URBANA — Food contaminated by E. coli bacteria sends more than 2,000 people in the U.S. to the hospital a year, but University of Illinois food scientists have developed a new way to make one source of sometimes contaminated food, fresh produce, much safer.
Produce such as spinach and lettuce is typically run through a continuous chlorine wash, but this eliminates only 90 percent of bacteria that can be present, says UI food processing professor Hao Feng.
He and his colleagues have added continuous high-powered ultrasound to the process, at an intensity high enough to generate small gas bubbles in the liquid, Feng says.
The result: Total infection-causing bacteria reduced by more than 99.9 percent.
Feng and his colleagues focused on spinach in their recently-published research, but have used their technology on lettuce and tomatoes, and it could work with a variety of fresh produce, Feng said.
Produce can become contaminated in the environment by bird droppings, dirt in the air, manure, irrigation water, even contact with soil, Feng said.
The chlorine wash isn't entirely effective, even when it's done continuously, he says, because the chlorine solution reacts with the juice from the fresh cut produce. And even the 10 percent of E. coli bacteria that can remain behind is enough to make people sick.
One in six people in the U.S. get sick from foodborne illnesses a year, and E. coli ranks among the top five pathogens that send people to the hospital, according to the Centers for Disease Control and Prevention.
This past spring, 29 people in 11 states were sickened in an E. coli outbreak linked to likely contamination of raw clover sprouts. Another produce-related E. coli illness outbreak occurred this past month: The Centers for Disease Control and Prevention said preliminary results from an ongoing investigation indicated an organic spinach and spring mix salad blend produced in Chelsea, Mass. was a likely source of the multi-state outbreak that had sickened 28 people as of Friday.
Feng, who has been researching fresh produce safety for nearly a decade and working with ultrasound technology for about 11 years, says increasing safety of produce is a balancing process.
Manufacturers could increase the chlorine concentration more now to kill more bacteria, he says, but they'd kill also kill the produce.
Even the combined ultrasound and chlorine wash technology won't eliminate the E. coli risk 100 percent, he says.
"Nobody dares to say that," he says.
The technology can be commercialized, Feng says, but it's hard to say if and when manufacturers would be willing to add the cost of ultrasound to the cleansing process — and if consumers would pay more for a bag of spinach or salad in exchange for higher safety.
Feng and co-authors, former UI doctoral student Bin Zhou and UI mechanical engineering professor Arne Pearlstein, published their research in September in Innovative Food Science & Emerging Technologies.