What Fridman and his team have to demonstrate is that the technology's use in a fresh-cut produce setting does not damage the fragile vegetables and yields an end product safe for human consumption.
"If we can produce fresh produce that's safe without chemicals, it's a big deal," he said. "That, I think, will be the biggest impact."
Joining Fridman as co-principle investigators from Drexel are Jasreen Sekhon, Ph.D.
, Department of Food and Hospitality Management; Christopher Sales, Ph.D.
, Department of Civil, Architectural and Environmental Engineering; and Alexander Rabinovich, Ph.D.
, an associate director of the C. & J. Nyheim Plasma Institute. Also involved are a handful of Drexel students.
As part of previous work, Drexel had developed an instrument known as the reverse vortex gliding arc plasmatron. When water is injected through the plasma stream, the ionized gas molecules initiate chemical reactions in the water that produce disinfectant compounds, such as ozone.
These reactions are very short lived and the compounds quickly break down into harmless products, such as water and oxygen. But during that split second, the compounds deactivate pathogens in the water.
"We're able to safely apply plasma to the water, and we're able to kill microorganisms without any chemicals," he said. "We're able to generate very energetic plasma very safely."
The plasmatron they're using only requires about 3 kilowatts of electricity - slightly more than a refrigerator uses - making it economical for industry use, Fridman said. And unlike many wash water systems that rely on chemical disinfectants, such as chlorine, cold plasma is not significantly affected by organic loading or water pH.
A year into the project, the researchers have already conducted a proof of concept in the laboratory. They are now validating the technology with a prototype model using a 100-gallon (400-liter) tub into which the plasmatron electrode has been submerged. The system has been modified and carefully grounded for safety.
As part of the project, they will simulate increased organic loading seen in a fresh-cut processing facility. Plasma-treated water will also be used to wash both produce inoculated with a microbial cocktail of E. coli strains and non-inoculated items.
Afterward, the produce and wash water will be tested for pathogens to determine the rate of inactivation. The washed produce also will be inspected and monitored for quality changes.
After the Drexel team optimizes the technology, Fridman said, the next step will be for project collaborator SmartWash Solutions LLC to install the pilot system in a commercial-scale fresh-cut wash system.