Proanthocyanidin

Proanthocyanidin
Epicatechin (EC), one of the building blocks of proanthocyanidins

Proanthocyanidins, also known as OPCs (oligomeric proanthocyanidins) or condensed tannins, are a subgroup of the flavonoid class of polyphenols. Essentially, they are oligomer chains of flavanols, such as the flavan-3-ol epicatechin.[citation needed]

They were discovered in 1948 by Jacques Masquelier, who developed and later patented techniques for the extraction of proanthocyanidins from pine needles and grape seeds.[citation needed]

Contents

Structure of proanthocyanidins

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 apples, maritime pine bark, cinnamon, aronia fruit, cocoa beans, grape seed, grape skin (procyanidins and prodelphinidins),[1] and red wines of Vitis vinifera (the common grape). However, bilberry, cranberry, black currant, green tea, black tea, and other plants also contain these flavonoids. Cocoa beans contain the highest concentrations.[2] Proanthocyanidins can also be isolated from Quercus petraea and Q. robur heartwood (wine barrel oaks).[3] Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), is rich in numerous procyanidin oligomers.[4]

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 and Granny Smith varieties.[5]

A patented extract of maritime pine bark called Pycnogenol bears 65-75 percent proanthocyanidins (procyanidins).[6] Thus a 100 mg serving would contain 65 to 75 mg of proanthocyanidins (procyanidins).

Proanthocyanidin glycosides can be isolated from cocoa liquor.[7]

The seed testas of field beans (Vicia faba) contain proanthocyanidins[8] that affect the digestibility in piglets[9] and could have an inhibitory activity on enzymes.[10]

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 is a dye that is particularly useful for localization of proanthocyanidin compounds in plant histology. The use of the reagent results in blue staining.[11] It can also be used to titrate proanthocyanidins.

Total phenols (or antioxidant effect) can be measured using the Folin-Ciocalteu reaction. Results are typically expressed as gallic acid equivalents (GAE).

Proanthocyanidins 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 proanthcyanidins.

Proanthocyanidins 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 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%.[14]

An improved colorimetric test, called the Porter Assay or butanol-HCl-iron method, is the most common OPC assay currently in use.[15] 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]

Gel permeation chromatography (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 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]

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 capacity (ORAC).

In red wines, total oligomeric proanthocyanidin content, including flavan-3-ols (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 compounds (r = 0.75, P < 0.10), and proanthocyanidins (r = 0.87, P < 0.05).[19]

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 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.[19][20]

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.[21] 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 were premature because of the negligible amount of resveratrol in red wine.

Proanthocyanidins suppress production of a protein endothelin-1 that constricts blood vessels.[21]

These studies provide data supporting the French Paradox 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.[21]

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.[citation needed] In preliminary research, proanthocyanidins were reported to have anti-mutagenic activity (i.e., to prevent chromosomal mutations).[citation needed]

Common antioxidants currently used are vitamin C and vitamin E; however, studies show that proanthocyanidins antioxidant capabilities are 20 times more powerful than vitamin C and 50 times more potent than vitamin E.[22] Proanthocyanidins found in French maritime pine 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.[citation needed] 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 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.[23] Additionally, this same preparation, Pycnogenol, has been found to normalize platelet adhesion (aggregation) so as to facilitate normal blood flow.[24]

Oligomeric proanthocyanidins

In 1948 Jack Masquelier discovered oligomeric proanthocyanidins (OPCs) in the skin of a peanut by accident. Oligomeric proanthocyanidins are a class of flavonoid 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 coconuts, 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.[25]

Oligomeric proanthocyanidins can be obtained by the mean of Vaccinium pahalae in vitro cell culture.[26]

Biological signifiance

In nature, it is possible that OPCs serve as a plant defense against herbivory.

Health benefits

Proanthocyanidins have strong anti-oxidant properties. Foods rich in proanthocyanidins have high oxygen radical absorbance capacity, which has been linked to numerous health benefits such as weight management, cell health, and cardiovascular health.[27] Scientists continue to research the relevance of proanthocyanidins' strong anti-oxidant properties in vivo for such applications as cancer prevention and cardiovascular health.[28] USDA does maintain a database of proanthocyanidin content and structure for many foods, but dietary supplements proanthocyanidin content has not been well documented.[29]

In the human body, they might act as antioxidants (free radical scavengers).[citation needed] 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 formation.[30]

Additionally, studies have shown that OPCs may prevent cardiovascular diseases by counteracting the negative effects of high cholesterol on the heart and blood vessels.

A French maritime pine bark extract of OPCs, Pycnogenol, has been shown to improve microcirculation, retinal edema and visual acuity in the early stages of diabetic retinopathy.[31] Further study has shown that Pycnogenol maintains antioxidant and anti-inflammatory properties, selectively binds to collagen and elastin in the body, and aids in the production of endothelial[32] nitric oxide. Pycnogenol has also been shown to help normalize blood glucose (sugar) levels,[33] and delay sugar absorption.[34]

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.[2][35] 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).[2]

Oxidative depolymerisation

Non oxidative chemical depolymerisation

The condensed tannins can nevertheless undergo acid-catalyzed cleavage in the presence of (an excess of) a nucleophile[36] like phloroglucinol (reaction called phloroglucinolysis), benzyl mercaptan (reaction called thiolysis), thioglycolic acid (reaction called thioglycolysis) or cysteamine. These techniques are generally called depolymerisation and give informations such as average degree of polymerisation or percentage of galloylation. These are SN1 reactions, a type of substitution reaction in organic chemistry, involving a carbocation intermediate under strongly acidic conditions in polar protic solvents like methanol. 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.

Reactions are generally made in methanol, 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 proanthocyanidins characterisation in wine[37] or in the grape seed and skin tissues.[38]

Thioglycolysis can be used to study proanthocyanidins[39] or the oxidation of condensed tannins.[40] It is also used for lignin quantitation.[41] Reaction on condensed tannins from Douglas fir bark produces epicatechin and catechin thioglycolates.[42]

Condensed tannins from Lithocarpus glaber leaves have been analysed through acid-catalyzed degradation in the presence of cysteamine.[43]

References

  1. ^ Souquet, J; Cheynier, Véronique; Brossaud, Franck; Moutounet, Michel (1996). "Polymeric proanthocyanidins from grape skins". Phytochemistry 43 (2): 509. doi:10.1016/0031-9422(96)00301-9. 
  2. ^ a b c USDA Database for the Proanthocyanidin Content of Selected Foods – 2004 <http://www.nal.usda.gov/fnic/foodcomp/Data/PA/PA.html>[verification needed][page needed]
  3. ^ Vivas, N; Nonier, M; Pianet, I; Vivasdegaulejac, N; Fouquet, E (2006). "Proanthocyanidins from Quercus petraea and Q. robur heartwood: quantification and structures". Comptes Rendus Chimie 9: 120. doi:10.1016/j.crci.2005.09.001. 
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  6. ^ Rohdewald, P (2002). "A review of the French maritime pine bark extract (Pycnogenol), a herbal medication with a diverse clinical pharmacology". International journal of clinical pharmacology and therapeutics 40 (4): 158–68. PMID 11996210. 
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  13. ^ A non-destructive screening method for proanthocyanidin-free barley mutants. Henriette Kristensen and Sten Aastrup, Carlsberg Research Communications, Volume 51, Number 7, 509-513 doi:10.1007/BF02906893
  14. ^ Grape Seed Extract, White paper, The Grape Seed Method Evaluation Committee, Under the Auspices of NNFA ComPli[unreliable medical source?]
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  19. ^ a b Sánchez-Moreno, Concepción; Cao, Guohua; Ou, Boxin; Prior, Ronald L. (2003). "Anthocyanin and Proanthocyanidin Content in Selected White and Red Wines. Oxygen Radical Absorbance Capacity Comparison with Nontraditional Wines Obtained from Highbush Blueberry". Journal of Agricultural and Food Chemistry 51 (17): 4889–96. doi:10.1021/jf030081t. PMID 12903941. 
  20. ^ ":: Blueberries ::". Blueberry.org. http://www.blueberry.org/antioxidants.htm. Retrieved 2011-05-23. 
  21. ^ a b c Corder, R.; Mullen, W.; Khan, N. Q.; Marks, S. C.; Wood, E. G.; Carrier, M. J.; Crozier, A. (2006). "Oenology: Red wine procyanidins and vascular health". Nature 444 (7119): 566. doi:10.1038/444566a. PMID 17136085. 
  22. ^ Shi, John; Yu, Jianmel; Pohorly, Joseph E.; Kakuda, Yukio (2003). "Polyphenolics in Grape SeedsBiochemistry and Functionality". Journal of Medicinal Food 6 (4): 291–9. doi:10.1089/109662003772519831. PMID 14977436. 
  23. ^ Nishioka, Kenji; Hidaka, Takayuki; Nakamura, Shuji; Umemura, Takashi; Jitsuiki, Daisuke; Soga, Junko; Goto, Chikara; Chayama, Kazuaki et al. (2007). "Pycnogenol, French Maritime Pine Bark Extract, Augments Endothelium-Dependent Vasodilation in Humans". Hypertension Research 30 (9): 775–80. doi:10.1291/hypres.30.775. PMID 18037769. 
  24. ^ Pütter, M; Grotemeyer, KH; Würthwein, G; Araghi-Niknam, M; Watson, RR; Hosseini, S; Rohdewald, P (1999). "Inhibition of smoking-induced platelet aggregation by aspirin and pycnogenol". Thrombosis research 95 (4): 155–61. doi:10.1016/S0049-3848(99)00030-4. PMID 10498385. 
  25. ^ Rösch, Daniel; Mügge, Clemens; Fogliano, Vincenzo; Kroh, Lothar W. (2004). "Antioxidant Oligomeric Proanthocyanidins from Sea Buckthorn (Hippophaë rhamnoides) Pomace". Journal of Agricultural and Food Chemistry 52 (22): 6712–8. doi:10.1021/jf040241g. PMID 15506806. 
  26. ^ Kandil, F. E.; Song, L.; Pezzuto, J. M.; Marley, K.; Seigler, D. S.; Smith, M. A. L. (2000). "Isolation of oligomeric proanthocyanidins from flavonoid-producing cell cultures". In Vitro Cellular & Developmental Biology - Plant 36 (6): 492. doi:10.1007/s11627-000-0088-1. 
  27. ^ Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods – 2007. November 2007. http://www.ars.usda.gov/sp2userfiles/place/12354500/data/orac/orac07.pdf. [page needed]
  28. ^ Cos, P; De Bruyne, T; Hermans, N; Apers, S; Berghe, DV; Vlietinck, AJ (2004). "Proanthocyanidins in health care: current and new trends". Current medicinal chemistry 11 (10): 1345–59. PMID 15134524. 
  29. ^ USDA Database for the Proanthocyanidin Content of Selected Foods. August 2004. http://www.nal.usda.gov/fnic/foodcomp/Data/PA/PA.pdf. [page needed]
  30. ^ Murphy, Karen J.; Chronopoulos, Andriana K.; Singh, Indu; Francis, Maureen A.; Moriarty, Helen; Pike, Marilyn J.; Turner, Alan H.; Mann, Neil J. et al. (June 2003). "Dietary flavanols and procyanidin oligomers from cocoa (Theobroma cacao) inhibit platelet function". The American journal of clinical nutrition 77 (6): 1466–73. PMID 12791625. http://www.ajcn.org/cgi/pmidlookup?view=long&pmid=12791625. 
  31. ^ Steigerwalt, Robert; Belcaro, Gianni; Cesarone, Maria Rosaria; Di Renzo, Andrea; Grossi, Maria Giovanna; Ricci, Andrea; Dugall, Mark; Cacchio, Marisa et al. (2009). "Pycnogenol Improves Microcirculation, Retinal Edema, and Visual Acuity in Early Diabetic Retinopathy". Journal of Ocular Pharmacology and Therapeutics 25 (6): 537–540. doi:10.1089/jop.2009.0023. PMID 19916788. Lay summary – Horphag Research (December 2, 2009). 
  32. ^ "Antioxidant May Help Lower Blood Pressure". http://www.webmd.com/hypertension-high-blood-pressure/news/20040220/antioxidant-help-lower-blood-pressure. 
  33. ^ Liu, Ximing; Zhou, Ha-Jun; Rohdewald, Peter (2004). "French Maritime Pine Bark Extract Pycnogenol Dose-Dependently Lowers Glucose in Type 2 Diabetic Patients". Diabetes Care 27 (3): 839. doi:10.2337/diacare.27.3.839. 
  34. ^ Schäfer, Angelika; Högger, Petra (2007). "Oligomeric procyanidins of French maritime pine bark extract (Pycnogenol) effectively inhibit α-glucosidase". Diabetes Research and Clinical Practice 77 (1): 41–6. doi:10.1016/j.diabres.2006.10.011. PMID 17098323. 
  35. ^ Grape Juice Beats Wine in New Antioxidant Tests <http://www.medicalnewstoday.com/medicalnews.php?newsid=15553>[unreliable medical source?]
  36. ^ Method for Estimation of Proanthocyanidins Based on Their Acid Depolymerization in the Presence of Nucleophiles. Sara Matthews, Isabelle Mila, Augustin Scalbert, Brigitte Pollet, Catherine Lapierre, Catherine L. M. Hervé du Penhoat, Christian Rolando and Dervilla M. X. Donnelly, J. Agric. Food Chem., 1997, 45 (4), pp. 1195–1201, doi:10.1021/jf9607573
  37. ^ Analysis of Tannins in Red Wine Using Multiple Methods: Correlation with Perceived Astringency by mean of depolymerisation. James A. Kennedy, Jordan Ferrier, James F. Harbertson and Catherine Peyrot des Gachons, Am. J. Enol. Vitic. 57:4, 2006, pp. 481-485
  38. ^ Analysis of Proanthocyanidin Cleavage Products Following Acid-Catalysis in the Presence of Excess Phloroglucinol. James A. Kennedy and Graham P. Jones, J. Agric. Food Chem., 2001, 49 (4), pp. 1740–1746, doi:10.1021/jf001030o
  39. ^ Cleavage of proanthocyanidins with thioglycollic acid. Karl D. Sears and Ronald L. Casebier, Chem. Commun. (London), 1968, pp. 1437-1438, doi:10.1039/C19680001437
  40. ^ Characterization of oxidized tannins: comparison of depolymerization methods, asymmetric flow field-flow fractionation and small-angle X-ray scattering. Vernhet A, Dubascoux S, Cabane B, Fulcrand H, Dubreucq E and Poncet-Legrand C, Anal Bioanal Chem. 2011 May 15, PubMed, doi:10.1007/s00216-011-5076-2
  41. ^ Elicitor-Induced Spruce Stress Lignin (Structural Similarity to Early Developmental Lignins). B. M. Lange, C. Lapierre and H. Sandermann Jr, Plant Physiology, July 1995, vol. 108, no. 3, pp. 1277-1287, doi:10.1104/pp.108.3.1277
  42. ^ Douglas-Fir Bark: Characterization of a Condensed Tannin Extract, by Hong-Keun Song, A thesis submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science, December 13, 1984
  43. ^ HPLC, NMR and MALDI-TOF MS analysis of condensed tannins from Lithocarpus glaber leaves with potent free radical scavenging activity. Liang Liang Zhang and Yi Ming Lin, 2008, Molecules, 2008, 13, pp. 2986-2997, doi:10.3390/molecules13122986
v · d · eTypes of Plant pigments
Flavonoids
Anthocyanins • Anthocyanidins • Anthoxanthins • Condensed tannins
Betalains
Betacyanins • Betaxanthins
Carotenoids
Xanthophylls • Carotenes • Retinoids
Other
Chlorophyll (a, b, c1, c2, d, f) • Allophycocyanin • Phycocyanin • Phycoerythrin • Phycoerythrocyanin • Quinones • Xanthonoids
v · d · eTypes of Flavonoids
Flavonoids
Flavones | Flavonols (Pyranoflavonols, Furanoflavonols) | Flavanones | Flavanonols | Flavans | Flavan-3-ols | Flavan-4-ols | Flavan-3,4-diols | Anthocyanidins (Anthocyanins) | Condensed tannins
Isoflavonoids
Isoflavones (Pyranoisoflavones) | Isoflavans | Pterocarpans
Neoflavonoids
Aurones
Aureusidin | Leptosidin
Other categories
C-methylated flavonoids | O-methylated flavonoids | Flavonolignans | Furanoflavonoids | Pyranoflavonoids | Methylenedioxyflavonoids | Prenylated flavonoids | Castavinols
Flavonoid biosynthesis
v · d · eTypes of tannins
Types
Hydrolysable | Condensed | Phlorotannins | Flavono-ellagitannins (complex tannins)
Tannin uses
Enological | Drilling | Ink | Tanning
Other
Tannin sources
Miscellaneous
Pseudo tannins | Synthetic tannins
v · condensed tannins
Oligomers
Proanthocyanidin | Prodelphinidin | Profisetinidin | Proguibourtinidin | Prorobinetidin
Misc.
Phlobaphenes (phlobatannins) | Tannin sources
v · condensed tannins
Oligomers
Proanthocyanidin | Prodelphinidin | Profisetinidin | Proguibourtinidin | Prorobinetidin
Misc.
Phlobaphenes (phlobatannins) | Tannin sources


v · d · eTypes of proanthocyanidins
A type proanthocyanidins
Dimers : Proanthocyanidin A1 | A2 | Trimers:Cinnamtannin B1 | Selligueain A | Selligueain B | Tetramers: Arecatannin A2
B type proanthocyanidins
Dimers : Proanthocyanidin B1 | B2 | B3 | B4 | B5 | B6 | B8 Trimers: Arecatannin B1 | Proanthocyanidin C1
Types
Arecatannins (Arecatannin A1 | Arecatannin A3 | Arecatannin B2 | Arecatannin C1)

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