Nonextractable Polyphenols: A Relevant Group with Health Effects

Abstract

Current research on dietary polyphenols is mostly focused on the so-called extractable polyphenols (EPP), those released from the food matrix by several solvent combinations. However, this ignores a relevant fraction of polyphenols remaining in the residues of those extractions, the nonextractable polyphenols (NEPP) or macromolecular antioxidants. These are either polymeric structures (mostly high molecular weight proanthocyanidins) or small phenolic structures closely linked to macromolecules such as proteins or dietary fiber. This partial approach to these dietary bioactive constituents may hamper our understanding of the relevance of dietary polyphenols. This chapter provides an overview of the current knowledge of NEPP. In particular, the following aspects are explored: strategies for the release and analysis of NEPP; contribution of these compounds to total polyphenol content in foods and therefore to total polyphenol intake in different populations; evidence of their metabolic fate as well as specific features compared to those of EPP; mechanism of biological action (antioxidant effects, modulation of colonic microbiota, biological activities of NEPP-derived metabolites, synergy with dietary fiber); evidence of biological activity (considering both local effects in the digestive tract and systemic effects through their metabolites). Finally, the chapter provides some perspectives on the main aspects that should be considered in order to advance scientific knowledge on NEPP in the future.