Titrating orange juice with KIO3, never changes color

[deleted-833402]

Hi! I am on a very tight clock here so if anyone knows the answer, please let me know.

In our lab, we were instructed to titrate ascorbic acid and a sample of vitamin c with NaOH, and then KIO3. So first we titrate with NaOH with phenolphthalein indicator, and then re-acidify with HCl, and then titrate with KIO3 and a starch indicator.
We did it with an ascorbic acid solution we made and it worked completely fine! The problem, however, is with our orange juice (vitamin C sample). We titrated with NaOH and phenolphthalein and that changed color and worked fine. But, after re-acidifying and titrating with KIO3, it NEVER turned blue/brown (as it should). Other lab groups used other beverages with Vit C and it worked for them. We titrated with over 150mL of KIO3 to no avail, while only using 6.5mL orange juice!!!! The potential from the ORP probe also never changed, remained constant throughout the titration. Does anyone know why this happened?

Thank you! Please answer ASAP.

[deleted-718508]

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