Retrospective analysis of a Listeria monocytogenes contamination episode in raw milk goat cheese using quantitative microbial risk assessment tools

• Published in: Journal of food protection Vol. 75; no. 12; pp. 2122 - 2135
• Main Author: Delhalle, Laurent
• Format: Journal Article Web Resource
• Language: English
• Published: Des Moines, IA International Association for Food Protection 01.12.2012; Elsevier Limited
• Subjects: Agriculture; Agriculture & agronomie; Agriculture & agronomy; agronomy; Animals; Asymptomatic; Belgium; Biological and medical sciences; Cheese; Cheese - microbiology; Colony Count, Microbial; Consumer Product Safety; Contamination; Dairy products; Exposure assessment; Food chains; Food contamination & poisoning; Food Contamination - analysis; Food Handling - methods; Food industries; Food Microbiology; Food safety; Food science; Fundamental and applied biological sciences. Psychology; goat-cheese; Goats; Goats - microbiology; Humans; Humidity; Hydrogen-Ion Concentration; L. monocytogenes; Laboratories; Life sciences; Listeria; Listeria monocytogenes; Listeria monocytogenes - growth & development; Listeria monocytogenes - isolation & purification; Microbiology; Microorganisms; Milk; Milk - microbiology; Milk and cheese industries. Ice creams; Models, Biological; Retrospective Studies; Risk Assessment; risk mitigation; Risk reduction; Sciences des denrées alimentaires; Sciences du vivant; Sensitivity analysis; Temperature; Time Factors; Belgium; Raw milk; Goat milk cheese; Dairy product; Listeria monocytogenes; Bacteria; Risk; Contamination
• ISSN: 0362-028X; 1944-9097; 1944-9097
• DOI: 10.4315/0362-028X.JFP-12-074

In 2005, the Belgian authorities reported a Listeria monocytogenes contamination episode in cheese made from raw goat's milk. The presence of an asymptomatic shedder goat in the herd caused this contamination. On the basis of data collected at the time of the episode, a retrospective study was performed using an exposure assessment model covering the production chain from the milking of goats up to delivery of cheese to the market. Predictive microbiology models were used to simulate the growth of L. monocytogenes during the cheese process in relation with temperature, pH, and water activity. The model showed significant growth of L. monocytogenes during chilling and storage of the milk collected the day before the cheese production (median increase of 2.2 log CFU/ml) and during the addition of starter and rennet to milk (median increase of 1.2 log CFU/ml). The L. monocytogenes concentration in the fresh unripened cheese was estimated to be 3.8 log CFU/g (median). This result is consistent with the number of L. monocytogenes in the fresh cheese (3.6 log CFU/g) reported during the cheese contamination episode. A variance-based method sensitivity analysis identified the most important factors impacting the cheese contamination, and a scenario analysis then evaluated several options for risk mitigation. Thus, by using quantitative microbial risk assessment tools, this study provides reliable information to identify and control critical steps in a local production chain of cheese made from raw goat's milk.