Flavonoids are a major class of plant phenolics that are widely distributed in
the human diet and have been related to health promotion. They may occur in their
natural sources in free forms (aglycones), as glycosylated or acylated derivatives, or as
oligomeric and polymerized structures. This structural diversity affects their
physicochemical behaviour and complicates their analysis. Thus, there is not a single
standardized procedure that can be recommended for all flavonoid groups and/or type of
samples, and the procedures have to be optimized depending on the nature of the
sample and the target analytes. Furthermore, when dealing with the analysis of
flavonoids biological samples (i.e., human and animal fluids and tissues) some
differential aspects have to be taken into account; the nature of the compounds that can
be found in those samples may differ from that present in plants and food, and
flavonoids and metabolites occur in much lower concentrations, which make their
analysis still more challenging. In this review the main techniques for extraction and
analysis of flavonoids in foodstuffs and biological fluids are revised. Discussion on
available databases including data on the contents of flavonoids in foods, useful for the
estimation of their dietary intake, and emerging biomarkers of flavonoid consumption is
also made.
Keywords: Analysis, biological fluids, biomarkers, extraction, flavonoid
metabolites, flavonoids, foods, HPLC, identification, LC-MS, occurrence in food,
phytochemical databases, polyphenols, sample preparation.
