title: Inactivation kinetics of inoculated Escherichia coli O157:H7 and Salmonella enterica on lettuce by chlorine dioxide gas.
abstract: The purpose of this investigation was to study inactivation kinetics of inoculated Escherichia coli O157:H7 and Salmonella enterica on lettuce leaves by ClO(2) gas at different concentrations (0.5, 1.0, 1.5, 3.0, and 5.0 mg l(-1)) for 10 min and to determine the effect of ClO(2) gas on the quality and shelf life of lettuce during storage at 4 degrees C for 7 days. One hundred microliters of each targeted organism was separately spot-inoculated onto the surface (5 cm(2)) of lettuce (approximately 8-9 log CFU ml(-1)), air-dried, and treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity for 10 min. Surviving bacterial populations on lettuce were determined using a membrane transferring method, which included a non-selective medium followed by a selective medium. The inactivation kinetics of E. coli O157:H7 and S. enterica was determined using first-order kinetics to establish D-values and z-values. The D-values of E. coli and S. enterica were 2.9+/-0.1 and 3.8+/-0.5 min, respectively, at 5.0 mg l(-1) ClO(2) gas. The z-values of E. coli and S. enterica were 16.2+/-2.4 and 21.4+/-0.5 mg l(-1), respectively. A 5 log CFU reduction (recommended by the United States Food and Drug Administration) for E. coli and S. enterica could be achieved with 5.0 mg l(-1) ClO(2) gas for 14.5 and 19.0 min, respectively. Treatment with ClO(2) gas significantly reduced inherent microflora on lettuce and microbial counts remained significantly (p<0.05) lower than the uninoculated control during storage at 4 degrees C for 7 days. However, treatment with ClO(2) gas had a significantly (p<0.05) negative impact on visual leaf quality. These results showed that treatment with ClO(2) gas significantly reduced selected pathogens and inherent microorganisms on lettuce; however, the processing conditions would likely need to be altered for consumer acceptance.
authors.affiliation: Department of Food Science, Purdue University, 745 Agriculture Mall Drive, West Lafayette, IN 47907-2009, USA.
authors.forename: B S M
authors.initials: BS
authors.lastname: Mahmoud
authors.forename: R H
authors.initials: RH
authors.lastname: Linton
mesh_terms: D017606:Chlorine Compounds / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004202:Disinfectants / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development; D005506:Food Contamination / Q000032:analysis / Q000517:prevention & control; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D006801:Humans; D007700:Kinetics; D018545:Lactuca / Q000382:microbiology* / Q000592:standards; D008826:Microbial Sensitivity Tests; D010087:Oxides / Q000494:pharmacology*; D011786:Quality Control; D019779:Salmonella enterica / Q000187:drug effects* / Q000254:growth & development; D013649:Taste; D013696:Temperature; D013997:Time Factors
chemical_list: D017606:Chlorine Compounds; D004202:Disinfectants; D010087:Oxides; C025109:chlorine dioxide