Ultimately, the U.S. Department of Agriculture would like technology that achieves a 4- to 6-log reduction in pathogen cells, according to a news release.
A 6-log reduction is a million-fold reduction.
Technologies used by processors currently achieve about a 1-log, or 10-fold, reduction.
The University of Illinois technology yields a 4-log reduction.
Hao Feng, a food science and human nutrition professor, developed a pilot-scale system that used three pairs of large-area ultrasonic tranducer boxes to form a channel.
Spinach leaves in a continuous-flow chlorine wash flowed through the channel.
The key to the success, Feng says, is continuous flow and uniformity of the ultrasound field.
“Placement of the produce as it makes its way through the channel turns out to be very important," he said in the release. "We had to find ways to make sure that leaves received similar exposure to ultrasound, taking care to minimize the chance that one leaf would block a nearby leaf’s exposure to the sound waves.”
If even part of a leaf escaped ultrasound treatment, it could potentially contaminate the rest of the load.
Feng and his colleagues also tested the technology on iceberg and romaine lettuce with similar results.