Vitamin C is the most unstable one. Its content in fresh products and the cooked ones differs a lot. As a result of wrong cooking 95% or more of vitamin C can be lost, i.e. sometimes there is almost nothing left in the end. For example, when you peel potatoes, more than 20% of ascorbic acid is lost. In sauerkraut just 40% of the initial vitamin content is left.
A lot can be lost in the process of cooking especially in alkaline medium and during contact with atmospheric oxygen. That is why it is better to keep your cooking pan closed (to limit the contact with air) and it is advisable to acidify soups, stews and other dishes (depending on compatibility). When food is cooked with the lid closed the amount of vitamin C lost decreases two times compared to cooking in an open pot.
Ascorbic acid also oxidizes in the presence of copper and iron ions. This means that it is better not to cook in iron or copper pots. Vitamin C can also be destroyed by ascorbinase – special enzyme, contained in many plants. They are sometimes called antivitamins. For example, in squash juice 90% of vitamin C is lost in 15 minutes, in cabbage juice – 53%. Antivitamins act in the most intense way in the temperature around 30-50°C and lose their activity during boiling. So, you can block their effect by putting products directly in the boiling water.
Duration of cooking is also very important. For example, when you stew cabbage for 30 minutes, around 35% of ascorbic acid is lost, when you cook it for an hour the loss can amount to 85%. When you boil cabbage in a soup up to 93-95% of vitamin C can be lost. And finally, let’s talk about storage of ready dishes. For example, just 20% of initial vitamin content is left in Shchi soup in 3 hours after it was cooked, and in 6 hours it is just 10% of the initial vitamin content. Stewed cabbage loses 50% of ascorbic acid in one hour. And when you warm up food again, almost everything is lost. Ascorbic acid is also destroyed in fresh salads if they are prepared a long time before eating. This happens mostly under effect of antivitamins, oxygen and sun light. The vitamin is lost unbelievably fast during defrosting (but it is well-preserved in the frozen products).
However, there is a way to preserve vitamins in food (not only vitamin C, but all the others as well) almost completely. This way is very simple, though many people struggle to implement it. Its main idea is to eat many vegetables and fruits raw and cut them, if necessary, only right before putting them in your mouth. However, raw food diet is not always beneficial. Cooking grains and some vegetables often increases their sattvicity, especially when adding a small amount of butter. But often raw food diet does good.
Text: from the book of A Eddar "The treatise of nutrition".