Extractable and Non-extractable Polyphenols: an Overview
Extractable polyphenols (EPP) are those that are present in free forms and are solubilised by aqueous–organic solvents. In contrast, non-EPP (NEPP) remain in the residue of aqueous–organic extraction and are either polymeric polyphenols (non-extractable proanthocyanidins) or small phenolic compounds bound to the food matrix (hydrolysable polyphenols). In this chapter, updated evidence concerning the nature, isolation, and analysis of EPP and NEPP is presented. Also, advanced technologies are discussed, particularly in relation to the circular economy and biorefinery. Besides analytical characterisation, studies of antioxidant properties, as a first step towards defining the potential beneficial properties of a food, are also needed in this field. We also require studies to unravel the physiological mechanisms of action and bioaccessibility of both EPP and NEPP. Current evidence from state-of-the-art research into these aspects is also provided. Finally, one aim of research in this field should be the inclusion of NEPP in comprehensive and harmonized food composition databases in order to ensure correct evaluation of dietary intakes.