title: Efficacy of UV, acidified sodium hypochlorite, and mild heat for decontamination of surface and infiltrated Escherichia coli O157:H7 on green onions and baby spinach.
abstract: Produce-associated foodborne illnesses outbreaks have highlighted the need for more effective decontamination methods to ensure the safety of fresh produce. The main objective of this study was to evaluate the individual and combined efficacies of germicidal UV light (12.5 to 500 mJ/cm(2)),  acidified sodium hypochlorite (ASC 10 to 200 ppm), and mild heat (40 to 50°C) for decontaminating green onions and baby spinach infected with Escherichia coli O157:H7. Samples were inoculated by spot and dip inoculation methods to mimic surface and infiltrated E. coli O157:H7  contamination, respectively. In green onions and baby spinach, the individual efficacies of UV, ASC, and mild-heat treatments varied based on the produce type and contamination method. Following analysis of the efficacies of the single treatments, a combined treatment with 125 mJ/cm(2)  UV and 200 ppm of ASC at 50°C was selected for spot-inoculated green onions, and a combined treatment with 125 mJ/cm(2) UV and 200 ppm of ASC at 20°C was selected for spot- and dip-inoculated baby spinach. While a >5-log reduction was achieved with the combination treatment  for spot-inoculated green onions with an initial contamination level of 7.2 log CFU per spot, the same treatment reduced E. coli O157:H7 populations below the detection limit (<1 log) on green onions spot inoculated at a lower contamination level (4.3 log CFU per spot). On spot-  and dip-inoculated baby spinach, the combined treatment reduced E. coli O157:H7 populations by 2.8 log CFU per spot and 2.6 log CFU/g, respectively. The combined treatment of 500 mJ/cm(2) UV and 200 ppm of ASC at 50°C selected for the decontamination of dip-inoculated green  onions resulted in a 2.2-log CFU/g reduction. These findings suggest that when foodborne pathogens contaminate produce and subsequently infiltrate, attach to, or become localized into protected areas, the individual or combined applications of UV, ASC, and mild-heat treatments have limited  decontamination efficacies on both green onions and baby spinach (<3 log). However, treatments combining UV, ASC, and mild heat could be a promising application for reducing pathogen populations (>5 log) on E. coli O157:H7 surface-contaminated green onions. This study also highlights  the importance of developing and optimizing produce-specific decontamination methods to ensure the safety of fresh produce commodities.
authors.affiliation: Department of Food Science, Cornell University, Geneva, NY 14456, USA.
authors.forename: M Zeki
authors.initials: MZ
authors.lastname: Durak
authors.forename: John J
authors.initials: JJ
authors.lastname: Churey
authors.forename: Randy W
authors.initials: RW
authors.lastname: Worobo
mesh_terms: D003257:Consumer Product Safety; D004202:Disinfectants / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D019453:Escherichia coli O157 / Q000187:drug effects / Q000254:growth & development* / Q000528:radiation effects; D005511:Food Handling / Q000379:methods*; D005514:Food Irradiation / Q000379:methods*; D006358:Hot Temperature; D006801:Humans; D019697:Onions / Q000382:microbiology*; D012973:Sodium Hypochlorite / Q000494:pharmacology*; D018724:Spinacia oleracea / Q000382:microbiology*; D014466:Ultraviolet Rays
chemical_list: D004202:Disinfectants; D012973:Sodium Hypochlorite