It’s likely you’ve seen it. You take a steak out of the package and you see brown or discolored spots. It is still safe to eat?
As long as the meat was kept cold and is not past its best-by date, most likely, it is safe to eat. If it smells, that indicates temperature abuse and some kind of bacterial growth. If it smells like good meat, it is safe. Cook it using a meat thermometer for best safety.
The color change is due to oxidation. This turns the red meat color to brown. Meat color is controlled by the protein myoglobin. Within myoglobin is iron. When iron loses an electron, the color changes from red to brown. That brown protein is metmyoglobin.
Oxidation occurs in several situations. Those situations include lack of oxygen, storage time, the presence of salts and marinades, freezing, and yes, bacterial growth.