Predictive model for the combined effect of temperature, sodium lactate, and sodium diacetate on the heat resistance of Listeria monocytogenes in beef

The effects of heating temperature (60 to 73.9degreesC), sodium lactate (NaL; 0.0 to 4.8% [wt/wt]), and/or sodium diacetate (SDA; 0.0 to 0.25% [wt/wt]) and of the interactions of these factors on the heat resistance of a five-strain mixture of Listeria monocytogenes in 75% lean ground beef were examined. Thermal death times for L monocytogenes in filtered stomacher bags in a circulating water bath were determined. The recovery medium was tryptic soy agar supplemented with 0.6% yeast extract and 1% sodium pyruvate. Decimal reduction times (D-values) were calculated by fitting a survival model to the data with a curve-fitting program. The D-values were analyzed by second-order response surface regression for temperature, NaL level, and SDA level. The D-values observed for beef with no NaL or SDA at 60, 65, 71.1, and 73.9degreesC were 4.67, 0.72, 0.17, and 0.04 min, respectively. The addition of 4.8% NaL to beef increased heat resistance at all temperatures, with D-values ranging from 14.3 min at 60degreesC to 0.13 min at 73.9degreesC. Sodium diacetate interacted with NaL, thereby reducing the protective effect of NaL and rendering L. monocytogenes in beef less resistant to heat. A mathematical model describing the combined effect of temperature, NaL level, and SDA level on the thermal inactivation of L. monocytogenes was developed. This model can predict D-values for any combination of temperature, NaL level, and SDA level that is within the range of those tested. This predictive model will have substantial practical importance to processors of cooked meat, allowing them to vary their thermal treatments of ready-to-eat meat products in a safe manner.