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From: Food Quality & Safety magazine, December/January 2012

The Cantaloupe Crisis: What’s Next?

Fruit linked to unprecedented listeriosis outbreak sparks renewed efforts to ensure produce safety

by Gina Shaw

Fruit linked to unprecedented listeriosis outbreak sparks renewed efforts to ensure produce safety

In September, when Steve Patricio learned of the Listeria outbreak traced to cantaloupes from a farm in Colorado—an outbreak that killed 29 people as of Nov. 9, sickened dozens, and caused one miscarriage—his mind immediately raced back two decades to a similar outbreak.

In the summer of 1991, more than 400 people in the Western United States developed Salmonella after eating tainted cantaloupes. In that case, the original source of the outbreak was never identified, although many suspected a grower in West Texas, who in turn pointed the finger at Mexican farms. No one died in that outbreak, but the cantaloupe industry took an enormous hit—just as it’s doing now.

“At the peak of the outbreak, demand for cantaloupes decreased by 60%,” said Patricio, chair of the California Cantaloupe Advisory Board. “Retail buyers believe that consumers are still walking past the product, and probably for good reason. There’s no way to adequately apologize for or explain (29) deaths and a hundred-plus illnesses. We’ll deal with the fallout from this for a generation.”

On Oct. 19, the FDA released a report indicating that the outbreak—the first-ever listeriosis outbreak associated with fresh, whole cantaloupe—was an outlier incident, primarily attributable to unsanitary conditions in the packing facility at Colorado grower Jensen Farms. The report found:

  • A truck used to haul culled cantaloupe to a cattle operation was parked adjacent to the packing facility and could have introduced contamination into the facility;
  • The packing facility’s design allowed water to pool on the floor near equipment and employee walkways;
  • The packing facility floor was constructed in a manner that made it difficult to clean;
  • The packing equipment was not easily cleaned and sanitized; washing and drying equipment used for cantaloupe packing had previously been used for post-harvest handling of another raw agricultural commodity; and
  • There was no pre-cooling step to remove field heat from the cantaloupes before cold storage. As the cantaloupes cooled, there may have been condensation that promoted the growth of Listeria monocytogenes.

A third-party auditor had also failed to cite Jensen Farms for any of these conditions in a glowing report after a visit to the facility in August—less than a month before the outbreak began.

But even if you consider Jensen Farms a “bad apple” in the produce trade, the safety of cantaloupes remains a persistent challenge for the industry. “Netted melons like cantaloupe grow on the ground and can come in contact with pathogens in non-composted fertilizer or through handling,” notes a report from the University of Wisconsin. “Unlike other fruits, cantaloupe are not acidic and readily support the growth of pathogens once they are sliced open.”

Craig Wilson, Costco’s vice president of food safety and quality assurance, has been characteristically candid in calling for stricter cantaloupe safety measures. In a late September New York Times article, he called for growers to get more aggressive about pathogen prevention and detection in cantaloupes and said Costco would consider setting standards for how melons are grown, cleaned, and handled.

“We want to move that type of testing to cantaloupe. It seems to make good sense to us, and to the vendors that we talk to, for the supplier to know the microbial quality of the fruit he’s putting into commerce.”

—Craig Wilson, Costco’s vice president of food safety and quality assurance

“Doing the same things that we’ve been doing for the last 10 years and expecting a different outcome isn’t the right thing to do,” he told Food Quality.

So what will Costco be calling for? First, said Wilson, the firm wants a finished-product testing program, much like programs that are now applied to ready-to-eat foods. “We want to move that type of testing to cantaloupe. It seems to make good sense to us, and to the vendors that we talk to, for the supplier to know the microbial quality of the fruit he’s putting into commerce.”

Wilson added that Costco is evaluating intervention strategies. “For example, we have some companies looking at steam pasteurization, surface pasteurization of the cantaloupe. That seems to work really well.” It’s an approach that’s been employed with beef carcasses ever since 1993’s deadly outbreak of E. coli in the Western states, in which four children died after eating tainted meat from Jack in the Box restaurants. Wilson, then in charge of special projects at Frigoscandia Equipment in Bellevue, Wash., worked with colleagues there to develop the steam pasteurization process.

“When we were doing the beef studies, we also tested cantaloupe,” he said, noting that the Jack in the Box outbreak occurred just two years after the Salmonella outbreak in cantaloupe. “By using steam at atmosphere, it turns to water when it goes through phase change on the surface of the cantaloupe, and it kills the bugs there. It’s pretty straightforward and efficacious, and I don’t really have an answer as to why it hasn’t been used widely in cantaloupe before. Right now, we have some pilots going on and it’s under serious review.”

Companies are also re-evaluating washing systems and what’s being used to wash the fruit. “Are they using surfactants, natural acids, or chlorine only?” Wilson asked. “And with all these intervention strategies, we also need to have something in place to prove they work. We’re asking vendors to work with us on that, and we’re getting a great response.”

But California’s Patricio said that a less-is-more approach to cleaning cantaloupes may be the best way to go—at least when it comes to melons grown in the specific growing conditions of his state—based on research conducted with the University of California-Davis in the wake of the 1991 outbreak.

“We did six years of sampling, and after that, we weren’t finding contamination even in greater risk areas, such as downwind of dairies and near corrals,” said Patricio. (The program looked for Salmonella and E. coli only—Listeria wasn’t a recognized issue at the time.) “Scientists concluded that the high heat, low humidity, and other climatic conditions in central California prevented the development and spread of those common bacteria in normal practice.”

So the researchers turned to industry cleaning practices. “At the time, there were probably 30-some shippers in California, with a dozen different techniques being used to prevent the spread of pathogens. We had elaborate wash systems, hydrocooling, deep cold and hot, hot, hot temperature—all sorts of things were being done to reduce risk,” said Patricio.

The scientists evaluated them all and concluded that most of them risked causing more contamination than they prevented. “They concluded that cantaloupes run more risk of contamination the more times they come in contact with people or common surfaces,” Patricio explained. “You want to limit human contact and get them as they are in nature as quickly as possible into a sealed container. This was a bit dismaying to those of us who had invested in elaborate systems, but field packing quickly became the norm.”

Patricio said that uncut cantaloupe with a whole, unbreached rind has a natural barrier against pathogens. “Years and years of research indicates that the rind and the biology of the melon prevent cantaloupe from uptaking bacteria into the edible portion. The best thing you can do is touch them as little as possible.”

Test-and-hold programs aren’t well suited for a product like cantaloupe, Patricio said. “They have a 72 - to 96 - hour window. If I still have product 36 hours after I pack it, I’m in trouble,” he noted. “A cantaloupe has such a short shelf life that I’ve got to get it out of the field, packaged, pre-cooled, and shipped within 36 hours. But things like steam pasteurization and other new strategies have good potential going forward.”

The Center for Produce Safety (CPS) at the University of California-Davis has undertaken a project to research and evaluate new methods for preventing cantaloupe contamination. Patricio, who became chair of CPS in June, said the California cantaloupe industry has pledged $200,000 toward this effort and is asking other cantaloupe stakeholders to match those funds.

With an additional $200,000 coming directly from CPS, Patricio expects approximately $1 million in research funding to be raised to support an independent review of options such as gases, ozone, and steam pasteurization. “We want these methods reviewed by a third party without a dog in the fight, and that’s what the Center for Produce Safety is,” said Patricio. “This isn’t going away quickly. But no matter what we do, we have to be sure to do our best to produce healthy food supply every day and every bite.”

Gina Shaw writes about the food industry in Food Quality’s weekly enewsletter.



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