|Paul Dawson, PhD, Clemson University|
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.