Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: INTERVENTION TECHNOLOGIES FOR ENHANCING THE SAFETY AND SECURITY OF FRESH AND MINIMALLY PROCESSED PRODUCE AND SOLID PLANT-DERIVED FOODS

Location: Food Safety and Intervention Technologies

Title: Sanitizer solutions containing detergents for inactivation of Escherichia coli O157:H7 on romaine lettuce

Authors
item Keskinen, Lindsey -
item Annous, Bassam

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 5, 2011
Publication Date: April 27, 2011
Repository URL: http://dx.doi.org/10.1016/j.ijfoodmicro.2011.04.002
Citation: Keskinen, L.A., Annous, B.A. 2011. Sanitizer solutions containing detergents for inactivation of Escherichia coli O157:H7 on romaine lettuce. International Journal of Food Microbiology. DOI: 10.1016.

Interpretive Summary: Leafy green vegetables contaminated with Escherichia coli O157:H7 have been responsible for at least 8 outbreaks of illness since 2000. Since leafy green vegetables such as Romaine lettuce is consumed raw, processors of ready-to-eat, pre-packaged salads have frequently used sanitizing washes to reduce surface contamination, but still had E. coli O157:H7 contaminating the finished product. Survival of bacterial cells during washing was attributed to poor contact between lettuce surfaces and the sanitizer solution. The addition of wetting agent to the wash solution could reduce the surface tension of the solution and thus improve the contact between the lettuce surface and sanitizing solution which might enhance bacterial inactivation/removal from the lettuce surfaces. Therefore, in this study aqueous chlorine or chlorine dioxide sanitizing solutions with or without wetting agents were evaluated for their effectiveness in reducing E. coli O157:H7 contamination of Romaine lettuce compared to an experimental formulation of short chain fatty acid (SCFA) wash solution. Romaine lettuce was inoculated with approximately 100,000,000 E. coli O157:H7 bacteria per gram, stored overnight under refrigeration (4C), and treated the next day with the sanitizers for 2 minutes. The efficacy of wash treatments, with or without the detergents, in inactivating E. coli O157:H7 cells on lettuce leaves were not significantly different. The most effective wash solution was SCFA, which was capable of reducing E. coli O157:H7 populations by more than 5 log CFU/g. The rest of the wash treatments resulted in a population reduction of less than 1 log CFU/g. The effectiveness of SCFA surpasses that of other sanitizer treatments tested in this study and requires further research to optimize treatments to preserve lettuce quality. Conventional detergents did not enhance the efficacy of any of the wash treatments tested during this study.

Technical Abstract: Numerous Escherichia coli O157:H7 outbreaks have been linked to consumption of fresh lettuce. The development of effective and easily implemented wash treatment could reduce such incidents. The purpose of this study was to evaluate the addition of food-grade detergents to sanitizer solutions for inactivation of E. coli O157:H7 on Romaine lettuce. Freshly-cut leaves of Romaine lettuce were dip-inoculated to achieve a final cell concentration of 7.8 ± 0.2 log CFU/g, air-dried for 2 h, and stored overnight at 4C. Leaves were then washed for 2 min in an experimental short chain fatty acid formulation (SCFA) or in one of the following solutions with or without 0.2% dodecylbenzenesulfonic acid or 0.2% sodium 2-ethyl hexyl sulfate: 1) deionized water; 2) 100 ppm chlorine dioxide; 3) 100 ppm chlorine; 4) 200 ppm chlorine. Following wash treatment, samples were blended in neutralizing buffer (1:3) and surface plated on the selective media CT-SMAC. The efficacy of wash treatments, with or without the detergents, in inactivating E. coli O157:H7 cells on lettuce leaves were not significantly different. The most effective wash solution was SCFA, which was capable of reducing E. coli O157:H7 populations by more than 5 log CFU/g. The rest of the wash treatments resulted in a population reduction of less than 1 log CFU/g. The effectiveness of SCFA surpasses that of other sanitizer treatments tested in this study and requires further research to optimize treatments to preserve lettuce quality. Conventional detergents did not enhance the efficacy of any of the wash treatments tested during this study.

Last Modified: 4/16/2014
Footer Content Back to Top of Page