Are you a fan of canned tuna?
Do you ever wonder why your tuna sometimes looks a little different than usual?
Maybe it’s turned orange or has dark streaks running through it.
Don’t worry, you’re not alone.
In this article, we’ll explore the reasons behind these color changes and what they mean for the safety and quality of your canned tuna.
So, grab a can of your favorite tuna and let’s dive in!
Why Is My Canned Tuna Orange?
Have you ever opened a can of tuna and noticed that the meat has turned orange? This can be a cause for concern, but it’s not always a sign that the tuna has gone bad.
One reason for this color change is due to the cooking process. If the liquid in the can is not sufficient to cover the top of the tuna, it can become scorched during cooking, causing the fish to turn orange in color. Additionally, if the tuna is overcooked or left in the sun or a hot car, it can also turn orange.
But what if the tuna meat appears to be orange even before cooking? This is actually a natural color variance for albacore tuna. It occurs when there is a higher concentration of sugar in the meat, which becomes caramelized when cooked.
So, if your canned tuna is orange in color, don’t immediately assume that it’s gone bad. Check for other signs of spoilage, such as discoloration or an off smell.
The Role Of Processing In Tuna Color
The color of tuna meat is primarily due to the presence of myoglobin, an oxygen-binding protein similar to hemoglobin. When tuna is freshly caught, the attractive red oxy-myoglobin dominates, but it degrades during storage to ultimately form brown metmyoglobin. Therefore, key management practices in tuna diets, fishing, farm husbandry, and processing have the potential to optimize flesh color and consistency.
Freezing processing technology is one of the main methods used in aquatic products processing at home and abroad to prevent the quality of fresh fish from declining rapidly after capture and prolong the shelf life of fish aquatic products. In order to eat tuna as sashimi, frozen processing is considered the best method. However, in tuna frozen storage, due to the oxidation of hemoglobin and myoglobin, the red browning of the original fish meat makes people feel stale. Therefore, there are many studies on the color change of tuna frozen products.
Researchers have taken the back muscle of yellowfin tuna as the research object and measured the effects of different frozen storage temperatures on muscle color (a* value), the content of ferrimyoglobin, and fat oxidation. The results showed that a* value of muscle changed significantly at different freezing temperatures. The lower the freezing temperature, the smaller the changes of a* value and lipid oxidation value, and the less the amount of myoglobin oxidized to methemoglobin. Therefore, in order to keep tuna meat color from browning, the lower the refrigeration temperature, the longer the storage time.
Furthermore, researchers have studied the preservation effect of tea polyphenols on tuna meat under freezing storage at -18°C. The results showed that when tuna muscle was treated with 6g/L tea polyphenol preservative solution, the freshness index of the first grade could still be reached on the 30th day, and the shelf life of second-grade freshness was prolonged at least 15 days compared with the compared group.
Another method used in processing tuna is carbon monoxide treatment. This method injects carbon monoxide into cut tuna meat to counteract oxidation and prevent it from turning brown in color. However, this method has been banned in some countries due to safety concerns related to salmonella outbreaks.
Lastly, high-pressure processing can impact the appearance of tuna flesh. The higher pressure applied during processing can cause fading in color and opaqueness. Therefore, a critical pressure for acceptable visual properties after pressurizing tuna flesh is 300 MPa for 5 minutes.
Natural Pigments In Tuna
Tuna is also known for its natural pigments, specifically myoglobin. Myoglobin is a blood pigment that is similar to the iron-containing pigment found in red meat. It is responsible for giving tuna its reddish-pink color, which can sometimes appear orange when cooked or canned.
However, myoglobin is not the only pigment found in tuna. Carotenoids, which are organic pigments found in plants and animals, can also be present in tuna. These carotenoids are often converted by marine animals into more active and beneficial forms through metabolic processes. For example, some marine invertebrates convert β-carotene to astaxanthin, which acts as an antioxidant and prevents oxidative stress.
It’s important to note that the presence of carotenoids in tuna can vary depending on the species and their diet. Albacore tuna, for example, has been found to have higher levels of carotenoids due to their diet of smaller fish and plankton. This can contribute to the orange color of the meat even before cooking or canning.
The Effect Of Light And Oxygen On Tuna Color
Another factor that can affect the color of tuna is exposure to light and oxygen. Tuna flesh contains myoglobin, a protein responsible for storing oxygen in the muscles. When myoglobin is exposed to oxygen, it forms a bright red pigment called oxy-myoglobin, which gives the tuna its characteristic red color. However, over time, oxy-myoglobin can break down and turn into a brown pigment called metmyoglobin, which causes the tuna to appear brown or gray.
To prevent this color change, tuna should be stored in airtight containers and kept away from light. Exposure to light can cause the breakdown of oxy-myoglobin into metmyoglobin even faster. Additionally, storing tuna at lower temperatures can slow down the breakdown of myoglobin and help maintain its red color.
It’s important to note that while the color change may affect the appearance of the tuna, it does not necessarily indicate spoilage or a loss of nutritional value. However, if the tuna has a strong odor or slimy texture, it should not be consumed.
How To Tell If Your Canned Tuna Is Safe To Eat
Canned tuna is a pantry staple for many households, but it’s important to know how to tell if it’s safe to eat. Here are some tips to ensure that your canned tuna is still good:
1. Check the expiration date: Always check the expiration date on the can before opening it. If it has expired, it’s best to dispose of it.
2. Look for leaks or damages: If the can is leaking or has any damages, it’s best to throw it away. This can be a sign that the tuna has been exposed to air and bacteria, which can cause spoilage.
3. Smell it: When you open the can, take a whiff of the tuna. It should have a meaty smell with hints of the ocean. If it smells off or acidic, this is a sign that the tuna is spoiled and should be thrown away.
4. Check for discoloration: Normal canned tuna can be anything from pale pink to beige, to bright red in color and may have a slight brown tint to it. However, if it has dark brown streaks running through it or is green in color, this is a sign that the tuna is spoiled and should be disposed of immediately.
5. Taste it: If you’re still unsure if your canned tuna is safe to eat after checking for all the above signs, you can take a small bite and see how it tastes. If the tuna has an off taste or tastes acidic, spit it out straight away and throw the fish out.
Tips For Storing Canned Tuna To Maintain Quality
When it comes to storing canned tuna, there are a few things to keep in mind to ensure that it maintains its quality and freshness. Here are some tips to follow:
1. Check the can for any damage: Before purchasing or storing canned tuna, always check the can for any signs of damage. Look for bulges, rust spots, dents, tears, or openings in the can. These may be signs that the tuna is spoiled and should not be consumed.
2. Store in a cool, dry place: Canned tuna should be stored in a cool, dry place such as a kitchen pantry or cupboard. Make sure to keep it away from hot water pipes and appliances that give off heat when in use, such as the stove, refrigerator, and dishwasher.
3. Keep it off the floor: To prevent the can from rusting, make sure to keep canned tuna off the floor. Do not store heavier items on top of cans of tuna to prevent them from being crushed.
4. Store newer cans behind older ones: To ensure that you use older canned tuna first, store newer cans behind older ones.
5. Refrigerate leftover canned tuna: Once opened, transfer leftover canned tuna to a tightly covered glass or plastic container and refrigerate it immediately. Do not leave the tuna in the opened can, as it may become rusty once open. You can refrigerate canned tuna in a tightly covered container for up to two days.
6. Use by expiration date: Always use canned tuna by the expiration date on the can. If the can doesn’t have a “best by” date, mark it with the date of purchase and use the tuna within 12 to 24 months of purchase.
By following these tips, you can ensure that your canned tuna stays fresh and maintains its quality and flavor for as long as possible.
