How to Kill E. coli on Vegetables
Can bleach, iodine, or vinegar kill E. coli on fresh produce? Is it safe to eat raw vegetables?
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Earlier this month, hundreds of people were sickened—and many died—in an E. coli outbreak that was eventually traced to some bean sprouts raised on an organic farm in Germany. E. coli outbreaks happen from time to time, of course, but this one was extra scary because it involved a particularly virulent strain of E. coli, making the death toll unusually high.
How to Kill E. Coli on Vegetables
Once the source was identified, the outbreak was quickly contained. But a lot of people are still nervous about eating raw vegetables. Not surprisingly, there is a lot of advice circulating on the internet right now about washing or soaking your vegetables in bleach, hydrogen peroxide, vinegar, iodine, or even dish soap.
Any of these methods can help remove surface dirt, pesticide residues, bugs, and some germs. (For that matter, so can washing produce with plain tap water.) But are any of these methods a reliable way to eliminate E. coli or other dangerous pathogens? To find out, I contacted the International Food Information Council, which kindly put me in touch with Dr. Robert Brackett, the Director of the Institute for Food Safety and Health at the Illinois Institute of Technology.
Dr. Brackett had sobering news: Although these sanitizing methods might make your produce slightly cleaner, none of them will make contaminated produce safe to eat.
Washing Vegetables Doesn’t Remove E. Coli Bacteria
Even if a sanitizer succeeded in killing 99.9% of the bacteria present, that could still leave thousands of viable cells—and it only takes one to make you sick.
I wondered whether these very toxic strains of E. coli might be especially hard to kill. It turns out that they’re not really that invincible—they’ve just developed some very clever survival tactics. “If these E. coli bacteria were just floating around in a bucket of water, a little bleach or even some vinegar would kill them right away,” Dr. Brackett explains. “But once the bacteria have attached themselves to the surface of a vegetable, they become much harder to kill.”
When these bacteria attach to a surface, they produce a substance called “biofilm,” which encases the bacteria in a sort of shell and helps them stick to whatever they’ve latched onto. This coating keeps them from being washed away and also protects them from chemicals that could otherwise disable them. In other words, adding a few drops of bleach to the water you use to wash vegetables will kill any bacteria in the water but won’t do much to the bacteria on the vegetables.
E. coli doesn’t just sit around on the surface of vegetables, either. The bacteria can also penetrate into the interior tissues of the plant, where no sanitizer can reach them. And here's another reason that chemical sanitization can’t guarantee your safety: Even if a sanitizer succeeded in killing 99.9% of the bacteria present, that could still leave thousands of viable cells--and it only takes one to make you sick.