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Effect of pH and Water Activity on the Growth Limits of Listeria monocytogenes in a Cheese Matrix at Two Contamination Levels

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Názov: Effect of pH and Water Activity on the Growth Limits of Listeria monocytogenes in a Cheese Matrix at Two Contamination Levels
Autori: Schvartzman Echenique, Maria Sol, Belessi, C., Butler, F., Skandamis, P. N., Jordan, K. N.
Zdroj: Journal of Food Protection. 74:1805-1813
Informácie o vydavateľovi: Elsevier BV, 2011.
Rok vydania: 2011
Predmety: 2. Zero hunger, Water/metabolism, Food Handling, Food Handling/methods, Colony Count, Microbial, Listeria monocytogenes/growth & development/metabolism, Water, Food Contamination, 04 agricultural and veterinary sciences, Hydrogen-Ion Concentration, Life sciences, Listeria monocytogenes, Electrophoresis, Gel, Pulsed-Field, Food science, 0404 agricultural biotechnology, Cheese, Consumer Product Safety, Cheese/microbiology, Sciences des denrées alimentaires, Fermentation, Sciences du vivant, Food Microbiology, Food Contamination/analysis, Humans, 0405 other agricultural sciences
Popis: 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.
Druh dokumentu: Article
Jazyk: English
ISSN: 0362-028X
DOI: 10.4315/0362-028x.jfp-11-102
Prístupová URL adresa: https://pubmed.ncbi.nlm.nih.gov/22054180
https://meridian.allenpress.com/jfp/article/74/11/1805/170581/Effect-of-pH-and-Water-Activity-on-the-Growth
https://www.ncbi.nlm.nih.gov/pubmed/22054180
http://europepmc.org/abstract/MED/22054180
http://orbi.ulg.ac.be/handle/2268/176536
https://orbi.uliege.be/handle/2268/176536
https://pubmed.ncbi.nlm.nih.gov/22054180/
Rights: Elsevier Non-Commercial
Prístupové číslo: edsair.doi.dedup.....11f4358079cedc5d214162a3c0bfa46f
Databáza: OpenAIRE
Popis
Abstrakt: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.
ISSN:0362028X
DOI:10.4315/0362-028x.jfp-11-102