Tuna as a fat burning powerhouse

Tuna has deeper coloured flesh than that of other fish as a result of the high myoglobin - oxygen-binding molecules - in the muscle tissue. This gives the fish meatier flavours than their white fleshed cousins. The colour of the tuna fish varies from pinkish red to deep brown. Prime raw tuna steaks look very much like raw beef, right down to the deep red colour of the flesh.

Not all tuna is the same and the quality of the tuna will dictate its price, particularly when buyers intend to use the tuna for sashimi when grade 1 tuna is absolutely necessary.

The quality, and therefore the price of tuna depends on species, size, core temperature and fishing methods as well as the more subjective, muscle colour, texture, clarity and fat content.

The most discriminating of Japanese sushi bars require tuna with a bright red colour, firm texture, translucency and fat content. As these qualities are hard to come by prices to these buyers are secondary. 

Tuna can be classified in four different grades as follows:

1.              
Tuna that has bright red muscle tissue, is firm in texture, has translucent flesh (clarity) and little or not fat.

2.              Tuna with red muscle tissue, are firm in texture, some translucency and no fat.

3.              Tuna with some red and some brown muscle tissue, is firm in texture, no translucency (opaque) and no fat.

4.              Tuna with brown and gray muscle tissue, soft in texture and no translucency.

Generally speaking Grade 1 tuna is used in higher end sashimi markets, usually the Japanese market, Grade 2 tuna is used in lower end sashimi markets or in high end restaurants when the tuna is prepared semi-cooked, Grade 3 in lower end restaurants and Grade 4 tuna is mostly canned or frozen. The European market uses mainly Grades 2 and 3 tuna.

The colour of lower grade tuna, 4 and even lower grades, known as chocolates can be upgraded using Carbon monoxide (Co), though it is banned in the EU as it is considered an additive.

The best quality tuna depends of a variety of factors including species, size, catch method and time taken to chill the fish, each which will affect the price of the meat sold.

Blue fin tuna is among the best, followed by Bigeye, Yellowfin and Alabacore.

The larger the fish the better the quality of meat.

Fish caught on a longline fetch higher prices than net caught specimens. 

The faster the fish is chilled to 0°C the better the quality of the meat.

Nutritional value

High in Omega-3 fatty acids and low in saturated fat, tuna is an ideal source of protein whilst remaining figure friendly. Tuna, as a protein is packed with tons of minerals including large amounts of iron, magnesium, phosphorus, potassium and selenium just to name a few, with small amounts of magnesium and magnase. With just a total of 2% fat, you can see why tuna is considered a fat burning powerhouse.

However, tuna's story is not all good. High levels of mercury have been associated with tuna, which, if consumed in large enough quantities can cause cognitive impairment and coordination problems.

While fresh tuna has been enjoyed by seacoastal populations throughout history, tuna in other forms of preparation has also been popular. In ancient times, smoked and pickled tuna were widely enjoyed. Today, canned tuna fish is extremely popular throughout the world.

Though tuna is best consumed as soon as it is purchased, if you need to store it, pat it dry, wrap securely in plastic wrap or foil and store in the coldest part of your refrigerator (optimum temperature of 31 degrees F.). If your refrigerator is not that cold, place the wrapped fish on a bed of ice or in a plastic bag filled with ice. Use within 24 hours.

Cooked fish will keep three to four days in the refrigerator. Leftover cooked tuna is excellent as a salad topper. Reheating is not recommended.

Though canned tuna is equally nutritious, it does not compare with the firm, dense, meaty flavours of a fresh tuna steak.

Whole chunks of smoked tuna will last up to ten days in the refrigerator. Be sure it is always kept tightly wrapped.