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Heat and Pressure Resistance of Escherichia coli and Its Inactivation In the Presence of Antimicrobial Compounds Open Access


Other title
Antimicrobial Compounds
Escherichia coli
Heat Pressure Resistance
Type of item
Degree grantor
University of Alberta
Author or creator
Liu, Yang
Supervisor and department
Gänzle, Michael (Agricultural, Food & Nutritional Science )
Betti, Mirko (Agricultural, Food & Nutritional Science )
Examining committee member and department
Gill, Alexander (Health Canada, Bureau of Microbial Hazards)
Holley, Rick (University of Manitoba)
Anders, Sven (Resource Economics and Environmental Sociology)
Gänzle, Michael (Agricultural, Food & Nutritional Science )
McMullen, Lynn (Agricultural, Food & Nutritional Science )
Betti, Mirko (Agricultural, Food & Nutritional Science )
Department of Agricultural, Food, and Nutritional Science
Food Science and Technology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Verotoxigenic Escherichia coli (VTEC) are pathogens causing severe foodborne disease. E. coli AW1.7 is a heat resistant beef carcass isolate that may be used as a surrogate organism to study the survival of VTEC on food. This dissertation examines the heat and pressure resistance of E. coli and the application of antimicrobial compounds to achieve its inactivation in food. The pressure resistance of E. coli AW1.7 was compared to the resistance of other foodborne pathogens and spoilage organisms relevant in meat. E. coli AW1.7 was the most pressure resistant organism tested. Moreover, the ability of E. coli AW1.7 to resist pressure was comparable to the pressure-resistant mutant E. coli LMM1030. To further study the heat- and pressure resistance of E. coli, E. coli AW1.7 was compared to the heat- and pressure resistance of VTEC strains from different serotypes and phylotypes. E. coli AW1.7 exhibited a higher heat resistance than VTEC strains; however, some VTEC strains also survived in hamburgers grilled to a core temperature of 71°C. Several strains of VTEC exhibited a higher resistance to pressure than E. coli AW1.7. Over one third of tested strains showed 3 log CFU/g or less cell count reduction under high pressure treatment of 600 MPa for 3 min. Therefore, additional treatment processes are required for elimination of VTEC in pressure treated food. Additional treatments were evaluated to achieve the elimination of E. coli in buffers and food matrices. Chitosan was effective in injury E. coli in imidazole and potassium phosphate buffer; chitosan, nisin and lactate combination were effective in yogurt serum; chitosan, nisin and heat were effective in apple juice; and chitosan, Micocin® X and heat had small bactericidal effects in ground beef. A combination of chitosan and high pressure was not effective against E. coli AW1.7 in potassium phosphate buffer, but addition of Micocin® X to increased killing of E. coli AW1.7. In conclusion, this thesis demonstrated that high pressure alone is insufficient to kill E. coli in meat. Bacteriocins, lactate, and chitosan can be applied as additional antimicrobial treatments to kill E. coli in food. And the bactericidal effect is strongly dependent on the food matrix and the preservation method. Some of the VTEC strains tested survived heat treatment and high hydrostatic pressure (HHP) permitted recommendations of E. coli by Canadian regulatory agencies (Health Canada and Canadian Food Inspection Agency). More studies need to be conducted to validate the results.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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