Submitted to: Journal of Food Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/21/2009
Publication Date: 1/1/2010
Citation: Juneja, V.K., Hwang, C., Friedman, M. 2010. Thermal inactivation and post-treatment growth during storage of multiple Salmonella serotypes in ground beef as affected by sodium lactate and oregano oil. Journal of Food Science. 75(1):M1-M6. Interpretive Summary: Salmonella is a food pathogen of major concern since documentation of its association with numerous outbreaks of foodborne illness. Undercooked meat and meat products are commonly implicated as transmission vehicles in these outbreaks. This emphasizes the need to better define and quantify the heat treatment given to these foods to provide an adequate degree of protection against survival of Salmonella. We determined that a combination of sodium lactate and oregano oil would be an effective formulation in beef to render Salmonella more sensitive to heat and to prevent growth of the injured pathogen during storage. This information will be of immediate use to consumers and to the food industry and regulatory agencies to aid in the development of guidelines to ensure the safety of cooked beef.
Technical Abstract: We assessed the heat resistance of Salmonella in raw ground beef in both the absence and presence of sodium lactate or oregano oil, and with combinations of these two GRAS-listed ingredients, and determined their bactericidal or bacteriostatic activities during post-thermal treatment storage at 15C. A cocktail of 8 strains of Salmonella spp. was inoculated into ground beef supplemented with sodium lactate (NaL) (1.5% and 3.0%) and/or oregano oil (0.5% and 1.0%) to obtain approximately 8.0 log CFU/g. The ground beef samples (3 g) were vacuum-packed and heated at 60, 65, or 71C in a circulating water bath for selected times to inactivate approximately 5.0 – 6.0 log CFU/g of the pathogen, and then stored at 15C for 15 d 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 compared to the control. Addition of combinations of oregano oil and NaL overcame this protective effect. During subsequent post-treatment storage for 15 d, Salmonella populations in the controls and in samples containing 0.5% oregano (60 and 65C) or 1% oregano oil (60C) increased to 4.5-6.0 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 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.