Chapter 4 Microbial and biochemical changes in food
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For my A2 investigation I need to find some detailed theory on how temperature affects vitamin C. I can't find the theory anywhere. I’m just told that temperature does affect it. Is it possible to tell me how at all? I’m particularly interested with how it affects the vitamin C contained in fruit juices. Thank you.
Igloo writes
I assume that you want to know more about the nature of the chemical process occurring when vitamin C “decomposes”. This “decomposition” is in fact an oxidation process.
I presume that you are carrying out this investigation in conjunction with the Food Science course. If so, you will know that the chemical name for vitamin C is ascorbic acid and that its structure is as shown on page 10 of the Nuffield Chemistry Food Science students' book, i.e.
When ascorbic acid “decomposes”, it is generally undergoing an oxidation process, which in a simplified form can be represented as:
This explains why air is needed for this process to take place.
Now you will already know that a rise in temperature increases the rate of reaction, so obviously the redox process above will occur at a greater rate at higher temperatures.
Incidentally it will also take place at a greater rate in the presence of the enzyme known as “ascorbic acid oxidase” which is also present in fruit and vegetables. When fruit and vegetables are damaged, e.g. by cutting or crushing, then the cell walls become destroyed, the enzyme comes into contact with the ascorbic acid and the redox process takes place very rapidly.
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updated: 11 April 2006
