Purpose: To determine the level of lactic acid, salt and pH to inactivate four different foodborne pathogens in a model low-sodium Cheddar cheese extract.
Methods: The Cheddar cheese model system employed a water extract of Cheddar cheese (CCE) as the medium. For Phase 1, CCE [1.89% salt-in-moisture (S/M); 2.7% lactate-in-moisture (L/M); pH 5.4] representing the most permissive conditions in low-sodium Cheddar, was inoculated with 4 log CFU/ml Salmonella, Listeria monocytogenes, Staphylococcus aureus or Shiga toxin-producing Escherichia coli (STEC) (3 strain mixtures of each). For Phase 2, eight CCE treatments (full-factorial design; 1.2 and 4.8% SIM; 2.7 and 4.3% LIM, pH 4.8 and 5.3) were inoculated with STEC. For both studies, treatments were dispensed into vials, and triplicate samples assayed weekly during six weeks storage at 11 °C. Each study was replicated twice.
Results: In the first study, STEC declined 0.4 log in the CCE, whereas populations of the other pathogens decreased an average 1.1 to 1.9 log during the 6 week storage. For the second study, STEC declined most rapidly in CCE with lower pH (4.8) and higher protonated lactic acid concentrations, whereas salt concentration (1.2 vs. 4.8%) did not have a significant effect on survival during the 42-day storage at 11 °C.
Significance: These results confirm that initial pH of cheese is essential in safety, regardless of salt content; this study will provide the cheese industry the levels of critical factors that must be present to produce a safe, low-sodium cheese.