That dark, nearly black area in the middle of your tuna or swordfish steak is nothing bad or unhealthy, although you may not like its strong flavor. It is a muscle that is rich in myoglobin, a blood pigment.
Myoglobin changes color, however, depending among other things on how much oxygen is available to it. The dark, purplish red color of freshly cut tuna is due to deoxymyoglobin, which in air changes first to bright red oxymyoglobin and then to brown metmyoglobin.
Overall, light tuna is considered to be slightly healthier than white tuna, and certainly more budget-friendly.
Tuna dark meat color will depend on the amount of hemoglobin and myoglobin contained inside the meat muscle. The darker the tuna meat is, meaning they have more hemoglobin and myoglobin inside while the lighter the tuna meat is, meaning they have less hemoglobin and myoglobin inside.
According to Ty Mahler, co-founder of Sushirrito, fresh, premium-grade tuna will show a deeper red color and often have a softer, more buttery texture.
Customers erroneously think all brownish-looking fish is old or bad, and will pay more for "fresher looking" fish. So in the 1990s, the FDA allowed companies to gas the tuna and keep it artificially bright red for long stretches at a time. "There's nothing wrong with a hot chocolate looking tuna loin," says Gomes.
The tuna should be bright red, shiny, and translucent. The core and tail sample should have this color. The bloodline from the samples should be a darker red than the meat.
This doesn't mean the tuna is going bad, but just that its meat is losing its red pigmentation. When you want to buy natural tuna yellowfin tuna fish, make sure it is carbon monoxide free. The tuna might look less red, or may get darker in color once stored in your freezer, but it will be healthy and of better quality.
If whole fish soon after capture are knocked against a hard surface, bruising of the flesh can occur in the form of a dark coloured patch in the fillet; this is caused by rupture of fine blood vessels in the flesh with consequent release of blood which does not drain away during gutting and icing.
Fish dark meat is the same thing as chicken dark meat: tougher muscles used continuously for support and locomotion (as opposed to white meat muscle, which is only used for short bursts of activity). Sure, the taste is a bit stronger, so we understand separating the dark from light meat (ie the loin).
For tuna varieties, skipjack earns the Best Choice label from the FDA, while yellowfin and albacore receive the Good Choice label. The FDA suggests avoiding bigeye tuna, which has the highest levels of mercury. Before consuming canned tuna, it is best to consult with your doctor if you have any questions or concerns.
Yellowfin tuna are torpedo-shaped with dark metallic blue backs, yellow sides, and a silver belly. They have very long anal and dorsal fins and finlets that are bright yellow. Yellowfin can live up to six or seven years. They are highly migratory and are found throughout the Pacific, Atlantic and Indian Oceans.
In 2019, a Japanese sushi tycoon named Kiyoshi Kimura made headlines by shelling out a staggering $3.1 million for a colossal bluefin tuna weighing 612 pounds. This extravagant purchase cemented its status as the world's most expensive tuna.
When canning tuna at home, however, you'll notice that on any fresh tuna steak, there will be a section of flesh that's much darker. Rich in myoglobin, a blood pigment, this part of the tuna is quite edible and highly nutritious, according to Sweetish Hill, but it has a strong flavor that some diners might not like.
Because tuna steaks get dry and chewy when overcooked, the center should still be pink when it's done cooking.
During cooking, fish myoglobins denature and turn gray-brown at around the same temperature as beef myoglobin, between 140 and 160°F/60 and 70°C. Like all fish, however, the connective tissues in tuna are much easier to break down by cooking than those of beef.
Fish do not need light at night. A period of darkness is necessary for the fish to sleep. Also, leaving the lights on all night could cause algae to rapidly grow and take over your aquarium.
Dark meat fish range in taste from the clean flavor of Norwegian salmon to the almost nutty flavor of red snapper. These filling fish make an excellent entrée.
"And while dark meat does also contain double the amount of less protective, saturated fat, it's also packed with micronutrients that play important roles in the metabolism of protein, carbs and fat. Overall, white meat is actually less nutrient dense than dark meat."
Tuna meat is red, but the shade of red is what dictates its color score, the deeper the red and the more translucent the meat, the higher the quality (this is often referred to as color and clarity).. Texture - the finer the better. #1 grade tuna should have a fine and smooth texture, it should not be coarse or grainy.
Canned Tuna or Salmon
Will stay fresh after opening for 1 to 2 days in the refrigerator. Transfer opened canned fish to a sealed glass container or plastic bag.
Carbon monoxide treated fish, (aka tasteless smoke, filtered wood smoke, CO treated) refers to a process by which tuna loins are treated with the gas to prevent oxidation and thereby alter the cosmetic appearance of the meat.
Fresh tuna, depending on its fat content, ranges in color from pale pink to deep red. (The more fat, the lighter the color.) Tuna tends to oxidize quickly, which cause it to turn an unappetizing grey or brown.
An off smell is a sure sign it's not safe to eat. Color has changed. Usually, canned tuna is between light brown and light pink, sometimes has a bit of a reddish hue. If it's dark brown or even black, it's no good.