CHAPTER 11: Metabolic Fate of Extractable and Non-extractable Polyphenols

(Poly)phenols, secondary plant products, have been linked with numerous health benefits associated with vegetable- and fruit-rich diets. Once ingested, (poly)phenols suffer extensive transformations during their passage through the gastrointestinal tract and it is their metabolites rather than the parent compounds present in food that might exert health benefits. The metabolic fate of (poly)phenols may depend on the molecular structure of the (poly)phenol and how the (poly)phenolic compound is linked to macromolecular food constituents. Extractable (poly)phenols may be bioaccessible in the upper gastrointestinal tract, while non-extractable (poly)phenols reach the lower gastrointestinal tract almost intact. This chapter summarises the most recent outcomes from in vivo and in vitro studies on the bioaccessibility, bioavailability and metabolism of hydrolysable tannins, proanthocyanidins and hydrolysable phenolics, highlighting the importance of the colonic microbiota.