October 14, 2020

Researchers seek field tool to refine sampling, sanitation intervals

Clemson University researchers are working to develop a user-friendly tool that can predict biofilm behavior in stone fruit packinghouses and produce more targeted sanitation recommendations.

An Excel-based add-on will factor in variables, such as packinghouse surface materials, temperature, water pH and relative humidity, said project leader Paul Dawson, Ph.D. and professor in Clemson University’s Department of Food Science and Human Nutrition.

Paul Dawson

“This tool could save time and money by allowing the appropriate sanitation protocol so you’re not under sanitizing and not over sanitizing,” he said. “You put in different conditions and then it provides the answer. This is a scientific approach.

“I think also for the regulators, most of them want you to have a science-based plan. And with this, they’ll understand you’ve done your due diligence.”

Joining him as an academic collaborator, titled “Verification and validation of environmental monitoring programs for biofilm control in the packinghouse,” is Claudia Ionita, Ph.D. and post-doctoral fellow at Clemson.

Frequently, foodborne pathogens — such as Listeria monocytogenes — aren’t found living as individual species on packinghouse surfaces but instead are part of microbial communities, or biofilms, that attach to materials.

The biofilms not only protect the organisms, but they also may inactivate chlorine-based disinfectants, complicating sanitation. The bacterial plaque found in your mouth and removed by a dental hygienist is an example of a biofilm.

What’s unique about the CPS-funded project is it will involve growing mixed biofilms of microbial species collected from working packinghouses in California and South Carolina and will add Listeria monocytogenes. The researchers have identified Pseudomonas and Bulkholderia species within the microbial communities of packinghouses.

So far, Ionita has visited a handful of California packinghouses to sample Zone 1, which are surfaces directly contacting the fruit and include conveyors and brushes. She also sampled other areas of the packinghouse, such as cracks, crevasses, walls, floors where water may pond, and cold-storage areas. This project does not include pathogen testing nor will that be a part of the project in the future.

Listeria monocytogenes is unique among pathogens because it will continue to grow and reproduce under refrigeration, just not as rapidly as under optimum temperatures, Dawson said. Other pathogens typically go dormant under cold conditions.

The researchers had planned to also sample South Carolina packinghouses this season, but the ongoing coronavirus pandemic prevented them from doing so. South Carolina ranks No. 2 in U.S. peach production, behind industry leader California.

Ionita plans to collect additional samples from California and South Carolina packinghouses next year during the early season as well as later in the fruit-production period.

Further slowing their project was that Clemson University’s microscopy facility was shut down for several months by COVID-19 protocols and just reopened.

“Because of the coronavirus, we haven’t been able to go back out to the packinghouses in the last six months and collect more samples,” Dawson said. “We’re behind where we wanted to be. Next year hopefully we can test this add-on and be able to start putting it to the test in the real world.”

As part of laboratory experiments, the researchers inoculated microbial colonies on two different surface materials and two different roughnesses, plotting growth rates under simulated packinghouse conditions.

Preliminary results showed biofilms produced more biomass on fabricated rough surfaces than on smooth surfaces.

The researchers also subjected the biofilms on the different surfaces to an industry standard of 200 ppm chlorine disinfectant to measure how long it took for inactivation.

Complete inactivation of the biofilm on smooth surfaces was achieved in 25 minutes, while listeria could still be detected on the rough surfaces within the same time period.

The data from the laboratory experiments will be used to build a mathematical model of biofilm development as well as sanitation recommendations. The model will then be validated in trials conducted in a pilot plant.

“That’s as close as you can get to going to a commercial operation,” Dawson said.

 — Center for Produce Safety

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