Hi everyone!
As I have said in a previous question, I plan to analyse some nutritional parameters en pepper fruits, among them the vitamin C content.
I am a beginner in this research field and, when I started my project (two months ago), I considered it was right to freeze them at -20 °C until further analysis (previously I had kept them refrigerated at 3 °C for one to two weeks). I assumed that refrigeration and freezing would prevent the loss of vitamin C.
Nevertheless, I later found out that vitamin C loss can happen even in frozen samples (see e.g. Spínola et al., 2014, who tell about an average loss of 50% of vitamin C content during the freezing time). It concerns me that this circumstance could affect to our project. Here in Spain winter is coming and we will not be able to have more pepper fruits until next year.
Therefore, I would like to know if there is some method (e.g. an spectrophotometric method) that will allow us to mesure the levels both of ascorbic acid and of dehydroascorbic acid in samples. I would also like to know if oxidation of dehydroascorbic acid to 2,3-diketogluconic acid may have been large enough as to decrease significantly the level of vitamin C, both in oxidazed and non-oxidazed form (i.e. dehydroascorbic acid and L-ascorbic acid).
Thanks in advance!
Pablo
Literature cited:
Spínola, V.; Llorent-Martínez, E.J.; Castilho, P.C. (2006). Determination of vitamin C in tropical fruits: A comparative evaluation of methods. Journal of Chromatography A 1369: 2–17.
When pepper stored at 20 degree centigrade the after 2 days its vitamin C decrease. If we store at - 20 or - 40 then we can measure its contents but in reduced quantities as compared to fresh
Why not, if you state that they were frozen at the reported conditions. Frozen (and chopped) peppers are used for cooking commercially and at home. However, they cannot be reported as fresh. Cooking will further deteriorate vitamin C.