With Cyclospora outbreaks linked to iceberg lettuce making headlines recently, and Salmonella now being found in jalapeño peppers, I’m wondering if an ozone or ultrasonic produce cleaner would be good to have on hand. Is using one better than just washing fruits and vegetables under running water?
We couldn’t find any published studies looking at the effectiveness of these consumer devices and therefore cannot recommend them at this time.
There’s reason to think they may be effective, however—at least when used by the food industry, which is pursuing these technologies both in the U.S. and elsewhere due to the high interest in keeping foods safe from disease-causing foodborne organisms and maintaining quality in efficient ways.
Ozone technologies are being employed industrially to reduce the growth of microorganisms that cause spoilage and foodborne illness. It works by causing an oxidation reaction that crumbles the cell walls of bacteria and fungi and breaks down vital proteins and enzymes inside, thereby killing or inactivating them.
As a potent oxidant, ozone is also capable of destroying certain viruses. In this case, it works primarily by damaging the lipid envelope surrounding such viruses as influenza and SARS-CoV-2 (which causes Covid). However, the two most common viral foodborne microbes are norovirus and rotavirus, neither of which are enveloped.
Ozone’s effectiveness also depends on several factors such as the concentration of microbes on the food, the type of microbe, and the food storage temperature and humidity, as well as the concentrations of ozone used. In addition, ozone doesn’t clean dirt and debris from the produce, and if the dirt isn’t removed first, it will react with the ozone, which will then get used up and not be available to disinfect the produce.
Ultrasonic devices produce sound waves that cause bubbles to form, which then burst and damage the cell membranes and other parts of bacteria and fungi. In addition, free radicals are formed, causing further destruction inside the microbe, such as to vital enzymes and other proteins. Research has demonstrated how ultrasound can inactivate microbes on the surface of fruits and vegetables. But as with ozone, ultrasonic devices have not demonstrated great effectiveness with non-enveloped viruses, the type that typically cause foodborne illness.
While these devices may indeed help reduce certain microbes in your produce, it’s premature to say that they are ready for prime time—thus, health experts continue to endorse just washing your produce, thoroughly. It’s generally recommended to rinse produce (whether store-bought or homegrown) under cool, running water before preparing or eating it—for 15 to 20 seconds—and to use a clean produce brush to scrub cucumbers, carrots, apples, potatoes, and other firm produce. Fragile fruits like berries and grapes should be rinsed gently under running water right before eating, making sure that the water pressure is not so high as to damage them. Clean mushrooms with a soft brush or a wet paper towel.
To clean leafy greens and herbs, swirl them in a bowl or pot of cold water to loosen any clinging dirt. Some research suggests that vinegar (acetic acid) solutions may reduce bacterial contamination on fresh produce, including leafy greens, but studies are mixed, and the effectiveness depends on factors such as the vinegar concentration, contact time, and type of produce. Vinegar also affects the taste and texture of the produce.
As for bagged lettuce—if the package is labeled “triple washed” or some variation, it’s generally considered ready to eat, and handling it further could introduce contaminants if hands, sinks, or utensils are not clean. However, bagged shredded iceberg lettuce has been implicated in the recent cyclosporiasis cases, suggesting that if you must use bagged salads during an outbreak, it’s a good idea to wash the greens as long as you do so under sanitary conditions. Bear in mind, also, that bagged salads and salad kits containing mixes of different lettuces may carry added risk because the ingredients can come from different farms and suppliers, which increases the chance of cross-contamination.
Be sure also to wash the skin, rinds, and peels of fruits—such as melons, oranges, and bananas—even if you are not going to be eating the outsides. That’s because if the exterior is contaminated with microbes, they can end up in the edible portion of the fruit when you slice into it. The grooves of some melons in particular, like cantaloupe, can especially trap bacteria.
After washing, dry the produce with a clean towel or paper towels to further reduce any contaminants on the surface. Salad spinners come in handy for removing any remaining moisture.
And it goes without saying that you should wash your hands before (and after) washing all produce.
But, as the FDA acknowledges, although washing produce under running water reduces bacteria and other microbes—and so may reduce the risk of foodborne illness—it doesn’t eliminate them all. Cooking is what kills most harmful microbes. Of course, you can’t (or rather don’t want to have to) cook all fruits and vegetables.
What about commercial produce washes, then? The FDA advises against using these products—or any sort of detergent or soap. Produce with thin skins or no peel at all (such as lettuce and berries) can absorb the chemicals in them—and if ingested, they could make you sick (including causing nausea and vomiting), while detergents can irritate or even burn your mouth. Moreover, the effectiveness of produce washes has not been thoroughly tested, and the safety of the residues they can leave behind is unknown.
University extensions, including Colorado State University Extension and the University of Minnesota Extension, offer more specific advice on how to effectively wash different sorts of fresh produce.
What to do: Washing your produce properly and thoroughly—along with your hands before and after all food preparation—is the primary recommended way to reduce the risk of foodborne illness from consuming fresh, uncooked fruits and vegetables. That said, it’s not possible to eliminate all risk, in part because some pathogens can be present not only on the surface of produce but also inside (making them impossible to wash off). While we don’t recommend purchasing an ozone or ultrasonic cleaning machine, there’s likely no harm in using one—as long as you continue to clean your produce well and don’t assume these devices fully sanitize your food or guarantee complete safety.
