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Effect of chitosan and other antimicrobial hurdles on the survival of foodborne pathogens and heat-resistant E. coli on meat
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- Author / Creator
- Ziyi Hu
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Listeria monocytogenes, Salmonella and Shiga-toxin producing E. coli (STEC) continue to cause disease outbreaks associated with meat. E. coli and Salmonellasurviving the recommended cooking procedures present an additional risk to meat safety. The objectives of this thesis were to explore the single and combined effects of chitosan and other antimicrobial hurdles on the survival of pathogens and heat-resistant strains on meat. Inhibitory effects of chitosan and bacteriocins in media were determined by a critical dilution assay; the antimicrobial activity of chitosan and a bacteriocin-producing strain of Carnobacterium maltaromaticum or the bacteriocins produced by this strain was evaluated on beef. Surface application of chitosan solution inactivated E. coli AW1.7 and S. Typhimurium by 1 log (CFU/g) on raw beef. Chitosan and purified bacteriocins acted synergistically in media but not on meat. The effects of NaCl, chitosan and other additives on the heat resistance of E. coli was evaluated in ground beef that was grilled to a core temperature of 71 °C immediately after inoculation or after storage for two days at 4 °C. Addition of 3% NaCl increased survival of heat-sensitive E. coli, while the protective effect of NaCl was not observed if cells were cooled to 4 °C before mixing with cold meat and NaCl. Chitosan enhanced the thermal destruction of LHR-positive E. coli in ground beef stored at 4 °C for 2 days, while marinade, carvacrol, or potassium lactate had no such effect. The combined lethality of chitosan and pressure was assessed with heat and pressure resistant strains of E. coli and S. Senftenberg in buffer and ground beef. Chitosan exhibited a bactericidal effect in both buffer and meat. Chitosan acted synergistically with treatment at 400 MPa in buffer but not in ground beef.To assess the effects of chitosan and other antimicrobial hurdles on the survival of L. monocytogenes on ham, ham formulated with chitosan or other preservatives were treated at 600 MPa at 5 °C for 3 min. Surviving cells were differentially enumerated after pressure treatment and after 4 weeks of refrigerated storage. The single or combined use of chitosan inhibited the growth of L. monocytogenes on ham, and chitosan exhibited higher inhibitory effect than sodium diacetate/sodium lactate. In conclusion, chitosan exhibits antimicrobial activity against E. coli, Salmonella and L. monocytogenes on meat, and is a useful hurdle concept for improving meat safety.
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- Graduation date
- Spring 2019
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- 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.