Polyphenol

Polyphenols (/ˌpɒliˈfiːnoʊl, -nɒl/; also known as polyhydroxyphenols) are a structural class of mainly natural, but also synthetic or semisynthetic, organic chemicals characterized by the presence of large multiples of phenol structural units. The number and characteristics of these phenol structures underlie the unique physical, chemical, and biological (metabolic, toxic, therapeutic, etc.) properties of particular members of the class. Examples include tannic acid (image at right) and ellagitannin (image below). The historically important chemical class of tannins is a subset of the polyphenols.The most important food sources are commodities widely consumed in large quantities such as fruit and vegetables, green tea, black tea, red wine, coffee, chocolate, olives, and extra virgin olive oil. Herbs and spices, nuts and algae are also potentially significant for supplying certain polyphenols. Some polyphenols are specific to particular food (flavanones in citrus fruit, isoflavones in soya, phloridzin in apples); whereas others, such as quercetin, are found in all plant products such as fruit, vegetables, cereals, leguminous plants, tea, and wine. Polyphenols (/ˌpɒliˈfiːnoʊl, -nɒl/; also known as polyhydroxyphenols) are a structural class of mainly natural, but also synthetic or semisynthetic, organic chemicals characterized by the presence of large multiples of phenol structural units. The number and characteristics of these phenol structures underlie the unique physical, chemical, and biological (metabolic, toxic, therapeutic, etc.) properties of particular members of the class. Examples include tannic acid (image at right) and ellagitannin (image below). The historically important chemical class of tannins is a subset of the polyphenols. The name derives from the Ancient Greek word πολύς (polus, meaning 'many, much') and the word phenol which refers to a chemical structure formed by attaching to an aromatic benzenoid (phenyl) ring a hydroxyl (-OH) group as is found in alcohols (hence the -ol suffix). The term polyphenol has been in use at least since 1894. As seen in the definitions and examples below, polyphenols are not polymers of phenol. Phenol can be polymerized by electrochemical oxidation but this yields compounds that are not referred to as 'polyphenols'.Polyphenols have more than one hydroxyl group attached to benzene rings, whereas phenol has one hydroxyl attached to one benzene ring. The earliest widely accepted definition of polyphenols, the White–Bate-Smith–Swain–Haslam (WBSSH) definition, was offered and justified by natural product and organic chemist Edwin Haslam and co-workers, based on the earlier natural products research of Edgar Charles Bate-Smith, Anthony Swain, and Theodore White that characterized specific structural characteristics common to plant phenolics used in tanning (i.e., the tannins). The WBSSH describes the polyphenol class as: where the limits to these ranges are somewhat flexible. The definition further states that polyphenols display unique physical and chemical behaviors related to their high molecular weights and profusion of phenolic substructures—precipitation of proteins and particular amine-containing organics (e.g., particular alkaloid natural products), and formation of particular metal complexes (e.g., intense blue-black iron(III) complexes). The need to clarify the definition of 'polyphenols' in the light of the extensive research into this large substance class and of increasingly ambiguous use of the polyphenol term led Stéphane Quideau, University of Bordeaux 1, France, to offer a definition not given formal status by IUPAC: