Thermal inactivation and postthermal treatment growth during storage of multiple Salmonella serotypes in ground beef as affected by sodium lactate and oregano oil.

We assessed the heat resistance of Salmonella in raw ground beef in both the absence and presence of sodium lactate, oregano oil, and in combinations of these 2 GRAS-listed ingredients, and determined their bactericidal or bacteriostatic activities during postthermal treatment storage at 15 degrees C. A cocktail of 8 serotypes of Salmonella spp. was inoculated into ground beef supplemented with sodium lactate (NaL) (1.5% and 3%) and/or oregano oil (0.5% and 1%) to obtain approximately 8 log CFU/g. The ground beef samples (3 g) were vacuum-packed and heated at 60, 65, or 71 degrees C in a circulating water bath for selected times to inactivate approximately 5 to 6 log CFU/g of the pathogen, and then stored at 15 degrees C for 15 and 30 d. Results show that especially at the lower cooking temperatures, addition of oregano oil increased the inactivation rate of Salmonella spp., whereas addition of NaL alone exhibited a protective effect against lethality and decreased the rate. Addition of combinations of oregano oil and NaL overcame this protective effect. During subsequent posttreatment storage for 15 d, Salmonella populations in the controls and in samples containing 0.5% oregano (60 and 65 degrees C) or 1% oregano oil (60 degrees C) increased to 4.5 to 6 log CFU/g. The values for all other samples were at or near undetectable levels. Results from the 30-d storage study were similar. These findings indicate that lactate and oregano oil may be used to render Salmonella spp. more susceptible to the lethal effect of heat and to inhibit growth of Salmonella spp. that survive heat treatments.