Correlation of Retail Temperatures with the Potential for E. coli O157:H7 Growth On Pre-Cut Greens

Pre-harvest sources for contamination of leafy greens are numerous and extremely varied with no microbial reduction strategies currently available to completely ensure the safety of fresh-cut leafy greens at the time of consumption.  It is therefore imperative that the cold-chain be established and maintained from packaging through retail purchase to minimize exposure to E. coli O157:H7 and other food-borne pathogens.  The specific objectives of this study are to:  measure the temperature of leafy greens in retail display cases as well as in back-room coolers, and, based on observed temperatures and microbial studies, determine the potential for infectious levels of E. coli O157:H7 in pre-cut salads, i.e., the potential for a food safety event with concomitant recall.  Continuous-read, low-profile temperature recorders were placed in retail display cases and storage rooms at 9 retail stores in a total of 3 regions in California:  Burbank (Southern California, moderated by the Pacific Ocean), Palm Springs (Southern California, desert),  and the Central Coast (Santa Barbara/San Luis Obispo; moderated by the Pacific Ocean).  Recorders were placed every 4 feet under the top , middle and bottom shelves and were located on each shelf at the front and back of the display cases.  Temperatures were surprisingly cold in the cases though temperature abuse was observed.  For some cases, temperatures above 10°C (but less than 15°C) were observed 5-7% of the total time.  Temperatures above 7.2°C occurred up to 65% of the total time.  Interestingly, some cases were too cold and temperatures below -0.28°C, the freezing point of lettuce, occurred up to 84% of the total time indicating a serious potential for tissue damage.  Temperature collection is on-going and will continue through at least August, 2011.  Initiation of this project was very slow due to concerns by the retail chain of unfavorable exposure and liability, and this will also be discussed.