The researchers' report -- published in the Nov. 29 issue of the Journal of Food and Agricultural Chemistry -- found that food coatings made from apple puree containing a natural antimicrobial compound made from oregano, lemongrass or cinnamon oil effectively killed E. coli bacteria.
Lead researcher Tara McHugh, a food chemist with the USDA's Agriculture Service in Albany, Calif., found that the apple puree mixed with oregano oil was the most effective, killing more than 50 percent of E. coli microorganisms within three minutes.
The apple puree coatings also contain sticky fats and sugars that allow them to stick to the surface of fruits and vegetables more effectively than water-based conventional antimicrobial washes, McHugh said.
"We hope that these coatings will have wide commercial potential," she said.
However, experts have called for more extensive testing to ensure that the coatings work in real-world settings. Former New York City health commissioner Dr. Pascal James Imperator says most produce is extensively handled and undergoes several changing environments and temperatures during shipment.
Another possible complication with the apple puree coatings is food allergies, Imperator said. "Suppose you have someone who's allergic to oregano?" he said. "I would view this study as showing interesting preliminary scientific results that would have to be corroborated by other scientists before these coatings are adopted by the commercial fresh produce industry."
McHugh says her recent findings are only the beginning of an extensive three-year project.
"We'll be testing a wide range of natural compounds, not just against E. coli but also against listeria and salmonella," McHugh said. "The ones that are shown to be effective will be tested directly on produce and meat products.
"We need to find out if these compounds are active against bacteria that adhere to different ways to different foods. But, at this point, it looks promising," she said.