Chapter 10 - Non-Extractable Polyphenols in Plant Foods: Nature, Isolation, and Analysis

Abstract

Polyphenol content in plant foods is usually considered as that found in their corresponding aqueous-organic extracts. Nevertheless, polyphenols found in these extracts would correspond only to a fraction of these phytochemicals, the extractable polyphenols (EPP). The extractions leave a residue, commonly neglected, containing an understudied fraction of plant foods polyphenols, the so-called non-extractable polyphenols (NEPP). NEPP comprise polyphenols belonging to different classes, such as macromolecular polyphenols or single polyphenols associated with cell wall macromolecules. Although only a minor part of the existing literature on polyphenols in plant foods have dealt with NEPP, the existing data show that they are even more abundant than EPP in many plant foods. The present chapter aims to provide an overview of NEPP in plant foods, including their nature, procedures for their isolation, current analytical methods, content in several foods and extracts, and potential applications.