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Researchers focus on preventing listeria contamination

Fear of listeria contamination in Michigan apples underscores the need for continued research to prevent any such problems with Washington apples.
Dan Wheat

Capital Press

Published on December 26, 2017 8:37AM

Ines Hanrahan, post-harvest physiologist, Washington Tree Fruit Research Commission.

Dan Wheat/Capital Press

Ines Hanrahan, post-harvest physiologist, Washington Tree Fruit Research Commission.


YAKIMA, Wash. — The recall of Michigan apples in Midwest and Southeastern states due to listeria contamination fears is unfortunate, and the Washington apple industry is working hard to avoid similar problems, a leading researcher says.

Grocery chains Kroger and Aldi have recalled several varieties of apples sold in several states since Dec. 12 after routine sampling by Jack Brown Produce, Sparta, Mich., found listeria in a shipment from one of its suppliers, Nyblad Orchards. No illnesses were reported, but both retailers advised people to throw apples away or return them for full refunds.

Listeria monocytogenes is a species of pathogenic bacteria that can cause serious or fatal infections in young children, the elderly and people with weakened immune systems as well as miscarriages and stillbirths in pregnant women, according to the U.S. Food and Drug Administration. In otherwise healthy people, it can cause high fever, severe headache, stiffness, nausea, abdominal pain and diarrhea.

“We don’t know a lot of details about what happened in Michigan but it is unfortunate. We are very concerned in Washington about listeria and have been trying to do everything possible to set up processes to avoid problems,” said Ines Hanrahan, post harvest physiologist and project manager with the Washington Tree Fruit Research Commission.

Not all listeria strains or species are deadly and where they live and what causes them to grow is not fully understood, Hanrahan said.

“We have no way of controlling or knowing when a potentially deadly strain enters our post-harvest environment,” she said. “However, we can set up very thorough systems to make sure we get alerted as soon as any listeria enters storage and packing and then we can eradicate them by thorough cleaning and sanitation programs for equipment.”

Furthermore, fruit is sprayed with chemicals that kill bacteria such as listeria and E. coli, she said. Ongoing research funded by the commission in collaboration with Washington State University has established that cold storage or controlled atmosphere storage of more than six weeks may reduce listeria species by up to 99.9 percent, she said.

Adding a continuous flow ozone generator to a controlled atmosphere storage room may lead to even higher levels of bacterial die-off, she said.

“We are currently conducting research to find out the best standard operating procedures for all these things to get the maximum bacterial reduction. We know these techniques work but we are trying to get the maximum effect,” Hanrahan said.

Hanrahan and scientists at WSU and the Center for Produce Safety in Davis, Calif., are working on studies, two of which will be done next year and others within three years.

Listeria is no more common in apples than other produce or processed foods. There was a rash of listeria outbreaks in cantaloupe several years ago in which more than two dozen people died. Outbreaks have also occurred in ice cream and cheese.

Any food that comes in contact with soil has potential for contamination, as does produce in which water is used in packing lines, Hanrahan said.

In late 2014 and early 2015, three deaths and 34 hospitalizations across the country were traced to caramel apples sold by three companies but originating as fresh apples from Bakersfield, Calif. In 2013, Crunch Pak, Cashmere, Wash., recalled sliced apples due to possible listeria contamination.

Listeria infections cause about 1,600 illnesses and 260 deaths annually in the U.S.



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