Inhibition of Listeria monocytogenes in White-Brined Cheese by Lactobacillus reuteri: Effect of L. reuteri Delivery Method, Brine Concentration, and Storage Temperature.

This study investigated the inhibitory effect of Lactobacillus reuteri with glycerol inoculated at different production stages of white-brined cheese (WBC) immersed in different concentrations of brine solutions under different storage temperatures as a bio-preservative against Listeria monocytogenes. Additionally, the physicochemical properties of WBC and brine solution were evaluated. A cocktail of five L. reuteri strains (~6 log CFU/g) with the addition of 100 mM glycerol was inoculated at either (1) water used to make the brine, (2) directly to the brine solution, or (3) pasteurized milk used to prepare cheese. The effect of L. reuteri against a cocktail of five L. monocytogenes strains (~5 log CFU/g) in WBC and stored in 10% or 15% brine at 4, 10, or 24 °C for 91 days was investigated. The salt content, pH, and water activity (aw) of WBC were also evaluated. L. reuteri inoculated in brine solution reduced the numbers of L. monocytogenes by 0.7-1.4 and 0.4-1.6 log CFU/g, in WBC and brines (10-15%), respectively, stored at different storage temperatures for 91 days compared to L. monocytogenes numbers in the absence of L. reuteri (control). When L. reuteri and glycerol were added to pasteurized milk during the production of WBC, the L. monocytogenes counts decreased by 1.2-2.9 and 1.4-2.5 log CFU/g in cheese and brines, respectively. However, the addition of L. reuteri and glycerol to water used in the preparation of brines reduced L. monocytogenes by 1.2-2.6 and 1.2-2.2 log CFU/g in cheese and brines, respectively. The highest inhibitory effect of L. reuteri was observed against L. monocytogenes in both cheese and brine with 10% NaCl and high temperatures (10-24 °C). The addition of L. reuteri with glycerol has the potential to reduce the risk of L. monocytogenes without negatively affecting the physicochemical characteristics of the cheese.