1 Introduction

The objective in extracting phenolic compounds from their plant sources is to liberate these compounds from the vacuolar structures where they are found, either through rupturing plant tissue or through a process of diffusion. The first case is accomplished by carrying out particle reduction generally by using a homogenizer in which the plant substance to be treated is interposed with the extraction solvent that will be used later. In the second case, nothing more than steeping is required.

In this chapter we will present a review of the most frequently used methods for extracting phenolic compounds, for analytical purposes from their plant sources, though it must be borne in mind that there is no single extraction protocol which can be considered optimally for all types of samples. There are three principal techniques that may be used: (1) extraction using solvents, (2) solid-phase extraction and (3) supercritical extraction. The latter method may also be considered as a type of solvent extraction in which the solvent is a fluid in a supercritical state, though it should be considered separately because of its peculiarities in technique and equipment.

2 Solvent Extraction

This is a process designed to separate soluble phenolic compounds by diffusion from a solid matrix (plant tissue) using a liquid matrix (solvent). The process can be divided into two stages:

1. Initial stage. Swelling of the particles or of the solid fragments is observed due to sorption of the solvent in the solid...