Chemistry in the Kitchen


Why would anyone add carbon monoxide to tuna?

Cutting a tuna fish exposes many muscle cells to oxygen, which slowly changes the bright red color of fresh tuna steaks to a darker brown. This is the result of iron-containing enzymes (myoglobin and hemoglobin) being oxidized from Fe(II) to Fe(III). Sushi lovers have come to understand that fresh raw tuna should be bright red and are skeptical of eating any brown-colored fish. The seafood industry figured out at some point that adding CO during the packaging step not only slows the rate of oxidation down, which increases shelf life, but also brightens the red color. It does this because CO binds more strongly to the Fe(II) center than Fe(III). The risk to consumers is not CO exposure here, but that you might be fooled into eating fish that isn’t as fresh as you might otherwise think if you judge its freshness based on color.


This is a web preview of the "The Handy Chemistry Answer Book" app. Many features only work on your mobile device. If you like what you see, we hope you will consider buying. Get the App