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KNOXVILLE, Tenn. – A simple marinade using oil of oregano or certain other spice extracts can kill some of the harmful bacteria that make food unsafe, researchers at the University of Tennessee have found.

The study involved marinating fresh fish in the extracts of 12 household spices and then checking for the presence of various bacteria, including E. coli O:157, listeria and staph.

“What we found was that certain spices added to foods would be useful in preventing and even killing organisms like E. coli that can cause disease,” said Dr. F. Ann Draughon, a UT microbiologist who is co-director of the UT Food Safety Initiative.

The team headed by Draughon studied the essential oils of angelica, basil, carrot, celery, cardamom, coriander, dill weed, fennel, oregano, parsley and rosemary. Essential oils are substances extracted from the spices that give them their characteristic flavor and aroma.

The treated fish was analyzed for the presence of nine food-borne microbes: Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O:157:H7, Yersinia enterocolitica, Pseudomonas aeruglinosa, Lactobacillus plantarum, Aspergillus niger, Geotrichum and Rhodotorula.

Fresh fish was chosen as the medium because it is especially prone to spoilage and contamination by pathogens.

The study found that oil of oregano was the most effective at killing all the pathogens, followed by oils of coriander and basil. Anise oil was effective against molds but did little against various bacteria.

“I would recommend a teriyaki-type marinade or an olive oil or Italian dressing that you can add these oils to, because they give the foods a lot of flavoring,” Draughon said. “It’s important to distribute the oil so that the entire surface would be decontaminated.

“Under refrigeration with a marinade, we could completely kill Listeria and E. coli O:157. That’s pretty impressive.”

The study does not mean that the more common powdered versions of these spices will provide the same level of safety as the extracts, Draughon said.

“We didn’t look at the dry spices,” she said. “It might take a lot more of the dry spice to get the same effect.”

Draughon said further study would be necessary to determine which components of the oils had the desired effect.

A second study tested the preservative properties of black cumin extract. One of Draughon’s graduate research assistants, Mona Elgayyar, found that black cumin extract was moderately effective in limiting the growth of Salmonella typhimurium, E. coli O:157:H7 and other microbes. Black cumin is a spice commonly used in Egyptian cooking.

The Tennessee Food Safety Initiative is a research program jointly supported by the U.S. Food and Drug Administration and the UT Agricultural Experiment Station. The initiative is focusing on the top four food-borne pathogens: E. coli O:157:H7, Y. enterocolitica, Salmonella, and C. jejuni and their presence in the products of private farms.