Preventing Salmonella in eggs using new technologies September 2010

In the midst of a massive recall of about 550 million shell eggs in the United States due to Salmonella contamination, it is obvious that the industry needs to find ways to prevent future occurrences. Here are three methods that have been in the news lately that may pose a solution for preventing Salmonella occurrence in eggs.


Cooling

Kevin Keener, a Purdue University food scientist, believes the poultry industry could implement a rapid egg cooling technology to reduce future outbreaks. He believes that the quick cooling of eggs after they are laid would significantly reduce the ability of Salmonella to grow inside eggs. While there are no federal guidelines for how quickly eggs should be cooled, 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 2–5 min.

Egg Cooling

Purdue Agricultural Communication photo/Keith Robinson

Keener said U.S. Food and Drug Administration studies show that if eggs were cooled and stored at 45°F or less within 12 hr of laying, there would be an estimated 78% fewer Salmonella illnesses from eggs in the United States each year.

The 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 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.


Heating

A study published in Poultry Science shows that using directional microwaves on shell eggs for 20 sec resulted in a 2-log reduction of Salmonella without causing any detrimental effects to quality. The researchers obtained 12 grade AA eggs (6 brown and 6 white) from a local grocery store and inoculated them with two different doses—1 high dose (105 cfu/mL) to measure actual log reductions and a low dose (102 cfu/mL)—to observe Salmonella presence by mimicking conditions that would be observed in naturally contaminated eggs.

A 2-log reduction would be appropriate to eliminate Salmonella Enteritidis in most naturally contaminated eggs; however, additional studies are required to achieve a 3- to 4-log reduction. The researchers concluded that directional microwaves can be used to reduce Salmonella Enteritidis in shell eggs; however, quality and nutritional parameters need to be examined to determine any detrimental changes that may occur due to the treatment. Future studies regarding this innovative technology will include quality and nutritional parameters.


Vaccine

According to the Associated Press, low-cost vaccines may help prevent the kind of Salmonella outbreak that has led to the recall of more than a half-billion eggs. The problem is that the vaccines aren’t required in the United States, although in Great Britain, officials say vaccinations have given them the safest egg supply in Europe. A survey conducted by the European Food Safety Agency in 2009 found about 1% of British flocks had Salmonella compared to about 60–70% of flocks elsewhere in Europe, said Amanda Cryer, spokeswoman for the British Egg Information Service.

Since Britain’s vaccinations began, the only Salmonella outbreaks in eggs have been linked to those imported from elsewhere in the European Union, Cryer said. Overall Salmonella cases in the country dropped by half within three years.

The U.S. Food and Drug Administration said in July that it doesn’t believe mandatory vaccination is necessary, but it supports farmers doing it voluntarily. Data on the vaccine’s effectiveness in field trials conducted in real-world conditions “was insufficient to support a mandatory vaccination requirement,” the agency said in the text of new rules requiring increased inspections and testing of eggs. “If individual producers have identified vaccines that are effective for particular farms, FDA encourages the use of vaccine as an additional preventative measure,” the agency said.


Increase FDA authority

While all three of these methods might help lower occurrences of Salmonella in eggs, it is vital for the industry and the FDA to step back and look at the bigger issue at hand—the need for improved food safety legislation. FDA Chief Margaret Hamburg said Aug. 23 that the agency is limited by law to a mostly reactive stance on food safety and argued that it needs a more “preventive approach.” In addition, she urged Congress to pass pending legislation that would provide her agency with greater enforcement power, including new authority over imported food.

“We need better abilities and authorities to put in place these preventive controls and hold companies accountable,” Hamburg said as she discussed the recall of roughly a half-billion eggs from two Iowa egg distributors.


References

Purdue egg cooling press release

Poultry Science abstract

AP article

NPR article