Polyphenol

Plant-derived polyphenol, tannic acid, formed by esterification of ten equivalents of the phenylpropanoid-derived gallic acid to a monosaccharide (glucose) core from primary metabolism
Curcumin, a bright yellow component of turmeric (Curcuma longa) is a well-studied polyphenol.
Ellagic acid, a polyphenol.
Raspberry ellagitannin, a tannin composed of 14 gallic acid units around a core of three units of glucose, with two gallic acids as simple esters, and the remaining 12 appearing in 6 ellagic acid-type units. Ester, ether, and biaryl linkages are present, see below.
Theaflavin-3-gallate, a plant-derived polyphenol, an ester of gallic acid and a theaflavin core. There are 9 phenolic hydroxyl groups and two phenolic ether linkages.
The C-glucoside substructure of polyphenols is exemplified by the phenol-saccharide conjugate puerarin, a midmolecular-weight plant natural product. The attachment of the phenol to the saccharide is by a carbon-carbon bond. The isoflavone and its 10-atom benzopyran "fused ring" system, also a structural feature here, is common in polyphenols.
An example of a synthetically achieved small ellagitannin, tellimagrandin II, derived biosynthetically and sometimes synthetically by oxidative joining of two of the galloyl moieties of 1,2,3,4,6-pentagalloyl-glucose
Reversed-phase HPLC plot of separation of phenolic compounds. Smaller natural phenols formed individual peaks while tannins form a hump.

Polyphenols are a large family of naturally occurring organic compounds characterized by multiples of phenol units.

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Quercetin

UV visible spectrum of quercetin, with lambda max at 369 nm
3-O-Glycosides of quercetin

Quercetin is a plant flavonol from the flavonoid group of polyphenols.

Catechin

Flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants.

Catechin numbered
3D view of "pseudoequatorial" (E) conformation of(+)-catechin
UV spectrum of catechin.
Human metabolites of epicatechin (excluding colonic metabolites)
Schematic representation of (−)-epicatechin metabolism in humans as a function of time post-oral intake. SREM: structurally related (−)-epicatechin metabolites. 5C-RFM: 5-carbon ring fission metabolites. 3/1C-RFM: 3- and 1-carbon-side chain ring fission metabolites. The structures of the most abundant (−)-epicatechin metabolites present in the systemic circulation and in urine are depicted.
(+)-catechin (2R,3S)
(-)-catechin (2S,3R)
(-)-epicatechin (2R,3R)
(+)-epicatechin (2S,3S)

It belongs to the subgroup of polyphenols called flavonoids.

Flavonoid

Molecular structure of the flavone backbone (2-phenyl-1,4-benzopyrone)
Isoflavan structure
Neoflavonoids structure
Flavylium skeleton of anthocyanidins
Flavan structure
Parsley is a source of flavones
Blueberries are a source of dietary anthocyanidins
A variety of flavonoids are found in citrus fruits, including grapefruit
Mean flavonoid intake in mg/d per country, the pie charts show the relative contribution of different types of flavonoids.
Data are based on mean flavonoid intake of all countries included in the 2011 EFSA Comprehensive European Food Consumption Database.

Flavonoids (or bioflavonoids; from the Latin word flavus, meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans.

Lignan

The lignans are a large group of low molecular weight polyphenols found in plants, particularly seeds, whole grains, and vegetables.

Proanthocyanidin

Plant-derived polyphenol, tannic acid, formed by esterification of ten equivalents of the phenylpropanoid-derived gallic acid to a monosaccharide (glucose) core from primary metabolism

Proanthocyanidins are a class of polyphenols found in many plants, such as cranberry, blueberry, and grape seeds.

Tannic acid

A bottle of tannic acid (water solution) from the redwood tree.
An electrostatic potential map (blue is positive and red is negative charge) of decagalloyl tannic acid, i.e. a tannic acid derived from ten molecules of gallic acid

Tannic acid is a specific form of tannin, a type of polyphenol.

Antioxidant

Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals and chain reactions that may damage the cells of organisms.

Structure of the antioxidant, glutathione
Structure of the metal chelator phytic acid
The structure of the antioxidant vitamin ascorbic acid (vitamin C)
The free radical mechanism of lipid peroxidation
Decameric structure of AhpC, a bacterial 2-cysteine peroxiredoxin from Salmonella typhimurium
Substituted phenols and derivatives of phenylenediamine are common antioxidants used to inhibit gum formation in gasoline (petrol).
Fruits and vegetables are good sources of antioxidant vitamins C and E.

Polyphenols, which have antioxidant properties in vitro, have unknown antioxidant activity in vivo due to extensive metabolism following digestion and little clinical evidence of efficacy.

Black tea

Type of tea that is more oxidized than oolong, yellow, white and green teas.

A cup of black tea
Tea plantation in Java, Indonesia
Black tea with Spices
Black tea grading
Fresh tea leaves of different sizes

The visible film often formed on black tea consists of oxidized polyphenols and calcium carbonate, and is therefore more pronounced for tea brewed with hard water.

Ellagic acid

UV visible spectrum of ellagic acid

Ellagic acid is a polyphenol found in numerous fruits and vegetables.

Flax

Flowering plant, Linum usitatissimum, in the family Linaceae.

Capsules
Flowers
Brown flax seeds
Golden flax seeds
Golden flax seed meal
An 18th century heckling shop once used to prepare flax fibers. North Ayrshire, Scotland.
A flax field in bloom in North Dakota
De vlasoogst (1904) ("The flax harvest") painting by Emile Claus, Royal Museums of Fine Arts of Belgium, Brussels, Belgium
A hackle or heckle, a tool for threshing flax and preparing the fiber
Flax tissues, Tacuinum sanitatis, 14th century
Stem cross-section, showing locations of underlying tissues: Ep = epidermis; C = cortex; BF = bast fibers; P = phloem; X = xylem; Pi = pith
Small flax plants
Four flax flowers pictured in the coat of arms of Mulgi Parish
Breaking flax
Scutching flax
Heckling flax
Flax fiber in different forms, before and after processing

Three phenolic glucosides—secoisolariciresinol diglucoside, p-coumaric acid glucoside, and ferulic acid glucoside—are present in commercial breads containing flax seed.