Carbon Monoxide-Treated Tuna: Should We Be Eating It?

Raw tuna has seen a huge spike in demand in recent decades. Spurred by the rise in popularity of Japanese-style sushi and sashimi, as well as the growth in demand for poke bowls, global tuna consumption in 2018 reached $11.38 billion and is expected to rise to $13.75 billion by 2023 according to PR Newswire.

Coinciding with the growth in demand for raw tuna is the search for optimal methods to extend tuna’s shelf life. The deep red color of tuna indicates freshness to consumers, and the tuna industry seeks to preserve this color. Buyers of fresh tuna, whether at the sushi restaurants or the supermarket, often look for deep red color which indicates that the fish is top-quality. However, it has become increasingly likely that the fish is bright red because it has been treated with carbon monoxide during processing.

The industry’s use of carbon monoxide (CO) (also known as filtered smoke, wood smoke or tasteless smoke) is used to treat tuna to cease the oxidation process and prevent browning, which permanently alters the color of tuna to bright pink, no matter what the storage temperature or conditions are. This is not a new phenomenon and has been used in the U.S. for decades.

This blog aims to dive into the world of CO-treated tuna, and the potential harmful effects it may cause to consumers. Along with this, explain why Culimer only uses superfrozen technologies as it is the only natural preservation method to maintain the deep red color of tuna.

Why Does Tuna Turn Brown?

From the moment tuna is caught, it begins to deteriorate in quality. Myoglobin is an oxygen-binding protein, found in red blooded mammals which contains iron. Following harvest and storage over a period of time with continued exposure to oxygen, the red color of the meat gradually changes into various shades of brown. This is known as oxidative browning which converts oxymyoglobin (red color) to metmyoglobin (brown pigment). 

This is a natural process, and is considered a quality issue, rather than a food safety issue. However, the brown color of tuna can turn consumers off, which is why the industry has turned to alternative methods, such as CO-treatment to aim to preserve the red color of tuna. 

CO Treatment: Preserving Appearance While Risking Food Safety

Tuna purveyors have a 3–5 day window to retain the tuna’s red color before it turns brown. A commonly used solution is to treat tuna with carbon monoxide, an antioxidant that inhibits lipid oxidation and maintains the red color that consumers value. The carbon monoxide reacts with the muscle pigments to form a very stable complex, carboxymyoglobin. The CO-treatment permanently turns the red tuna to an unnatural, watermelon pink color as a result of this process.

To meet the surge in global demand, the fishing industry has developed an industrial process that involves a complex supply chain, with many players from fishing vessels, processors, transport and storage. The process involves multiple touchpoints, increasing opportunities for mishandling and spoilage. 

This practice of CO-treated tuna meat could mislead consumers into thinking that the tuna is fresher or of higher value than it actually is. The issue is the misuse of carbon monoxide to conceal tuna spoilage, as it only preserves the color of the fish, not the quality and has the potential to deceive consumers.

CO Tuna Treatment: Illegal Elsewhere, Safe in the U.S.?

The Food and Drug Administration (FDA) class CO-treatment of fish as Generally Recognized as Safe (GRAS) and describe the process as harmless. The agency permits its use to preserve the color of fresh tuna, not to enhance brown tuna, and requires retailers to label treated fish, however, most do not comply. Around the world, CO-treatment of fish is illegal, as Japan, Canada, China and the European Union have banned the practice because of fears that it could be used to mask spoiled fish.

In 2003 the European Union unilaterally banned the use of carbon monoxide in both meat and seafood citing that CO may mask visual evidence of spoilage and deceive consumers. This begs the question, if it is illegal elsewhere, why is it common practice in the U.S.? 

Is CO-Treated Tuna Actually Consumer Fraud?

Opinion about CO-treated tuna is divided and highlights the complex issue of consumers trying to make informed decisions about the fish they are buying, when they do not understand the full story.

CO-treated tuna is not by itself unsafe to eat, however the process deprives consumers of visual cues about the freshness of the fish they are buying. Consumers believe the redder the tuna, the fresher the fish. However, they may not be aware that bright pink tuna does not always mean fresh. In some cases, the bright, unnatural-looking watermelon pink indicates the tuna might be illegally treated to conceal malpractice or poorer quality fish.

There are no direct health implications from eating CO-treated tuna. However, CO treatment makes tuna appear to be fresh for longer, despite any temperature or storage abuse. As tuna ages, it becomes more likely to build up toxins such as scombrotoxin or histamine. Some experts believe that anything to intentionally mask the true age of a piece of fish, should be considered a public safety risk. 

SuperFrozen Tuna Treatment: The Right Solution at the Right Time

There is a natural solution to the problem of browning in tuna and that is in superfrozen technologies for tuna. The key to superfrozen  tuna comes from the eutectic point (EP), which is an ultra-low temperature of -76°F (-60°C). This is the temperature at which all chemical and biological activity is halted completely, meaning no degradation can take place.

Unlike conventional freezing, which causes water loss and color change, superfrozen tuna revives to the exact condition it was in before freezing, resulting in a bright, red color and high-quality flavor.

SuperFreezing is already a common practice in Japan, a country known for its obsession with quality and cleanliness, as 80% of all tuna processed in Japan is superfrozen. Japan values the superfreezing process because it maintains consistent, fresh quality without any manipulation.

Conclusion

Those of us who remember the Starkist Tuna commercials look back fondly on the days of “Sorry Charlie.” Today’s tuna is fresher, redder and tastier. However, the use of carbon monoxide to treat tuna during processing to extend shelf life is a process fraught with controversy and potential public safety risks.

Employing CO to manipulate tuna’s signature bright red color can conceal spoiled and contaminated fish while appearing fresh to the consumer. Culimer recommends knowing the source of your tuna to ensure the best quality and choosing for superfrozen tuna.

Culimer never uses any form of manipulation on our tuna and strictly processes and stores all tuna using superfrozen techniques, for fresher than fresh quality, perfect for sushi and sashimi.