Salmonella in eggs problem cracked through radio frequency technique

04-Sep-2013 - Last updated on 10-Sep-2013 at 11:32 GMT

Christopher Brunkhorst displays an egg while a computer image simulates the levels of radio frequency power that different parts of an egg absorbed during an experiment. Photo: Elle Starkman, PPPL Office of Communications

A novel technique for rapidly pasteurizing eggs in the shell without damaging the egg white could reduce salmonella, according to researchers.

The method uses radio frequency (RF) energy to transmit heat through the shell and into the yolk while the egg rotates, said Princeton Plasma Physics Laboratory (PPPL) and the US Department of Agriculture (USDA).

Streams of cool water simultaneously flow over the egg to protect the white and then the egg is bathed in hot water to pasteurize the white and finish pasteurizing the yolk.

It works by ohmic heating, in which the RF energy creates an electric current that produces heat inside the egg.

The goal is to reach a certain temperature for a certain time and then researchers take a sample of the egg and do a bacteria count.

Patent application

USDA has applied to patent the technology which couples RF energy through the shell by placing electrodes against opposite sides of the egg, which rests on rollers that turn it to distribute the heat and cooling water evenly.

Food-processing firms use a similar system for heating, baking and drying a wide range of products.

USDA estimates that pasteurizing all US-produced shell eggs could reduce the number of egg-borne salmonella illnesses by up to 85% or more than 110,000 cases a year.

Complicating the process is that the egg white is more sensitive to overheating than the yolk but the RF energy must pass through the white in order to reach the yolk, which requires a higher temperature to pasteurize.

Pasteurized egg properties

The aim is to produce a pasteurized egg that is "hardly discernible from a fresh, nonpasteurized egg," said David Geveke, lead scientist, at the USDA Agricultural Research Service in Wyndmoor, Pennsylvania.

The prototype, which is roughly the size of a shoebox, can pasteurize shell eggs in about one-third of the time of current methods, Geveke said. Currently, eggs are placed in heated water for about an hour which visibly changes the appearance of the egg white.

While only a small fraction of shell eggs may harbor salmonella, the public health risk posed by raw or undercooked eggs stems from the millions of eggs eaten daily, said the researchers.

Geveke’s team partnered with PPPL engineer Christopher Brunkhorst, an expert in RF heating, to develop the device.

"You have to raise the temperature high enough to kill bacteria, but not high enough to cook the egg," Brunkhorst said. "You're really threading the needle on this."

USDA is seeking a licensee to commercialize the product and Geveke added that they have received interest from industry and expect to have a partner within the next few months.