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In
biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
, naturally occurring phenols are natural products containing at least one
phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...
functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
. Phenolic compounds are produced by plants and microorganisms. Organisms sometimes synthesize phenolic compounds in response to ecological pressures such as pathogen and insect attack, UV radiation and wounding. As they are present in food consumed in human diets and in plants used in
traditional medicine Traditional medicine (also known as indigenous medicine or folk medicine) comprises medical aspects of traditional knowledge that developed over generations within the folk beliefs of various societies, including indigenous peoples, before the ...
of several cultures, their role in human health and disease is a subject of research. Some phenols are germicidal and are used in formulating disinfectants.


Classification

Various classification schemes can be applied. A commonly used scheme is based on the number of carbons and was devised by Jeffrey Harborne and Simmonds in 1964 and published in 1980: C6-C7-C6
Diarylheptanoid The diarylheptanoids (also known as diphenylheptanoids) are a relatively small class of plant secondary metabolites. Diarylheptanoids consist of two aromatic rings (aryl groups) joined by a seven carbons chain (heptane) and having various substitue ...
s are not included in this Harborne classification. They can also be classified on the basis of their number of phenol groups. They can therefore be called ''simple phenols'' or ''monophenols'', with only one phenolic group, or ''di-'' (''bi-''), ''tri-'' and ''oligophenols'', with two, three or several phenolic groups respectively. A diverse family natural phenols are the
flavonoid 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. Chemically, flavonoids ...
s, which include several thousand compounds, among them the
flavonol Flavonols are a class of flavonoids that have the 3-hydroxyflavone backbone (IUPAC name : 3-hydroxy-2-phenylchromen-4-one). Their diversity stems from the different positions of the phenolic -OH groups. They are distinct from flavanols (with " ...
s, flavones, flavan-3ol (''catechins''),
flavanone The flavanones, a type of flavonoids, are various aromatic, colorless ketones derived from flavone that often occur in plants as glycosides. List of flavanones * Blumeatin * Butin * Eriodictyol * Hesperetin * Hesperidin * Homoeriodictyol * Iso ...
s,
anthocyanidin Anthocyanidins are common plant pigments, the sugar-free counterparts of anthocyanins. They are based on the flavylium cation, an oxonium ion, with various groups substituted for its hydrogen atoms. They generally change color from red through ...
s, and
isoflavonoid Isoflavonoids are a class of flavonoid phenolic compounds, many of which are biologically active. Isoflavonoids and their derivatives are sometimes referred to as phytoestrogens, as many isoflavonoid compounds have biological effects via the estr ...
s. The phenolic unit can be found dimerized or further polymerized, creating a new class of polyphenol. For example,
ellagic acid Ellagic acid is a polyphenol found in numerous fruits and vegetables. It is the dilactone of hexahydroxydiphenic acid. Name The name comes from the French term ''acide ellagique'', from the word ''galle'' spelled backwards because it can be ...
is a dimer of gallic acid and forms the class of ellagitannins, or a
catechin Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids. The name of the catechin chemical family derives from ''catechu'', which is the tannic ...
and a gallocatechin can combine to form the red compound
theaflavin Theaflavin (TF) and its derivatives, known collectively as ''theaflavins'', are antioxidant polyphenols that are formed from the condensation of flavan-3-ols in tea leaves during the enzymatic oxidation (sometimes erroneously referred to as fermen ...
, a process that also results in the large class of brown
thearubigin Thearubigins are polymeric polyphenols that are formed during the enzymatic oxidation and condensation of two gallocatechins (epigallocatechin and epigallocatechin gallate) with the participation of polyphenol oxidases during the fermentation rea ...
s in tea. Two natural phenols from two different categories, for instance a flavonoid and a lignan, can combine to form a hybrid class like the
flavonolignan Flavonolignans are natural phenols composed of a part flavonoid and a part phenylpropane. Examples Flavonolignans identified in ''Silybum marianum'' (milk thistle) silymarin complex include silibinin, silychristin, silydianin, dehydrosilybin, ...
s. Nomenclature of
polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s:


Hybrid chemical classes

Plants in the genus ''
Humulus ''Humulus'', hop, is a small genus of flowering plants in the family Cannabaceae. The hop is native to temperate regions of the Northern Hemisphere. Hops are the female flowers (seed cones, strobiles) of the hop species '' H. lupulus''; as a main ...
'' and ''
Cannabis ''Cannabis'' () is a genus of flowering plants in the family Cannabaceae. The number of species within the genus is disputed. Three species may be recognized: ''Cannabis sativa'', '' C. indica'', and '' C. ruderalis''. Alternatively ...
'' produce terpenophenolic metabolites, compounds that are meroterpenes.
Phenolic lipid Phenolic lipids are a class of natural products composed of long aliphatic chains and phenolic rings. Phenolic lipids occur in plants, fungi and bacteria. Types * Alkylcatechols * Alkylphenols (nonylphenol, cardanol) * Alkylresorcinols * Anac ...
s are long aliphatic chains bonded to a phenolic moiety.


Chirality

Many natural phenols are
chiral Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from ...
. An example of such molecules is
catechin Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids. The name of the catechin chemical family derives from ''catechu'', which is the tannic ...
.
Cavicularin Cavicularin is a natural phenolic secondary metabolite Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fungi, animal ...
is an unusual macrocycle because it was the first compound isolated from nature displaying optical activity due to the presence of
planar chirality Planar chirality, also known as 2D chirality, is the special case of chirality for two dimensions. Most fundamentally, planar chirality is a mathematical term, finding use in chemistry, physics and related physical sciences, for example, in astrono ...
and axial chirality.


UV visible absorbance

Natural phenols show optical properties characteristic of benzene, e.g. absorption near 270 nm. According to
Woodward's rules Woodward's rules, named after Robert Burns Woodward and also known as Woodward–Fieser rules (for Louis Fieser) are several sets of empirically derived rules which attempt to predict the wavelength of the Absorption (light), absorption maximum (λ ...
,
bathochromic shift Bathochromic shift (from Greek βαθύς ''bathys'', "deep"; and χρῶμα ''chrōma'', "color"; hence less common alternate spelling "bathychromic") is a change of spectral band position in the absorption, reflectance, transmittance, or emissi ...
s often also happen suggesting the presence of delocalised π electrons arising from a
conjugation Conjugation or conjugate may refer to: Linguistics * Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics * Complex conjugation, the chang ...
between the benzene and
vinyl Vinyl may refer to: Chemistry * Polyvinyl chloride (PVC), a particular vinyl polymer * Vinyl cation, a type of carbocation * Vinyl group, a broad class of organic molecules in chemistry * Vinyl polymer, a group of polymers derived from vinyl m ...
s groups. As molecules with higher conjugation levels undergo this bathochromic shift phenomenon, a part of the visible spectrum is absorbed. The wavelengths left in the process (generally in red section of the spectrum) recompose the
color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
of the particular substance. Acylation with cinnamic acids of
anthocyanidin Anthocyanidins are common plant pigments, the sugar-free counterparts of anthocyanins. They are based on the flavylium cation, an oxonium ion, with various groups substituted for its hydrogen atoms. They generally change color from red through ...
s shifted color tonality (CIE Lab hue angle) to
purple Purple is any of a variety of colors with hue between red and blue. In the RGB color model used in computer and television screens, purples are produced by mixing red and blue light. In the RYB color model historically used by painters, ...
. Here is a series of UV
visible Visibility, in meteorology, is a measure of the distance at which an object or light can be seen. Visibility may also refer to: * A measure of turbidity in water quality control * Interferometric visibility, which quantifies interference contrast ...
spectra of molecules classified from left to right according to their conjugation level: The absorbance pattern responsible for the red color of
anthocyanin Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...
s may be complementary to that of green chlorophyll in photosynthetically active tissues such as young ''
Quercus coccifera ''Quercus coccifera'', the kermes oak, is an oak bush in the ''Ilex'' section of the genus. It is native to the Mediterranean region and Northern African Maghreb, south to north from Morocco to France and west to east from Portugal to Cyprus an ...
'' leaves.


Oxidation

Natural phenols are
reactive Reactive may refer to: *Generally, capable of having a reaction (disambiguation) *An adjective abbreviation denoting a bowling ball coverstock made of reactive resin *Reactivity (chemistry) *Reactive mind *Reactive programming See also *Reactanc ...
species toward
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
, notably the complex mixture of phenolics, found in food for example, can undergo
autoxidation Autoxidation (sometimes auto-oxidation) refers to oxidations brought about by reactions with oxygen at normal temperatures, without the intervention of flame or electric spark. The term is usually used to describe the gradual degradation of organi ...
during the ageing process. Simple natural phenols can lead to the formation of
B type proanthocyanidin B type proanthocyanidins are a specific type of proanthocyanidin, which are a class of flavanoids. They are oligomers of flavan-3-ols. Dimeric B type proanthocyanidins These molecules have the molecular formula C30H26O12 (molar mass : 578.52 g/m ...
s in wines or in model solutions. This is correlated to the
non-enzymatic browning Browning is the process of food turning brown due to the chemical reactions that take place within. The process of browning is one of the chemical reactions that take place in food chemistry and represents an interesting research topic regarding ...
color change characteristic of this process. This phenomenon can be observed in foods like carrot purees. Browning associated with oxidation of phenolic compounds has also been given as the cause of cells death in calli formed in ''in vitro'' cultures. Those phenolics originate both from explant tissues and from explant secretions.


Phenolic compounds


Naturally occurring


Synthetic


Biosynthesis

Phenolics are formed by three different biosynthetic pathways: (i) the shikimate/chorizmate or succinylbenzoate pathway, which produces the phenyl propanoid derivatives (C6–C3); (ii) the acetate/malonate or polyketide pathway, which produces the side-chain-elongated phenyl propanoids, including the large group of flavonoids (C6–C3–C6) and some quinones; and (iii) the acetate/mevalonate pathway, which produces the aromatic terpenoids, mostly monoterpenes, by dehydrogenation reactions. The aromatic amino acid phenylalanine, synthesized in the
shikimic acid pathway The shikimate pathway (shikimic acid pathway) is a seven-step metabolic pathway used by bacteria, archaea, fungi, algae, some protozoans, and plants for the biosynthesis of folates and aromatic amino acids (tryptophan, phenylalanine, and tyrosin ...
, is the common precursor of phenol containing amino acids and phenolic compounds. In plants, the phenolic units are
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
ified or
methylated In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These ...
and are submitted to
conjugation Conjugation or conjugate may refer to: Linguistics * Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics * Complex conjugation, the chang ...
, which means that the natural phenols are mostly found in the
glycoside In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycoside ...
form instead of the
aglycone An aglycone (aglycon or genin) is the compound remaining after the glycosyl group on a glycoside is replaced by a hydrogen atom. For example, the aglycone of a cardiac glycoside would be a steroid molecule. Detection A way to identify aglycone ...
form. In olive oil,
tyrosol Tyrosol is an organic compound with the formula . Classified as a phenylethanoid, i.e. a derivative of phenethyl alcohol, It is found in a variety of natural sources. The compound is colorless solid. The principal source in the human diet is ol ...
forms esters with fatty acids. In rye,
alkylresorcinol Alkylresorcinols, also known as resorcinolic lipids, are phenolic lipids composed of long aliphatic chains and resorcinol-type phenolic rings. Natural sources of alkylresorcinols Alkylresorcinols are relatively rare in nature, with the main know ...
s are phenolic lipids. Some acetylations involve
terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ...
s like
geraniol Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil, palmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility in w ...
. Those molecules are called meroterpenes (a chemical compound having a partial terpenoid structure). Methylations can occur by the formation of an
ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be c ...
bond on hydroxyl groups forming O-methylated polyphenols. In the case of the
O-methylated flavone The O-methylated flavonoids or methoxyflavonoids are flavonoids with methylations on hydroxyl groups (methoxy bonds). O-methylation has an effect on the solubility of flavonoids. Enzymes O-methylated flavonoids formation implies the presence of spe ...
tangeritin Tangeretin is an O- polymethoxylated flavone that is found in tangerine and other citrus ''Citrus'' is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops ...
, all of the five hydroxyls are methylated, leaving no free hydroxyls of the phenol group. Methylations can also occur on directly on a carbon of the benzene ring like in the case of poriol, a C-methylated flavonoid.


Biodegradation

The white rot fungus ''
Phanerochaete chrysosporium ''Phanerochaete'' is a genus of crust fungi in the family Phanerochaetaceae. Taxonomy The genus was circumscribed by Finnish mycologist Petter Karsten in 1889. Marinus Anton Donk redefined the limits of the genus in two publications in 1957 ...
'' can remove up to 80% of phenolic compounds from
coking Coking is the heating of coal in the absence of oxygen to a temperature above 600 °C to drive off the volatile components of the raw coal, leaving a hard, strong, porous material of high carbon content called coke. Coke consists almost ent ...
waste water.


Applications

Tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' (from Anglo-Norman ''tanner'' ...
s are used in the tanning industry. Some natural phenols can be used as
biopesticide A Biopesticide is a biological substance or organism that damages, kills, or repels organisms seens as pests. Biological pest management intervention involves predatory, parasitic, or chemical relationships. They are obtained from organisms inclu ...
s. Furanoflavonoids like karanjin or
rotenoid Rotenoids are naturally occurring substances containing a cis-fused tetrahydrochromeno ,4-bhromene nucleus. Many have insecticidal activity, such as the prototypical member of the family, rotenone. Rotenoids are related to the isoflavones. Natu ...
s are used as
acaricide Acaricides are pesticides that kill members of the arachnid subclass ''Acari'', which includes ticks and mites. Acaricides are used both in medicine and agriculture, although the desired selective toxicity differs between the two fields. Termino ...
or insecticide.
Enological tannin The phenolic content in wine refers to the phenolic compounds— natural phenol and polyphenols—in wine, which include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. These compounds includ ...
s are important elements in the flavor of wine. Some phenols are sold as dietary supplements. Phenols have been investigated as drugs. For instance,
Crofelemer Crofelemer (USAN, trade name Mytesi) is an antidiarrheal indicated for the symptomatic relief of non-infectious diarrhea in adult patients with HIV/AIDS on antiretroviral therapy. Other possible uses include diarrhea in children, acute infectious ...
(USAN trade name Fulyzaq) is a drug under development for the treatment of diarrhea associated with anti-HIV drugs. Additionally, derivatives have been made of phenolic compound, combretastatin A-4, an anticancer molecule, including nitrogen or halogens atoms to increase the efficacy of the treatment.


Industrial processing and analysis


Phenol extraction

Phenol extraction Phenol extraction is a processing technology used to prepare phenols as raw materials, compounds, or additives for industrial wood processing and for chemical industries. Phenol extraction is also a laboratory process to purify DNA and RNA contain ...
is a processing technology used to prepare phenols as raw materials, compounds or additives for industrial
wood processing Wood processing is an engineering discipline in the wood industry comprising the production of forest products, such as pulp and paper, construction materials, and tall oil. Paper engineering is a subfield of wood processing. The major wood pro ...
and for chemical industries. Extraction can be performed using different solvents. There is a risk that
polyphenol oxidase Polyphenol oxidase (PPO; also polyphenol oxidase i, chloroplastic), an enzyme involved in fruit browning, is a tetramer that contains four atoms of copper per molecule. PPO may accept monophenols and/or ''o''-diphenols as substrates. The ...
(PPO) degrades the phenolic content of the sample therefore there is a need to use PPO inhibitors like potassium
dithionite The dithionite is the oxyanion with the formula 2O4sup>2−. It is commonly encountered as the salt sodium dithionite. For historical reasons, it is sometimes called hydrosulfite, but it contains no hydrogen and is not a sulfite. The diani ...
(K2S2O4) or to perform experiment using liquid nitrogen or to boil the sample for a few seconds (
blanching Blanch or blanching may refer to: People * Andrea Blanch (born 1935), portrait, commercial, and fine art photographer * Arnold Blanch (1896–1968), born and raised in Mantorville, Minnesota * Stuart Blanch, Baron Blanch (1918–1994), Anglican bi ...
) to inactivate the enzyme. Further
fractionation Fractionation is a separation process in which a certain quantity of a mixture (of gases, solids, liquids, enzymes, or isotopes, or a suspension) is divided during a phase transition, into a number of smaller quantities (fractions) in which the ...
of the extract can be achieved using
solid phase extraction Solid-phase extraction (SPE) is an extractive technique by which compounds that are dissolved or suspended in a liquid mixture are separated from other compounds in the mixture according to their physical and chemical properties. Analytical labor ...
columns, and may lead to isolation of individual compounds. The recovery of natural phenols from biomass residue is part of
biorefining Biorefining is the process of "building" multiple products from biomass as a feedstock or raw material much like a petroleum refinery that is currently in use. A biorefinery is a facility like a petroleum refinery that comprises the various process ...
.


Separation

The pKa of phenolic compounds can be calculated from the
retention time In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system (a ...
in
liquid chromatography In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system (a ...
.


Analytical methods

Studies on evaluating antioxidant capacity can use
electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outc ...
methods. Detection can be made by recombinant
luminescent Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light". It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a crystal ...
bacterial sensors.


Profiling

Phenolic profiling can be achieved with
liquid chromatography–mass spectrometry Liquid chromatography–mass spectrometry (LC–MS) is an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography (or HPLC) with the mass analysis capabilities of mass spectrometry (MS). Coupled ...
(LC/MS).


Quantification

A method for phenolic content quantification is volumetric titration. An oxidizing agent,
permanganate A permanganate () is a chemical compound containing the manganate(VII) ion, , the conjugate base of permanganic acid. Because the manganese atom is in the +7 oxidation state, the permanganate(VII) ion is a strong oxidizing agent. The ion is a tr ...
, is used to oxidize known concentrations of a standard solution, producing a standard curve. The content of the unknown phenols is then expressed as equivalents of the appropriate standard. Some methods for quantification of total phenolic content are based on
colorimetric Colorimetry is "the science and technology used to quantify and describe physically the human color perception". It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color ...
measurements. Total phenols (or antioxidant effect) can be measured using the Folin-Ciocalteu reaction. Results are typically expressed as ''gallic acid equivalents'' (GAE). Ferric chloride (FeCl3) test is also a colorimetric assay. Lamaison and Carnet have designed a test for the determination of the total flavonoid content of a sample (AlCI3 method). After proper mixing of the sample and the reagent, the mixture is incubated for 10 minutes at ambient temperature and the absorbance of the solution is read at 440 nm. Flavonoid content is expressed in mg/g of quercetin. Quantitation results produced by the means of
diode array detector A chromatography detector is a device used in gas chromatography (GC) or liquid chromatography (LC) to detect components of the mixture being eluted off the chromatography column. There are two general types of detectors: destructive and non-destruc ...
-coupled HPLC are generally given as relative rather than
absolute value In mathematics, the absolute value or modulus of a real number x, is the non-negative value without regard to its sign. Namely, , x, =x if is a positive number, and , x, =-x if x is negative (in which case negating x makes -x positive), an ...
s as there is a lack of commercially available
standard Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object th ...
s for every phenolic molecules. The technique can also be coupled with
mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...
(for example, HPLC–DAD– ESI/MS) for more precise molecule identification.


Antioxidant effect assessment

; ''In vitro'' measurements Other tests measure the antioxidant capacity of a fraction. Some make use of the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (
ABTS In biochemistry, ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) is a chemical compound used to observe the reaction kinetics of specific enzymes. A common use for it is in the enzyme-linked immunosorbent assay (ELISA) to detect the ...
) radical cation, which is reactive towards most antioxidants including phenolics,
thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
s and
vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...
. During this reaction, the blue ABTS radical cation is converted back to its colorless neutral form. The reaction may be monitored spectrophotometrically. This assay is often referred to as the
Trolox equivalent antioxidant capacity The Trolox equivalent antioxidant capacity (TEAC) assay measures the antioxidant capacity of a given substance, as compared to the standard, Trolox. Most commonly, antioxidant capacity is measured using the ABTS Decolorization Assay. Other antioxi ...
(TEAC) assay. The reactivity of the various antioxidants tested are compared to that of
Trolox Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) is a water-soluble analog of vitamin E sold by Hoffman-LaRoche. It is an antioxidant like vitamin E and it is used in biological or biochemical applications to reduce oxidative stre ...
, which is a
vitamin E Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vi ...
analog. Other antioxidant capacity assays that use Trolox as a standard include the
diphenylpicrylhydrazyl DPPH is a common abbreviation for the organic chemical compound 2,2-diphenyl-1-picrylhydrazyl. It is a dark-colored crystalline powder composed of stable free radical molecules. DPPH has two major applications, both in laboratory research: one is ...
(DPPH),
oxygen radical absorbance capacity Oxygen radical absorbance capacity (ORAC) was a method of measuring antioxidant capacities in biological samples ''in vitro''. Because no physiological proof ''in vivo'' existed in support of the free-radical theory or that ORAC provided informat ...
(ORAC),
ferric reducing ability of plasma Ferric reducing ability of plasma (FRAP, also ''Ferric ion reducing antioxidant power'') is an antioxidant capacity assay that uses Trolox as a standard. The FRAP assay was first performed by Iris Benzie and J. J. Strain of the Human Nutrition Resea ...
(FRAP) assays or inhibition of copper-catalyzed ''in vitro'' human
low-density lipoprotein Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densit ...
oxidation. A cellular antioxidant activity (CAA) assay also exists. Dichlorofluorescin is a probe that is trapped within cells and is easily oxidized to fluorescent dichlorofluorescein (DCF). The method measures the ability of compounds to prevent the formation of DCF by 2,2'-Azobis(2-amidinopropane) dihydrochloride (ABAP)-generated peroxyl radicals in human hepatocarcinoma HepG2 cells. Other methods include
butylated hydroxytoluene Butylated hydroxytoluene (BHT), also known as dibutylhydroxytoluene, is a lipophilic organic compound, chemically a derivative of phenol, that is useful for its antioxidant properties. BHT is widely used to prevent free radical-mediated oxidat ...
(BHT),
butylated hydroxyanisole Butylated hydroxyanisole (BHA) is a synthetic, waxy, solid petrochemical. Its antioxidant properties have caused it to be widely used as a preservative in food, food packaging, animal feed, cosmetics, pharmaceuticals, rubber, and petroleum produ ...
(BHA),
Rancimat method Rancidification is the process of complete or incomplete autoxidation or hydrolysis of fats and oils when exposed to air, light, moisture, or bacterial action, producing short-chain aldehydes, ketones and free fatty acids. When these processes o ...
(rancidification assessment of fat). ; ''In vivo'' models Larvae of the model animal ''
Galleria mellonella ''Galleria mellonella'', the greater wax moth or honeycomb moth, is a moth of the family Pyralidae. ''G. mellonella'' is found throughout the world. It is one of two species of wax moths, with the other being the lesser wax moth. ''G. mellonella' ...
'', also called
waxworm Waxworms are the caterpillar larvae of wax moths, which belong to the family Pyralidae (snout moths). Two closely related species are commercially bred – the lesser wax moth (''Achroia grisella'') and the greater wax moth (''Galleria ...
s, can be used to test the antioxidant effect of individual molecules using
boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolve ...
in food to induce an oxidative stress. The content of
malondialdehyde Malondialdehyde (MDA) is the organic compound with the nominal formula CH2(CHO)2. A colorless liquid, malondialdehyde is a highly reactive compound that occurs as the enol. It occurs naturally and is a marker for oxidative stress. Structure and ...
, an oxidative stress indicator, and activities of the antioxidant enzymes superoxide dismutase, catalase,
glutathione S-transferase Glutathione ''S''-transferases (GSTs), previously known as ligandins, are a family of eukaryotic and prokaryotic phase II metabolic isozymes best known for their ability to catalyze the conjugation of the reduced form of glutathione (GSH) ...
and
glutathione peroxidase Glutathione peroxidase (GPx) () is the general name of an enzyme family with peroxidase activity whose main biological role is to protect the organism from oxidative damage. The biochemical function of glutathione peroxidase is to reduce lipid h ...
can be monitored. A pro
phenoloxidase Polyphenol oxidase (PPO; also polyphenol oxidase i, chloroplastic), an enzyme involved in Browning (food process), fruit browning, is a tetramer that contains four atoms of copper per molecule. PPO may accept monophenol , monophenols and/or ...
can also be recovered from the insect.


Genetic analysis

The phenolic biosynthetic and metabolic pathways and enzymes can be studied by means of
transgenesis Gene delivery is the process of introducing foreign genetic material, such as DNA or RNA, into host cells. Gene delivery must reach the genome of the host cell to induce gene expression. Successful gene delivery requires the foreign gene deli ...
of genes. The ''
Arabidopsis ''Arabidopsis'' (rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress (''Arabidopsis thaliana''), one of the model organi ...
'' regulatory gene for production of
Anthocyanin Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...
Pigment 1 (AtPAP1) can be expressed in other plant species.


Natural occurrences

Phenols are found in the natural world, especially in the plant kingdom.


Occurrences in prokaryotes

Orobol can be found in '' Streptomyces neyagawaensis'' (an Actinobacterium). Phenolic compounds can be found in the
cyanobacterium Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
''
Arthrospira ''Arthrospira'' is a genus of free-floating filamentous cyanobacteria characterized by cylindrical, multicellular trichomes in an open left-hand helix. A dietary supplement is made from ''A. platensis'' and ''A. maxima'', known as spirulina. ...
maxima'', used in the dietary supplement, Spirulina. The three cyanobacteria ''
Microcystis aeruginosa ''Microcystis aeruginosa'' is a species of freshwater cyanobacteria that can form harmful algal blooms of economic and ecological importance. They are the most common toxic cyanobacterial bloom in eutrophic fresh water. Cyanobacteria produce ne ...
'', ''
Cylindrospermopsis raciborskii ''Cylindrospermopsis raciborskii'' is a freshwater cyanobacterium. Introduction This bacterium is an aquatic photosynthetic bacteria belonging to the phylum Cyanobacteria. They are composed of chained filaments known as trichomes that can show ...
'' and ''
Oscillatoria ''Oscillatoria'' is a genus of filamentous cyanobacterium which is often found in freshwater environments, such as hot springs, and appears blue-green. Its name refers to the oscillating motion of its filaments as they slide against each other ...
sp.'' are the subject of research into the natural production of
butylated hydroxytoluene Butylated hydroxytoluene (BHT), also known as dibutylhydroxytoluene, is a lipophilic organic compound, chemically a derivative of phenol, that is useful for its antioxidant properties. BHT is widely used to prevent free radical-mediated oxidat ...
(BHT), an antioxidant, food additive and industrial chemical. The proteobacterium '' Pseudomonas fluorescens'' produces
phloroglucinol Phloroglucinol is an organic compound with the formula C6H3(OH)3. It is a colorless solid. It is used in the synthesis of pharmaceuticals and explosives. Phloroglucinol is one of three isomeric benzenetriols. The other two isomers are hydroxyqu ...
, phloroglucinol carboxylic acid and diacetylphloroglucinol. Another example of phenolics produced in proteobacteria is 3,5-dihydroxy-4-isopropyl-trans-stilbene, a bacterial stilbenoid produced in '' Photorhabdus'' bacterial symbionts of ''Heterorhabditis'' nematodes.


Occurrences in fungi

Phenolic acid Phenolic acids or phenolcarboxylic acids are types of aromatic acid compounds. Included in that class are substances containing a phenolic ring and an organic carboxylic acid function (C6-C1 skeleton). Two important naturally occurring types of ...
s can be found in mushroom
basidiomycetes Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Ba ...
species. For example,
protocatechuic acid Protocatechuic acid (PCA) is a dihydroxybenzoic acid, a type of phenolic acid. It is a major metabolite of antioxidant polyphenols found in green tea. It has mixed effects on normal and cancer cells in ''in vitro'' and ''in vivo'' studies. Biolo ...
and
pyrocatechol Catechol ( or ), also known as pyrocatechol or 1,2-dihydroxybenzene, is a toxic organic compound with the molecular formula . It is the ''ortho'' isomer of the three isomeric benzenediols. This colorless compound occurs naturally in trace amoun ...
are found in ''
Agaricus bisporus ''Agaricus bisporus'' is an edible basidiomycete mushroom native to grasslands in Eurasia and North America. It has two color states while immature – white and brown – both of which have various names, with additional names for the mature ...
'' as well as other phenylated substances like phenylacetic and
phenylpyruvic acid Phenylpyruvic acid is the organic compound with the formula C6H5CH2C(O)CO2H. It is a keto acid. Occurrence and properties The compound exists in equilibrium with its E- and Z-enol tautomers. It is a product from the oxidative deamination of p ...
s. Other compounds like
atromentin Atromentin is a natural chemical compound found in Agaricomycetes fungi in the orders Agaricales and Thelephorales. It can also be prepared by laboratory synthesis. Chemically, it is a polyphenol and a benzoquinone. Occurrences Atromentin has ...
and thelephoric acid can also be isolated from fungi in the Agaricomycetes class. Orobol, an
isoflavone Isoflavones are substituted derivatives of isoflavone, a type of naturally occurring isoflavonoids, many of which act as phytoestrogens in mammals. Isoflavones are produced almost exclusively by the members of the bean family, Fabaceae (Leguminosae ...
, can be isolated from ''
Aspergillus niger ''Aspergillus niger'' is a mold classified within the ''Nigri'' section of the ''Aspergillus'' genus. The ''Aspergillus'' genus consists of common molds found throughout the environment within soil and water, on vegetation, in fecal matter, on de ...
''. ; In yeasts Aromatic alcohols (example:
tyrosol Tyrosol is an organic compound with the formula . Classified as a phenylethanoid, i.e. a derivative of phenethyl alcohol, It is found in a variety of natural sources. The compound is colorless solid. The principal source in the human diet is ol ...
) are produced by the yeast ''
Candida albicans ''Candida albicans'' is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is usu ...
''. They are also found in
beer Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
. These molecules are
quorum sensing In biology, quorum sensing or quorum signalling (QS) is the ability to detect and respond to cell population density by gene regulation. As one example, QS enables bacteria to restrict the expression of specific genes to the high cell densities at ...
compounds for ''
Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...
''. ; Metabolism
Aryl-alcohol dehydrogenase In enzymology, an aryl-alcohol dehydrogenase () is an enzyme that catalyzes the chemical reaction :an aromatic alcohol + NAD+ \rightleftharpoons an aromatic aldehyde + NADH + H+ Thus, the two substrates of this enzyme are aromatic alcohol and ...
uses an aromatic alcohol and NAD+ to produce an aromatic aldehyde, NADH and H+.
Aryl-alcohol dehydrogenase (NADP+) In enzymology, an aryl-alcohol dehydrogenase () is an enzyme that catalyzes the chemical reaction :an aromatic alcohol + NAD+ \rightleftharpoons an aromatic aldehyde + NADH + H+ Thus, the two substrates of this enzyme are aromatic alcohol and ...
uses an aromatic alcohol and NADP+ to produce an aromatic aldehyde, NADPH and H+. Aryldialkylphosphatase (also known as organophosphorus hydrolase, phosphotriesterase, and paraoxon hydrolase) uses an aryl dialkyl phosphate and H2O to produce dialkyl phosphate and an aryl alcohol.


Occurrences in lichen

Gyrophoric acid Gyrophoric acid is a depside that can be found in the lichen ''Cryptothecia rubrocincta'' and in '' Xanthoparmelia pokomyi''. It can also be found in most of the species of the '' Actinogyra'', ''Lasallia'', and ''Umbilicaria'' genera. See also ...
, a
depside A depside is a type of polyphenolic compound composed of two or more monocyclic aromatic units linked by an ester bond. Depsides are most often found in lichens, but have also been isolated from higher plants, including species of the Ericaceae, L ...
, and
orcinol Orcinol is an organic compound with the formula CH3C6H3(OH)2. It occurs in many species of lichens including '' Roccella tinctoria'' and ''Lecanora''. Orcinol has been detected in the "toxic glue" of the ant species ''Camponotus saundersi''. It is ...
are found in
lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...
''
Botryococcus braunii ''Botryococcus braunii'' is a green, pyramid-shaped planktonic microalga that is of potentially great importance in the field of biotechnology. Colonies held together by a lipid biofilm matrix can be found in temperate or tropical oligotrophic l ...
'' is the subject of research into the natural production of
butylated hydroxytoluene Butylated hydroxytoluene (BHT), also known as dibutylhydroxytoluene, is a lipophilic organic compound, chemically a derivative of phenol, that is useful for its antioxidant properties. BHT is widely used to prevent free radical-mediated oxidat ...
(BHT), an antioxidant, food additive and industrial chemical. Phenolic acids such as protocatechuic, p-hydroxybenzoic, 2,3-dihydroxybenzoic, chlorogenic, vanillic, caffeic, ''p''-coumaric and salicylic acid,
cinnamic acid Cinnamic acid is an organic compound with the formula C6H5-CH=CH- COOH. It is a white crystalline compound that is slightly soluble in water, and freely soluble in many organic solvents. Classified as an unsaturated carboxylic acid, it occurs n ...
and hydroxybenzaldehydes such as p-hydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde,
vanillin Vanillin is an organic compound with the molecular formula . It is a phenolic aldehyde. Its functional groups include aldehyde, hydroxyl, and ether. It is the primary component of the extract of the vanilla bean. Synthetic vanillin is now used ...
have been isolated from in vitro culture of the freshwater green alga '' Spongiochloris spongiosa''.
Phlorotannin Phlorotannins are a type of tannins found in brown algae such as kelps and rockweeds or sargassacean species, and in a lower amount also in some red algae. Contrary to hydrolysable or condensed tannins, these compounds are oligomers of phloro ...
s, for instance
eckol Eckol is a phlorotannin isolated from brown algae in the family Lessoniaceae such as species in the genus '' Ecklonia'' such as '' E. cava'' or '' E. kurome'' or in the genus '' Eisenia'' such as '' Eisenia bicyclis''. The molecule possesses a d ...
, are found in
brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and po ...
. Vidalenolone can be found in the tropical
red alga Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...
'' Vidalia sp''.


Occurrence in land plants (embryophytes)


Occurrences in vascular plants

Phenolic compounds are mostly found in
vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They al ...
s (tracheophytes) i.e.
Lycopodiophyta The lycophytes, when broadly circumscribed, are a vascular plant (tracheophyte) subgroup of the kingdom Plantae. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldes ...
(lycopods),
Pteridophyta A pteridophyte is a vascular plant (with xylem and phloem) that disperses spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as " cryptogams", meaning that their means of reproduction is hidden. Ferns ...
(ferns and horsetails),
Angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s (flowering plants or Magnoliophyta) and
Gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό ...
s (
conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...
s,
cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...
s,
Ginkgo ''Ginkgo'' is a genus of non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and is now the only living genus with ...
and
Gnetales Gnetophyta () is a division of plants (alternatively considered the subclass Gnetidae or order Gnetales), grouped within the gymnosperms (which also includes conifers, cycads, and ginkgos), that consists of some 70 species across the three reli ...
). In ferns, compounds such as
kaempferol Kaempferol (3,4′,5,7-tetrahydroxyflavone) is a natural flavonol, a type of flavonoid, found in a variety of plants and plant-derived foods including kale, beans, tea, spinach, and broccoli. Kaempferol is a yellow crystalline solid with a meltin ...
and its
glucoside A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes. The name was o ...
can be isolated from the
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
ic extract of fronds of ''
Phegopteris connectilis ''Phegopteris connectilis'', commonly known as long beech fern, northern beech fern, and narrow beech fern, is a species of fern native to forests of the Northern Hemisphere. Unlike its close relative, ''Phegopteris hexagonoptera'', which is ter ...
'' or kaempferol-3-O-rutinoside, a known bitter-tasting flavonoid glycoside, can be isolated from the rhizomes of '' Selliguea feei''.
Hypogallic acid 2,3-Dihydroxybenzoic acid is a natural phenol found in '' Phyllanthus acidus'' and in the aquatic fern ''Salvinia molesta''. It is also abundant in the fruits of ''Flacourtia inermis''. It is a dihydroxybenzoic acid, a type of organic compound. Th ...
,
caffeic acid Caffeic acid is an organic compound that is classified as a hydroxycinnamic acid. This yellow solid consists of both phenolic and acrylic functional groups. It is found in all plants because it is an intermediate in the biosynthesis of lignin, one ...
, paeoniflorin and pikuroside can be isolated from the freshwater fern ''
Salvinia molesta ''Salvinia molesta'', commonly known as giant salvinia, or as kariba weed after it infested a large portion of Lake Kariba between Zimbabwe and Zambia, is an aquatic fern, native to south-eastern Brazil. It is a free-floating plant that does ...
''. In conifers (Pinophyta), phenolics are stored in polyphenolic parenchyma cells, a tissue abundant in the
phloem Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...
of all conifers. The
aquatic plant Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...
''
Myriophyllum spicatum ''Myriophyllum spicatum'' (Eurasian watermilfoil or spiked water-milfoil) is native to Europe, Asia, and north Africa, but has a wide geographic and climatic distribution among some 57 countries, extending from northern Canada to South Africa. It ...
'' produces ellagic, gallic and
pyrogallic acid Pyrogallol is an organic compound with the formula C6H3(OH)3. It is a water-soluble, white solid although samples are typically brownish because of its sensitivity toward oxygen. It is one of three isomers of benzenetriols. Production and reac ...
s and (+)-
catechin Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids. The name of the catechin chemical family derives from ''catechu'', which is the tannic ...
.


Occurrences in monocotyledons

Alkylresorcinol Alkylresorcinols, also known as resorcinolic lipids, are phenolic lipids composed of long aliphatic chains and resorcinol-type phenolic rings. Natural sources of alkylresorcinols Alkylresorcinols are relatively rare in nature, with the main know ...
s can be found in cereals. 2,4-Bis(4-hydroxybenzyl)phenol is a phenolic compound found in the orchids ''
Gastrodia elata ''Gastrodia elata'' is a saprophytic perennial herb in the family Orchidaceae. It is found in Nepal, Bhutan, India, Japan, North Korea, Siberia, Taiwan, and China. Description The orchid has an 8–12 centimeters long elliptical underground rhiz ...
'' and ''
Galeola faberi ''Galeola faberi'' is an orchid species in the genus ''Galeola'' found in central and southern China, as well as in Nepal, the eastern Himalayas, Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Viet ...
''.


Occurrences in non-vascular plants

Phenolics can also be found in non-vascular land plants (
bryophyte The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited in ...
s).
Dihydrostilbenoid Dihydrostilbenoids (bibenzyls) are natural phenols formed from the dihydrostilbene ( bibenzyl) backbone. Examples Dihydro-resveratrol is a natural phenol with a bibenzyl structure found in wine. It is also a metabolite of trans-resveratrol for ...
s and bis(dibenzyls) can be found in liverworts (
Marchantiophyta The Marchantiophyta () are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of ...
), for instance, the macrocycles
cavicularin Cavicularin is a natural phenolic secondary metabolite Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fungi, animal ...
and
riccardin C Riccardin C is a macrocyclic bis(bibenzyl). It is a secondary metabolite isolated from the Siberian cowslip subspecies '' Primula veris subsp. macrocalyx'', in '' Reboulia hemisphaerica'' and in the Chinese liverwort '' Plagiochasma intermedium'' ...
. Though lignin is absent in
moss Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...
es (Bryophyta) and
hornwort Hornworts are a group of non-vascular Embryophytes (land plants) constituting the division Anthocerotophyta (). The common name refers to the elongated horn-like structure, which is the sporophyte. As in mosses and liverworts, hornworts have a ...
s (Anthocerotophyta), some phenolics can be found in those two taxa. For instance,
rosmarinic acid Rosmarinic acid, named after rosemary (''Salvia rosmarinus'' Linn.), is a polyphenol constituent of many culinary herbs, including rosemary (''Salvia rosmarinus'' L.), perilla (''Perilla frutescens'' L.), Salvia officinalis, sage (''Salvia offic ...
and a rosmarinic acid 3'-O-β-D-glucoside can be found in the hornwort '' Anthoceros agrestis''.


Occurrences in other eukaryotes


Occurrences in insects

The hardening of the protein component of
insect cuticle The cuticle forms the major part of the integument of the Arthropoda. It includes most of the material of the exoskeleton of the insects, Crustacea, Arachnida, and Myriapoda. Morphology In arthropods, the integument, the external "skin", or "s ...
has been shown to be due to the tanning action of an agent produced by oxidation of a phenolic substance forming
sclerotin Sclerotin is a component of the cuticle of various Arthropoda, most familiarly insects. It is formed by cross-linking members of particular classes of protein molecules, a biochemical process called sclerotization, a form of tanning in which qu ...
. In the analogous hardening of the cockroach
ootheca An ootheca (pl. ''oothecae'' ) is a type of egg mass made by any member of a variety of species including mollusks (such as ''Turbinella laevigata''), mantises, and cockroaches. The word is a Latinized combination of ''oo-'', meaning "egg", f ...
, the phenolic substance concerned is 3:4-dihydroxybenzoic acid (
protocatechuic acid Protocatechuic acid (PCA) is a dihydroxybenzoic acid, a type of phenolic acid. It is a major metabolite of antioxidant polyphenols found in green tea. It has mixed effects on normal and cancer cells in ''in vitro'' and ''in vivo'' studies. Biolo ...
).
Acetosyringone Acetosyringone is a phenolic natural product and a chemical compound related to acetophenone and 2,6-dimethoxyphenol. It was first described in relation to lignan/phenylpropanoid-type phytochemicals, with isolation from a variety of plant source ...
is produced by the male leaffooted bug ('' Leptoglossus phyllopus'') and used in its communication system.Acetosyringone on www.pherobase.com, the pheromones data base
/ref>
Guaiacol Guaiacol () is an organic compound with the formula C6H4(OH)(OCH3). It is a phenolic compound containing an methoxy functional group. Guaiacol appears as a viscous colorless oil, although aged or impure samples are often yellowish. It occurs wid ...
is produced in the gut of
Desert locust The desert locust (''Schistocerca gregaria'') is a species of locust, a periodically swarming, short-horned grasshopper in the family Acrididae. They are found primarily in the deserts and dry areas of northern and eastern Africa, Arabia, and sou ...
s, ''Schistocerca gregaria'', by the breakdown of plant material. This process is undertaken by the gut bacterium ''
Pantoea agglomerans ''Pantoea agglomerans'' is a Gram-negative bacterium that belongs to the family Erwiniaceae. It was formerly called ''Enterobacter agglomerans'', or ''Erwinia herbicola'' and is a ubiquitous bacterium commonly isolated from plant surfaces, seed ...
''. Guaiacol is one of the main components of the pheromones that cause locust swarming.
Orcinol Orcinol is an organic compound with the formula CH3C6H3(OH)2. It occurs in many species of lichens including '' Roccella tinctoria'' and ''Lecanora''. Orcinol has been detected in the "toxic glue" of the ant species ''Camponotus saundersi''. It is ...
has been detected in the "toxic glue" of the ant species ''
Camponotus saundersi ''Colobopsis saundersi'', synonym ''Camponotus saundersi'', is a species of ant found in Malaysia and Brunei, belonging to the genus ''Colobopsis''. A worker can explode suicidally and aggressively as an ultimate act of defense, an ability it has ...
''. ''
Rhynchophorus ferrugineus The palm weevil ''Rhynchophorus ferrugineus'' is one of two species of snout beetle known as the red palm weevil, Asian palm weevil or sago palm weevil. The adult beetles are relatively large, ranging between long, and are usually a rusty red c ...
'' (red palm weevil) use 2-methoxy-4-vinylphenol for chemical signaling (
pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s). Other simple and complex phenols can be found in eusocial ants (such as
Crematogaster ''Crematogaster'' is an ecologically diverse genus of ants found worldwide, which are characterised by a distinctive heart-shaped gaster (abdomen), which gives them one of their common names, the Saint Valentine ant. Members of this genus are ...
) as components of venom.


Occurrences in mammals

In female elephants, the two compounds 3-ethyl phenol and 2-ethyl 4,5 dimethylphenol have been detected in urine samples. Temporal glands secretion examination showed the presence of
phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...
,
m-cresol ''meta''-Cresol, also 3-methylphenol, is an organic compound with the formula CH3C6H4(OH). It is a colourless, viscous liquid that is used as an intermediate in the production of other chemicals. It is a derivative of phenol and is an isomer of ...
and
p-cresol ''para''-Cresol, also 4-methylphenol, is an organic compound with the formula CH3C6H4(OH). It is a colourless solid that is widely used intermediate in the production of other chemicals. It is a derivative of phenol and is an isomer of ''o'' ...
(4-methyl phenol) during
musth Musth or must (from Persian, )''The Oxford Dictionary and Thesaurus: American edition'', published 1996 by Oxford University Press; p. 984 is a periodic condition in bull (male) elephants characterized by aggressive behavior and accompanied ...
in male
elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae an ...
s.
p-Cresol ''para''-Cresol, also 4-methylphenol, is an organic compound with the formula CH3C6H4(OH). It is a colourless solid that is widely used intermediate in the production of other chemicals. It is a derivative of phenol and is an isomer of ''o'' ...
and
o-cresol ''ortho''-Cresol, also called 2-methylphenol, or 2-hydroxytoluene, is an organic compound with the formula CH3C6H4(OH). It is a colourless solid that is widely used intermediate in the production of other chemicals. It is a derivative of phenol a ...
are also components of the human
sweat Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distrib ...
. P-cresol is also a major component in
pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...
odor. 4-Ethylphenol, 1,2-dihydroxybenzene, 3-hydroxyacetophenone, 4-methyl-1,2-dihydroxybenzene, 4-methoxyacetophenone, 5-methoxysalicylic acid,
salicylaldehyde Salicylic aldehyde (2-hydroxybenzaldehyde) is the organic compound with the formula (C7 H6 O2) C6H4CHO-2-OH. Along with 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, it is one of the three isomers of hydroxybenzaldehyde. This colorless oily ...
, and 3-hydroxybenzoic acid are components of
castoreum Castoreum is a yellowish exudate from the castor sacs of mature beavers. Beavers use castoreum in combination with urine to scent mark their territory. Both beaver sexes have a pair of castor sacs and a pair of anal glands, located in two cavitie ...
, the exudate from the castor sacs of the mature North American beaver (''
Castor canadensis The North American beaver (''Castor canadensis'') is one of two extant beaver species, along with the Eurasian beaver (''Castor fiber''). It is native to North America and introduced in South America (Patagonia) and Europe (primarily Finland ...
'') and the European beaver (''
Castor fiber The Eurasian beaver (''Castor fiber'') or European beaver is a beaver species that was once widespread in Eurasia, but was hunted to near-extinction for both its fur and castoreum. At the turn of the 20th century, only about 1,200 beavers survi ...
''), used in perfumery.


Roles

In some cases of natural phenols, they are present in vegetative
foliage A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, s ...
to discourage
herbivory A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
, such as in the case of
Western poison oak ''Toxicodendron diversilobum'' (syn. ''Rhus diversiloba''), commonly named Pacific poison oak or western poison oak, is a woody vine or shrub in the sumac family, Anacardiaceae. It is widely distributed in western North America, inhabiting coni ...
.


Role in soils

In
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
s, it is assumed that larger amounts of phenols are released from decomposing
plant litter Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constitue ...
rather than from throughfall in any natural plant community. Decomposition of dead plant material causes complex organic compounds to be slowly oxidized lignin-like
humus In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...
or to break down into simpler forms (sugars and amino sugars, aliphatic and phenolic organic acids), which are further transformed into microbial biomass (microbial humus) or are reorganized, and further oxidized, into humic assemblages ( fulvic and
humic Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th an ...
acids), which bind to clay minerals and
metal hydroxide Metal hydroxides are hydroxides of metals. They are often strong bases. They consist of hydroxide anions and metallic cations. Some metal hydroxides, such as alkali metal hydroxides, ionize completely when dissolved. Certain metal hydroxides ar ...
s. There has been a long debate about the ability of plants to uptake humic substances from their root systems and to metabolize them. There is now a consensus about how humus plays a hormonal role rather than simply a nutritional role in plant physiology. In the soil, soluble phenols face four different fates. They might be degraded and mineralized as a carbon source by heterotrophic microorganisms; they can be transformed into insoluble and recalcitrant
humic Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th an ...
substances by polymerization and condensation reactions (with the contribution of soil organisms); they might adsorb to clay minerals or form
chelate Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...
s with aluminium or iron ions; or they might remain in dissolved form, leached by percolating water, and finally leave the ecosystem as part of
dissolved organic carbon Dissolved organic carbon (DOC) is the fraction of organic carbon operationally defined as that which can pass through a filter with a pore size typically between 0.22 and 0.7 micrometers. The fraction remaining on the filter is called partic ...
(DOC).
Leaching Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to: * Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amou ...
is the process by which cations such as
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
(Fe) and
aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
(Al), as well as organic matter, are removed from the litterfall and transported downward into the soil below. This process is known as
podzolization Podsolisation is an extreme form of leaching which causes the eluviation of iron and aluminium sesquioxides. The process generally occurs in areas where precipitation is greater than evapotranspiration. The minerals are removed by a process kno ...
and is particularly intense in boreal and cool temperate forests that are mainly constituted by coniferous pines, whose litterfall is rich in phenolic compounds and
fulvic acid Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th an ...
.''Biogeochemistry: An Analysis of Global Change''. 2nd Edition. William H. Schlesinger, Academic Press, 1997, 108, 135, 152–158, 180–183, 191–194


Role in survival

Phenolic compounds can act as protective agents, inhibitors, natural animal toxicants and pesticides against invading organisms, i.e. herbivores, nematodes, phytophagous insects, and fungal and bacterial pathogens. The scent and pigmentation conferred by other phenolics can attract symbiotic microbes, pollinators and animals that disperse fruits.


Defense against predators

Volatile phenolic compounds are found in plant
resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on natu ...
where they may attract benefactors such as
parasitoid In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...
s or
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
s of the herbivores that attack the plant. In the kelp species ''
Alaria marginata ''Alaria marginata'', the winged kelp, is a brown alga species in the genus '' Alaria''. It can grow up to 13 feet. Fronds are long and narrow with raised midrib and wavy edges. Each frond has two rows of several smooth, oblong, 5 inch spore-bear ...
'', phenolics act as chemical defence against herbivores. In tropical ''
Sargassum ''Sargassum'' is a genus of brown (class Phaeophyceae) macroalgae ( seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral ...
'' and '' Turbinaria'' species that are often preferentially consumed by
herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
es and
echinoid Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...
s, there is a relatively low level of phenolics and tannins. Marine allelochemicals generally are present in greater quantity and diversity in tropical than in temperate regions. Marine algal phenolics have been reported as an apparent exception to this biogeographic trend. High phenolic concentrations occur in brown algae species (orders
Dictyotales Dictyotales is a large order in the brown algae (class Phaeophyceae). Members of this order generally prefer warmer waters than other brown algae. One genus in this order is calcareous, '' Padina'', the only calcareous member of this phylum. ' ...
and
Fucales The Fucales (fucoids) are an order in the brown algae (class Phaeophyceae). The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebaseref name="Guiry and Guiry">Guiry, M.D. and ...
) from both temperate and tropical regions, indicating that
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
alone is not a reasonable predictor of plant phenolic concentrations.


Defense against infection

In ''
Vitis vinifera ''Vitis vinifera'', the common grape vine, is a species of flowering plant, native to the Mediterranean region, Central Europe, and southwestern Asia, from Morocco and Portugal north to southern Germany and east to northern Iran. There are curre ...
'' grape, ''trans''- resveratrol is a phytoalexin produced against the growth of fungal pathogens such as ''
Botrytis cinerea ''Botrytis cinerea'' is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" o ...
'' and
delta-viniferin δ-Viniferin is a resveratrol dehydrodimer. It is an isomer of epsilon-viniferin. It can be isolated from stressed grapevine (''Vitis vinifera'') leaves. It is also found in plant cell cultures and wine. It can also be found in ''Rheum maximowicz ...
is another grapevine
phytoalexin Phytoalexins are antimicrobial substances, some of which are antioxidative as well. They are defined, not by their having any particular chemical structure or character, but by the fact that they are defensively synthesized ''de novo'' by plants t ...
produced following fungal infection by ''
Plasmopara viticola ''Plasmopara viticola'', the causal agent of grapevine downy mildew, is a heterothallic oomycete that overwinters as oospores in leaf litter and soil. In the spring, oospores germinate to produce macrosporangia, which under wet condition releas ...
''.
Pinosylvin Pinosylvin is an organic compound with the formula C6H5CH=CHC6H3(OH)2. A white solid, it is related to trans-stilbene, but with two hydroxy groups on one of the phenyl substituents. It is very soluble in many organic solvents, such as acetone. O ...
is a pre-infectious
stilbenoid Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C2–C6 structure. In biochemical terms, they belong to the family of phenylpropanoids and share most of their biosynthesis pathway with chalcones. Most stilbenoids are prod ...
toxin (i.e. synthesized prior to infection), contrary to
phytoalexin Phytoalexins are antimicrobial substances, some of which are antioxidative as well. They are defined, not by their having any particular chemical structure or character, but by the fact that they are defensively synthesized ''de novo'' by plants t ...
s, which are synthesized during infection. It is present in the
heartwood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin t ...
of
Pinaceae The Pinaceae, or pine family, are conifer trees or shrubs, including many of the well-known conifers of commercial importance such as Cedrus, cedars, firs, Tsuga, hemlocks, larches, pines and spruces. The family is included in the order Pinales, ...
. It is a fungitoxin protecting the wood from fungal infection.
Sakuranetin Sakuranetin is a flavan-on, the 7-methoxy derivative of naringenin, found in Polymnia fruticosa and rice, where it acts as a phytoalexin against spore germination of '' Pyricularia oryzae''. Glycosides Sakuranin is the 5-O- glucoside of sakura ...
is a
flavanone The flavanones, a type of flavonoids, are various aromatic, colorless ketones derived from flavone that often occur in plants as glycosides. List of flavanones * Blumeatin * Butin * Eriodictyol * Hesperetin * Hesperidin * Homoeriodictyol * Iso ...
, a type of flavonoid. It can be found in '' Polymnia fruticosa'' and
rice Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima ''Oryza glaberrima'', commonly known as African rice, is one of the two domesticated rice species. It was first domesticated and grown i ...
, where it acts as a
phytoalexin Phytoalexins are antimicrobial substances, some of which are antioxidative as well. They are defined, not by their having any particular chemical structure or character, but by the fact that they are defensively synthesized ''de novo'' by plants t ...
against spore germination of ''
Pyricularia oryzae ''Pyricularia'' is a genus of fungi which was named by Saccardo in 1880.Saccardo, P.A. Michelia 2(no. 6): 20. 1880 The polyphyletic nature of ''Pyricularia'' has been resolved and species of ''Pyricularia s. str.'' were shown to belong to a mon ...
''. In ''
Sorghum ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many othe ...
'', the ''SbF3'H2'' gene, encoding a flavonoid 3'-hydroxylase, seems to be expressed in
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
-specific 3-deoxyanthocyanidin
phytoalexin Phytoalexins are antimicrobial substances, some of which are antioxidative as well. They are defined, not by their having any particular chemical structure or character, but by the fact that they are defensively synthesized ''de novo'' by plants t ...
s synthesis, for example in ''Sorghum-
Colletotrichum ''Colletotrichum'' (sexual stage: ''Glomerella'') is a genus of fungi that are symbionts to plants as endophytes (living within the plant) or phytopathogens. Many of the species in this genus are plant pathogens, but some species may have a mutu ...
'' interactions. 6-Methoxymellein is a
dihydroisocoumarin Dihydroisocoumarins are phenolic compounds related to isocoumarin. Dihydroisocoumarin glucosides can be found in ''Caryocar glabrum ''Caryocar glabrum'' is a species of tree in the family Caryocaraceae. It is native to South America ...
and a
phytoalexin Phytoalexins are antimicrobial substances, some of which are antioxidative as well. They are defined, not by their having any particular chemical structure or character, but by the fact that they are defensively synthesized ''de novo'' by plants t ...
induced in carrot slices by
UV-C Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
, that allows resistance to ''
Botrytis cinerea ''Botrytis cinerea'' is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" o ...
'' and other
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s. Danielone is a
phytoalexin Phytoalexins are antimicrobial substances, some of which are antioxidative as well. They are defined, not by their having any particular chemical structure or character, but by the fact that they are defensively synthesized ''de novo'' by plants t ...
found in the
papaya The papaya (, ), papaw, () or pawpaw () is the plant species ''Carica papaya'', one of the 21 accepted species in the genus ''Carica'' of the family Caricaceae. It was first domesticated in Mesoamerica, within modern-day southern Mexico and ...
fruit. This compound showed high antifungal activity against '' Colletotrichum gloesporioides'', a pathogenic fungus of papaya. Stilbenes are produced in ''
Eucalyptus sideroxylon ''Eucalyptus sideroxylon'', commonly known as mugga ironbark, or red ironbark is a small to medium-sized tree that is endemic to eastern Australia. It has dark, deeply furrowed ironbark, lance-shaped adult leaves, flower buds in groups of se ...
'' in case of pathogens attacks. Such compounds can be implied in the
hypersensitive response Hypersensitive response (HR) is a mechanism used by plants to prevent the spread of infection by microbial pathogens. HR is characterized by the rapid death of cells in the local region surrounding an infection and it serves to restrict the growt ...
of plants. High levels of phenolics in some woods can explain their natural
preservation Preservation may refer to: Heritage and conservation * Preservation (library and archival science), activities aimed at prolonging the life of a record while making as few changes as possible * ''Preservation'' (magazine), published by the Nat ...
against rot. In plants, VirA is a protein
histidine kinase Histidine kinases (HK) are multifunctional, and in non-animal kingdoms, typically transmembrane, proteins of the transferase class of enzymes that play a role in signal transduction across the cellular membrane. The vast majority of HKs are hom ...
which senses certain sugars and phenolic compounds. These compounds are typically found from wounded plants, and as a result VirA is used by ''Agrobacterium tumefaciens'' to locate potential host organisms for infection.


Role in allelopathic interactions

Natural phenols can be involved in allelopathic interactions, for example in
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
or in water.
Juglone Juglone, also called 5-hydroxy-1,4-naphthalenedione (IUPAC) is an organic compound with the molecular formula C10H6O3. In the food industry, juglone is also known as C.I. Natural Brown 7 and C.I. 75500. It is insoluble in benzene but soluble i ...
is an example of such a molecule inhibiting the growth of other plant species around walnut trees. The aquatic vascular plant ''
Myriophyllum spicatum ''Myriophyllum spicatum'' (Eurasian watermilfoil or spiked water-milfoil) is native to Europe, Asia, and north Africa, but has a wide geographic and climatic distribution among some 57 countries, extending from northern Canada to South Africa. It ...
'' produces ellagic, gallic and
pyrogallic acid Pyrogallol is an organic compound with the formula C6H3(OH)3. It is a water-soluble, white solid although samples are typically brownish because of its sensitivity toward oxygen. It is one of three isomers of benzenetriols. Production and reac ...
s and (+)-
catechin Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids. The name of the catechin chemical family derives from ''catechu'', which is the tannic ...
, allelopathic phenolic compounds inhibiting the growth of blue-green alga ''
Microcystis aeruginosa ''Microcystis aeruginosa'' is a species of freshwater cyanobacteria that can form harmful algal blooms of economic and ecological importance. They are the most common toxic cyanobacterial bloom in eutrophic fresh water. Cyanobacteria produce ne ...
''. Phenolics, and in particular
flavonoid 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. Chemically, flavonoids ...
s and
isoflavonoid Isoflavonoids are a class of flavonoid phenolic compounds, many of which are biologically active. Isoflavonoids and their derivatives are sometimes referred to as phytoestrogens, as many isoflavonoid compounds have biological effects via the estr ...
s, may be involved in endomycorrhizae formation.
Acetosyringone Acetosyringone is a phenolic natural product and a chemical compound related to acetophenone and 2,6-dimethoxyphenol. It was first described in relation to lignan/phenylpropanoid-type phytochemicals, with isolation from a variety of plant source ...
has been best known for its involvement in plant-pathogen recognition, especially its role as a signal attracting and transforming unique, oncogenic bacteria in genus ''
Agrobacterium ''Agrobacterium'' is a genus of Gram-negative bacteria established by H. J. Conn that uses horizontal gene transfer to cause tumors in plants. '' Agrobacterium tumefaciens'' is the most commonly studied species in this genus. ''Agrobacterium'' i ...
''. The virA gene on the
Ti plasmid A tumour inducing (Ti) plasmid is a plasmid found in pathogenic species of ''Agrobacterium'', including ''A. tumefaciens, ''A. rhizogenes'', ''A. rubi'' and ''A. vitis''. Evolutionarily, the Ti plasmid is part of a family of plasmids carried b ...
in the genome of ''
Agrobacterium tumefaciens ''Agrobacterium radiobacter'' (more commonly known as ''Agrobacterium tumefaciens'') is the causal agent of crown gall disease (the formation of tumours) in over 140 species of eudicots. It is a rod-shaped, Gram-negative soil bacterium. Sympto ...
'' and ''
Agrobacterium rhizogenes ''Rhizobium rhizogenes'' (formerly ''Agrobacterium rhizogenes'') is a Gram-negative soil bacterium that produces hairy root disease in dicotyledonous plants. ''R. rhizogenes'' induces the formation of proliferative multiple-branched adventitious ...
'' is used by these soil bacteria to infect plants, via its encoding for a receptor for acetosyringone and other phenolic phytochemicals exuded by plant wounds. This compound also allows higher transformation efficiency in plants, in A. tumefaciens mediated transformation procedures, and so is of importance in plant biotechnology.


Content in human food

Notable sources of natural phenols in
human nutrition Human nutrition deals with the provision of essential nutrients in food that are necessary to support human life and good health. Poor nutrition is a chronic problem often linked to poverty, food security, or a poor understanding of nutritiona ...
include
berries A berry is a small, pulpy, and often edible fruit. Typically, berries are juicy, rounded, brightly colored, sweet, sour or tart, and do not have a stone or pit, although many pips or seeds may be present. Common examples are strawberries, rasp ...
,
tea Tea is an aromatic beverage prepared by pouring hot or boiling water over cured or fresh leaves of ''Camellia sinensis'', an evergreen shrub native to East Asia which probably originated in the borderlands of southwestern China and north ...
,
beer Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...
,
olive oil Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: f ...
,
chocolate Chocolate is a food made from roasted and ground cacao seed kernels that is available as a liquid, solid, or paste, either on its own or as a flavoring agent in other foods. Cacao has been consumed in some form since at least the Olmec civ ...
or
cocoa Cocoa may refer to: Chocolate * Chocolate * ''Theobroma cacao'', the cocoa tree * Cocoa bean, seed of ''Theobroma cacao'' * Chocolate liquor, or cocoa liquor, pure, liquid chocolate extracted from the cocoa bean, including both cocoa butter and ...
,
coffee Coffee is a drink prepared from roasted coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulant, stimulating effect on humans, primarily due to its caffeine content. It is the most popular hot drink in the world. S ...
,
pomegranate The pomegranate (''Punica granatum'') is a fruit-bearing deciduous shrub in the family Lythraceae, subfamily Punicoideae, that grows between tall. The pomegranate was originally described throughout the Mediterranean Basin, Mediterranean re ...
s,
popcorn Popcorn (also called popped corn, popcorns or pop-corn) is a variety of corn kernel which expands and puffs up when heated; the same names also refer to the foodstuff produced by the expansion. A popcorn kernel's strong hull contains the se ...
,
yerba maté Yerba mate or yerba-maté (''Ilex paraguariensis''; from Spanish ; pt, erva-mate, or ; gn, ka'a, ) is a plant species of the holly genus '' Ilex'' native to South America. It was named by the French botanist Augustin Saint-Hilaire. The leav ...
,
fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
s and fruit based drinks (including cider, wine and
vinegar Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting simple sugars to eth ...
) and
vegetable Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the flowers, fruits, stems, ...
s.
Herb In general use, herbs are a widely distributed and widespread group of plants, excluding vegetables and other plants consumed for macronutrients, with savory or aromatic properties that are used for flavoring and garnishing food, for medicinal ...
s and
spice A spice is a seed, fruit, root, bark, or other plant substance primarily used for flavoring or coloring food. Spices are distinguished from herbs, which are the leaves, flowers, or stems of plants used for flavoring or as a garnish. Spices a ...
s,
nut Nut often refers to: * Nut (fruit), fruit composed of a hard shell and a seed, or a collective noun for dry and edible fruits or seeds * Nut (hardware), fastener used with a bolt Nut or Nuts may also refer to: Arts, entertainment, and media Co ...
s (walnuts, peanut) and
alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...
e are also potentially significant for supplying certain natural phenols. Natural phenols can also be found in fatty matrices like
olive oil Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: f ...
.
Unfiltered olive oil Unfiltered olive oil (also known as ''cloudy olive oil'', ''veiled olive oil'', or ''olio nuovo'') is an intermediate product of olive oil extraction. It is actually the initial cloudy juice of the olive drupes soon after crushing, separation an ...
has the higher levels of phenols, or polar phenols that form a complex phenol-protein complex. Phenolic compounds, when used in
beverage A drink or beverage is a liquid intended for human consumption. In addition to their basic function of satisfying thirst, drinks play important roles in human culture. Common types of drinks include plain drinking water, milk, juice, smoo ...
s, such as
prune juice Prune juice is a fruit juice derived from prunes (dried plums) that have been rehydrated. It is a mass-produced product that is often produced using a hot extraction method, and juice concentrate is typically produced using a low-temperature ext ...
, have been shown to be helpful in the color and sensory components, such as alleviating bitterness. Some advocates for
organic farming Organic farming, also known as ecological farming or biological farming,Labelling, article 30 o''Regulation (EU) 2018/848 of the European Parliament and of the Council of 30 May 2018 on organic production and labelling of organic products and re ...
claim that organically grown
potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Unit ...
es,
orange Orange most often refers to: *Orange (fruit), the fruit of the tree species '' Citrus'' × ''sinensis'' ** Orange blossom, its fragrant flower *Orange (colour), from the color of an orange, occurs between red and yellow in the visible spectrum * ...
s, and
leaf vegetable Leaf vegetables, also called leafy greens, pot herbs, vegetable greens, or simply greens, are plant leaves eaten as a vegetable, sometimes accompanied by tender petioles and shoots. Leaf vegetables eaten raw in a salad can be called salad gre ...
s have more phenolic compounds and these may provide
antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...
protection against
heart disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, hea ...
and
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
. However, evidence on substantial differences between organic food and conventional food is insufficient to support claims that organic food is safer or healthier than conventional food.Blair, Robert. (2012). ''Organic Production and Food Quality: A Down to Earth Analysis''. Wiley-Blackwell, Oxford, UK.


Human metabolism

In animals and humans, after ingestion, natural phenols become part of the
xenobiotic metabolism Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set o ...
. In subsequent phase II reactions, these activated metabolites are conjugated with charged species such as
glutathione Glutathione (GSH, ) is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, pe ...
,
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
,
glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid (carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinogeni ...
or glucuronic acid. These reactions are catalysed by a large group of broad-specificity transferases.
UGT1A6 UDP-glucuronosyltransferase 1-6 is an enzyme that in humans is encoded by the ''UGT1A6'' gene. Function UDP-glucuronosyltransferase 1-6 is a UDP-glucuronosyltransferase, an enzyme of the glucuronidation pathway that transforms small lipophilic ...
is a human gene encoding a phenol UDP glucuronosyltransferase active on simple phenols."Cloning and substrate specificity of a human phenol UDP glucuronosyltransferase expressed in COS-7 cells". David Harding, Sylvie Fournel-Gigleux, Michael R. Jackson and Brian Burchell, ''Proc. Natl. Acad. Sci. USA'', November 1988, Volume 85, pp. 8381–8385,
abstract
The enzyme encoded by the gene UGT1A8 has glucuronidase activity with many substrates including
coumarin Coumarin () or 2''H''-chromen-2-one is an aromatic organic chemical compound with formula . Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by a lactone-like chain , forming a second six-membered h ...
s,
anthraquinone Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic organic compound with formula . Isomers include various quinone derivatives. The term anthraquinone however refers to the isomer, 9,10-anthraquinone (IUPAC: 9,10-dioxoan ...
s and flavones.


References


Books

* ''Biochemistry of phenolic compounds'', by J. B. Harborne, 1964, Academic Press
Google Books
* ''Plant phenolics'', by Pascal Ribéreau-Gayon, 1972, Oliver and Boyd Editions
Google Books
, ) * ''The Biochemistry of plant phenolics'', by C. F. van Sumere and P. J. Lea, Phytochemical Society of Europe, 1985, Clarendon Press
Google Books
) * ''Biochemistry of Phenolic Compounds'', by Wilfred Vermerris and Ralph Nicholson, 2006, Springer
Google book


External links


Natural sources of phenols on www.britannica.com


Databases

*
Phenol-Explorer Phenol-Explorer is a comprehensive database on natural phenols and polyphenol Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally ...

phenol-explorer.eu
, a database dedicated to phenolics found in food by Augustin Scalbert, INRA Clermont-Ferrand, Unité de Nutrition Humaine (Human food unit)
Phenols
at
ChEBI Chemical Entities of Biological Interest, also known as ChEBI, is a chemical database and ontology of molecular entities focused on 'small' chemical compounds, that is part of the Open Biomedical Ontologies (OBO) effort at the European Bioinf ...
(Chemical Entities of Biological Interest)
ChEMBLdb
a database of bioactive drug-like small molecules by the European Bioinformatics Institute *
Foodb FooDB (The Food Database) is a freely available, open-access database containing chemical ( micronutrient and macronutrient) composition data on common, unprocessed foods. It also contains extensive data on flavour and aroma constituents, food ad ...
, a database of compounds found in food {{Authority control Functional groups Disinfectants