Tuna, a widely consumed and prized fish, is a staple in diets around the globe. Many people recognize tuna meat by its distinctive reddish hue, often seen in sushi or seared steaks. However, tuna meat is not uniformly one color; its appearance can vary significantly, ranging from deep red to light pink, and even to an almost white shade. This variation depends on the tuna species, its biology, and how it is handled after being caught.
The Diverse Colors of Tuna Meat
Bluefin tuna is renowned for its deep, vibrant red meat, highly sought after for sushi and sashimi due to its rich flavor and texture. Yellowfin tuna also displays a bright to darker red flesh in its raw state.
In contrast, Albacore tuna, often marketed as “white tuna,” has a much lighter, almost white or pale pink flesh. While canned Albacore is typically light, natural variations can occur, sometimes appearing light pink, beige, or tan.
Scientific Reasons Behind Tuna’s Hue
The primary determinant of tuna’s meat color is a protein called myoglobin, found in muscle tissue. Myoglobin binds and stores oxygen within muscle cells, and its concentration directly influences how red the meat appears. Highly active fish, like many tuna species that are continuous swimmers, have muscles rich in myoglobin to support their sustained activity, resulting in darker red meat.
The specific tuna species also plays a significant role in myoglobin levels; bluefin tuna, known for its deep red color, has a very high myoglobin content. While myoglobin is the main factor, diet can also contribute to certain hues, though to a lesser extent than for fish like salmon. Some marine organisms, like crustaceans, contain carotenoids such as astaxanthin, which can impart reddish or pinkish pigments if consumed.
Color Changes and What They Mean
Tuna meat undergoes various color changes after being caught, which can indicate its freshness and quality. When raw tuna is exposed to air, the myoglobin in its flesh reacts with oxygen, a process called oxidation. This oxidation can cause the bright red oxymyoglobin to transform into metmyoglobin, which has a brown or grey color, signaling a loss of freshness. Consumers often associate this browning with spoilage, even though the meat might still be safe to eat.
Cooking also dramatically alters tuna’s color due to protein denaturation. As tuna cooks, its red or pink flesh turns opaque white or grey, similar to other meats. This is a natural consequence of heat changing the structure of the myoglobin and other proteins. While some processing methods, like carbon monoxide treatment, can artificially maintain a bright red color in raw tuna, this practice is banned in some regions because it can mask signs of spoilage. Therefore, understanding these natural color transformations helps consumers assess the true condition and safety of tuna meat.