Battling microbes: disinfecting water during fresh-cut lettuce processing

Abstract

Fresh leafy greens like lettuce are often consumed raw and can be contaminated by foodborne pathogens. Washing fresh-cut lettuce can help alleviate foodborne outbreaks and diffuse cases, but the washing process must be controlled to avoid pathogenic cross-contamination. The thesis aimed to evaluate the effectiveness of chemical disinfection of the water during fresh-cut lettuce washing to reduce pathogenic crosscontamination. First, the effectiveness of chlorine, chlorine dioxide (ClO2), ozone, and peracetic acid (PAA) during produce processing was studied along with legislation and disinfection by-product production. Next, the effectiveness of sodium hypochlorite, ClO2, and a silver-copper solution to reduce Salmonella enterica serovar Typhimurium and pathogenic Escherichia coli were assessed on the laboratory scale. Results showed that the water's organic load, wash water temperature, and pathogenic characteristics influenced the effectiveness. Then, the effectiveness of ClO2 (5 mg/L and 3 mg/L) on reducing supplemented nonpathogenic E. coli during fresh-cut lettuce washing at the industrial scale was studied. Also, the effectiveness of a PAA solution (75 mg/L) on reducing supplemented nonpathogenic E. coli during fresh-cut lettuce washing at the laboratory and industrial scales was studied. The results showed that laboratory experiments disinfecting water with ClO2 and a PAA solution had similar findings, which were also confirmed at the industrial scale. Finally, a multi-criteria decision analysis was applied to a case study to determine the best control strategy during fresh-cut lettuce processing when disinfection was applied directly in the wash tank. Results showed that PAA was the overall preferred control strategy. This proposed disinfection strategy appears to be the right balance between safety and effective fresh-cut produce disinfection. Table of Contents Chapter 1General introduction Chapter 2Effect of disinfectants on preventing the crosscontamination of pathogens in fresh produce washing Chapter 3 The efficacy of chemical sanitizers on the reduction of Salmonella Typhimurium and Escherichia coli affected by bacterial cell history and water quality Chapter 4 Efficacy of chlorine dioxide on Escherichia coli inactivation during pilot-scale fresh-cut lettuce processing Chapter 5 Effectiveness of a peracetic acid solution on Escherichia coli reduction during fresh-cut lettuce processing at the laboratory and industrial scales Chapter 6 Multi-criteria decision analysis to evaluate control strategies for preventing cross-contamination during fresh-cut lettuce washing Chapter 7 General discussion Summary Annexes Acknowledgments, About the author, List of publications, and Overview of completed training activities General introduction 19 Outline of the thesisThis thesis consists of seven chapters, of which Chapters 2, 3, 4, 5, and 6 focus on the five sub-objectives mentioned above. Chapter 7 presents a synthesis of the findings of this thesis, as well as overall conclusions. Figure 1.6 summarizes the outl...