|MadSci Network: Chemistry|
The reason you could not find a simple one temperature to answer your question is that there is no one temperature that will apply to all foods and cooking processes. The destruction of the vitamin is dependent on the food or source of the vitamin. Nature has put many things in the food to protect the food from losing the vitamin. Take for instance an orange. As long as you keep the orange intact with the skin you will keep most of the vitamin. But as the fruit ripens and the cell walls start to break down the vitamin is gradually destroyed. This happens less rapidly if the orange is keep refrigerated. This is partly due to the fact that the cell wall destruction is slowed down, so the two work together. Also another factor is the pH of the food or the source of the vitamin. Vitamin C or Ascorbic Acid is a weak acid and is more stable (not destroyed as rapidly) if it is in this environment. Like the orange. There are many acids in addition to ascorbic acid in the orange. This help to keep the vitamin from being destroyed. Therefore, temperature is only one factor that will result in the destruction of Vitamin C. There are others, like oxidation. After you cut the orange the cut part is now exposed to oxygen. Oxygen causes the destruction of the vitamin C. After a short period of time the vitamin in the orange will be destroyed without any change in temperature. Now let us put them all together into a food. Like oranges. We squeeze the juice from the orange. This starts the destruction of vitamin. We know from research studies that this actually results in a greater loss than the short time high temperature exposure from the pasteurization used by most juice companies. If the juice is exposed to a lower temperature for a long time you will actually destroy more of the vitamin C than if you flash pasteurize short time high temperature. So the temperature is not as important as some of the other factors that you need to control in cooking foods. We know that cooking food in small amounts of water is less destructive to the vitamin than in large amounts because the vitamin is water soluble. So cooking in a microwave for a short time is less destructive than cooking a food in hot water for a long time even though the temperature may be higher in the microwave. One more example: Potatoes are a very good source of vitamin C. But most of our potatoes are eaten as french fries. These potatoes are cooked at a very high temperature. But because they are not in a water solution (FAT) the vitamin is not destroyed as rapidly as if you boiled them in water to have mashed potatoes. In one medium potato that is peeled and boiled you will get about 10 milligrams of vitamin C . If you take this same potato and French Fry it you will receive about 15 milligrams. Vitamins are very interesting. There is a lot more too it than you think. Also if you take the vitamin out of the food source altogether and place it in a vitamin pill the vitamin is very easily destroyed. So if you take vitamin pills and have had a bottle on your counter you may not have any of the vitamin C left in the bottle if it has been there for a long time. If you have any other questions e-mail us again and I will try to answer any other questions you might have.
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