Decontamination of Escherichia coli O157:H7 and Salmonella in Lettuce, Chicken, and Apples by Chlorine Dioxide and Ultrasound
Type of DegreeThesis
Nutrition and Food Science
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Chlorine dioxide (ClO2) has been used for many years by the food industry and public water suppliers as a sanitizing and disinfecting agents. The mechanisms of microbial inactivation by ultrasonication are mainly due to thinning of the cell membranes, localized heating, production of free radicals and formation of hydrogen peroxide. Non-thermal disinfectants combined with ultrasonication treatments may be relatively more effective for pathogen removal and inactivation. In this study, decontamination efficiencies of ClO2 alone and ClO2 combined with ultrasonication on foodborne pathogens inoculated foods at different times were performed. Lettuce, chicken breasts, and apples were inoculated with E. coli O157:H7 and Salmonella, and treated with the combination of ClO2 at 5, 10, 20, and 40 ppm, and with ultrasonication at 120 and 170 kHz for 1, 3, 6, and 10 min. The efficacies of removing and inactivating E. coli or Salmonella on lettuce were mainly dependant on ClO2 concentration but not on the treatment time and ultrasonic frequency. Various ClO2 concentrations had significantly different log reductions in this study. The efficacies of removing and inactivating E. coli or Salmonella on chicken breasts were mainly based on treatment time and not on ClO2 concentration and ultrasonication. Longer treatment times had significantly higher log reductions for both high and low inoculation levels of the pathogens, especially for Salmonella. The efficacies of removing and inactivating Salmonella on apples were mainly dependant on the ClO2 concentration and ultrasonication but not on treatment times; for E. coli O157:H7, it mainly depended on the ClO2 concentration, not treatment time and ultrasound. The ClO2 residual and temperature change after treatment were also investigated. For chicken breasts, the ClO2 residuals dropped dramatically with longer treatment times, while, ClO2 residuals only dropped a little for lettuce and apples. ClO2 residual dropped more dramatically in combination treatments, than in ClO2 treatments alone. However, no significant differences were found between these two treatments on lettuce and apples. These results indicated that ultrasonication accelerated the reaction of ClO2 with chicken breast tissue but not with lettuce and apples. In different foods, temperature changes were similar for the same treatments. Temperature increased to near 60°C after the application of ultrasonication, and it elevated more dramatically with ClO2 combined with ultrasonication than with ClO2 treatment alone.