Apr 16, 2015
Celery packing lines susceptible to foodborne pathogens

An increasing number of foodborne outbreaks traced to fresh fruits and vegetables are being partially attributed to current production and processing methods.

In the United States, the progression from locally grown produce to centralized production has led to numerous multi-state and nationwide outbreaks of foodborne illness.

“During postharvest processing, fresh produce, including celery, is prone to contamination from other products, wash water or processing equipment – including from conveyors or knives – allowing the spread of microbial pathogens,” said Elliot Ryser, a professor in Michigan State University’s Department of Food Science and Human Nutrition.

In many cases, fruits and vegetables are grown on centralized, large-scale farms in locations that specialize in a specific product, Ryser noted in a presentation at the Great Lakes Fruit, Vegetable & Farm Market EXPO in Grand Rapids, Michigan.

Under these conditions, one contamination event at a large centralized grower or packer could lead to a potential recall and/or outbreak of foodborne illness, as has been seen for leafy greens, tomatoes and cantaloupe.

“Listeria monocytogenes is one serious foodborne pathogen (a cause of meningitis, abortions and perinatal septicemia) that has been identified in ready-to-eat salads containing raw celery, as well as in other types of ready-to-eat salads,” Ryser said.

In 1979, an outbreak of listeriosis involving 23 individuals was epidemiologically linked to consumption of raw celery, tomatoes and lettuce.

Nine years later, an outbreak of gastroenteritis at the U.S. Air Force Academy originally attributed to salmonella was later traced to diced celery that was washed and stored in non-potable water that was contaminated with norovirus, Ryser said.

In 2010, 10 listeriosis cases, including five deaths, were traced to diced celery from a produce processing facility in San Antonio, Texas, with this contaminated celery subsequently used as an ingredient in chicken salad that was served to hospital patients .

Outbreaks such as these can result from microbial contamination of fresh produce at any point in the farm-to-fork continuum. During harvesting, foodborne pathogens may contaminate celery via decaying vegetation, feces, soil, irrigation water or sewage effluent, or through dissemination by animals such as wild birds, Ryser said.

“Worker handling during harvest and postharvest processing may also lead to contamination if inadequate hygiene and sanitation practices are followed,” he said.

Post-processing such as slicing and dicing can further spread these microbial contaminants, with storage at improper temperatures then permitting growth of foodborne pathogens to levels potentially hazardous to consumers, Ryser said.

“Nearly all Michigan celery is grown in muck soil. This floodwater is a potential source for foodborne pathogens, including Escherichia coli, salmonella and listeria, due to run-off from nearby fields and livestock operations,” Ryser said.

“Celery can be readily contaminated with a wide range of microorganisms – including potential foodborne pathogens – during mechanical harvesting. Hence, both the harvester – including the wheels and frame – and the harvest wagon may need to be periodically cleaned during extended harvesting periods to prevent the unwanted build-up of soil and other organic debris.”

Upon delivering the celery to the packing shed, the field worker driving the tractor should remain on the tractor, with those in the packing shed unloading the incoming celery, Ryser cautioned.

“Worker hygiene is critically important during the unloading and trimming of celery,” Ryser said. “Special attention needs to be given to the cleanliness of the workers’ gloves, aprons and trimming knives. Periodically sanitizing the trimming knives will help decrease the transfer and subsequent spread of microorganisms during long periods of use.”

Mechanical conveyors of various types are universally used in celery packing lines, Ryser said. It is critically important that the belts be properly designed for effective cleaning and sanitizing, with continuous belts much preferred over pleated varieties, since the latter types are highly prone to organic build-up and biofilm formation.

Spraying the belt with an appropriate sanitizer (such as chlorine or peroxyacetic

acid) should be considered to minimize the spread of microbial contaminants.

“All celery trim should be segregated from the trimmed celery and conveyed away from the processing area,” he said. “After trimming, the celery is mechanically cut and conveyed to the washing station, where it is washed in water containing a chlorine- or peroxyacetic acid-based sanitizer.”

Regardless of the type of wash system used (including open flume or spray cabinet), the effectiveness of this washing step is dictated by the sanitizer concentration and contact time with the celery.

Thereafter, the washed celery is conveyed to the packaging area with smooth belting materials, with a sanitizer spray again recommended to minimize contamination, Ryser said.

“Lastly, it is important that packing sheds be properly designed in terms of product flow,” Ryser said. “Incoming product from the field should move linearly through the facility, from receiving to packaging, with all of the heavily contaminated trim and waste exiting the facility in the opposite direction from the packaging area.

“Every attempt should also be made to minimize haphazard movement of the workers in the packing shed during production,” Ryser said.

Gary Pullano

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