USDA develops new shell egg pasteurization process

The Holy Grail of any food safety program for raw food is a “kill-step” that eliminates pathogens in the food product without negatively impacting the functional and organoleptic properties of the food. United States Department of Agriculture Agricultural Research Service scientists have developed a process for pasteurization of shell eggs that may make pasteurized eggs a lot more commonplace.

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The Holy Grail of any food safety program for raw food is a “kill-step” that eliminates pathogens in the food product without negatively impacting the functional and organoleptic properties of the food. Perhaps the best example of success in this area is pasteurized milk. With the exception of a relatively small group of raw food consumers, pasteurized milk has been very well accepted by the public. United States Department of Agriculture Agricultural Research Service scientists have developed a process for pasteurization of shell eggs that may make pasteurized eggs a lot more commonplace.

Pasteurization of eggs

It takes a higher temperature to kill or inactivate Salmonella in egg yolk than in albumen (see sidebar). The functional properties of albumen are negatively impacted at lower temperatures than for egg yolk. These facts complicate the puzzle of how to pasteurize eggs still in the shell, particularly since the yolk is in the middle of the egg, and most heating methods rely on transfer of heat from the outside into the center of the egg.
Existing patents for pasteurizing eggs in the shell utilize a heated water bath for immersion of the eggs for approximately one hour. Radio frequency energy is used in the food processing industry for heating, baking and drying, and it provides a means of transmitting energy to the middle of the egg.

Dr. David Geveke, lead scientist, USDA Agricultural Research Service, said that he has been working with radio frequency heating for approximately 15 years. The process, which Agricultural Research Service scientists have applied for patent protection, uses penetrating radio frequency energy passing between electrodes on either side of an egg to quickly heat the yolk while the egg is rotated and cool water is streamed on the shell. This initiates pasteurization of the yolk while maintaining a low temperature in the heat-sensitive albumen (see photo). Immediately after the radio frequency heating process, the egg is placed in hot water to pasteurize the albumen and to complete pasteurization of the yolk.

Saving time

The current process for pasteurizing shell eggs—immersing eggs in a water bath at a temperature that is low enough not to affect the functional properties of the egg white—means that you need a relatively long dwell time. It takes approximately 20 minutes to get the yolk up to the temperature that will start inactivating the Salmonella, and then you need to hold this temperature for approximately 35 more minutes. When asked how long the Agricultural Research Service process would take to pasteurize a shell egg, Geveke said, “It takes less than half the time of the current process. We are making inroads in making it faster. Physically, it could be about two minutes, similar to pasteurization of liquid egg products, but realistically it is not going to be that quick.” He explained that the process would have to be almost perfect to do the heating that fast without damaging the egg white.

Geveke said that the way the prototype is designed now the eggs are sized and run in batches by size. He said that the equipment could be modified to be adjustable based on information given to it regarding the specific size of an individual egg.

Developing a market

The goal, said Geveke, is to make pasteurized eggs virtually indistinguishable from fresh unpasteurized eggs. He envisions pasteurized shell eggs developing a growing niche market for at risk consumers. One could also envision pasteurization developing a market in eggs produced in higher-risk environments like free-range or cage-free. Geveke said that the Agricultural Research Service is looking for a Cooperative Research and Developments partner or licensee that has the experience in radio frequency technology or in egg processing technology to commercialize this process, and he can be contacted at [email protected].

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