by Monica Reinagel, M.S., L.D./N.
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.
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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.
Does Irradiation Kill E. Coli?
There are really only two reliable ways to kill E. coli in food: irradiation and cooking. I talked about the pros and cons of irradiation in a recent article. Although irradiation is both safe and effective, it is not widely used in the U.S., largely because consumers don’t yet feel comfortable with the technology. (Organic certification also prohibits irradiation of foods.)
Is it Safe to Eat Raw Vegetables?
So, do we need to say good-bye to salads and other raw vegetables forever? Not necessarily. I think it’s a matter of understanding and managing the risks. Overall, your chances of being infected with E. coli or other dangerous food-borne pathogens from raw vegetables are quite small. Nonetheless, small children, the elderly, pregnant women, and others with weakened immune systems might have a much harder time fighting off a food-borne pathogen. If your resistance is lowered—or you simply want to reduce your risk of being infected to zero—avoid all uncooked fruits and vegetables, as well as unpasteurized dairy products, and be sure that all eggs, meat, and fish are cooked thoroughly.
Even if you're hale, hearty, and risk-tolerant, it would probably be wise to avoid raw vegetables and fruits if some sort of contamination is reported or suspected—such as during an active outbreak—until the source is identified. Otherwise, I think the nutritional benefits—not to mention the culinary pleasures—of fresh raw fruits and vegetables generally outweigh the small risk.
See also: Benefits of a Raw Food Diet
How to Wash Your Vegetables
Even though it is no guarantee against E. coli, you still want to wash raw fruits and vegetables well before you eat them. If you want to use something more than tap water, I recommend distilled white vinegar. It’s inexpensive, safe, and effective in reducing surface dirt, wax, and pesticide residues. Vinegar can even kill some germs.
Also, don’t discount the value of a little elbow grease. Rubbing produce vigorously with your hands or scrubbing with a soft brush is a good way to remove dirt. Just be sure your hands and/or vegetable brush are clean so that you don’t end up transferring dirt or bacteria to the produce.
One last tip: If you do use bleach, iodine, or another sanitizing agent on your veggies, be sure to rinse them thoroughly before eating them. In particular, Dr. Brackett recommends against using dish or hand soap to clean produce because they commonly contain ingredients that can make you sick to your stomach if ingested.
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More information on the recent E. coli outbreak (IFIC Foundation)
E. Coli Fallout: My Salad, My Health (New York Times)