Factors affecting ascorbic acid oxidation are investigated in this paper.
In foods containing ascorbic acid, no vitamin C is lost as long as ascorbic acid and dehydroscorbic acid (the molecule formed by the oxidation of ascorbate are dehydroascorbic acid) react with each other. However, dehydroscorbic acid can react more in irreversible reactions. If that happened then we would all be in big trouble.
In general, food manufacturers and consumers do not want vitamin C to be lost before we can consume it and function in our body.
Therefore, food scientists have studied how to control the oxidation of ascorbic acid as well as the decomposition of dehydroscorbic acid. Five influential parameters were found.
1. Oxidation of oxygen and ascorbic acid
In the absence of oxidizer, oxidation of ascorbic acid can be slowed or prevented. In other words, there must be a molecule that receives electrons. Oxygen is known as a very good oxidizer.
In fact, the name “oxidizer” is derived from oxygen, because oxygen was one of the first oxidizers to be discovered.
When ascorbic acid is left open in the open air, which contains oxygen, it is prone to oxidation. Therefore, in the absence of oxygen, oxidation of ascorbic acid occurs less. There may be other oxidants, but removing this important substance will be very effective.
Manufacturers solve this problem by aerating the juice. With water aeration, most of the oxygen is released from the water. After aeration, as little air as possible remains in the bottle. Therefore, they are often filled at a high level.
Keep orange juice in a sealed bottle at home and be sure to close it after use. This limits the amount of oxygen entering the orange juice and the oxidation of ascorbic acid.
2. Metal ions and reduction reactions
Metal ions also work well in co-oxidation and reduction reactions. In the case of ascorbic acid, metal ions can catalyze the reaction. This means that they do not get used to the reaction, but can act as a temporary storage place for electrons.
There is a practical advice in this regard, it is better not to store orange juice in a copper container. Copper ions greatly accelerate the reaction.
3. PH has a great effect on oxidation.
For many reactions, pH affects the reaction rate. This is especially important for reactions involving an acidic or alkaline component.
In the ascorbic acid oxidation reaction, you saw that protons (H +) and electrons (e -) were released. But if ascorbic acid is in a very acidic environment, there are many protons around it. It can slow down the reaction. It has been shown that the reaction takes place faster at pH 4.
At higher pH (more alkaline) or lower (more acidic), the reaction proceeds more slowly. Since the pH of an orange is around 3-4, orange juice is actually a good place for this reaction to occur.
As long as the orange is ripe, it does not react, it is protected from oxygen and light. But when you start slicing and juicing oranges, oxidation happens.
4. Oxidation of light and vitamin C.
It is known that light affects the oxidation rate of vitamin C, such as the oxidation of olive oil.
However, the exact effect of light is complex and its exact mechanism is still unknown. But the general recommendation is to keep the orange juice in a dark place.
5. Temperature and speed of reaction
Temperature determines the movement of molecules in food. The higher the temperature, the more atoms and molecules move around. This causes the molecules to be close to each other and thus react. Therefore, higher temperatures often lead to higher reaction rates. The same is true of the oxidation of vitamin C, as investigated by researchers in strawberry juice.
Millard reaction of vitamin C.
When vitamin C is oxidized, it can show more reactions in different ways. One of them is Millard’s reaction. Millard’s reaction turns many food products brown through a series of complex reactions.
In addition to the Millard reaction, there are several ways that dehydroscorbic acid can react, which are not discussed further in this article. Also, trying to prevent ascorbic acid oxidation is probably a better way than preventing other reactions. Dehydroscorbic acid is simply more stable and probably more difficult to control.
If you do not want to suffer from scurvy, please do not store orange juice and products containing ascorbic acid in a copper container, in a warm place, with plenty of oxygen and in bright sunlight.