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

  • Author / Creator
    Liu, Yang
  • 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.

  • Subjects / Keywords
  • Graduation date
    Fall 2014
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.