Vitamin C (Ascorbic acid) when oxidized will create brown decomposition. But it is used as an antioxidant excipient in pharmaceuticals or an anti-brown substances in fruit & vegetable. Does its brown decomposition affect the appearance of the drug solution or create its own brown in fruit & vegetable. Could anyone having experience give me opinion about these applications of Ascorbic acid ? How can we prevent brown colors created from Ascorbic acid.
Does it help?
Article Discoloration in Raw and Processed Fruits and Vegetables
According to the following link, vitamin C serves as a reducing agent and reduces iodine to iodide ions (colorless in solution)...So, if vitamin C is present, the brownish color of the iodine solution will become colorless:
https://uwaterloo.ca/chem13-news-magazine/september-2015/activities/sharing-chemistry-community-c-difference
Dear Ngọc Bảo thank you for sharing this interesting technical question on RG. The brown coloration in fruits and vegetables comes from oxidation of polyphenolic components by oxygen (which is present in the air) in the presence of an anzyme called polyphenol oxidase (PPO). All three come together when you for example slice up an apple. The brown color color then comes form oxidation products of the polyphenols which are called ortho-quinones. Ortho-quinones can have yellow, orange, red, or even brown colors. The color of the ortho-quionones comes from two carbonyl groups(C=O) in direct neighborhood on a benzene ring. The process can be slowed down by adding antioxidants like ascorbic acid or chelating ligands like citric acid. The first oxidation product of vitamin C (ascorbic acid) is the so-called dehydroascorbic acid. It has even three neighboring C=O groups, but it easily reacts with water to form a colorless hydrate. Thus, to the best of my knowledge, ascorbic acid is not responsible for brown colorations in fruit.
Good luck with your work and best wishes!
Indeed, ascorbic acid becomes brownish colored after oxidation by air. However, this is well seen only at high concentrations of ascorbic acid, much higher than in fruits/vegetables. I agree with Frank T. Edelmann that "ascorbic acid is not responsible for brown colorations in fruit."" In opposite, ascorbic acid as a strong antioxidant protects polyphenolics from oxidation. A slice of apple becomes brown due to oxidation of Fe(II) to Fe(III), the latter one is reduced by ascorbic acid. However, the concentration of ascorbic acid is too low and quickly depleted.
By the way, the color of fruits comes mostly from their skin reach in polyphenols
Dear Frank T. Edelmann, Thanks all for your kind supports, your information help me understand more about ascorbic acid (AA), especially in fruits and vegetables. In my work, AA is used as an antioxidant in the colorless solution, and the solution turns yellow after about 6 months. This problem with phenomenon in fruit seems similar but actually different, I understand this after getting your suggestions. I’m really interested with information that you have given that "The first oxidation product of vitamin C (ascorbic acid) is the so-called dehydroascorbic acid. It has even three neighboring C=O groups, but it easily reacts with water to form a colorless hydrate.". Could you kindly share with me some more in-depth articles about this information or give me some advices on this.
Thank you & Best regards.
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