Inactivation kinetics of inoculated Escherichia coli O157:H7 and Salmonella enterica on lettuce by chlorine dioxide gas

• Published in: Food microbiology Vol. 25; no. 2; pp. 244 - 252
• Main Authors: Mahmoud, B.S.M., Linton, R.H.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.02.2008
• Subjects: antibacterial properties; bacterial contamination; Chlorine Compounds - pharmacology; chlorine dioxide; Chlorine dioxide (ClO 2) gas; Colony Count, Microbial; Consumer Product Safety; decontamination; Disinfectants - pharmacology; Dose-Response Relationship, Drug; E. coli O157:H7; Escherichia coli; Escherichia coli O157 - drug effects; Escherichia coli O157 - growth & development; Escherichia coli O157:H7; food contamination; Food Contamination - analysis; Food Contamination - prevention & control; Food Microbiology; food pathogens; Food Preservation - methods; food storage; gases; Humans; inactivation; Inactivation kinetics; Kinetics; Lactuca - microbiology; Lactuca - standards; Lettuce; Microbial Sensitivity Tests; Oxides - pharmacology; plate count; predictive microbiology; Quality; Quality Control; refrigeration; Salmonella enterica; Salmonella enterica - drug effects; Salmonella enterica - growth & development; sanitizers; sanitizing; Shelf life; Taste; Temperature; Time Factors; Salmonella enterica; Chlorine dioxide (ClO 2) gas; Lettuce; Quality; E. coli O157:H7; Shelf life; Inactivation kinetics
• ISSN: 0740-0020; 1095-9998
• DOI: 10.1016/j.fm.2007.10.015

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 °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 °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 °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.