Influence of traditional brine washing of smear taleggio cheese on the surface spreading of Listeria innocua

Abstract

The influence of a traditional procedure of washing of smear Taleggio cheese on surface spreading of Listeria innocua was studied. This practice is carried out during ripening to remove molds, to select the surface microflora, and to control the ripening process. One cheese, both of 2 (i) and 4 (ii) weeks of ripening, was surface-inoculated with approximately 3 log CFU of L. innocua per entire cheese surface. The inoculated cheeses and others of the same age were weekly washed with brine solution. Listeria was spread both on the surface of the inoculated cheese and on the other cheeses, and it was also found in the brines and on the wooden boxes where the cheeses were ripened. The time of ripening when contamination occurs influenced the behavior of Listeria. At the moment of contamination, the smear surface microflora of (i) cheese was ~2 log CFU/g higher than of (ii) cheese. Listeria inoculated on 2-week-ripened cheese was able to colonize the entire surface of the cheese and to cross-contaminate the other cheeses. On the contrary, Listeria inoculated on a 4-week-ripened cheese was partially spread on the surface of the originally inoculated cheese, and the transfer of contamination by the washing procedure was restrained. Because a random distribution of Listeria on cheese surface was observed, the importance of the mode of sampling was discussed. Because of the lack of critical control points during ripening of Taleggio cheese, the Listeria hazard needs to be controlled by taking appropriate control measures to break off the contamination cycle (cheese → brine → wooden boxes → cheese).