Canned tuna turns orange primarily because of a natural chemical change in myoglobin, the protein that gives tuna its color. When the iron in myoglobin oxidizes during processing or storage, the flesh shifts from its original pink or red toward orange, amber, or brown tones. This is common and, in most cases, perfectly safe to eat.
Several factors can contribute to that orange hue, from the species of tuna in the can to how it was processed and stored. Here’s what’s actually going on inside your can.
Myoglobin Oxidation Is the Main Cause
Tuna meat gets its color from myoglobin, a pigment protein found in muscle tissue. Fresh tuna contains oxymyoglobin, which gives it a bright reddish color. Over time, the iron atom inside myoglobin oxidizes from a ferrous to a ferric state, creating a form called metmyoglobin. This oxidized form produces brownish and orange tones instead of red or pink.
This process happens naturally during handling, storage, and especially during the high-heat canning process. It’s the same basic chemistry that turns a fresh steak from red to brown when it sits in the fridge. In tuna, the shift often lands somewhere in the orange-to-amber range rather than going straight to brown, depending on how far the oxidation has progressed and what else is in the can.
The Canning Process Itself Changes Color
Commercial canning involves cooking tuna at temperatures between 110°C and 125°C (230°F to 257°F) to kill bacteria and make the product shelf-stable. These temperatures are high enough to trigger something called the Maillard reaction, the same chemical browning that gives toast its golden color or seared meat its crust. In canned tuna, this reaction occurs between naturally present sugars and the amino acids in tuna protein, producing pigments called melanoidins that darken and warm the color of the flesh.
This effect is even more pronounced in canned tuna packed with vegetables, oil, or seasonings. Ingredients like sugar, salt, vinegar, and oil all influence how aggressively the browning reaction proceeds. Even slight differences in processing time or temperature between batches can produce noticeable color variation from one can to the next.
Tuna Species Have Different Natural Colors
Not all canned tuna starts from the same baseline color. The species in your can makes a big difference in what you see when you open it.
- Albacore (white tuna): The palest variety, with flesh that ranges from light pink to beige. When oxidized, it can take on a peach or light orange tone.
- Skipjack: The most commonly canned species (often labeled “chunk light”), with darker pinkish-red flesh that can shift toward deeper orange or brown tones after processing.
- Yellowfin: Has a naturally reddish, somewhat translucent flesh when fresh. After canning, it often develops warm amber or orange hues.
- Tongol (longtail tuna): A lighter-fleshed species sometimes used in canned products, particularly susceptible to myoglobin oxidation during refrigerated or shelf storage.
If your can says “light tuna,” it likely contains skipjack or yellowfin, both of which are more prone to showing orange tones than albacore.
Fat Content Plays a Role
Tuna with higher fat content tends to show warmer, more orange-tinted coloring. Fat interacts with the oxidation process and can itself undergo changes that produce yellowish pigments. If you’ve opened a can of tuna packed in oil, the oil can amplify these warm tones visually, making the flesh look more orange than it would if packed in water. The fat in the tuna itself, which varies by species, season, and the part of the fish used, also contributes. Belly meat, for example, is fattier and often darker or more richly colored than loin meat.
When Orange Tuna Is a Safety Concern
In most cases, orange-tinted canned tuna is a cosmetic issue, not a safety one. But there are signs that something more serious is going on.
Tuna that has decomposed can produce dangerously high levels of histamine, a compound that causes scombroid poisoning. The FDA considers histamine levels above 50 mg per 100 grams of tuna to be unsafe, and actual illness cases typically involve levels near or above 100 mg per 100 grams. You can’t test for histamine at home, but you can use your senses. Tuna that smells sour, peppery, or ammonia-like, has an unusually mushy texture, or shows discoloration alongside an off-putting odor is worth discarding. Scombroid poisoning causes symptoms similar to an allergic reaction: flushing, headache, cramps, and diarrhea, usually within minutes to a couple hours of eating.
A uniform orange or amber color with a normal “tuna” smell and firm texture is almost certainly fine. Patchy discoloration, greenish or grayish spots, or any foul smell is a different story. If the can was bulging, dented at the seam, or hissed loudly when opened, throw it out regardless of color.
How to Minimize Color Changes
You can’t fully prevent the color shift in canned tuna since it happens during manufacturing. But a few things affect how pronounced it becomes after the can reaches your pantry. Storing cans in a cool, dark place slows ongoing oxidation. Cans stored in warm environments, like above a stove or in a garage, will see more color change over time. Using cans well before their expiration date also helps, as the oxidation process continues slowly even inside a sealed can.
If the orange color bothers you, albacore (white) tuna tends to show less dramatic color shifts than chunk light varieties. Tuna packed in water also generally looks lighter than tuna packed in oil, simply because oil amplifies warm tones visually.