Food Science
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I'm doing my A2 investigation on the effect of heat and increased oxygen exposure on the concentration of Vitamin C in different orange juices. I'm really confused about the role of enzymes in this process. Some people have told me that ascorbic acid oxidase is present, but some have said that the reason the rate of oxidation increases in warm temperatures is simply related to kinetics. I'm just wondering if you can shed some light?!
210208
Corrie writes ......
Here's part of an answer to an earlier question on orange juice by our biochemistry expert (who is away at the moment):
Vitamin C (ascorbic acid) can be oxidised by oxygen in the air to form dehydroascorbic acid. Look for standard diagrams of these two structures (You can find them in the answer to Q.5 on our new list of 'Sorted FAQs on Vitamin C Investigations' - follow the 'Practical Investigations' link on the Re:act Homepage).
At room temperature and in the absence of enzyme catalysts, this process is fairly slow, and vitamin C can be regarded as being fairly stable, especially in acidic conditions, which is how it is found in most fruit.
However, the redox process above rapidly accelerates in the presence of the enzyme ascorbic acid oxidase, and, as I have described in a previous answer, fruit damage causes the plant cells to rupture allowing this enzyme to mix freely with the fruit juice. So, as a result, the concentration of vitamin C falls fairly rapidly.
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updated: 21 February 2008
