Growth Behavior of Listeria monocytogenes during over 60-Day Ripening of Camembert Cheeses Produced by Unpasteurized Raw Milk

Abstract

Although the USA, Canada, and several EU countries allow raw milk cheese to be aged more than 60 days, these countries have strict standards for its aging conditions, such as temperature. Many developed countries have employed standards of identity which effectively prevent the manufacture and sale, of cheese made from unpasteurized milk (i.e., raw milk) in interstate commerce, unless such cheese has been aged for a minimum of 60 days. The microbiological safety of raw milk Camembert cheese, aged for more than 60 days, was evaluated using spiking experiments. We spiked Listeria monocytogenes into raw milk with different inoculation levels (high, medium and low). Camembert cheese was prepared from the inoculated raw milk, then aged in an incubator for up to 9 weeks (63 days). The number of cells was determined every week using the agar-plating method. Inoculated cells were completely eliminated, especially in Camembert cheese, after 60 days, and the reduction rate of cells was much faster in Camembert cheese. There were no significant differences in pH and water activity (aW) between the uninoculated cheese and the cheese samples in which Listeria monocytogenes was inoculated (p<0.05). The pH and aW of the Camembert cheese decreased throughout the storage period. In conclusion, the pathogenic bacteria used in this study did not affect the pH and aW of the Camembert cheese samples.