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Effects of Metal Ions on Proanthocyanidin‐Protein Interactions
Author(s) -
Geibel Mary Allison,
Hagerman Ann
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.887.2
Subject(s) - polyphenol , proanthocyanidin , bioavailability , chemistry , tannin , metal , condensed tannin , food science , metal ions in aqueous solution , wine , biochemistry , chromatography , organic chemistry , antioxidant , biology , bioinformatics
The polyphenolic compounds known as tannins are present in many plant‐based foods and beverages, and may be responsible for the putative beneficial effects of foods such as green tea, chocolate and red wine. Bioavailability of polyphenols can be low, in part because of strong interactions with protein that impede uptake. In this study, the role of metals as mediators of protein binding was assessed for a well‐characterized proanthocyanidin‐type polyphenol. We hypothesized that metals may change the amount of polyphenol that is protein bound and may change the nature of the interaction between polyphenol and protein. Metals including Fe, Al, Cu, Mn, and Zn were introduced at various levels into proanthocyanidin‐proteinl mixtures, and UV‐Visible Spectroscopy and HPLC were employed to measure the amount of tannin in the resulting precipitates. None of the metals tested changed the amount of tannin bound by the protein, but Al(III) converted the complexed precipitate into a highly cross‐linked form that was only disrupted by depolymerization of the tannin precipitate. We attribute the low bioavailability of tea polyphenols (EGCg) at least in part to the naturally high levels of Al in tea, and suggest that increased bioavailability could be achieved if Al was removed from tea products. We are now using radiochemical methods and ICP to determine the stoichiometries of polyphenol, metal and protein in the complexes, with the goal of better understanding how metals mediate the bioactivities of natural polyphenols.