Procyanidins are members of the proanthocyanidin (or condensed tannins) class of flavonoids. They are oligomeric compounds, formed from catechin and epicatechin molecules. They yield cyanidin when depolymerized under oxidative conditions.
See the box below entitled "Types of procyanidins" for links to articles on the various types.
Procyanidins, including the lesser bioactive / bioavailable polymers (4 or more catechines), represent a group of condensed flavan-3-ols that can be found in many plants, most notably apples, maritime pine bark, cinnamon, aronia fruit, cocoa beans, grape seed, grape skin, [1] and red wines of Vitis vinifera (the common grape). [2] However, bilberry, cranberry, black currant, green tea, black tea, and other plants also contain these flavonoids. [3] Procyanidins can also be isolated from Quercus petraea and Q. robur heartwood (wine barrel oaks). [4] Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), is rich in numerous procyanidin oligomers. [5]
Apples contain on average per serving about eight times the amount of procyanidin found in wine, with some of the highest amounts found in the Red Delicious and Granny Smith varieties. [6]
The seed testas of field beans ( Vicia faba ) contain procyanidins [7] that affect the digestibility in piglets [8] and could have an inhibitory activity on enzymes. [9] Cistus salviifolius also contains oligomeric procyanidins. [10]
Condensed tannins can be characterised by a number of techniques including depolymerisation, asymmetric flow field flow fractionation or small-angle X-ray scattering. DMACA is a dye used for localization of procyanidin compounds in plant histology. The use of the reagent results in blue staining. [11] It can also be used to titrate procyanidins. Total phenols (or antioxidant effect) can be measured using the Folin-Ciocalteu reaction. Results are typically expressed as gallic acid equivalents (GAE).
Procyanidins from field beans ( Vicia faba ) [12] or barley [13] have been estimated using the vanillin-HCl method, resulting in a red color of the test in the presence of catechin or proanthocyanidins.
Procyanidins can be titrated using the Procyanidolic Index (also called the Bates-Smith 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 PCOs content is. However, 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% PCO by some and began appearing on the labels of finished products. All current methods of analysis suggest that the actual PCO content of these products is much lower than 95%. [14] [ unreliable medical source? ]
An improved colorimetric test, called the Porter Assay or butanol-HCl-iron method, is the most common PCO assay currently in use. [15] [ self-published source? ] 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. [16] [ unreliable medical source? ]
Gel permeation chromatography (GPC) analysis allows to separate monomers from larger PCO molecules.
Monomers of procyanidins can be characterized by HPLC analysis. Condensed tannins can undergo acid-catalyzed cleavage in the presence of a nucleophile like phloroglucinol (reaction called phloroglucinolysis), thioglycolic acid (thioglycolysis), benzyl mercaptan or cysteamine (processes called thiolysis [17] ) leading to the formation of oligomers that can be further analyzed. [18]
Phloroglucinolysis can be used for instance for procyanidins characterisation in wine [19] or in the grape seed and skin tissues. [20]
Thioglycolysis can be used to study procyanidins [21] or the oxidation of condensed tannins. [22] It is also used for lignin quantitation. [23] Reaction on condensed tannins from Douglas fir bark produces epicatechin and catechin thioglycolates. [24]
Condensed tannins from Lithocarpus glaber leaves have been analysed through acid-catalyzed degradation in the presence of cysteamine. [25]
Procyanidin content in dietary supplements has not been well documented. [26] Pycnogenol is a dietary supplement derived from extracts from maritime pine bark that contains 70% procyanidins, and is marketed with claims it can treat many conditions. The medical evidence is insufficient to support its use for the treatment of seven different chronic disorders. [27]
Tannins are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
Polyphenols are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of which have been used historically as dyes and for tanning garments.
Grape seed extract is an industrial derivative of whole grape seeds. The extract contains proanthocyanidins. Grape seed extract quality is measured by the content of procyanidins which are formed from proanthocyanidins. Generally, grape seed extract quality contains 95% procyanidins, but potency varies among products. Eating foods or beverages high in procyanidin results in the sensation of the mouth puckering and dehydration, otherwise known as astringency, as felt after certain alcoholic drinks.
Proanthocyanidins are a class of polyphenols found in many plants, such as cranberry, blueberry, and grape seeds. Chemically, they are oligomeric flavonoids. Many are oligomers of catechin and epicatechin and their gallic acid esters. More complex polyphenols, having the same polymeric building block, form the group of tannins.
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 include phenolic acids, stilbenoids, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). This large group of natural phenols can be broadly separated into two categories, flavonoids and non-flavonoids. Flavonoids include the anthocyanins and tannins which contribute to the color and mouthfeel of the wine. The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.
Prodelphinidin is a name for the polymeric tannins composed of gallocatechin. It yields delphinidin during depolymerisation under oxidative conditions.
Leucocyanidin is a colorless chemical compound that is a member of the class of natural products known as leucoanthocyanidins.
Oenin is an anthocyanin. It is the 3-glucoside of malvidin. It is one of the red pigments found in the skin of purple grapes and in wine.
Procyanidin C2 is a B type proanthocyanidin trimer, a type of condensed tannin.
Procyanidin B2 is a B type proanthocyanidin. Its structure is (−)-Epicatechin-(4β→8)-(−)-epicatechin.
A type proanthocyanidins are a specific type of proanthocyanidins, which are a class of flavonoid. Proanthocyanidins fall under a wide range of names in the nutritional and scientific vernacular, including oligomeric proanthocyanidins, flavonoids, polyphenols, condensed tannins, and OPCs. Proanthocyanidins were first popularized by French scientist Jacques Masquelier.
Procyanidin B1 is a procyanidin dimer.
Procyanidin B3 is a B type proanthocyanidin. Procyanidin B3 is a catechin dimer.
Procyanidin B4 is a B type proanthocyanidin.
Procyanidin B6 is a B type proanthocyanidin.
Procyanidin C1 (PCC1) is a B type proanthocyanidin. It is an epicatechin trimer found in grape, unripe apples, and cinnamon.
Condensed tannins are polymers formed by the condensation of flavans. They do not contain sugar residues.
Gambier or gambir is an extract derived from the leaves of Uncaria gambir, a climbing shrub native to tropical Southeast Asia. Gambier is produced in Indonesia and Malaysia where it was an important trade item into the late nineteenth century. It can be used as a tanning agent, a brown dye, a food additive and as herbal medicine. Also known as pale catechu, white catechu or Japan Earth, it is often confused with other forms of catechu.
Figure 5
