Purpose: To identify natural fermentates or protection cultures to enhance the inactivation of Listeria monocytogenes (Lm) and Shiga toxin-producing E. coli (STEC) in a model cheese system.
Methods: Low-salt Cheddar aqueous extract (CCE; adjusted to 1.89% salt-in-moisture, 2.7% lactate-in-moisture, pH 5.6) was supplemented with commercial fermentates (0.1% or 0.2% Fermentate B, 0.5% or 1.0% Fermentate A or C) or 5-log CFU/ml of protective cultures X, Y, or Z (Bifidobacteria, Lactobacillus, or Lactococcus). In addition, a Control without additives was tested. Treatments were inoculated with 3.5-log CFU/ml Lm or 5-log CFU/ml STEC (3-strain mixtures for each inoculum type) and triplicate samples assayed weekly for changes in microbial populations during 60 days storage at 10 °C. Each study was replicated twice.
Results: STEC survived longer than Lm in Control CCE stored 60 days at 10 °C; populations of STEC decreased an average 1 log in 60 days and Lm decreased 3 logs in 42 days. None of the fermentates changed the inactivation rate of STEC, but populations of Lm decreased 3.3 and 2.9 log at D-7 for 1.0 and 0.5% Fermentates A, respectively, and 1.8 log decrease for 1.0% Fermentate C. STEC populations declined 2 and >5 log at D-42 and 60 in CCE supplemented with Culture Z, respectively, and Lm declined 3 logs in 28 days. Cultures X and Y had no significant effect on the inactivation of STEC or Lm compared to the Control.
Significance: This study identified fermentates and protective cultures to enhance the inactivation of Lm and STEC in a model low-sodium cheese system. Additional studies should confirm efficacy in natural cheeses such as Cheddar and Mozzarella.