time of use unless specifically directed on the label.

Leafy green food safety risks need to be addressed before they get to me, all I can do by washing it again is increase the chance I cross-contaminate the salad precursor in my home. My purchasing choice is based in trust that growers, packers and processors know what they are doing, and do it. But at best, they can only remove 90% of what is there with a wash.

Last week some research was presented at the American Chemical Society National Meeting & Exposition, prior to peer-review, that states what lots of food safety folks have published over the past decade: washing leafy greens doesn’t result in a sterile salad and the bumpy leaves protect pathogens.


I talked to Korin Miller at Yahoo News about it,

Labels like “thoroughly washed” and “triple washed” make us feel comfortable chowing down on pre-washed baby spinach straight from the container. But researchers from the University of California, Riverside, say we might want to rethink that habit.

They discovered that the small peaks and valleys in baby spinach leaves can harbor bacteria — even during the washing process they often undergo in food-processing plants.

While the news is shocking to most people, “this is not a surprise to many of us in the food safety arena,” Mike Doyle, director of the Center for Food Safety at the University of Georgia, tells Yahoo Health.

Unfortunately, washing your pre-washed baby spinach before eating it doesn’t make a difference, says Benjamin Chapman, PhD, an assistant professor and food safety extension specialist at North Carolina State University.

“Rinsing isn’t going to do a whole heck of a lot for food safety,” Chapman tells Yahoo Health — it just may remove dirt or other physical objects that you can see. Cooking the spinach, however, will kill potentially harmful bacteria.

I don’t agree with this comment, ‘pre-washed baby spinach is typically treated using a bleach disinfectant’

But what about the whole “triple wash” label? Does that make pre-washed spinach safer? Chapman says there’s some confusion about what it means. Companies don’t triple wash spinach to disinfect it, he explains — they do it to reduce the likelihood of cross-contamination from one piece of spinach to another during the washing process.

The water is treated to reduce cross-contamination in the processing water; 2-log reduction, at the very best, is not an effective surface disinfectant.

Food safety culture means employees don’t contaminate food with brooms or forklift tires

If a company making ready-to-eat refrigerated deli-meats has a “strong culture of food safety,” would an employee shake a broom over a line of processed product?

If more inspectors are the answer to safer food, why would the inspectors need publicly reported accounts of foodborne illness and death to try harder?

And if the company and inspectors are doing lots of tests to ensure enhanced food safety, why aren’t they bragging about it instead of requiring an Access to Information request by a media outlet to discover that inspectors continue to find problems with Maple Leaf Foods infamous Bartor Road plant in Weston, Ontario.

Last night, Steve Rennie of The Canadian Press reported that Canadian federal food safety types found a troubling lack of hygiene at Maple Leaf Foods’ Toronto facility just weeks after it reopened last year from a temporary shutdown for cleaning – after 22 people were killed and 53 sickened with listeria linked to deli meat.

A Canadian Food Inspection Agency inspection report dated Oct. 10, 2008, found:

• slime on part of the meat-trimming table in the curing room;
• meat debris on two steel container bins and unidentified debris on the brine tank in the curing room;
•a moist and mouldy cardboard sheet on the base of a skid in the curing room that holds bags of salt;
•mouldy caulking on the walls of the meat-defrosting room;
•a stack of dirty, mouldy and broken skids left in the frozen packoff room during cleaning;
• food debris on knife holders, floor and meat containers in the formulation room; and,
• rust on equipment used to process mock chicken.

The Canadian Press obtained that inspection report and others under the Access to Information Act.

Another report says during visits on Oct. 20 and 21, an inspector watched as "an employee in a grey jacket lifted a floor broom over a finished food product conveyor belt during operation to sweep in between the conveyors." (No additional information as to whether the product was packaged or not).

Then on Oct. 22, the inspector saw a worker using a forklift to move ready-to-eat link sausages from the cooler to a line for packaging. The report notes the meat at the bottom part of the lift "was not protected for the potential wheel over spray or splash cross contamination."

That part is gross. And unacceptable.

On Aug. 23, 2008, ( passim ad nauseum) Maple Leaf CEO Michael McCain took to the Intertubes to apologize for an expanding outbreak of listeriosis that would eventually kill 22 people. As part of his speech, McCain said that Maple Leaf has “a strong culture of food safety.”???

On Aug. 27, 2008, McCain told a press conference, ??????“As I’ve said before, Maple Leaf Foods is 23,000 people who live in a culture of food safety. We have an unwavering commitment to keep our food safe, and we have excellent systems and processes in place.

Dr. Randy Huffman, Maple Leaf’s chief food-safety officer, took to his company’s Journey (worst band ever)-inspired Journey to Food Safety Leadership blog to say today,

“The average reader must be wondering how this plant could have so many issues only a month after re-opening from causing one of the worst food safety crises in Canada.”

I’m not sure what he means by average. I consider myself dull and below-average; does that mean I won’t be able to understand what he is saying?

Huffman: Over the past 12 -14 months- since these inspections were conducted – we have invested over $5 million in upgrades at the Bartor Road plant. This includes repair of floors and wall surfaces, air handling systems, caulking, better separation of raw and cooked areas of the plant, new pallets and new slicing and packaging equipment. We have implemented over 200 new operating procedures.

Why did it take 22 deaths and 53 illnesses to make this food safety investment?

Huffman: CFIA generates these reports and so does Maple Leaf, through our own inspections across all our plants. We welcome this government scrutiny.  Canadians hold us to a higher standard, as they should.

So why did the reports have to be obtained through an Access to Information request, and why doesn’t Maple Leaf just sidestep the government and make the reports public, along with other data, as it becomes available, to build trust with the buying consumer?

Would more inspectors have helped? Maybe if they were looking. Federal food inspection union thingy Bob Kingston said,

"In a normal operation that had not been through what they had been through, that might be a common occurrence. But in this facility, it’s very surprising that that would still be there. Because you would expect it to be spotless."

The best food producers, processors, retailers and restaurants will go above and beyond minimal government and auditor standards and sell food safety solutions directly to the public. The best organizations will use their own people to demand ingredients from the best suppliers; use a mixture of encouragement and enforcement to foster a food safety culture; and use technology to be transparent — whether it’s live webcams in the facility or real-time test results on the website — to help restore the shattered trust with the buying public.

And the best cold-cut companies may stop dancing around and tell pregnant women, old people and other immunocompromised folks, don’t eat this food unless it’s heated