Scientists have invented a machine that can clean bacteria from salad using gentle streams of water carrying sound and microscopic air bubbles.

Tests show it is much more effective than current washing methods used by households and food producers involving just water, and could reduce cases of food poisoning.

Professor Timothy Leighton of the University of Southampton, who invented the technology said: “Our streams of water carry microscopic bubbles and acoustic waves down to the leaf. There the sound field sets up echoes at the surface of the leaves, and within the leaf crevices, that attract the bubbles towards the leaf and into the crevices.

“The sound field also causes the walls of the bubbles to ripple very quickly, turning them into microscopic ‘scrubbing’ machines. The rippling bubble wall causes strong currents to move in the water around the bubble, and sweep the microbes off the leaf. The bacteria, biofilms, and the bubbles themselves, are then rinsed off the leaf, leaving it clean and free of residues.”

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Salad and leafy green vegetables may be contaminated with harmful bacteria during growing, harvesting, preparation and retail leading to outbreaks of food poisoning.

Because there is no cooking process to reduce the microbial load in fresh salads, washing is vital by the supplier and the consumer.

Washing with soap, detergent bleach or other disinfectants is not recommended and the crevices in the leaf surface means washing with plain water may leave an infectious dose on the leaf. Even if chemicals are used, they may not penetrate the crevices, Prof Leighton said.

The results of the tests showed that the microbial load on samples cleaned with the acoustic streams for two minutes was significantly lower six days after cleaning than on those treated without the added sound and bubbles.

The results are published in the journal Ultrasound in Medicine and Biology.

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