Gassing the Tuna - Unnatural Pink Comes to Dinner

Sushi, sashimi, salad nicoise, carpaccio or lightly seared are all delicious ways to prepare extremely fresh tuna. Many people adorn their beautifully red tuna steaks with exotic ingredients such as fiery wasabi, white truffle oil and sometimes even Hawaiian seaweed. Others enjoy their tuna undressed, finding simplicity in preparation paramount to tuna's gastronomic rewards. Unfortunately a vast majority of tuna lovers are sold fish that has been adulterated, without their knowledge, by Carbon Monoxide (CO) before they ever place it in their grocery carts. CO treated tuna, also known as "tail-pipe tuna" has quietly permeated our local market.

CO is a gas that when added to fish, prevents natural oxidation in the flesh. CO changes the color to an artificial pink, stable pigment called carboxymyoglobin which stays in the fish indefinitely. Cookbooks often use treated tuna in their photographs because the fish does not change color while sitting under hot lights. CO does nothing to improve or preserve fish quality, it merely masks normal decomposition. In tuna, quality and freshness can be easily determined by the process of oxidation. As the fish deteriorates it slowly turns brown. The flesh becomes unappealing to consumers and the fish is thrown away. With CO added to the flesh this natural process is halted. Buyers are purchasing fish that can be past its prime and in many cases rotten, even though the flesh still looks fresh. In fact, many stores are selling this treated fish as sashimi (suitable for eating raw) at extremely low prices. Additionally, treated tuna can pose as a higher grade than it actually is which fraudulently raises the price of the fish. If you encounter bright red tuna that is selling for less than $14 a pound it has most likely been treated. Many countries have banned CO as an additive including Japan, Canada, and the European Union for fear that people would be able to sell rotten fish to unknowing consumers. The Food and Drug Administration has referred to CO treated fish as harmless, however; rotten fish can have adverse health effects in people that are susceptible to histamine producing scombroid fish, like tuna.

Scombrotoxin, a common form of food poisoning accumulates in tuna if the temperature warms to over 40 degrees F. Above 40 degrees, tuna flesh deteriorates rapidly changing color from red to brown. This is an extremely reliable way to tell if tuna has high levels of histamine. CO masks the browning process making it impossible to tell if the fish has produced dangerous levels of toxins. In a particular test 27% of the treated tuna had elevated levels of histamine - 7% of which had levels greater than the FDA's poisonous action level of 500 ppm, ranging up to 2060 ppm.

Tuna treated with CO is present in our local marketplace. Most grocery stores, local fish wholesalers and sushi bars sell CO tuna exclusively. Many restaurants have begun using CO treated fish as well, which is intriguing (and unnecessary) because most tuna preparation in these establishments includes cooking the fish, which turns the fish opaque, negating any aesthetic benefit of bright pink tuna. The FDA does require stores that sell CO treated fish to properly label it as such; however, many of the grocery stores in Minnesota have yet to do so. Neither Coastal Seafoods nor your local food co-op sell CO treated tuna.

Find out if your fish has been treated with CO by asking. Grocery stores and restaurants must provide this information; however, many employees are uninformed about CO treated fish and may not know that they are selling it. Look for fresh tuna that has a deep red color (untreated), not an unnatural bright pink color (treated). And remember bright pink tuna selling for less than $14 a pound has most likely been treated with CO. Remember, freshness, is the single most important factor in ensuring great tasting fish, not color. In nature, the color of tuna varies from fish to fish due to diet, metabolism, oil content and species. Try the many varieties of tuna both raw and cooked and enjoy their subtle differences. Save the treated tuna for food stylists to photograph.