Article (Scientific journals)
Effect of pH and water activity on the growth limits of Listeria monocytogenes in a cheese matrix at two contamination levels.
Schvartzman Echenique, Maria Sol; Belessi, C.; Butler, F. et al.
2011In Journal of Food Protection, 74 (11), p. 1805-13
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Keywords :
Cheese/microbiology; Colony Count, Microbial; Consumer Product Safety; Electrophoresis, Gel, Pulsed-Field; Fermentation; Food Contamination/analysis; Food Handling/methods; Food Microbiology; Humans; Hydrogen-Ion Concentration; Listeria monocytogenes/growth & development/metabolism; Water/metabolism
Abstract :
[en] Listeria monocytogenes can proliferate at the beginning of cheesemaking as the conditions favor growth. The objective of this study was to establish the growth limits of L. monocytogenes in a cheese matrix, in case of potential contamination of the milk prior to cheese manufacture. A semisoft laboratory scale model cheese system was made at different initial pH and water activity (a(w)) levels with a mix of two strains of L. monocytogenes. A factorial design of five pH values (5.6 to 6.5), four a(w) values (0.938 to 0.96), and two L. monocytogenes inoculation levels (1 to 20 CFU/ml and 500 to 1,000 CFU/ml) was carried out. Each combination was evaluated in six independent replicates. In order to determine if there was a dominant strain, isolated colonies from the cheeses were analyzed by pulsed-field gel electrophoresis. The data relating to growth initiation were fitted to a logistic regression model. The a(w) of milk influenced the probability of growth initiation of L. monocytogenes at both low and high contamination levels. The pH, at the concentrations tested, had a lower effect on the probability of growth initiation. At pH 6.5 and a(w) of 0.99 for low contamination levels and pH 6.5 and a(w) of 0.97 for high contamination levels, increases in population of up to 4 and 2 log were observed at low and high contamination levels, respectively. This shows that if conditions are favorable for growth initiation at the early stages of the cheesemaking process, contamination of milk, even with low numbers, could lead to L. monocytogenes populations that exceed the European Union's microbiological limit of 100 CFU/g of cheese.
Disciplines :
Food science
Author, co-author :
Schvartzman Echenique, Maria Sol ;  Université de Liège - ULiège > Département des sciences de la vie > Génomique fonctionnelle et imagerie moléculaire végétale
Belessi, C.
Butler, F.
Skandamis, P. N.
Jordan, K. N.
Language :
English
Title :
Effect of pH and water activity on the growth limits of Listeria monocytogenes in a cheese matrix at two contamination levels.
Publication date :
2011
Journal title :
Journal of Food Protection
ISSN :
0362-028X
eISSN :
1944-9097
Publisher :
International Association for Food Protection, United States - Iowa
Volume :
74
Issue :
11
Pages :
1805-13
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 14 January 2015

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