Condensed tannin

Source: Wikipedia, the free encyclopedia.
Schematic representation of a condensed tannin molecule. Condensed tannins can be linear (with 4→8 bounds) or branched (with 4→6 bounds - dotted line).

Condensed tannins (proanthocyanidins, polyflavonoid tannins, catechol-type tannins, pyrocatecollic type tannins, non-hydrolyzable tannins or flavolans) are polymers formed by the condensation of flavans. They do not contain sugar residues.[1]

They are called

leuco-fisetinidin form profisetinidin, and flavan-4-ols form condensed tannins, e.g. 3',4',5,7-flavan-4-ol form proluteolinidin (luteoforolor).[2] One particular type of condensed tannin, found in grape, are procyanidins, which are polymers of 2 to 50 (or more) catechin units joined by carbon-carbon bonds. These are not susceptible to being cleaved by hydrolysis
.

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

Natural occurrences

Tannins of

temperate woods.[5]

Condensed tannins can be recovered from Lithocarpus glaber[6] or can be found in Prunus sp.[7] The bark of Commiphora angolensis contains condensed tannins.[8]

Commercial sources of condensed tannins are

Acacia mollissima), grape seeds (Vitis vinifera), pine barks and spruce barks.[9][10]

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

Dietary supplement

Pycnogenol is a dietary supplement derived from extracts from maritime pine bark, is standardised to contain 70% procyanidin and is marketed with claims it can treat many conditions; however, according to a 2020 Cochrane review, the evidence is insufficient to support its use for the treatment of any chronic disorder.[12][13]

Analysis

Condensed tannins can be characterised by a number of modern techniques including depolymerisation,

MALDI-TOF mass spectrometry.[15] Their interactions with proteins can be studied by isothermal titration calorimetry[16]
and this provides information on the affinity constant, enthalpy and stoichiometry in the tannin-protein complex.

Depolymerisation

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 average

degree of polymerisation, percentage of galloylation, etc. The depolymerised sample can be injected on a mass spectrometer with an electrospray ionization
source, only able to form ions with smaller molecules.

Oxidative depolymerisation

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 corresponding anthocyanidins.[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

The condensed tannins can nevertheless undergo acid-catalyzed cleavage in the presence of (an excess of) a

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 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 in

Epimerisation may 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

thioglycolates.[17]

Condensed tannins from Lithocarpus glaber leaves have been analysed through acid-catalyzed degradation in the presence of cysteamine.[6]

References

  1. ISBN 0198529171
    .
  2. ^ "Phenolics in Food and Nutraceuticals" by Fereidoon Shahidi and Marian Naczk, CRC press, page 44
  3. PMID 17567141
    .
  4. 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 from the original (PDF) on 2013-08-01. Retrieved 2012-08-28.
  6. ^
    PMID 19052523
    .
  7. 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. 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. PMID 32990945
    .
  13. ^ D'Andrea, G. (2010). Pycnogenol: a blend of procyanidins with multifaceted therapeutic applications?. Fitoterapia, 81(7), 724-736.
  14. ^
    S2CID 4645218
    .
  15. PMID 21488615
    .
  16. PMID 21250665
    .
  17. ^ a b "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. Retrieved 19 April 2018.
  18. ^ Acid butanol assy for proanthocyanidins. by Ann E. Hagermann, 2002 (article)
  19. doi:10.1016/S0031-9422(00)94533-3
    .
  20. doi:10.1016/S0308-8146(99)00043-6
    .
  21. PMID 23383722
    .
  22. doi:10.1021/jf9607573
    .
  23. PMID 21175139
    .
  24. S2CID 83830030
    . Retrieved 19 April 2018.
  25. PMID 11308320
    .
  26. doi:10.1039/C19680001437
    .
  27. PMID 12228544
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=Condensed_tannin&oldid=1190889766"