Bloomy rind cheeses, including Camembert and Brie type cheeses, are highly susceptible to contamination by environmental pathogens during their manufacture and ripening. These cheeses undergo many physiochemical changes during ripening that provides these pathogens with a suitable environment to grow. One example of this change is an increase of pH to greater than 7 during the initial stages of the cheese ripening. The risk associated with this cheese type has been well documented and people with compromised immune systems are advised against consuming these cheeses. Currently, there are no options available for bloomy rind cheese producers to add a kill step in late in the manufacture/ripening of bloomy rind cheeses. Due to the lack of kill step, cheese makers are forced to rely on stringent sanitation techniques and environmental monitoring to mitigate the risk of contamination.
There are many ways to manufacture bloomy rind cheeses, and we hypothesized that different cheese recipes would perform differently under HPP condition with the stabilized cheeses being most likely to withstand this treatment with minimal impact on the overall quality. To be able to test this hypothesis we first manufactured five varieties of bloomy rind cheeses to investigate the composition and characteristics of the recipes as a baseline for the expected quality from these different bloomy rind cheese varieties. Next, we evaluated the effect of HPP on cheese quality for selected cheese varieties. Finally, HPP was evaluated for the overall reduction of Listeria monocytogenes. The overall hypothesis of this research is that HPP (high hydrostatic pressure processing) could be effectively used on bloomy rind cheeses as a post-manufacture kill step, and that the cheese making practices used will influence how the cheeses withstand HPP.
Camembert cheese varieties varied in composition and characteristics that were influenced by the cheese making practices. The most notable difference between the varieties was the paste stability. Paste stability is defined by the distance that the center of the cheese is displaced from the rind after slicing. Another notable observation is the variation in total Ca content, which is related to the amount of colloidal calcium phosphate that is associated with the protein matrix that retains the cheese structure. When determining the effect of HPP on cheese quality, the most notable discovery was the destruction of the mycelium from the surface fungi used to ripen these cheeses. HPP treatment caused significant discoloration, from white to brown/yellow, and would be unacceptable to consumers of bloomy rind cheeses. Finally, when evaluating the reduction of L. monocytogenes using HPP there were large reductions (> 5-log CFU/g) in the microbial load at greater than 450 MPa for 10 minutes.
Based on the evidence provided, HPP successfully reduces L. monocytogenes in Camembert; however, the tested treatments produced unacceptable changes in cheese appearance. Until a technology is found that can be successfully applied to bloomy rind cheeses, cheese makers must emphasize proper sanitation procedures and environmental monitoring to control the risk of contamination.