If you’ve heard that ground beef packaging is pumped with gases like nitrogen — well, it’s true, but it’s also not something to be worried about. This process is sometimes called “modified atmosphere packaging,” and it works to maintain the red color of ground beef. Oxygen makes meat change color, becoming more brown or gray within a couple of days of exposure. Packaging full of nitrogen gets rid of the chemical element, helping the meat stay red.
It’s not just nitrogen that gets added to ground beef packaging: Carbon dioxide and carbon monoxide are also usually in the mix. This combination of gases can keep beef looking an appetizing red color for around two weeks (and maybe more). This trick doesn’t just work for ground beef, either — it’s also used on other beef products (like steak and non-ground cuts), as well as other red meats like lamb. The FDA and USDA approves of these uses of gases in meat packaging, although they may not be listed on the ingredients list because they’re not part of the actual meat per se.
https://www.chowhound.com/1596282/why-ground-beef-contains-nitrogen/