|MARKS, HARRY - Food Safety Inspection Service (FSIS)|
Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2013
Publication Date: 6/1/2013
Citation: Gurtler, J., Marks, H.M., Bailey, R., Juneja, V.K., Jones, D.R. 2013. Kinetics model comparison for the inactivation of Salmonella Enteritidis and Oranienburg in 10% salted liquid whole egg. Foodborne Pathogens and Disease. 10:492-499.
Interpretive Summary: The U.S. food industry presently uses large quantities of salted liquid whole egg as an ingredient in many further-processed foodstuffs, sauces, dressings, etc. The USDA Food Safety and Inspection Service (FSIS) requires that liquid whole egg with 2 percent or more salt be thermally pasteurized at 63.3 degrees Celsius for 3.5 min to inactivate Salmonella. These conditions, established in 1970, may not be effective because of the different Salmonella strains and variations in liquid egg products and processing conditions that have arisen since that time. We tested the survival of heat resistant-Salmonella in 10 percent salted liquid egg yolk and developed a mathematical model describing the inactivation. This model indicates that salted liquid egg yolk now must be processed at 63.3 deg C for at least 7.8 minutes, or 62.2 deg C for 9.8 minutes in order to inactivate at least 99.9999 percent of Salmonella. These results may be used by liquid egg processors to ensure the production of a safe product.
Technical Abstract: Current data does not exist sufficient for predicting thermal inactivation kinetics of Salmonella spp. for many types of liquid egg products, including salted liquid whole egg, for use in updating pasteurization guidelines. This is, in part, due to variations in Salmonella strains and changes in the processing of liquid egg products that have arisen in the past 40 years. Liquid egg pasteurization requirements are based on time/temperature combinations in the Code of Federal Regulations, Title 9, Ch. III, Sec. 590.570 from data acquired prior to 1970. These guidelines are being reevaluated in light of recent risk assessments. The goal of this study was to determine the inactivation kinetics of thermally-resistant Salmonella in commercially-acquired 10 percent salted liquid whole egg (LWE). Heat-resistant Salmonella Enteritidis and Oranienburg were grown in Tryptic Soy Broth at 37C, composited and added to 10 percent salted LWE and mixed, resulting in final populations of ca. 5.7-7.8 log CFU/ml. Inoculated egg was injected into glass capillary tubes, flame-sealed and heated in a water bath at 60, 62.2, 63.3, 64.3 or 66C. Contents were surface plated, incubated at 37C for 24 h, and colonies were enumerated. Random presumptive positive colonies were confirmed by selective differential plating and serological agglutination. Survival curves were not log-linear (log levels versus time), but decreased rapidly, and after initial periods became linear. Asymptotic decimal reduction values at each temperature were calculated from survivor curves with a minimum inactivation of 5.0 log CFU/ml. The asymptotic thermal D-values for salted LWE were 3.47, 2.23, 1.79, 1.46, and 1.04 min at 60, 62.2, 63.3 64.3 or 66 deg C, respectively. The calculated thermal z-value was 11.5C. A model that predicts lethality for given times and temperatures was developed. The D- and z-values reported in our study are higher than those reported in the literature and confirm that the current pasteurization requirements for 10 percent salted LWE of minimum temperatures, times of 63.3 deg C for 3.5 min, or 62.2 deg C for 6.2 min, are not sufficient to inactivate 7 log CFU/ml of Salmonella and are estimated to provide ca. 2 – 3 log CFU/ml of destruction. This model will assist the USDA, FSIS in issuing pasteurization performance standards and provide industry guidance for designing pasteurization processes that will ensure safe product. The model’s primary survival curves are characterized by a convex shape with asymptotic D-values, involving values of three parameters to describe a curve (besides an initial level). This model can be used to help processors design their pasteurization systems to ensure production of safe, 10 percent salted liquid egg yolk.