Quantitative examination of oxidized polyphenol-protein complexes.

We quantitatively examined interactions between polyphenols and proteins under oxidizing conditions, using radiolabeled 1,2,3,4,6-penta-O-galloyl-d-glucopyranose (PGG) and bovine serum albumin (BSA) as model compounds. We tested NaIO(4), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS.+), and 2,2'-azobis(isobutyramidine) dihydrochloride (AAPH) as model oxidants and used sodium dodecyl sulfate to disrupt noncovalent PGG-BSA interactions after the oxidation. We used trichloroacetic acid to isolate the PGG-BSA products after oxidation for radiochemical quantitation. NaIO(4) and ABTS.+ oxidized PGG-BSA complexes more rapidly than AAPH. Using NaIO(4) as the oxidant, we found that soluble oxidized PGG-BSA complexes formed rapidly and were converted to insoluble complexes if PGG was present in excess over BSA.