Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 30, 2002
Publication Date: N/A
Interpretive Summary: The objective of this study is to examine the effect of sodium lactate (NaL), a well known antimicrobial agent, on the survival of E. coli O157:H7 in 93% lean ground beef. Experimental results indicate that NaL at a low concentration (1.5%) significantly reduce the thermal resistance (D-values) of E. coli O157:H7 in ground beef at temperatures below 60 C, although its lethal effect diminishes at higher heating temperatures or at higher concentrations (3.0% or 4.5%). Survivor curves of the thermal inactivation study were fitted to four different mathematical models, including linear, mixed-culture, log-logistic, and a newly proposed nonlinear model. Results of statistical analysis show that the mixed-culture model is not suitable for analyzing the survivor curves of E. coli O157:H7 in 93% lean ground beef, while the newly proposed nonlinear model is capable of describing both linear and nonlinear thermal inactivation kinetics with significantly improved accuracy. This model is recommendation for analyzing thermal inactivation kinetics of foodborne pathogens.
Technical Abstract: A study was conducted to investigate the antimicrobial effect of sodium lactate (NaL) (0, 1.5, 3.0, and 4.5%) on the survival of E. coli O157: H7 in 93% lean ground beef. Samples inoculated with a mixture of four strains of E. coli O157:H7 (6-7 log CFU/g) were subjected to immersion heating in a water bath stabilized at 55, 57.5, 60, 62.5, or 65C. With a low concentration (1.5%) of NaL added to the ground beef, the thermal resistance of E. coli O157:H7 was significantly decreased at temperatures below 60C and was slightly increased at 62.5 and 65C. Except at 55C with 3.0% NaL, no significant changes in D-values were observed in the samples with 3.0% and 4.5% NaL. Regression curves were fitted to the experimental thermal inactivation kinetics data using four different mathematical models: linear inactivation kinetics, a mixed-culture model, a log-logistic model, and a newly proposed nonlinear model. Among all the models investigated, the new nonlinear model is capable of describing both linear and nonlinear (upwardly or downwardly concaved) survivor curves, while the mixed-culture model was not found suitable for analyzing the survivor curves of E. coli O157:H7 in 93% lean ground beef. Statistical analyses revealed that the nonlinear model can significantly improve predictive accuracy and is superior to all other models used in this study. Accordingly, the nonlinear model is therefore recommended for application in evaluating the thermal inactivation kinetics of foodborne pathogens.