Nov 9, 2026 - Foods
Color manipulation in tuna: CO, nitrite and nitrate in focus
Tuna is considered a high-quality delicacy. Its intense red color signals freshness and quality – a trait that can, however, be deliberately manipulated through the use of carbon monoxide (CO), nitrite (NO2-) and nitrate (NO3-).
A recent market inspection by the Cantonal Laboratory Basel-Stadt shows how widespread this practice can be: four of 16 tuna samples examined were found to be non-compliant due to illegal reddening. Three of these had been treated with both carbon monoxide and nitrite-/nitrate-containing additives.
When treated with CO, the gas binds directly to the red muscle pigment myoglobin. Nitrite and nitrate, by contrast, are first converted into nitric oxide, which also produces a stable red coloration. Ascorbic acid is often used to accelerate this reaction. It can contribute to nitrite in the fish becoming undetectable and can serve as an initial indication of possible nitrite treatment.
In addition to color manipulation, the histamine content of tuna is an important aspect. Because artificial reddening obscures the natural color and thus makes assessment of freshness more difficult, histamine determination takes on particular importance. Elevated levels can indicate a compromised cold chain and can cause health complaints.
In our Tentamus laboratories we perform analyses for nitrite, nitrate, ascorbic acid and histamine.
We provide fast and reliable results and are happy to advise you on all matters relating to product safety. If you have any questions, our customer advisors will be happy to assist you.
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