Effect of different sanitizing methods and incubation time and temperature on inactivation of Escherichia coli on lettuce

The goal of this study was to compare the antimicrobial activities of different sanitizing treatments and to assess the effects of incubation time and temperature on the efficacy of ozone treatment against Escherıchıa coli attached to lettuce. Lettuce leaves were inoculated to contain a predetermined initial level of E. coli, held overnight at 4C, and treated with the following sanitizers: 100 ppm sodium hypochlorite; 0.25% citric acid plus 0.50% ascorbic acid; bubbling ozone; and 1.5 ppm ozone. The combination of citric acid and ascorbic acid dip for 2 min resulted in the least microbial reduction. Dipping into 1.5 ppm ozonated water proved to be less effective than bubbling ozone for 2 min. Moreover, treatment with bubbling ozone was found to be as effective as sodium hypochlorite solution. It was observed that, for short exposure times (2-5 min), the temperature (4-20C) of the washing water did not have a significant effect on the activity of ozone in terms of E. coli inactivation. Prior incubation time and temperature of inoculated lettuce leaves were shown to have a significant effect on the efficacy of the sanitizing treatment. Scanning electron microscopy images were used to visualize the E. coli populations on lettuce. The effects of incubation time and incubation temperature on the efficacy of sanitizing treatments applied in artificially inoculated lettuce samples were evaluated using E. coli as the model microorganism. This study demonstrates the importance of the inoculation method applied in assessing the effectiveness of a sanitizing method. Moreover, the effect of ozone treatment in comparison with the sodium hypochlorite and organic acid treatments that are currently being used by the industry for the disinfection of fresh-cut vegetables were evaluated.