Oh YES; in alkaline conditions they are very generally much more prone to oxidation and they can become ionised. Some of them change solubility, e.g. ferulic acid, soem change colour e.g. anthocyans, ...

It is usually best to work in mild acidic conditions for polyphenols.

Thankyou so much 👍

Dear Sir. Concerning your issue about the effect of acids,bases on the activities and properties of polyphenols. Plant polyphenols have drawn increasing scientific attention due to their multiple functions on health care.The antioxidant properties and stability of the polyphenol crude extract from Spinacia oleracea were studied. Two common methods including 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and ferric reducing antioxidant power (FRAP) assay were employed for the evaluation of antioxidant activity of spinach polyphenol. In addition, the effects of pH value, temperature, light and preservative on the antioxidant stability of spinach polyphenol were also discussed. Results showed that spinach polyphenol had a certain antioxidant activity, and its antioxidant ability increased with the increase of sample concentration. External factors, such as pH value, temperature, light and preservative, have different effects on their antioxidantstability. This study has a certain reference value for better research and utilization of plant polyphenols. I think the following below links may help you in your analysis:

http://www.btsjournals.com/assets/2018v9p8-13.pdf

https://www.scripps.edu/baran/images/grpmtgpdf/Peters_May_16.pdf

Thanks