A Better Way to Kill E. coli?

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The March 2008 issue of Miller-McCune magazine examined the debate surrounding the U.S. Department of Agriculture’s rules for leafy green safety certification; in particular, the article highlighted proposed changes in industry practice in the wake of the 2006 E. coli outbreak in spinach, which killed three people and sickened more than 200 across the United States and Canada.

According to the Centers for Disease Control and Prevention, about 40,000 cases of salmonellosis, an infection caused by salmonella, occur each year in the United States causing 400 deaths. In addition, about 70,000 E. coli infections are reported each year, killing dozens.

How to kill the bacteria? Irradiation has been a widespread but costly practice in Europe, and studies in the U.S. have shown that irradiation of leafy green vegetables eliminates most bacterial contamination, leaving the treated greens largely indistinguishable from untreated produce. Although food irradiation is allowed in nearly 40 countries and is endorsed by the World Health Organization, for the American Medical Association and many other organizations, it remains a controversial option.

A Purdue University researcher has discovered a simpler way to eliminate bacteria in packaged foods like spinach. By placing two high-voltage, low-watt coils on the outside of a sealed food package, a plasma field is formed in which oxygen is ionized and converted into ozone, which then kills bacteria such as E. coli and salmonella. The process is outlined in an article in LWT — Food Science and Technology, a journal for the Swiss Society of Food Science and Technology and the International Union of Food Science and Technology.

“Conceptually, we can put any kind of packaged food we want in there,” said Kevin Keener, an associate professor in Purdue’s department of food science, in a release announcing his discovery. “So far, it has worked on spinach and tomatoes, but it could work on any type of produce or other food.”

The process uses only 30 to 40 watts of electricity, making it less of a power drain than most incandescent light bulbs. Because the container’s exterior only increases a few degrees in temperature, the food inside is not cooked or otherwise altered during the treatment, which can range from 30 seconds to five minutes. The longer the gas in the package remains ionized, the more bacteria are killed before the ionized gas eventually reverts to its original composition.

“It’s kind of like charging a battery. We’re charging that sample,” Keener said. “We’re doing it without electrode intrusion. We’re not sticking a probe in the package. We can do this in a sealed package.”

Glass containers, flexible food-storage bags and rigid plastics, such as strawberry cartons and pill bottles, have all stood up to testing. A patent on the technology is pending, and Keener said the next step is to create a commercial prototype of the device for large amounts of food.

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