ORLANDO, Fla. -- Central Florida grocery stores are selling ground beef with an invisible extra that may be fooling unsuspecting shoppers, according to a Problem Solvers investigation.

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The controversial ingredient is not listed on the label but popular Central Florida stores are selling it.

Local 6 News reported that the "extra" is called modified atmosphere, which is a mixture of nitrogen, carbon dioxide and a small amount of carbon monoxide.

"The carbon monoxide enhances the red pigment giving the beef 'shelf appeal,'" Local 6 reporter Mike Holfeld said.

Dr. Hordu Kristinsson of the University of Florida co-authored a book on modified atmosphere and was featured in the report.

His research showed that the meat is perfectly safe but he admitted that what you see might not be what you get, Holfeld said.

"I can say this, that you could buy beef that still looks red but could be spoiled," Kristinsson said.

"What's the intent of putting this stuff?" Holfeld asked.

"Mainly, prolong the red color," Kristinsson said.

"You're prolonging the look?" Holfeld said.

"You're prolonging the look," Kristinsson said.

"So, it appears fresh?" Holfeld said.

"Yes," Kristinsson said.

Local 6 News showed video of case-ready beef packaged with carbon monoxide inoculated with salmonella and then showed that it looked OK eight days later.

The report then showed video of beef not packaged with carbon monoxide that looked brown.

Both the United States Department of Agriculture and the Food and Drug Administration said the process is "generally regarded as safe," Holfeld said.

Still, supermarkets such as Publix have rejected the modified atmosphere products.

A Publix spokeswoman told Local 6 News, "Because we adhere to strict quality standards, we will never sell modified atmospheric case-ready beef. Our beef is ground fresh daily."

In Chicago, the City Council is considering a resolution that would ban the sale of case-ready beef packed in carbon monoxide.

The report also showed ground beef purchased in the middle of March with a sell-by date of March 30. Nearly a month later, the beef was still cherry red, Local 6 News reported.

A representative for Target stores told Local 6 News that the beef was safe.

"Target has high food-quality standards," the representative said. "Meat packaged in this manner is manufactured in USDA-inspected facilities."

The Local 6 News investigation has already caught the attention of Orange County officials.

Commissioner Linda Stewart has asked key county staff to review the Chicago ordinance and the possibility of action in Orange County.

The commissioner co-hosted a community meeting with Local 6 on this very issue, Holfeld said.

Click here to see the Chicago ordinance.

Watch Local 6 News for more on this story.