Submitted to: Journal of Food Processing and Preservation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/21/2012
Publication Date: 10/14/2012
Citation: Yossa, N., Patel, J.R., Millner, P.D., Murphy, C.F., Bauchan, G.R., Lo, M. 2012. Antibacterial activity of cinnamaldehyde and Sporan against Escherichia coli O157:H7 and Salmonella. Journal of Food Processing and Preservation. DOI: 10.1111/jfpp.12026. Interpretive Summary: Foodborne illnesses associated with the consumption of fresh produce have increased in recent years. Escherichia coli O157:H7 and Salmonella have been implicated as pathogens involved in these illnesses. Consumers’ preference for fewer chemicals in food has prompted research on the use of natural antimicrobials for controlling pathogens on fresh produce. We evaluated the effect of natural antimicrobials: cinnamaldehyde and Sporan on E. coli O157: H7 and Salmonella. A five strain cocktail of E. coli O157:H7 and Salmonella were inoculated into bacterial growth medium at one million cells per milliltere containing cinnamaldehyde (0.08%) or Sporan (0.1%) alone, or in combination with 0.2% acetic acid. In the presence of cinnamaldehyde no E. coli O157:H7 were undetected after one hour, while fewer than ten Salmonella were recovered after 6 hours. Likewise, a Sporan significantly reduced E. coli O157:H7 and Salmonella populations by approx 5 and 4 logs respectively after 4 h. Scanning and Transmission electron microscopy of oil-treated bacterial cells revealed cell structural damage and leakage of cellular content. This information will be useful for other researchers, government regulatory agencies, and the food industry.
Technical Abstract: The in vitro antimicrobial effect of cinnamaldehyde and Sporan in combination with acetic acid against E. coli O157:H7 and Salmonella was investigated. A five strain cocktail of E. coli O157:H7 and Salmonella were inoculated in Luria-Bertoni broth (LB broth, 7 log CFU ml-1) containing cinnamaldehyde or Sporan (800 and 1000 ppm) alone or in combination with 200 ppm acetic acid, and incubated at 37°C for up to 6 h. Surviving populations of test pathogens were determined every h by spiral plating on XLT4 and Sorbitol MacConkey Agar for Salmonella and E. coli O157:H7, respectively. Bacterial cells treated with oils were observed under electron microscopy to determine the mode of antimicrobial action. E. coli O157:H7 and Salmonella were undetectable after 1 h in presence of 800 ppm cinnamaldehyde. A 1000 ppm Sporan significantly reduced Salmonella and E. coli O157:H7 populations by 1.83- and 3.02 log CFU ml-1 within 2 and 4 h, respectively. The synergistic effect of acetic acid was not evident as it did not enhance (P > 0.05) the bactericidal activity of oils. Scanning and Transmission electron microscopy of oil-treated bacterial cells revealed cell structural damage and leakage of cellular content. Cinnamaldehyde was highly effective against both E. coli O157:H7 and Salmonella whereas the effect of Sporan was dependent on its concentration, exposure time, and pathogen. E. coli O157:H7 was more sensitive to the oils than Salmonella. Cinnamaldehyde and Sporan may be effective in reducing or eliminating the growth of E. coli O157:H7 and Salmonella in foods.