August 30, 2010
US researcher suggests rapid egg cooling system to tackle salmonella
Amid recent salmonella outbreaks in eggs, a 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, said quick cooling of eggs after they are laid would significantly reduce the ability of salmonella to grow inside eggs.
There are no federal guidelines for how quickly eggs should be cooled, but current industry procedures can take as long as six days to cool eggs to 45°F, the temperature at which salmonella can no longer grow. Keener's rapid-cooling technology would take two to five minutes.
He said eggs can be more than 100°F after washing and packaging in cartons. Thirty dozen eggs are then packed in a case, and 30 cases are stacked onto pallets and placed in refrigerated coolers. The eggs in the middle of the pallet can take up to 142 hours to cool to 45°F. He said scientists estimate that one in about every 20,000 eggs has salmonella naturally inside.
"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 said.
He noted Food and Drug Administration studies showed that if eggs were cooled and stored at 45° or less within 12 hours of laying, there would be an estimated 78% fewer salmonella illnesses from eggs in the United States each year.
His 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 minus 110° 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°. 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.
Meanwhile, the FDA this month has ordered a recall of hundreds of millions of eggs thought to be contaminated by salmonella. Iowa's Hillendale Farms and Wright County Eggs are thought to be the sources of the salmonella outbreak. Salmonella poisoning can cause fever, diarrhea, nausea, vomiting and abdominal pain. More serious illnesses such as arterial infections, endocarditis and arthritis are possible but rare.