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Stone fruit Listeria research highlights synergy of scientist-industry partnerships

February 22, 2018
In 2014, when Listeria monocytogenes was implicated in an illness outbreak associated with  peaches, nectarines, plums and pluots, the industry was left questioning what it knew about the survival and risks associated with the pathogen.

Dr. Mary Anne Amalaradjou, an assistant professor of animal science at the University of Connecticut, said she hoped her recently completed research would provide the science-based data the stone fruit industry needed to develop additional preventive controls. To ensure the results were pertinent, she worked closely with industry cooperators throughout her research project, titledListeria monocytogenes growth and survival on peaches and nectarines as influenced by stone fruit packinghouse operations, storage and transportation conditions.”

“My knowledge or understanding of how stone fruit are handled was all based on literature and I didn’t have any first-hand information,” Amalaradjou said. “That’s where the industry stepped in. They were very patient with all of my questions as I put my proposal together. Once CPS decided to fund it, I went back and talked to them to make sure what I was doing in the lab would be applicable and real world.”

George Nikolich, vice president, technical operations, for Gerawan Farming Inc. in Reedley, California, was one of the stone fruit industry cooperators who saw a pressing need for her project.

“There’s a lot we know about Listeria with other commodities, but our understanding of Listeria on stone fruit is limited,” he said. “Before the 2014 recall, our industry was supporting food safety research. But after the 2014 recall, we had to redouble our efforts. In a way, we’re starting from square one to make sure we haven't made any incorrect assumptions.”

The 2014 outbreak to which Nikolich referred marked the first time a Listeria monocytogenes outbreak had been linked to stone fruit, according to the Centers for Disease Control. The voluntary recall involved whole peaches, nectarines, plums and pluots from a single producer in central California.

As part of the CPS-funded project, Nikolich hosted Amalaradjou last summer and toured her around the family-owned stone fruit growing and packing operation. She was able to see first-hand how the fruit was handled as it was harvested, packed and then cooled for shipment. Amalaradjou also met with other representatives of the Fresno-based California Fresh Fruit Association and visited their operations to observe subtle differences among facilities.

“That’s a huge, very important component of the whole process,” Nikolich said. “Mary Anne came out and visited with us as well as other members of the Fresh Fruit Association. She was able to gain first-hand experiences looking at operations and gain a better understanding of what we do. That’s critical. One of CPS’s greatest strengths is to connect research scientists and people in the field and develop this type of understanding.”

Amalaradjou agreed and praised Nikolich and other members of the California stone fruit industry for their input as she drafted her research proposal and for their openness during last summer’s visit.

Her one-year research project involved examining Listeria survival during three distinct post-harvest steps: unloading and staging in the packinghouse; fruit waxing and fungicide application; and cooling, storage and transportation. Amalaradjou patterned the processes in her laboratory as closely as possible to what she saw in the packinghouses.

Because wax and fungicide applications could potentially affect pathogen survival, Gerawan Farming shipped her fruit fresh from the field for her experiments.

Although Amalaradjou plans to discuss her results in detail during the CPS Research Symposium, June 19-20, in Charlotte, North Carolina, she did provide a glimpse of the project’s outcome.

On the plus side, Amalaradjou found Listeria populations did not increase during each of the three packinghouse steps. On the other hand, populations did not decline, either.

“The conditions that the industry are using don’t speed Listeria growth, but we saw it still survived,” she said. “Since we can show it doesn’t grow, that’s good news for the producer. But it still shows it can survive on the fruit so that’s a potential contamination risk.”

Interestingly, Listeria survival on peaches, which have fuzzy or pubescent skins, was about the same as for smooth-skinned nectarines, Amalaradjou said.

Key Takeaways
Stone fruit industry input and packinghouse tours were critical to make research applicable.
2014 Listeria outbreak in stone fruit prompted the need for more science-based data.
Experiments found Listeria populations didn’t increase on stone fruit during each of three distinct packinghouse stages nor did numbers decrease.

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