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Condensed tannin

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Schematic representation of a condensed tannin molecule. Condensed tannins can be linear (with 4→8 bounds) orbranched(with 4→6 bounds - dotted line).

Condensed tannins(proanthocyanidins,polyflavonoid tannins,catechol-type tannins,pyrocatecollic type tannins,non-hydrolyzable tanninsorflavolans) arepolymersformed by thecondensationofflavans.They do not contain sugar residues.[1]

They are calledproanthocyanidinsas they yieldanthocyanidinswhen depolymerized under oxidative conditions. Different types of condensed tannins exist, such as theprocyanidins,propelargonidins,prodelphinidins,profisetinidins,proteracacinidins,proguibourtinidinsorprorobinetidins.All of the above are formed fromflavan-3-ols,but flavan-3,4-diols, called (leucoanthocyanidin) also form condensed tannin oligomers, e.g.leuco-fisetinidinformprofisetinidin,andflavan-4-olsform condensed tannins, e.g. 3',4',5,7-flavan-4-ol form proluteolinidin (luteoforolor).[2]One particular type of condensed tannin, found in grape, areprocyanidins,which are polymers of 2 to 50 (or more)catechinunits joined by carbon-carbon bonds. These are not susceptible to being cleaved byhydrolysis.

While many hydrolyzable tannins and most condensed tannins are water-soluble, several tannins are also highlyoctanol-soluble.[3][4]Some large condensed tannins are insoluble. Differences in solubilities are likely to affect their biological functions.

Natural occurrences

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Tannins oftropical woodstend to be of a catechin nature rather than of the gallic type present intemperate woods.[5]

Condensed tannins can be recovered fromLithocarpus glaber[6]or can be found inPrunussp.[7]The bark ofCommiphora angolensiscontains condensed tannins.[8]

Commercial sources of condensed tannins areplantssuch asquebracho wood(Schinopsis lorentzii), mimosa bark (Acacia mollissima),grape seeds(Vitis vinifera),pinebarks andsprucebarks.[9][10]

Condensed tannins are formed intannosomes,specialized organelles, in Tracheophytes, i.e.vascular plants.[11]

Dietary supplement

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Pycnogenolis adietary supplementderived from extracts frommaritime pinebark, is standardised to contain 70%procyanidinand is marketed with claims it can treat many conditions; however, according to a 2020Cochrane review,the evidence is insufficient to support its use for the treatment of any chronic disorder.[12][13]

Analysis

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Condensed tannins can be characterised by a number of modern techniques including depolymerisation,asymmetric flow field flow fractionation,small-angle X-ray scattering[14]andMALDI-TOFmass spectrometry.[15]Their interactions with proteins can be studied byisothermal titration calorimetry[16]and this provides information on the affinity constant, enthalpy and stoichiometry in the tannin-protein complex.

Depolymerisation

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Depolymerisation reactions are mainly analytical techniques but it is envisaged to use them as means to produce molecules for the chemical industry derived from waste products, such as bark from the wood industry[17]or pomaces from the wine industry.

Depolymerisation is an indirect method of analysis allowing to gain information such as averagedegree of polymerisation,percentage of galloylation, etc. The depolymerised sample can be injected on a mass spectrometer with anelectrospray ionizationsource, only able to form ions with smaller molecules.

Oxidative depolymerisation

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The butanol–hydrochloric acid–iron assay[18](Porter assay) is a colorimetric assay. It is based on acid catalysed oxidative depolymerization of condensed tannins into correspondinganthocyanidins.[19]The method has also been used for determination of bound condensed tannins, but has limitations.[20] This reagent has recently been improved considerably by inclusion of acetone.[21]

Non-oxidative chemical depolymerisation

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The condensed tannins can nevertheless undergo acid-catalyzed cleavage in the presence of (an excess of) anucleophile[22]likephloroglucinol(reaction called phloroglucinolysis),benzyl mercaptan(reaction calledthiolysis),thioglycolic acid(reaction called thioglycolysis) orcysteamine.These techniques are generally calleddepolymerisationand give information such asaverage degree of polymerisationor percentage of galloylation. These areSN1 reactions,a type of substitution reaction in organic chemistry, involving acarbocationintermediate under strongly acidic conditions in polarprotic solventslikemethanol.The reaction leads to the formation of free and derived monomers that can be further analyzed. The free monomers correspond to the terminal units of the condensed tannins chains. If thiolysis is done directly on plant material (rather than on purified tannins), it is, however, important to subtract naturally occurring free flavanol monomers from the concentration of terminal units that are released during depolymerisation.

Reactions are generally made inmethanol,especially thiolysis, as benzyl mercaptan has a low solubility in water. They involve a moderate (40 to 90 °C (104 to 194 °F)) heating for a few minutes.Epimerisationmay happen.[23]

Phloroglucinolysis can be used for instance for proanthocyanidins characterisation in wine[24]or in the grape seed and skin tissues.[25]

Thioglycolysis can be used to study proanthocyanidins[26]or the oxidation of condensed tannins.[14]It is also used forligninquantitation.[27]Reaction on condensed tannins fromDouglas firbark producesepicatechinandcatechinthioglycolates.[17]

Condensed tannins fromLithocarpus glaberleaves have been analysed through acid-catalyzed degradation in the presence ofcysteamine.[6]

References

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  1. ^Teresa K. Attwood and Richard Cammack (2006).Oxford dictionary of biochemistry and molecular biology.ISBN0198529171.
  2. ^"Phenolics in Food and Nutraceuticals" by Fereidoon Shahidi and Marian Naczk, CRC press, page 44
  3. ^Mueller-Harvey, I.; Mlambo, V.; Sikosana, J.L.N.; Smith, T.; Owen, E.; Brown, R.H. (2007). "Octanol-water partition coefficients for predicting the effects of tannins in ruminant nutrition".J. Agric. Food Chem.55(14): 5436–5444.doi:10.1021/jf070308a.PMID17567141.
  4. ^Mueller-Harvey, I (2010). "Unravelling the conundrum of tannins in animal nutrition and health".J. Sci. Food Agric.86(13): 2006–2037.doi:10.1002/jsfa.2577.
  5. ^"Les tannins dans les bois tropicaux (Tannin in tropical woods), by Jacqueline Doat, Revue bois et forêts des tropiques, 1978, n° 182 (French)"(PDF).Archived fromthe original(PDF)on 2013-08-01.Retrieved2012-08-28.
  6. ^abZhang, L. L.; Lin, Y. M. (2008)."HPLC, NMR and MALDI-TOF MS Analysis of Condensed Tannins from Lithocarpus glaber Leaves with Potent Free Radical Scavenging Activity".Molecules.13(12): 2986–2997.doi:10.3390/molecules13122986.PMC6245341.PMID19052523.
  7. ^Feucht, W.; Nachit, M. (1977). "Flavolans and Growth-Promoting Catechins in Young Shoot Tips of Prunus Species and Hybrids".Physiologia Plantarum.40(4): 230.doi:10.1111/j.1399-3054.1977.tb04063.x.
  8. ^Chemical study of bark from Commiphora angolensis Engl. Cardoso Do Vale, J., Bol Escola Farm Univ Coimbra Edicao Cient, 1962, volume 3, page 128 (abstract)
  9. ^Haslam E. Plant Polyphenols, Vegetable Tannins Revisited. Cambridge University Press, Cambridge, UK (1989).
  10. ^Ping, L; Laurent Chrusciel, L; Navarrete, P; Pizzi, A (2011). "Extraction of condensed tannins from grape pomace for use as wood adhesives".Industrial Crops and Products.33:253–257.doi:10.1016/j.indcrop.2010.10.007.
  11. ^[1]Annals of Botany: The tannosome is an organelle forming condensed tannins in the chlorophyllous organs of Tracheophyta
  12. ^Robertson, Nina U.; Schoonees, Anel; Brand, Amanda; Visser, Janicke (29 September 2020)."Pine bark (Pinus spp.) extract for treating chronic disorders".The Cochrane Database of Systematic Reviews.2020(9): CD008294.doi:10.1002/14651858.CD008294.pub5.ISSN1469-493X.PMC8094515.PMID32990945.
  13. ^D'Andrea, G. (2010). Pycnogenol: a blend of procyanidins with multifaceted therapeutic applications?. Fitoterapia, 81(7), 724-736.
  14. ^abVernhet, A.; Dubascoux, S. P.; Cabane, B.; Fulcrand, H. L. N.; Dubreucq, E.; Poncet-Legrand, C. L. (2011). "Characterization of oxidized tannins: Comparison of depolymerization methods, asymmetric flow field-flow fractionation and small-angle X-ray scattering".Analytical and Bioanalytical Chemistry.401(5): 1559–1569.doi:10.1007/s00216-011-5076-2.PMID21573842.S2CID4645218.
  15. ^Stringano, E.; Cramer, R.; Hayes, W.; Smith, C.; Gibson, T.; Mueller-Harvey, I. (2011). "Deciphering the complexity of sainfoin (Onobrychis viciifolia) proanthocyanidins by MALDI-TOF mass spectrometry with a judicious choice of isotope patterns and matrices".Analytical Chemistry.2011(83): 4147–4153.doi:10.1021/ac2003856.PMID21488615.
  16. ^Dobreva, M.A.; Frazier, R.A.; Mueller-Harvey, I.; Clifton, L.A.; Gea, A.; Green, R.J. (2011). "Binding of pentagalloyl glucose to two globular proteins occurs via multiple surface sites".Biomacromolecules.12(3): 710–715.doi:10.1021/bm101341s.PMID21250665.
  17. ^ab"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"(PDF).oregonstate.edu.Retrieved19 April2018.
  18. ^Acid butanol assay for proanthocyanidins. by Ann E. Hagermann, 2002 (article)
  19. ^Porter, Lawrence J.; Hrstich, Liana N.; Chana, Bock G. (1985)."The conversion of procyanidins and prodelphinidins to cyanidin and delphinidin".Phytochemistry.25:223–230.doi:10.1016/S0031-9422(00)94533-3.
  20. ^Makkar, H. P. S.; Gamble, G.; Becker, K. (1999). "Limitation of the butanol–hydrochloric acid–iron assay for bound condensed tannins".Food Chemistry.66:129–133.doi:10.1016/S0308-8146(99)00043-6.
  21. ^Grabber, J.; Zeller, W.E.; Mueller-Harvey, I. (2013). "Acetone enhances the direct analysis of procyanidin- and prodelphinidin-based condensed tannins in Lotus species by the butanol-HCl-iron assay".J. Agric. Food Chem.61(11): 2669–2678.doi:10.1021/jf304158m.PMID23383722.
  22. ^Matthews, Sara; Mila, Isabelle; Scalbert, Augustin; Pollet, Brigitte; Lapierre, Catherine; Hervé du Penhoat, Catherine L. M.; Rolando, Christian; Donnelly, Dervilla M. X. (April 1997). "Method for estimation of proanthocyanidins based on their acid depolymerization in the presence of nucleophiles".Journal of Agricultural and Food Chemistry.45(4): 1195–1201.doi:10.1021/jf9607573.
  23. ^Gea, An; Stringano, Elisabetta; Brown, Ron H.; Mueller-Harvey, Irene (26 January 2011). "In situanalysis and structural elucidation of sainfoin (Onobrychis viciifolia) tannins for high-throughput germplasm screening ".Journal of Agricultural and Food Chemistry.59(2): 495–503.doi:10.1021/jf103609p.PMID21175139.
  24. ^Kennedy, James A.; Ferrier, Jordan; Harbertson, James F.; des Gachons, Catherine Peyrot (1 December 2006)."Analysis of Tannins in Red Wine Using Multiple Methods: Correlation with Perceived Astringency".American Journal of Enology and Viticulture.57(4): 481–485.doi:10.5344/ajev.2006.57.4.481.S2CID83830030.Retrieved19 April2018.
  25. ^Kennedy, James A.; Jones, Graham P. (April 2001). "Analysis of Proanthocyanidin Cleavage Products Following Acid-Catalysis in the Presence of Excess Phloroglucinol".Journal of Agricultural and Food Chemistry.49(4): 1740–1746.doi:10.1021/jf001030o.PMID11308320.
  26. ^Sears, Karl D.; Casebier, Ronald L. (1968). "Cleavage of proanthocyanidins with thioglycollic acid".Chemical Communications(22): 1437–8.doi:10.1039/C19680001437.
  27. ^Lange, B. M.; Lapierre, C.; Sandermann Jr, H. (1 July 1995)."Elicitor-induced spruce stress lignin (structural similarity to early developmental lignins)".Plant Physiology.108(3): 1277–1287.doi:10.1104/pp.108.3.1277.PMC157483.PMID12228544.
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