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Impact of Sodium Reduction on the Microbiota of Ready-to-Eat Meats Open Access


Other title
Sodium reduction
Flow cytometry
Spoilage microorganisms
Meat microbiota
Ready-to-eat meat
Listeria monocytogenes
Microbial stress
Type of item
Degree grantor
University of Alberta
Author or creator
Liu, Xiaoji
Supervisor and department
McMullen, Lynn (Agricultural, Food and Nutritional Science)
Examining committee member and department
Shand, Phyllis (Food and Bioproduct Sciences, University of Saskatchewan)
McMullen, Lynn (Agricultural, Food and Nutritional Science)
Jeon, Byeonghwa (Public Health)
Cutter, Catherine (Food Science, Penn State University)
Bruce, Heather (Agricultural, Food and Nutritional Science)
Department of Agricultural, Food, and Nutritional Science
Food Science and Technology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
The growth of Listeria monocytogenes and spoilage microorganisms is a concern in sodium-reduced ready-to-eat (RTE) meats. To assess the microbial risk of sodium-reduced RTE meats, the microbiota of retail RTE meats was profiled and the growth of L. monocytogenes and an autochthonous microbiota was examined under experimental conditions relevant to sodium reduction. To determine the effect of sodium reduction on the growth of L. monocytogenes, ham was manufactured with different concentrations of sodium chloride. Results confirmed that L. monocytogenes had shorter lag phase on ham formulated with less NaCl when no autochthonous microbiota was present. The autochthonous microbiota effectively controlled the growth of L. monocytogenes through competition regardless of the concentration of sodium chloride. The antilisterial effect of carnocyclin A (CCLA) was examined. Global gene expression, protein production and morphological changes were profiled in L. monocytogenes exposed to a sublethal dose of CCLA in a low sodium environment. CCLA exposure resulted in down-regulation of genes involved in cell division, cell wall synthesis and motility in L. monocytogenes after 4 h and 30 h of exposure. Absence of flagella from the cell surface was observed. The filamentation of L. monocytogenes was examined following exposure of cells to stress including acid, salt and antimicrobial peptides. Listeria formed filaments in low concentrations of acids and salts but not with purified CCLA. L. monocytogenes was able to form filaments both in vitro and in situ. Down-regulation of cell division gene ftsX could be involved in filamentation. The effect of a mixture of sodium lactate and sodium diacetate (NaL/DA) on gene expression in L. monocytogenes was examined. Global gene expression was examined after Listeria cells were exposed to NaL/DA in broth. The genes encoding glycolytic enzymes were down-regulated. The DNA repair gene, cell division gene and cell structure synthesis genes were up-regulated. The addition of NaL/DA inhibited the growth of Listeria on low sodium ham products. In conclusion, this work demonstrated that the use of preservatives (CCLA and NaL/DA) and the presence of an autochthonous microbiota can effectively inhibit the growth and down-regulate the expression of genes essential for cellular functions in L. monocytogenes.
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.
Citation for previous publication
Liu X, Basu U, Miller P, McMullen LM. 2014. Stress and adaptation of Listeria monocytogenes 08-5923 exposed to a sublethal dose of carnocyclin A. Applied Environmental Microbiology. 80:3835–3841.Liu X, Miller P, Shand PJ, McMullen LM. 2012. Growth of Listeria monocytogenes on sodium-reduced ham. Proceedings of the 58th International Congress of Meat Science and Technology (12-17 August 2012), ICoMST2012paper421.pdf. 4 pp. Montreal, Canada.

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