Method Aims to Boost Eggs’ Defenses

A specialized cooling system that could strengthen eggs’ natural defenses against Salmonella is edging closer to market, reported the system’s developer, Kevin Keener, PhD, an associate professor of food science at Purdue University.

An enzyme called lysozyme found within eggs helps to defend the whites from bacteria. Freshly laid eggs are saturated with carbon dioxide and have pH levels of about seven. Over time, the pH level rises to nine and carbon dioxide escapes; as that happens, lysozyme activity begins to wear down and, with it, the eggs’ natural resistance to pathogens like Salmonella.

For nearly two decades, Dr. Keener has been working on a system that would cool eggs in the shell, boosting their bacterial resistance. His system uses carbon dioxide to rapidly lower the eggs’ temperature. His findings on a key element of that system were published in the journal Poultry Science in June

(P. Banerjee, K. M. Keener, V. D. Lukito. Influence of carbon dioxide on the activity of chicken egg white lysozyme. Poultry Science, 2011;90(4):889 DOI: 10.3382/ps.2010-00854.).

“We found that both pH levels and carbon dioxide affect the activity of lysozyme,” Dr. Keener said. “Manipulating levels of these two elements had both a combined and an independent effect on the activity of lysozyme.”

Dr. Keener noted that a 2005 risk assessment report for Salmonella in egg products, published by the U.S. Department of Agriculture’s Food Safety Information Service, shows that if eggs were cooled and stored at 45 degrees or less within 12 hours of laying—as they are in this system—the annual incidence of Salmonella illnesses in the U.S. would drop by 100,000 cases. “With rapid cooling of eggs using this process, you can bring the egg back up to the conditions it had right after the chicken laid it, and even extend its shelf life beyond the traditional four-week storage period,” Dr. Keener said.

Dr. Keener said he plans to inoculate eggs with Salmonella to see if the carbon dioxide element of his cooling process has an independent effect that helps to prevent the bacterium from growing beyond just the impact of cooling alone. “We want to identify the mechanism involved, so we can enhance it,” he said.