4 Sep 2009 --- Oregano, allspice and garlic essential oils (EOs) can be effective, natural barriers against E. coli, Salmonella and Listeria, according to a study in the Journal of Food Science, published by the Institute of Food Technologists.  The new study from government researchers revealed that oregano oil was found to be the most effective antimicrobial, followed by allspice and garlic.

Researchers at Processed Foods Research and Produce Safety and Microbiology units of Western Regional Research Center from the U.S. Department of Agriculture (USDA) investigated the effectiveness of the oils by incorporating them in thin, tomato-based antimicrobial coatings known as edible films. In addition to its flavor properties, tomatoes are reported to possess numerous beneficial nutritional and bioactive components that may benefit human health. Edible tomato films containing antimicrobials may protect food against contamination by pathogenic microorganisms.

Testing was done by laying the films on top of the bacteria and also by exposing the bacteria to the vapors arising from the film.  According to researchers:

• Oregano oilconsistently inhibited the growth of all three bacteria.
• Garlic oil was not effective against E. coli or Salmonella, but was effective against Listeria.
• Oregano and allspice oils were effective against E coli and Salmonella. Vapor tests of oregano and allspice oils indicated that these two oils diffuse more efficiently through the air than through direct contact with the bacteria.
• Listeria was less resistant to EO vapors while E. coli was more resistant.

“Incorporating essential oils into edible films provides a new way to improve the safety and shelf life of foods, which will provide multiple benefits to consumers,” says lead researcher W. X. Du.

Edible films for fruits and vegetables can serve as carriers for food additives including plant-derived, safe antimicrobials. The increased interest in antimicrobial films is the result of increased consumption of contaminated fresh-cut produce.

In a related study from the same USDA research group, it was found that cinnamon, allspice and clove might have a new use in the kitchen. Essential oils (EOs) from these plants could be used to protect food from bacteria according to a study in the Journal of Food Science. They evaluated the physical and antimicrobial properties of allspice, cinnamon and clove bud oils in edible films of apple puree after 24 and 48 hours.  Edible films and coatings on food products can serve as carriers for a wide range of beneficial food additives, including antimicrobials. The oils were incorporated into edible apple puree film at ranges of 0 to 3 percent. Researchers found:

• The antimicrobial activity of cinnamon oil was significantly greater than allspice and clove bud oils against E. coli, Salmonella and Listeria.
• Ediblefilms containing 3 percent or less of cinnamon oil were found to be effective against the three pathogens.
• Salmonella showed the leastresistance to the EOs, while E. coli showed the most. 
• Low concentrations (1 percent and 1.5 percent) of allspice and clove bud oils suppressed the growth of Listeria.

“The results show that apple-based films with allspice, cinnamon or clove bud oils were effective against the three bacteria. The essential oils have the potential to provide multiple benefits to consumers,” says lead researcher R. J. Avena-Bustillos.

Note: This research was supported by USDA-CSREES, NRI grant #2006-01321.