How does very perishable food like tuna fish last so long in an unopened can without preservatives?
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this idea is pretty much to kill or inactivate all possible sources of spoilage still there after a food-compatible amount of ingredient-cleaning through various conservation agents (heat, ethylene oxide, etc). for canned tuna it’s mainly heat.
The idea is that if there is no sources for spoilage and no residual contaminated gas in contact with the food in the packaging, your food will be stockable for longer without the use of preservatives.
Canned food has been subjected to pasteurization, which kills any food borne illnesses present before canning. The good is put into the can and then sealed, before heating (temperate vary, but are usually under 100C/212F).
off the top of my head there are three main methods of keeping food from spoiling pasteurization, fermentation, and irradiation
Food doesn’t need preservatives unless there’s something in the food that would make it go bad over time. The enemies are basically moisture (although it depends), oxygen, and pathogens.
Putting the tuna in an airtight bag and then sucking out all the air can greatly extend its life. You can buy some tuna that’s vacuum-packed this way.
Another option is canning. The can is airtight, and most of the air inside the can has been replaced with water or oil, and then the cans were heated to kill any pathogens already inside. This cooks the fish, by the way. I used to think I was eating raw tuna when I ate it right out of the can…then I tried sushi.
Being moist organic material, it does still break down and have a limited shelf life, but it’s way longer than it would be if you let it react with air.
The canning process itself is a form of preservation. Canned tuna is cooked and then sealed in an airtight can, which prevents bacteria from getting in and spoiling the food.
Exposure to oxygen is one of the main reasons food goes bad. When canned the food is exposed to very little oxygen and can survive longer
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