MONTEREY Calif. Restaurateurs joined grocers, growers and processors here recently for a download of new research information about how E. coli O157:H7 contaminates leafy greens.
The daylong event at the Monterey Plaza Hotel marked the disclosure of findings from nine, multi-discipline studies funded at a reported cost of $2 million by Salinas, Calif.-based Fresh Express, the fresh-cut greens division of Chiquita Brands International Inc.
Some of the findings supported conventional thinking about the importance of controlling the temperature at which greens are held to discourage pathogen growth. Others systematically illustrated the potential for cross-contamination of fresh-cut produce if manufacturing systems are not properly used, maintained and sanitized.
But some of the results were head-turning, according to moderators and speakers. Among them were those that suggested:
- Uptake of E. coli by plant root systems appears to be much less of a potential problem than initially believed, according to independent research projects by Michael Doyle of the University of Georgia and Manan Sharma, of the Agricultural Research Service of the U.S. Department of Agriculture.
- E. coli can induce spinach plant stomata to open so that it can better colonize within the under-leaf portals used to take in carbon dioxide and release oxygen and water as part of the photosynthesis process. Researcher Jorge Girón, of the University of Arizona, indicated that it appears E. coli, once inside, can also manipulate the stomata to close for greater protection, possibly explaining why the pathogen appears resistant to washing during processing.
- "Filth flies" were seen in larger numbers than expected in some leafy greens fields and can be carriers of E. coli. Researchers from Oklahoma State University, including principal investigator Jacqueline Fletcher, said additional study is needed to ascertain whether the flies actually transfer E. coli to plants, what attracts them to greens fields -- aphids were mentioned as one possibility -- and whether the flies seen were associated with nearby compost piles, cattle operations or another environmental factor.
- Once in contact with E. coli-contaminated soil, the tools used to core lettuce heads in the field are not easily disinfected and may cross contaminate subsequent cored heads, research by the University of Georgia's Doyle suggested.
Conference moderator and research coordinator Michael Osterholm, director of the University of Minnesota Center for Infectious Disease Research & Policy, pointed out that corer use is widespread, but E. coli outbreaks are relatively rare. This suggests that E. coli is not often found in field soil or that there is some other "real world" deterrent to cross contamination, he said.
Findings from more than one study indicated that ozone gas is a much more effective E. coli sanitizing agent than water or chlorinated water. A presentation by Ahmed Yousef and Sadhir Satry of Ohio State University centered on a test system that uses ozone gas in conjunction with standard vacuum chilling to increase the effectiveness of post-harvest sanitizing efforts. When combined with ozone-enhanced storage practices, research indicated, the hybrid system nearly triples the effectiveness of E. coli elimination and growth-inhibiting processes, compared with a chlorine wash.
An established, if not controversial technology, irradiation, also was addressed at the conference. Recent approval by the U.S. Food & Drug Administration of irradiation of fresh spinach and lettuce to kill off E. coli and salmonella, among other harmful bugs, was seen as a positive step by some of the attendees. However, others pointed to the regulatory roadblocks that may still need to be cleared. Attendees also cited the educational effort that will be needed to win consumer support of a process that is considered a lifesaver by some users but decried as a potentially dangerous diversion from sound production methods by some public advocacy groups.
Moderator Osterholm praised Fresh Express for its financial commitment to the E. coli research and its hands-off approach in the name of protecting the integrity of the findings. In suggesting that other companies with an interest in safe produce emulate that financial commitment and integrity, he said, "All the rest of the industry really needs to look at this example, here, that really was a shining star of how to do it right."
"We heard a lot of great science today. Now the challenge is to go home and figure out how to use it," Jim Lugg, Fresh Express executive vice president of science and quality, told the multi-industry audience.
Among the attendees were representatives of McDonald's Corp., Yum! Brands Inc., Burger King Holdings Inc., Chick-fil-A and Chipotle Mexican Grill Inc.
