Submitted to: Journal of Food Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2007
Publication Date: 1/1/2008
Citation: Jin, Z.T., Zhang, H.Q., Boyd, G., Tang, J. 2008. Thermal resistance of Salmonella enteritidis and Escherichia coli K12 in liquid egg determined by thermal-death-time disks. Journal of Food Engineering. 84:608-614. Interpretive Summary: Using a surrogate microorganism with equivalent to or higher thermal resistance than a targeted human pathogen is a key procedure in process validation to ensure that harmful organisms are inactivated. This study demonstrated that non-pathogenic Escherichia coli K12 may serve as a surrogate for pathogenic Salmonella enteritidis in liquid egg products. The thermal inactivation kinetic data from this study may be used in design, operate and regulate a thermal pasteurization process for liquid egg products.
Technical Abstract: A thermal-death-time (TDT) disk was designed to evaluate microbiological inactivation kinetics by heat. A first order inactivation kinetic model is described by the D value as the hold time at a specific temperature that causes 90% reduction in microbial viability and the z value as the increase in temperature that causes 90% reduction in the D value. These kinetic data are critical in the design, operation and regulation of thermal pasteurization. D and z values of Salmonella enteritidis and Escherichia coli K12 in liquid whole egg and liquid egg white were determined over the temperature range from 52 to 60C. In liquid whole egg, D(54C), D(56C), D(58C) and D(60C) values of S. enteritidis were 5.70, 0.82, 0.27 and 0.17 min, respectively, and D(54C), D(56C), D(58C) and D(60C) values of E. coli K12 were 9.10, 1.41, 0.67 and 0.22 min, respectively. In liquid egg white, D(52C), D(54C), D(56C) and D(58C) values of S. enteritidis were 6.12, 1.51, 0.42 and 0.19 min, respectively, and D(52C), D(54C), D(56C) and D(58C) values of E. coli K12 were 10.18, 1.82, 0.78 and 0.28 min, respectively. The z values for S. enteritidis and E. coli K12 ranged from 3.95 to 4.03C. The results showed that D values of S. enteritidis and E. coli K12 in liquid whole egg were higher than those in liquid egg white. E. coli K12 exhibited similar kinetic behavior, but higher thermal resistance than S. enteritidis in both liquid egg white and liquid whole egg. This study demonstrated that non-pathogenic E. coli K12 may serve as a surrogate for pathogenic S. enteritidis in liquid egg in the validation of a thermal pasteurization.