Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2015
Publication Date: 1/30/2016
Citation: Geveke, D.J., Gurtler, J., Jones, D.R., Bigley, A.R. 2016. Inactivation of salmonella in shell eggs by hot water immersion and its effect on quality. Journal of Food Science. 81(3):M709-M714.
Interpretive Summary: Eggs were recently ranked among the riskiest foods in the U.S. We inoculated eggs with Salmonella bacteria and placed them in water that was hot enough to kill the Salmonella, but not too hot to severely damage the delicate egg whites. At a temperature of 56.7 degrees C (134 F), we found that 99.997% of the Salmonella was killed within 60 minutes. When we used a lower temperature, 55.6 degrees C (132 F), it took 100 minutes to achieve the same kill. We also found that eggs processed using these time and temperature combinations showed some degradation of quality, but should still be acceptable. We concluded that processing shell eggs with hot water for 60 minutes damaged the quality somewhat, but it also killed 99.997% of the Salmonella, which could prevent many thousands of food illnesses per year in the U.S.
Technical Abstract: Thermal inactivation kinetics of heat resistant strains of Salmonella Enteritidis in shell eggs processed by hot water immersion were determined, and the effects of the processing on egg quality were evaluated. Shell eggs were inoculated with a composite of heat resistant Salmonella Enteritidis (SE) strains PT8 C405, 2 (FSIS # OB030832) and 6 (FSIS # OB040159). Eggs were immersed in a circulating hot water bath for various times and temperatures. Come-up time of the coldest location within the egg was 21 minutes. SE was reduced by 4.5 log at both hot water immersion treatments of 56.7 degrees C for 60 min and 55.6 degrees C for 100 min. Decimal reduction times (D–values) at 54.4, 55.6, and 56.7 degrees C were 51.8, 14.6, and 9.33 min, respectively. The z-value was 3.07 degrees C. Following treatments that resulted in a 4.5 log reduction (56.7 degrees C/60 min and 55.6 degrees C/100 min), the surviving population of SE remained static during 4 weeks of refrigerated storage. After processing under conditions resulting in 4.5 log reductions, the Haugh unit and albumen height significantly increased (P < 0.01) and yolk index significantly decreased (P < 0.05). The shell dynamic stiffness significantly increased (P < 0.05), while shell strength showed no significant difference (P < 0.05). Vitelline membrane strength significantly increased (P < 0.05); although, no significant difference (P < 0.05) was observed in vitelline membrane elasticity. In summary, the hot water immersion process inactivated heat resistant SE in shell eggs by 4.5 log, but also significantly affected several egg quality characteristics.