An improved radio frequency method to pasteurize salmonella in shell eggs

Authors: Geveke, David; BIGLEY, ANDREW - Former ARS Employee; BRUNKHORST, CHRISTOPHER - Princeton University; Jones, Deana; Tilman, Eric

Submitted to: International Journal of Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2018
Publication Date: 6/13/2018
Citation: Geveke, D.J., Bigley, A., Brunkhorst, C., Jones, D.R., Tilman, E.D. 2018. An improved radio frequency method to pasteurize salmonella in shell eggs. International Journal of Food Science and Technology. https://doi.org/10.1111/ijfs.13843.
DOI: https://doi.org/10.1111/ijfs.13843

Interpretive Summary: USDA ARS and Princeton University engineers invented a radio frequency (RF) technology that rapidly pasteurizes shell eggs without affecting the appearance of the heat-sensitive egg white. However, the prototype equipment was impractical. We improved the technology by automating it and reducing its cost. Using the new RF equipment, Salmonella in shell eggs was reduced by 99.9999% in 21 minutes which is approximately one-third the time of the existing industrial pasteurization process. The RF process maintains the fresh appearance of egg whites and produces significantly better angel food cakes compared to those from the current industrial process. The RF pasteurization process is now more commercially feasible and its use will reduce the number of foodborne illnesses.

Technical Abstract: The goals of this study were to improve radio frequency (RF) shell egg pasteurization technology to make it more commercially feasible, to evaluate its efficacy in reducing Salmonella, and to determine its effect on the quality changes of the egg. The original RF technology inactivated 6.8 log of E. coli in eggs in approximately 40% of the time required for the hot water process currently used by industry. However, the original RF equipment required manual rotation of the egg and deionized water. In the present study, a unique RF apparatus was constructed that automatically rotates the egg and works with municipal water (350 micro S/cm). A two-step process first heated the shell egg using the new RF apparatus for 6.0 min, and then heated the egg for an additional 15 min in 56.7 C water. Additionally, the impedance of the egg was measured in the frequency range of 1 – 100 MHz, the temperature distribution following RF processing was evaluated, and the effect of RF pasteurization on the properties of egg components and angel food cakes were determined. The 21 min RF process reduced the population of Salmonella typhimurium in the center of a shell egg by 6.2 log without affecting the appearance of the albumen. By contrast, processing for 60 min was required to reduce the Salmonella by 5.0 log using 56.7 C water only, and the albumen became cloudy. While there were no significant differences in the quality and foam stability of eggs pasteurized using the two-step RF process and the hot water process (P < 0.05), angel food cakes made from RF eggs had significantly greater volumes (P < 0.0001). The results of the impedance analysis revealed that at the frequency used in this study, 60 MHz, a good match between the egg and power generator was obtained; this was confirmed by measuring the forward and reflected power which showed the process was more than 97% efficient. The temperature distribution investigation indicated that the RF process preferentially heats the center of the shell egg; this is important because Salmonella grows best in the nutrient-rich yolk and the albumen is very heat sensitive. The novel RF pasteurization process presented in this study is 65% faster and less damaging than the existing industrial pasteurization process. In addition, the RF process was improved to make it more commercially feasible by enabling it to work with tap water and by adding mechanical rotation.