Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/15/2012
Publication Date: 1/1/2013
Citation: Yossa, N., Patel, J.R., Millner, P.D., Ravishankar, S., Martin Lo, Y. 2013. Antimicrobial activity of Cinnamaldehyde and Sporan against Escherichia coli O157:H7 and Salmonella on lettuce. Foodborne Pathogens and Disease. 10(1):87-96. Interpretive Summary: In an effort to identify natural antimicrobial agents that may be used during fresh produce washing; the effect of essential oils in killing E. coli O157:H7 and Salmonella on iceberg and romaine lettuce was evaluated. Cut lettuce pieces were inoculated with five strains of E. coli O157:H7 or Salmonella. The lettuce leaves were then immerged in either chlorine (5 ppm), cinnamaldehyde and Sporan formulations (800 ppm, 1000 ppm) alone, or in combination with acetic acid for 1 min, and then stored at 4°C. Pathogen populations surviving on lettuce leaves were determined during storage at day 0, 2, 7, and 14. Quality parameters (color and texture) of treated leaves were also determined. Up to 1000-fold reductions in E. coli O157:H7 populations were observed on iceberg lettuce following treatment with cinnamaldehyde-Tween and Sporan with acetic acid. Likewise, Sporan with acetic acid significantly reduced E. coli O157:H7 populations on romaine lettuce at day 0. The effect of essential oils was comparable to chlorine in reducing Salmonella populations on iceberg and romaine lettuce throughout the storage time. The population of background microorganisms was not affected by cinnamaldehyde or Sporan. The color and texture of Sporan treated lettuce leaves were not significantly different from control leaves. This study demonstrates the potential of GRAS (Generally Recognized As Safe) plant extracts, Sporan and cinnamaldehyde as disinfectants during lettuce washing without adversely affecting quality. This information will be useful to other researchers, government regulatory agencies, and the produce industry.
Technical Abstract: Foodborne outbreaks associated with the consumption of fresh produce have increased. In an effort to identify natural antimicrobial agents as fresh produce wash; the effect of essential oils in reducing enteric pathogens on iceberg and romaine lettuce was investigated. Lettuce were cut into pieces (3 x 2 cm), inoculated with a five-strain cocktail of Escherichia coli O157:H7 or Salmonella enterica (5 log CFU/g), air-dried for ca. 30 min, and then immersed in a treatment solution containing 5 ppm free chlorine, cinnamaldehyde or Sporan (800 and 1000 ppm) alone or in combination with 200 ppm acetic acid (20%) for 1 min. Treated leaves were spin-dried and stored at 4°C. Samples were taken for determining the surviving populations of E. coli O157:H7, Salmonella, total coliforms, mesophilic and psychrotrophic bacteria, and yeasts and molds during 14 days storage period. The effect of treatments on lettuce color and texture was also determined. Cinnamaldehyde-Tween (800 ppm, 800T) reduced E. coli O157:H7 by 2.89 log CFU/g (P < 0.05) on iceberg lettuce at day 0; Sporan-acetic acid (1000SV) reduced E. coli O157:H7 and Salmonella on iceberg and romaine lettuce by 2.68 and 1.56 log CFU/g (P < 0.05), respectively, at day 0. The effect of essential oils was comparable to that of 5 ppm free chlorine in reducing E. coli O157:H7 and Salmonella populations on iceberg and romaine lettuce throughout the storage time. The natural microbiota on treated lettuce leaves increased during the storage time, but remained similar (P> 0.05) to those treated with chlorine and control (water). The texture and the color of iceberg and romaine lettuce treated with essential oils were not different from the control lettuce after 14 days. This study demonstrates the potential of Sporan and cinnamaldehyde as effective lettuce washes that do not affect lettuce color and texture.