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What is the fate of Listeria monocytogenes in various types of Belgian artisanal cheeses?

A. Gérard




What is the fate of Listeria monocytogenes in various types of Belgian artisanal cheeses?
A. Gérard*1, E. Van Coillie2, A. Bentaib3, G. Daube4, M. Sindic1. 1Laboratory of Quality and Safety of Agro-Food Products, Gembloux Agro-Bio Tech, University of Liège Gembloux, Belgium, 2Flanders Research Institute for Agriculture, Fisheries and Food (ILVO), Technology and Food Science Unit Melle, Belgium, 3Quality Partner sa Herstal, Belgium, 4Faculty of Veterinary Medicine, Food Science Department, FARAH, University of Liège Liège, Belgium.

Cheese has generally to be considered as ready-to-eat food allowing the growth of Listeria monocytogenes, although cheeses unable to support this growth were already observed. Consequently, the absence of the pathogen in 25 g of cheese has to be guaranteed, before placing it on the market, while up to 100 cfu/g are tolerated for food not allowing the growth of L. monocytogenes. The presence of L. monocytogenes in cheese can lead to harmful economic consequences for producers. Defining more accurately cheeses allowing or not the growth of L. monocytogenes is thus a priority. Predictive microbiology is not an optimal solution, since artisanal cheeses present specific characteristics that are not taken into account by current models. Challenge-tests seem more accurate. The goal of this study was to assess the growth potential of L. monocytogenes in cheeses from 32 artisanal factories using challenge-tests. Were considered: (a) unripened cheeses (12), (b) mold-ripened soft cheeses (4), (c) smear-ripened soft cheeses (4) and (d) ripened semi-hard cheeses (12). The number of batches to test was determined using Sym'Previus, an online tool for growth predictions in food microbiology. A cocktail of 3 strains was inoculated in cheeses, targeting a contamination of 100 cfu/g. Cheeses were stored at refrigeration temperature during the whole shelf-life. Growth potentials were calculated as the difference between median contaminations at the use-by date and at the first day of storage, as recommended by the European Union Reference Laboratory for L. monocytogenes. Twenty-three cheeses out of 32 did not allow the growth of L. monocytogenes, i.e., the growth potential was ≤0.5 log10 cfu/g. It was the case of all unripened cheeses (−1.0 ± 0.3 log10 cfu/g on average), meaning that Belgian unripened cheeses should not represent a threat for food safety. On the opposite, soft cheeses allowed growth of L. monocytogenes up to 4.5 log10 cfu/g. Regarding semi-hard cheeses, a huge inter- and intra-batch variability was observed. In the latter case, recommended method for growth potential calculation underestimated the growth and led to inaccurate conclusions concerning product safety.

Keywords: Listeria monocytogenes, cheese, challenge test.

Biography: Master's degree in Bioscience Engineering in Chemistry and Bioindustries (2016) from Gembloux Agro-Bio Tech - University of Liège (Belgium), master thesis about the development of molecular methods to detect insects in food matrices. Currently: PhD Candidate at Gemblux Agro-Bio Tech - University of Liège (Belgium), aiming to characterize physicochemically and microbiologically Belgian artisanal cheeses, and focusing on the behavior of Listeria monocytogenes in these products. Co-author of at least three scientific papers in relation with dairy products.