NIZO predicts Listeria growth in cheese

To safely market and export cheese, you need to comply with food safety criteria and determine the risk of L. monocytogenes growth. For some products, this is easy: for instance, if the pH is below 4.4 or the water activity is below 0.92, Listeria will not grow. But many cheeses fall outside of these limits.

A validated model for assessing the risk

To gain fast insight into whether a cheese is at risk for supporting L. monocytogenes growth, Nizo created a predictive model. They began by researching Gouda, which has never been associated with listeriosis, despite a pH above 5.0 and a water activity above 0.94. The research determined that the undissociated lactic acid concentrations (above 6.35 millimolar) in the Gouda, were fully inhibiting L. monocytogenes growth. The study also demonstrated that, even when undissociated lactic acid concentrations fall below the critical level, L. monocytogenes growth in cheese can still be sufficiently inhibited by additional factors including pH, water activity and temperature. Using this scientific insight, Nizo developed and successfully validated a model to calculate the potential of Listeria growth in many other cheeses. These include soft cheeses (blue cheese, Camembert, cottage cheese, ricotta, queso fresco, Mozzarella), semi-hard cheeses (Cheddar, feta-style) and cheeses prepared with milk from animals other than cows (goats, sheep and buffalos).

nizo.com