1 Introduction

Research on the absorption, metabolism and tissue distribution of dietary polyphenols in human and animals studies relies on efficient extraction of the polyphenol or putative polyphenol metabolites from the blood, urine or organ under investigation. Though analysis of polyphenols in food (necessarily involving extraction) has received much critical attention and review over many years, resulting in the reaching of general consensus as to optimum procedures, the more recent interest in animal fluids and tissues has moved quickly and, we suggest, without full regard for analytical efficiency. Additional factors to those relevant to extraction from plants and food matrices need to be considered when dealing with mammalian metabolism, and extraction procedures require full validation even if similar procedures are employed for the two purposes. In addition, different polyphenol classes may require different extraction techniques. It must also be remembered that sophistication of analytical detection and quantification - and there are now some highly sophistication instrumental techniques available - cannot compensate for inefficient analyte extraction.

Our present aim is to review some of the methods that have been used for extraction of polyphenols in human and animal studies, to discuss the major problems that may occur during extraction, and to show that more attention needs to be paid to validation of analytical and extraction procedures.

It is our opinion that some of the results presented in the literature, and the conclusions derived therefrom, are incorrect because of the use of non-validated and...