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Ultrasound Treatment Helps Kill E. Coli on Leafy Greens

Ultrasound treatments may help reduce E. coli numbers on leafy greens by as much as 90 percent more than solely using conventional chlorine washes, according to new study by researchers at the University of Illinois.

Today, growers will often clean leafy greens such as spinach in chlorine baths. By lining the sides of these tubs with panels that fire ultrasound waves — sounds in a frequency too high for humans to hear — the researchers found they could knock a significantly larger amount of the bacteria into the deadly wash.

The system works by channeling leafy greens through a continuous-flow chlorine wash as they pass by three pairs of ultrasonic transducer boxes operating at different frequencies.

In total, the combined ultrasound-chlorine treatment has shown to reduce the number of harmful bacteria on spinach by more than 99.99 percent. The technique works on iceberg and romaine lettuce, too.

Hao Feng, associate professor of food engineering at the University of Illinois and lead author on the study, told NPR that he had to be very careful to determine just the right amount of ultrasound intensity for hitting the spinach. If hit too hard, the leaves will develop watery spots and rot, but too little will leave behind higher levels of bacteria.

Operating the technique on a commercial scale would cost more than the conventional chlorine wash, but the researchers are confident the invention could work in a commercial environment.

The full study, published in ScienceDirect, can be read here.

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