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US: Study suggests ozone gas to kill E. coli in greens

Ozone gas, commonly used to disinfect wine barrels, also could help the produce industry keep the nation's salad clean. Research on E. coli transmission released Thursday said ozone gas is faster and more effective than chlorinated water at sanitizing leafy greens. Scientists said it could be pumped into cooling vacuums where lettuce is stored after arriving from the fields.

"This is great, it's really simple to do," said Steve Scaroni, a grower and shipper who works in California and Mexico. "This could be the answer." nScaroni was among 300 food industry executives, growers and regulators who gathered in Monterey to learn the results of the $2 million research, funded by Fresh Express, in response to the 2006 E. coli outbreak in spinach that killed three people, sickened 200 others and cost the leafy greens industry about $80 million.

Fresh Express was not linked to the 2006 spinach recall but funded the studies to help the industry avoid another outbreak.

Among the research findings:
  • Contamination can spread during washing, cutting and the tumble drying of greens, and chlorinated water alone isn't enough to kill the pathogens;
  • Some varieties of spinach with textured leaves have greater potential for harboring pathogens than smooth-leaf varieties;
  • E. coli can paralyze pore closures on spinach leaves and allow bacteria into the plant;
  • Even cooked compost used in organic operations can retain traces of live E. coli cells that can reconstitute under the right conditions;
  • Spinach and lettuce harvested on hotter days are more likely to create an environment for pathogen growth.
"I think one of the most important things these studies have shown is that temperature control is a key issue," said Linda Harris of the University of California, Davis. "Lower temperatures reduce the statistical probability (that harmful pathogens will develop)."

The research is just the beginning in the industry's effort to determine how E. coli is transmitted and how it reproduces in processed foods.

The exact source of the 2006 contamination was never discovered, but scientists suspect that cattle, feral pigs or other wildlife may have spread the E. coli by defecating near crops.

Researchers on Thursday said they're conducting experiments to find out if contamination also can be spread by flies or other insects.

"Leafhoppers and aphids did excrete bacteria in their fecal droplets," said Jacqueline Fletcher of Oklahoma State University. "I don't think these present a hazard, but the flies, on the other hand, do pick up E. coli from manure and move it to plant surfaces. It could be a source of contamination."

Scientists also seemed to be able to rule things out. University of Georgia researchers said their studies showed that lettuce and other leafy greens do not seem to absorb a deadly E. coli pathogen through water applied to the roots.

Michael Doyle of the University of Georgia said absorption "may not be a big issue."

Last year, growers, packers and shippers adopted new food-safety standards for farms, including a requirement that farmers establish buffers between their fields and grazing land for cattle, which are known carriers of E. coli.

Fresh Express has been criticized by some farming organizations for requiring stricter standards for growers than called for under the industry-written guidelines. The company's requirements have led to destruction of some habitat to keep wildlife from entering fields and possibly contaminating greens.

It's unknown if any of the recommendations presented Thursday, including using ozone gas to sanitize crops, will be adopted.

"That is the question," said Ahmed Yousef, Ohio State University who studied integrating gaseous ozone into the packing process. "Many traditions, like the use of chlorinated water, are ingrained. People might be slow to embrace change."


Publication date: 9/12/2008


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