Dairy Foods: Cheese

摘要

Cheese has generally to be considered as ready-to-eat food allowing thegrowth of Listeria monocytogenes, although cheeses unable to supportthis growth were already observed. Consequently, the absence of thepathogen in 25 g of cheese has to be guaranteed, before placing it onthe market, while up to 100 cfu/g are tolerated for food not allowing thegrowth of L. monocytogenes. The presence of L. monocytogenes in cheesecan lead to harmful economic consequences for producers. Defining moreaccurately cheeses allowing or not the growth of L. monocytogenes isthus a priority. Predictive microbiology is not an optimal solution, sinceartisanal cheeses present specific characteristics that are not taken intoaccount by current models. Challenge-tests seem more accurate. Thegoal of this study was to assess the growth potential of L. monocytogenesin 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 cocktailof 3 strains was inoculated in cheeses, targeting a contamination of100 cfu/g. Cheeses were stored at refrigeration temperature during thewhole shelf-life. Growth potentials were calculated as the difference betweenmedian contaminations at the use-by date and at the first day ofstorage, as recommended by the European Union Reference Laboratoryfor L. monocytogenes. Twenty-three cheeses out of 32 did not allowthe growth of L. monocytogenes, i.e., the growth potential was ≤0.5 log_(10)cfu/g. It was the case of all unripened cheeses (−1.0 ± 0.3 log_(10) cfu/g onaverage), meaning that Belgian unripened cheeses should not representa threat for food safety. On the opposite, soft cheeses allowed growth ofL. monocytogenes up to 4.5 log_(10) cfu/g. Regarding semi-hard cheeses, ahuge inter- and intra-batch variability was observed. In the latter case,recommended method for growth potential calculation underestimatedthe growth and led to inaccurate conclusions concerning product safety.