A study published in the magazine Ultrasound in Medicine and Biology reveals that cleaning salad with an ultrasound system would be the best way to reduce the microbial load in fresh salads.
Since salad is rarely cooked, it is essential to wash it before eating it. Water cannot however remove all harmful bacteria, and the use of cleaning products, bleach or other disinfectants is not recommended.
Professor Timothy Leighton from the University of Southampton has invented a technology to clean salad with ultrasound. He uses gentle streams of water carrying sound and microscopic air bubbles in order to remove bacteria from salad leaves.
“The sound field creates echoes on the surface and in the crevices of the leaves, which attract the bubbles to the leaf or in the crevices,” explains the researcher. “The sound field also causes the bubble walls to ripple very rapidly, turning them into microscopic "scrubbing" machines. The undulating bubble walls make strong currents flow in the water around the bubble and sweep the microbes from the leaf. The bacteria, biofilms and bubbles themselves are then rinsed from the leaf, leaving it clean and without residue.”
The results have shown that the samples cleaned with acoustic currents for 2 minutes had fewer bacteria than those treated without sound and microbubbles.
This solution could improve the way food suppliers clean fresh products. It could help prevent the deadly outbreaks of different strains of E. Coli that affected romaine lettuce in the USA and Canada in 2018 and 2019.