Proanthocyanidin
Encyclopedia
Flavonoid
Flavonoids , are a class of plant secondary metabolites....
class of polyphenols. In essence, they are oligomer
Oligomer
In chemistry, an oligomer is a molecule that consists of a few monomer units , in contrast to a polymer that, at least in principle, consists of an unlimited number of monomers. Dimers, trimers, and tetramers are oligomers. Many oils are oligomeric, such as liquid paraffin...
chains of flavanols, such as the flavan-3-ol
Flavan-3-ol
Flavan-3-ols are a class of flavonoids that use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton. These compounds include the catechins and the catechin gallates....
epicatechin.
They were discovered in 1948 by Jacques Masquelier
Jacques Masquelier
Jacques Masquelier is a French scientist. He is the discoverer of oligomeric proanthocyanidins or OPCs....
, who developed and later patented techniques for the extraction of proanthocyanidins from pine needles and grape seeds.
Distribution in plants
Proanthocyanidins represent a group of condensed flavan-3-ols, such as procyanidins, prodelphinidins and propelargonidins, that can be found in many plants, most notably appleApple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
s, maritime pine
Maritime Pine
Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern Mediterranean region. The pejorative name 'pinaster' is derived from pinus + aster, translating as 'a poor imitation of a pine' Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern...
bark, cinnamon, aronia fruit, cocoa beans, grape seed, grape skin (procyanidins and prodelphinidin
Prodelphinidin
Prodelphinidin is a name for the polymeric tannins composed of gallocatechin.Prodelphinidin can be found in the pomegranate, in green tea leaves and in Myrica rubra....
s), and red wines of Vitis vinifera
Vitis vinifera
Vitis vinifera is a species of Vitis, native to the Mediterranean region, central Europe, and southwestern Asia, from Morocco and Portugal north to southern Germany and east to northern Iran....
(the common grape). However, bilberry
Bilberry
Bilberry is any of several species of low-growing shrubs in the genus Vaccinium , bearing edible berries. The species most often referred to is Vaccinium myrtillus L., but there are several other closely related species....
, cranberry
Cranberry
Cranberries are a group of evergreen dwarf shrubs or trailing vines in the subgenus Oxycoccus of the genus Vaccinium. In some methods of classification, Oxycoccus is regarded as a genus in its own right...
, black currant, green tea
Green tea
Green tea is made solely from the leaves of Camellia sinensis that have undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures throughout Asia. It has recently become more widespread in the West, where black tea is traditionally...
, black tea
Black tea
Black tea is a variety of tea that is more oxidized than the oolong, green, and white varieties.All four varieties are made from leaves of the shrub Camellia sinensis. Black tea is generally stronger in flavor and contains more caffeine than the less oxidized teas. Two principal varieties of the...
, and other plants also contain these flavonoids. Cocoa beans contain the highest concentrations. Proanthocyanidins can also be isolated from Quercus petraea and Q. robur heartwood (wine barrel oaks). Açaí oil
Acai oil
Açaí oil is obtained from the fruit of Euterpe oleracea , which grows in the Amazon Rainforest. The oil is rich in phenolic compounds similar in profile to the pulp itself, such as vanillic acid, syringic acid, p-hydroxybenzoic acid, protocatechuic acid and ferulic acid as well as -catechin and...
, obtained from the fruit of the açaí palm (Euterpe oleracea), is rich in numerous procyanidin oligomers.
Apples contain on average per serving about eight times the amount of proanthocyanidin found in wine, with some of the highest amounts found in the Red Delicious
Red Delicious
The Red Delicious is a clone of apple cultigen, now comprising more than 50 cultivars, that was recognized in Madison County, Iowa, United States, in 1880...
and Granny Smith
Granny Smith
The Granny Ramsey Smith green apple is a tip-bearing apple cultivar, which originated in Australia in 1868. It is named after Maria Ann Smith, who propagated the cultivar from a chance seedling. The tree is thought to be a hybrid of Malus sylvestris, the European Wild Apple, with the domestic...
varieties.
A patented extract of maritime pine
Maritime Pine
Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern Mediterranean region. The pejorative name 'pinaster' is derived from pinus + aster, translating as 'a poor imitation of a pine' Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern...
bark called Pycnogenol bears 65-75 percent proanthocyanidins (procyanidins). Thus a 100 mg serving would contain 65 to 75 mg of proanthocyanidins (procyanidins).
Proanthocyanidin glycoside
Glycoside
In chemistry, a glycoside is a molecule in which a sugar is bound to a non-carbohydrate moiety, usually a small organic molecule. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme...
s can be isolated from cocoa liquor.
The seed testas of field beans (Vicia faba
Vicia faba
This article refers to the Broad Bean plant. For Broadbean the company, see Broadbean, Inc.Vicia faba, the Broad Bean, Fava Bean, Field Bean, Bell Bean or Tic Bean, is a species of bean native to north Africa and southwest Asia, and extensively cultivated elsewhere. A variety is provisionally...
) contain proanthocyanidins that affect the digestibility in piglets and could have an inhibitory activity on enzymes.
Analysis
Condensed tannins can be characterised by a number of techniques including depolymerisation, asymmetric flow field flow fractionation or small-angle X-ray scattering.[4]DMACA
DMACA reagent
DMACA is an histological dye used to detect indole production in cells. It is used for the rapid identification of bacteria containing tryptophanase enzyme systems....
is a dye that is particularly useful for localization of proanthocyanidin compounds in plant histology. The use of the reagent results in blue staining. It can also be used to titrate proanthocyanidins.
Total phenols (or antioxidant effect) can be measured using the Folin-Ciocalteu reaction
Folin-Ciocalteu reagent
The Folin–Ciocalteu reagent or Folin's phenol reagent or Folin–Denis reagent, also called the Gallic Acid Equivalence method , is a mixture of phosphomolybdate and phosphotungstate used for the colorimetric assay of phenolic and polyphenolic antioxidants...
. Results are typically expressed as gallic acid equivalents (GAE).
Proanthocyanidins from field beans (Vicia faba
Vicia faba
This article refers to the Broad Bean plant. For Broadbean the company, see Broadbean, Inc.Vicia faba, the Broad Bean, Fava Bean, Field Bean, Bell Bean or Tic Bean, is a species of bean native to north Africa and southwest Asia, and extensively cultivated elsewhere. A variety is provisionally...
) or barley
Barley
Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...
have been estimated using the vanillin-HCl method, resulting in a red color of the test in the presence of catechin or proanthcyanidins.
Proanthocyanidins can be titrated using the Procyanidolic Index (also called the Bates-Smith
Edgar Charles Bate-Smith
Edgar Charles Bate-Smith was an English chemist and phytochemist specialising in food chemistry. He worked in the Low Temperature Research Station in Cambridge where his main fields of research were meat and polyphenols....
Assay). It is a testing method that measures the change in color when the product is mixed with certain chemicals. The greater the color changes, the higher the OPCs content is. It must be noted, however, that the Procyanidolic Index is a relative value that can measure well over 100. Unfortunately, a Procyanidolic Index of 95 was erroneously taken to mean 95% OPC by some and began appearing on the labels of finished products. All current methods of analysis suggest that the actual OPC content of these products is much lower than 95%.
An improved colorimetric test, called the Porter Assay or butanol-HCl-iron method, is the most common OPC assay currently in use. The unit of measurement of the Porter Assay is the PVU (Porter Value Unit). The Porter Assay is a chemical test to help determine the potency of procyanidin containing compounds, such as grape seed extract. It is an acid hydrolysis, which splits larger chain units (dimers and trimers) into single unit monomers and oxidizes them. This leads to a colour change, which can be measured using a spectrophotometer. The greater the absorbance at a certain wavelength of light, the greater the potency. Ranges for grape seed extract are from 25 PVU for low grade material to over 300 for premium grape seed extracts.
Gel permeation chromatography
Gel Permeation Chromatography
Gel permeation chromatography is a type of size exclusion chromatography , that separates analytes on the basis of size. The technique is often used for the analysis of polymers. As a technique, SEC was first developed in 1955 by Lathe and Ruthven. The term gel permeation chromatography can be...
(GPC) analysis allows to separate monomers from larger OPC molecules.
Monomers of proanthocyanidins can be characterized by HPLC analysis. Condensed tannins can undergo acid-catalyzed cleavage in the presence of a nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
like phloroglucinol
Phloroglucinol
Phloroglucinol is a benzenetriol. It is an organic compound that is used in the synthesis of pharmaceuticals and explosives. This molecule exists in two forms, or tautomers, 1,3,5-trihydroxybenzene, which has phenol-like, and 1,3,5-cyclohexanetrione , which has ketone-like character. These two...
(reaction called phloroglucinolysis), thioglycolic acid
Thioglycolic acid
Thioglycolic acid is the organic compound HSCH2CO2H. It contains both a thiol and a carboxylic acid. It is a clear liquid with a strong unpleasant odor...
(thioglycolysis), benzyl mercaptan or cysteamine
Cysteamine
Cysteamine is the chemical compound with the formula HSCH2CH2NH2. It is the simplest stable aminothiol and a degradation product of the amino acid cysteine. It is often used as the hydrochloride salt, HSCH2CH2NH3Cl....
(processes called thiolysis
Thiolysis
Thiolysis is a reaction with a thiol that cleaves one compound into two. This reaction is similar to hydrolysis, which involves water instead of a thiol. This reaction is seen in β-oxidation of fatty acids. The depolymerisation of condensed tannins with the use of benzyl mercaptan as...
) leading to the formation of oligomers that can be further analyzed.
Uses
This information attracted the attention of public news media, describing that red wine consumption is associated with favorable intake of health-promoting flavonoids that correlate positively with oxygen radical absorbance capacityOxygen radical absorbance capacity
Oxygen Radical Absorbance Capacity is a method of measuring antioxidant capacities in biological samples in vitro.A wide variety of foods has been tested using this method, with certain spices, berries and legumes rated highly. There exists no physiological proof in vivo that free-radical theory...
(ORAC).
In red wines, total oligomeric proanthocyanidin content, including flavan-3-ol
Flavan-3-ol
Flavan-3-ols are a class of flavonoids that use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton. These compounds include the catechins and the catechin gallates....
s (catechins), was substantially higher (177.18 ± 96.06 mg/L) than that in white wines (8.75 ± 4.53 mg/L). A relative high correlation in red wines was found between ORAC values and malvidin
Malvidin
Malvidin is an O-methylated anthocyanidin. As a primary plant pigment, its glycosides are highly abundant in nature. It is responsible primarily for the color of red wine, Vitis vinifera being one of its sources...
compounds (r = 0.75, P < 0.10), and proanthocyanidins (r = 0.87, P < 0.05).
In white wines, a significant correlation was found between the trimeric proanthocyanidin fraction and peroxyl radical scavenging values (r = 0.86, P < 0.10).
A moderate drink (1 drink per day, about 140 mL) of red wine, or white wine, or wine made from highbush blueberry
Blueberry
Blueberries are flowering plants of the genus Vaccinium with dark-blue berries and are perennial...
corresponded to an intake of 2.04 ± 0.81 mmol of TE (Trolox equivalents), 0.47 ± 0.15 mmol of TE, and 2.42 ± 0.88 mmol of TE of ORAC/day, respectively.
Proanthocyanidins are the principal vasoactive polyphenols in red wine that are linked to a reduced risk of coronary heart disease and to lower overall mortality. Proanthocyanidins are present at higher concentrations in wines from areas of southwestern France and Sardinia, which are associated with increased longevity in the population. Earlier studies that attributed this health benefit to resveratrol
Resveratrol
Resveratrol is a stilbenoid, a type of natural phenol, and a phytoalexin produced naturally by several plants when under attack by pathogens such as bacteria or fungi....
were premature because of the negligible amount of resveratrol in red wine.
Proanthocyanidins suppress production of a protein endothelin-1 that constricts blood vessels.
These studies provide data supporting the French Paradox
French paradox
The French Paradox is the observation that French people suffer a relatively low incidence of coronary heart disease, despite having a diet relatively rich in saturated fats...
that hypothesizes that intake of proanthocyanidins and other flavonoids from regular consumption of red wines prevents occurrence of a higher disease rate (cardiovascular diseases, diabetes) in French citizens on high-fat diets.
Proanthocyanidins have antioxidant activity and they play a role in the stabilization of collagen and maintenance of elastin — two critical proteins in connective tissue that support organs, joints, blood vessels, and muscle. Possibly because of their effects on blood vessels, proanthocyanidins have been reported in double-blind research to reduce the duration of edema after face-lift surgery from 15.9 to 11.5 days. In preliminary research, proanthocyanidins were reported to have anti-mutagenic activity (i.e., to prevent chromosomal mutations).
Common antioxidants currently used are vitamin C
Vitamin C
Vitamin C or L-ascorbic acid or L-ascorbate is an essential nutrient for humans and certain other animal species. In living organisms ascorbate acts as an antioxidant by protecting the body against oxidative stress...
and vitamin E
Vitamin E
Vitamin E is used to refer to a group of fat-soluble compounds that include both tocopherols and tocotrienols. There are many different forms of vitamin E, of which γ-tocopherol is the most common in the North American diet. γ-Tocopherol can be found in corn oil, soybean oil, margarine and dressings...
; however, studies show that proanthocyanidins antioxidant capabilities are 20 times more powerful than vitamin C and 50 times more potent than vitamin E
Vitamin E
Vitamin E is used to refer to a group of fat-soluble compounds that include both tocopherols and tocotrienols. There are many different forms of vitamin E, of which γ-tocopherol is the most common in the North American diet. γ-Tocopherol can be found in corn oil, soybean oil, margarine and dressings...
. Proanthocyanidins found in French maritime pine
Maritime Pine
Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern Mediterranean region. The pejorative name 'pinaster' is derived from pinus + aster, translating as 'a poor imitation of a pine' Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern...
bark and grape seed extract work directly to help strengthen all the blood vessels and improve the delivery of oxygen to the cells. Proanthocyanidins also have an affinity for cell membranes, providing nutritional support to reduce capillary permeability and fragility. Although flavonoids are widespread in nature, the powerful proanthocyanidin compound is most abundant and available from the bark of the maritime pine and in grape seeds, or pips. In addition, the particular proanthocyanidins found in the proprietary extract of maritime pine
Maritime Pine
Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern Mediterranean region. The pejorative name 'pinaster' is derived from pinus + aster, translating as 'a poor imitation of a pine' Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern...
bark called Pycnogenol have been shown to optimize the production of nitric oxide in the artery walls so as to relax them and allow greater blood flow and reduced pressure. Additionally, this same preparation, Pycnogenol, has been found to normalize platelet adhesion (aggregation) so as to facilitate normal blood flow.
Oligomeric proanthocyanidins
In 1948 Jack Masquelier discovered oligomeric proanthocyanidins (OPCs) in the skin of a peanutPeanut
The peanut, or groundnut , is a species in the legume or "bean" family , so it is not a nut. The peanut was probably first cultivated in the valleys of Peru. It is an annual herbaceous plant growing tall...
by accident. Oligomeric proanthocyanidins are a class of flavonoid
Flavonoid
Flavonoids , are a class of plant secondary metabolites....
complexes. OPCs are found in most plants and thus are a part of the human diet. Especially the skin, seeds and seed coverings of plants contain large amounts of oligomeric proanthocyanidins. They can be found in large quantities in grape seed extract and skin, in red grapes, in the red skins of peanuts, in coconut
Coconut
The coconut palm, Cocos nucifera, is a member of the family Arecaceae . It is the only accepted species in the genus Cocos. The term coconut can refer to the entire coconut palm, the seed, or the fruit, which is not a botanical nut. The spelling cocoanut is an old-fashioned form of the word...
s, apples (dimeric procyanidin B2), in cocoa, and in the bark of Pinus pinaster (formerly known as Pinus maritima). It can also be found in sea buckthorn oil
Sea buckthorn oil
Sea-buckthorn identifies a group of species in the genus Hippophae, the most commonly used of which is Hippophae rhamnoides. Oil can be extracted from either the seeds or the pulp of the fruit.-Chemical constituents:...
.
Oligomeric proanthocyanidins can be obtained by the mean of Vaccinium pahalae in vitro cell culture.
Biological signifiance
In nature, it is possible that OPCs serve as a plant defense against herbivoryPlant defense against herbivory
Plant defense against herbivory or host-plant resistance describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores. Plants use several strategies to defend against damage caused by herbivores...
.
Health benefits
Proanthocyanidins have strong anti-oxidant properties. Foods rich in proanthocyanidins have high oxygen radical absorbance capacityOxygen radical absorbance capacity
Oxygen Radical Absorbance Capacity is a method of measuring antioxidant capacities in biological samples in vitro.A wide variety of foods has been tested using this method, with certain spices, berries and legumes rated highly. There exists no physiological proof in vivo that free-radical theory...
, which has been linked to numerous health benefits such as weight management, cell health, and cardiovascular health. Scientists continue to research the relevance of proanthocyanidins' strong anti-oxidant properties in vivo for such applications as cancer prevention and cardiovascular health.
USDA does maintain a database of proanthocyanidin content and structure for many foods, but dietary supplements proanthocyanidin content has not been well documented.
In the human body, they might act as antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
s (free radical scavengers). OPCs may help protect against the effects of internal and environmental stresses such as cigarette smoking and pollution, as well as supporting normal body metabolic processes. The effects may include depressing blood fat, emolliating blood vessels, lowering blood pressure, preventing blood vessel scleroses, dropping blood viscidity and preventing thrombus
Thrombus
A thrombus , or blood clot, is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system...
formation.
Additionally, studies have shown that OPCs may prevent cardiovascular disease
Cardiovascular disease
Heart disease or cardiovascular disease are the class of diseases that involve the heart or blood vessels . While the term technically refers to any disease that affects the cardiovascular system , it is usually used to refer to those related to atherosclerosis...
s by counteracting the negative effects of high cholesterol
Cholesterol
Cholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...
on the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
and blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s.
A French maritime pine
Maritime Pine
Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern Mediterranean region. The pejorative name 'pinaster' is derived from pinus + aster, translating as 'a poor imitation of a pine' Pinus pinaster, the Maritime Pine, is a pine native to the western and southwestern...
bark extract of OPCs, Pycnogenol, has been shown to improve microcirculation, retinal edema and visual acuity in the early stages of diabetic retinopathy
Diabetic retinopathy
Diabetic retinopathy is retinopathy caused by complications of diabetes mellitus, which can eventually lead to blindness....
. Further study has shown that Pycnogenol maintains antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
and anti-inflammatory properties, selectively binds to collagen and elastin in the body, and aids in the production of endothelial nitric oxide. Pycnogenol has also been shown to help normalize blood glucose (sugar) levels, and delay sugar absorption.
OPCs are available from fresh grapes, grape juice, and red wine. Although in milligrams per ounce red wine may contain more OPCs than red grape juice, red grape juice contains more OPCs per average serving size. An 8-ounce serving of grape juice averages 124 milligrams OPCs, whereas a 5-ounce serving of red wine averages 91 milligrams. Many other foods and beverages also contain high amounts of OPCs, but very few come close to the levels found in red grape seeds and skins (which readily disperse into grape juice when crushed).
Non oxidative chemical depolymerisation
The condensed tannins can nevertheless undergo acid-catalyzed cleavage in the presence of (an excess of) a nucleophileNucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
like phloroglucinol
Phloroglucinol
Phloroglucinol is a benzenetriol. It is an organic compound that is used in the synthesis of pharmaceuticals and explosives. This molecule exists in two forms, or tautomers, 1,3,5-trihydroxybenzene, which has phenol-like, and 1,3,5-cyclohexanetrione , which has ketone-like character. These two...
(reaction called phloroglucinolysis), benzyl mercaptan (reaction called thiolysis
Thiolysis
Thiolysis is a reaction with a thiol that cleaves one compound into two. This reaction is similar to hydrolysis, which involves water instead of a thiol. This reaction is seen in β-oxidation of fatty acids. The depolymerisation of condensed tannins with the use of benzyl mercaptan as...
), thioglycolic acid
Thioglycolic acid
Thioglycolic acid is the organic compound HSCH2CO2H. It contains both a thiol and a carboxylic acid. It is a clear liquid with a strong unpleasant odor...
(reaction called thioglycolysis) or cysteamine
Cysteamine
Cysteamine is the chemical compound with the formula HSCH2CH2NH2. It is the simplest stable aminothiol and a degradation product of the amino acid cysteine. It is often used as the hydrochloride salt, HSCH2CH2NH3Cl....
. These techniques are generally called depolymerisation and give informations such as average degree of polymerisation or percentage of galloylation. These are SN1 reaction
SN1 reaction
The SN1 reaction is a substitution reaction in organic chemistry. "SN" stands for nucleophilic substitution and the "1" represents the fact that the rate-determining step is unimolecular...
s, a type of substitution reaction in organic chemistry, involving a carbocation
Carbocation
A carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer valence shell instead of the eight valence electrons that ensures maximum stability . Therefore carbocations are often reactive,...
intermediate under strongly acidic conditions in polar protic solvent
Protic solvent
In chemistry a protic solvent is a solvent that has a hydrogen atom bound to an oxygen or a nitrogen . In general terms, any molecular solvent that contains dissociable H+ is called a protic solvent. The molecules of such solvents can donate an H+...
s like methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
. The reaction leads to the formation of free and derivated monomers that can be further analyzed. The free monomers correspond to the terminal units of the condensed tannins chains.
In general, reactions are made in methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
, especially thiolysis, as benzyl mercaptan has a low solubility in water. They involve a moderate (50 to 90°C) heating for a few minutes. Epimerisation may happen.
Phloroglucinolysis can be used for instance for proanthocyanidin
Proanthocyanidin
Proanthocyanidins, also known as OPCs or condensed tannins, are a subgroup of the flavonoid class of polyphenols...
s characterisation in wine or in the grape seed and skin tissues.
Thioglycolysis can be used to study proanthocyanidin
Proanthocyanidin
Proanthocyanidins, also known as OPCs or condensed tannins, are a subgroup of the flavonoid class of polyphenols...
s or the oxidation of condensed tannins. It is also used for lignin
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
quantitation. Reaction on condensed tannins from Douglas fir bark produces epicatechin and catechin
Catechin
Catechin is a natural phenol antioxidant plant secondary metabolite. The term catechins is also commonly used to refer to the related family of flavonoids and the subgroup flavan-3-ols ....
thioglycolates.
Condensed tannins from Lithocarpus glaber
Lithocarpus glaber
Lithocarpus glaber, the Japanese oak, is a tree species in the genus Lithocarpus found in Japan, China and Taïwan.Mitami Shrine, a Shinto shrine in Sakai, Osaka Prefecture, Japan, is famous locally for its comparatively large population of Lithocarpus glaber, known as Shiribukagashi . In China, it...
leaves have been analysed through acid-catalyzed degradation in the presence of cysteamine
Cysteamine
Cysteamine is the chemical compound with the formula HSCH2CH2NH2. It is the simplest stable aminothiol and a degradation product of the amino acid cysteine. It is often used as the hydrochloride salt, HSCH2CH2NH3Cl....
.