title: Inactivation dynamics of Salmonella enterica, Listeria monocytogenes, and Escherichia coli O157:H7 in wash water during simulated chlorine depletion and replenishment processes.
abstract: Maintaining effective sanitizer concentration is of critical importance for preventing pathogen survival and transference during fresh-cut produce wash operation and for ensuring the safety of finished products. However, maintaining an adequate level of sanitizer in wash water can be challenging for processors due to the large organic load in the wash system. In this study, we investigated how the survival of human pathogens was affected by the dynamic changes in water quality during chlorine depletion and replenishment in simulated produce washing operations. Lettuce extract was added incrementally into water containing pre-set levels of free chlorine to simulate the chlorine depletion process, and sodium hypochlorite was added incrementally into water containing pre-set levels of lettuce extract to simulate chlorine replenishment. Key water quality parameters were closely monitored and the bactericidal activity of the wash water was evaluated using three-strain cocktails of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes. In both chlorine depletion and replenishment processes, no pathogen survival was observed when wash water free chlorine level was maintained above 3.66 mg/L, irrespective of the initial free chlorine levels (10, 50, 100 and 200 mg/L) or organic loading (chemical oxidation demand levels of 0, 532, 1013 and 1705 mg/L). At this free chlorine concentration, the measured ORP was 843 mV and pH was 5.12 for the chlorine depletion process; the measured ORP was 714 mV and pH was 6.97 for the chlorine replenishment process. This study provides quantitative data needed by the fresh-cut produce industry and the regulatory agencies to establish critical operational control parameters to prevent pathogen survival and cross-contamination during fresh produce washing.
authors.affiliation: U. S. Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Environmental Microbiology and Food Safety Laboratory, 10300 Baltimore Ave, Beltsville, MD 20705, USA; Department of Nutrition and Food Science, University of Maryland, 0112 Skinner Building, College Park, MD 20742, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhou
authors.affiliation: U. S. Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Environmental Microbiology and Food Safety Laboratory, 10300 Baltimore Ave, Beltsville, MD 20705, USA. Electronic address: yaguang.luo@ars.usda.gov.
authors.forename: Yaguang
authors.initials: Y
authors.lastname: Luo
authors.affiliation: U. S. Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Environmental Microbiology and Food Safety Laboratory, 10300 Baltimore Ave, Beltsville, MD 20705, USA.
authors.forename: Xiangwu
authors.initials: X
authors.lastname: Nou
authors.affiliation: College of Biological Sciences and Technology, Shenyang Agricultural University, Shenyang, PR China.
authors.forename: Shuxia
authors.initials: S
authors.lastname: Lyu
authors.affiliation: Department of Nutrition and Food Science, University of Maryland, 0112 Skinner Building, College Park, MD 20742, USA.
authors.forename: Qin
authors.initials: Q
authors.lastname: Wang
mesh_terms: D002713:Chlorine / Q000032:analysis*; D015169:Colony Count, Microbial; D004202:Disinfectants / Q000032:analysis*; D004755:Enterobacteriaceae / Q000502:physiology*; D019453:Escherichia coli O157 / Q000502:physiology; D005506:Food Contamination / Q000517:prevention & control*; D005511:Food Handling; D005516:Food Microbiology; D059022:Food Safety; D006801:Humans; D006863:Hydrogen-Ion Concentration; D018545:Lactuca / Q000382:microbiology; D008089:Listeria monocytogenes / Q000502:physiology*; D050296:Microbial Viability; D019779:Salmonella enterica / Q000502:physiology; D012973:Sodium Hypochlorite / Q000032:analysis; D014867:Water / Q000737:chemistry*
chemical_list: D004202:Disinfectants; D014867:Water; D002713:Chlorine; D012973:Sodium Hypochlorite
keywords: Chlorine depletion; Chlorine replenishment; Human pathogen; Organic load; Wash water