Egg Cooling Would Lessen Salmonella Illnesses, Scientist Says
September 21, 2010
People across the country were sickened by outbreak of salmonella poisoning in August, which was preliminarily linked to eggs from Iowa producers. One Purdue University food scientist believes the poultry industry could implement a rapid egg cooling technology to reduce future outbreaks.
Kevin Keener, an associate professor of food science, says quick cooling of eggs after they are laid would significantly reduce the ability of salmonella to grow inside eggs - and potentially keep consumers from getting sick.
No federal guidelines currently exist for how quickly eggs should be cooled, but industry standard procedures can mean that it takes as long as six days to cool eggs to 45°F (7°C), the temperature at which salmonella can no longer grow. Keener's rapid-cooling technology would take two to five minutes.
Keener says eggs can be more than 100°F (38°C) after washing and packaging in cartons. Thirty dozen eggs are then packed in a case, and 30 cases are stacked onto pallets, and then placed in refrigerated coolers. The eggs in the middle of the pallet can take up to 142 hours to cool to 45°F. Scientists estimate that one in about every 20,000 eggs has salmonella naturally inside, Keener notes.
"The eggs in the middle of a pallet may take up to six days to cool, and if the one in 20,000 that has salmonella is in the middle, the bacteria will grow," Keener says. "In reality, some eggs don't cool to 45°F until they're in the refrigerator in your home."
Keener said Food and Drug Administration studies show that if eggs were cooled and stored at 45°F or less within 12 hours of laying, there would be an estimated 78 percent fewer salmonella illnesses from eggs in the United States each year.
Keener's cooling technology uses carbon dioxide "snow" to rapidly lower the eggs' temperature. Eggs are placed in a cooling chamber and carbon dioxide gas at about -110°F (-78.8°C) is generated. The cold gas is circulated around the eggs and forms a thin layer of ice inside the eggshell. After treatment, the ice layer melts and quickly lowers an egg's internal temperature to below 45°F. The eggshell does not crack during this process because the shell can resist expansion from a thin ice layer.
Previous studies have shown the cooling treatment would increase shelf life by four weeks.
The potential benefits are attracting attention from poultry producers. Paul Brennan, executive vice president of the Purdue-based Indiana State Poultry Association, said so long as it did not negatively impact egg quality or producers, he would be intrigued by Keener's cooling technology.
"Our industry is good at adopting practical solutions," Brennan says. "If there is a technology that we could adopt to address an issue and it was cost effective, I'm sure we would embrace it."
Keener has a prototype of his rapid-cooling technology in his Purdue laboratory and is working to optimize its function.