Tannins

Tannins

1. Tannins
By
Dr. AhmedMetwaly

2. Objectives:
1.Definition
2.Classification
3.General characters
4.Distribution and physiological role
5.Tests for identification
6.Quantitative determination
7.Medicinal and biological properties
8.Economic importance

3. Definition;
•They are high molecular weight phenolic compounds
capable of precipitation of animal proteins in hides and
converting them into leather. “Tanning Industry”
.

5. They are condensation products of Gallic acid or
Flavan-3-ol as well as their glycosides.
Gallic acid Flavan-3-ol

6. True Tannins
(High molecular weight compounds)
Hydrolysable Tannins
(Pyrogallol)
Condensed Tannins
(Catechol)
Pseudotannins
Low molecular weight compounds
e.g. Gallic acid, Flavan-3,4-diol Gallitannins Ellagitannins
HexahydroxydiphenicacidGallic acid
Flavan-3-ol
Complex
tannins

7. Truetannins
Thesearecomplexphenoliccompoundsofhigh
molecularweightsrangingfromabout1000to5000.
Theydisplaythegeneralpropertiesoftanninsand
precipitatedbygelatinin1%solution.
Truetanninscanbesub-classifiedintohydrolysable
tannins,condensedtanninsandcomplextannins.

8. Hydrolysabletannins(pyrogalloltannins)
Thesemaybehydrolyzedbyacidsorenzymessuchas
tannase.
Theyareformedfromseveralmoleculesofphenolic
acidssuchasgallicandhexahydroxydiphenicacids
whichareunitedbyesterlinkagestoacentralsugar
(mainlyglucose)molecule.
Likegallicacidtheirsolutionsturnbluewithironsalts.
Theywereformerlyknownaspyrogalloltannins,because
ondrydistillationgallicacidandsimilarcomponentsare
convertedintopyrogallol.
Twoprincipaltypesofhydrolysabletanninsare
gallitanninsandellagitanninswhichare,respectively,
composedofgallicacidandhexahydroxydiphenic
acidunits.

9. Tannaseisanenzymethatcatalyzesthechemical reaction
digallate+ H
2
O 2 gallate
This enzyme belongs to the family ofhydrolases, specifically
those acting on carboxylicesterbonds. The systematic name
of this enzyme class istannin acylhydrolase. Other names in
common use includetannase S, andtannin acetylhydrolase.
Tannase is a key enzyme in the degradation ofgallotannins.
It is present in a diverse group of microorganisms,
includingrumen bacteria

10. ThedifferencebetweenEllagitanninsandgallotannins
that;galloylgroupsarelinkedthroughC-Cbondsinellagitannins,
whereasthegalloylgroupsingallotanninsarelinkedbydepside
bonds.
Adepsideisatypeofpolyphenoliccompoundcomposedoftwoor
moremonocyclicaromaticunitslinkedbyanesterbond.
Ellagicacid(thedepsideofHexahydroxydiphenicacid)canarise
bylactonizationduringchemicalhydrolysisofthetannin;thus,the
termellagitanninisamisnomer.
C-glucosidicellagitanninsarecommoninanumberoffamilies
includingtheMyrtaceae,Hamamelidaceae,Punicaceaeand
Rosaceae.
Ellagic acidHexahydroxydiphenic acid

11. Tannic acid 1,2,3,4,6-Pentagalloyl glucose
Grandinin

12. Casuarictin
raspberry ellagitannin

13. Condensedtannins
(Catechol)(proanthocyanidins)
Unlikehydrolysabletannins,thesearenotreadily
hydrolyzabletosimplermoleculesandtheydonotcontain
asugarmoiety.
Theyarerelatedtoflavonoidpigmentsandhave
polymericflavan-3-olstructures(usuallydi-andtrimers).
•On dry distillation they yield catecholand these
tannins are therefore sometimes called catechol
tannins.
•Like catecholitself, their solutions turn to green with
ferric chloride.

14. Catechinswhichalsooccurwiththetanninsandflavan-
3,4-diols(leucoanthocyanidins)areintermediatesinthe
biosynthesisofthepolymericmolecules.
Stereochemicalvariationsaddtothevarietyofpossible
structures.
Ontreatmentwithacidsorenzymescondensedtannins
areconvertedintoredinsolublecompoundsknownas
phlobaphenes.
Phlobaphenesgivethecharacteristicredcolortomany
drugssuchasredcinchonabark,whichcontainthese
phlobatanninsandtheirdecompositionproducts.

15. Catechin Epicatechin
Schematic representation of a
condensed tannin molecule.
Condensed tannins can be linear (with
4→8 bounds) orbranched(with 4→6
bounds)

16. Complextannins
Theserepresentagroupoftanninsthatare
biosynthesizedfrombothhydrolysabletannin(mostly
aC-glucosideellagitannin)(flavono-ellagitannin)and
condensedtannin.

17. AcutissiminA

19. Pseudotannins
Pseudotanninsarepolyphenoliccompoundsoflowermolecular
weightthantruetannins.
Theydonotrespondtothegoldbeater'sskintestandmay,
undercertainconditions,e.g.inconcentratedsolutions,give
precipitateswithgelatinandbepartlyretainedbyhidepowder.
Examplesaregallicacid,catechinsandchlorogenicacid.
Chlorogenic acidCatechinGallic acid

20. Distribution
Type of tannin Plant name and organ
Hydrolysable tannins
Gallitannins
Ellagitannins
Rhubarbrhizome,clovebuds,redrosepetals,galls,hamamelisleavesand
chestnutbark.
Pomegranaterindandbark,eucalyptusleaves,myrobolansandoakbark.
Condensed tannins Barks:e.g.cinnamon,hamamelisandcinchona.
Rootsandrhizomes:e.g.krameriaandmalefern.
Flowers:e.g.limeandhawthorn.
Seeds:e.g.cocoa,kolaandareca.
Leaves:e.g.hamamelis,hawthornandtea,especiallygreentea.
Extractsanddriedjuices:catechuandIndiankino.
Complex tannins MembersofFam.Combretaceae,MyrtaceaeandFagaceae.
Pseudotannins
Gallic acid
Catechins
Chlorogenicacid
Ipecacuanhicacid
Galls,rhubarbandmostdrugsthatcontaingallitannins.
Catechu,cocoaandmostdrugscontainingcondensedtannins.
Coffeeparticularlywhenunroasted.
Ipecacuanha.

21. Majorsourcesofcommercialtannins,foruseinleatherindustry,are
obtainedfromchestnutbarktrees.
Pharmaceuticaltanninispreparedfromoakgalls.
Chestnut bark
Castalagin
Oak galls
Tannic acid

22. Physiological role
Theyexertaninhibitoryeffectonmanyenzymesduetoprotein
precipitationand,hence,maycontributeaprotectivefunctioninbarks
andheartwoods.
•They play an important role in the mechanism of hydrogen transferin
plant cells, probably due to their high affinity for oxygen.
•Certain drugs contain only one typeof tannin. Others may contain
more than one typee.g. tea, hamamelisleaves and bark contain both
hydrolysable and condensed tannins.

23. Physicalproperties
Tanninsarenon-crystallizablecompounds.
Theyaresolubleinwaterformingcolloidalsolutions
withacidicreactionandsharpastringenttaste.
Theyaresolubleindilutealkalis,alcohol,glyceroland
acetone,butonlysparinglysolubleinotherorganic
solvents.
Theirsolutionsprecipitateheavymetals,alkaloids,
glycosidesandprotein(e.g.gelatin).

24. Testsforidentification
•Goldbeater'sskintest(Skintanningtest):
Goldbeater'sskinisamembranepreparedfromtheintestineoftheox
andbehavessimilartoanuntannedhide.
Soakasmallpieceofgoldbeater'sskinin25%HCl;rinsewithdistilled
waterandplaceinthesolutiontobetestedfor5min.Washwithdistilled
waterandtransfertoa15%solutionofferroussulphate.
Abrownorblackcolorontheskindenotesthepresenceoftrue
tannins.
•Gelatintest:
Solutionsoftruetannins(about0.5-1%)precipitatea1%solutionof
gelatincontaining10%sodiumchloride.
Gallicacidandotherpseudotanninsmayreactinconcentrated
solutions.
•Testwithphenazone:
Add0.5gofsodiumacidphosphatetoabout5mlofanaqueousextract
ofthedrug;warm,coolandfilter.Tothefiltrateadd2%phenazone
solution.
Alltanninsareprecipitated,theprecipitatebeingbulkyandoften
colored.

25. •Testwithferricchloride:
Add5%ferricchloridesolutiondropbydropto2-3mloftheextractand
observethecolorproduced.
Hydrolysabletannins(gallitanninsandellagitannins)givebluish-blackcolor
orprecipitateandcondensedtanninsbrownish-greenones.
Ifthetestiscarriedonanextractthatcontainsbothtypesoftannins,ablue
colorisproducedwhichchangestoolive-greenasmoreferricchlorideis
added.
•Testwithbrominewater:
Addbrominewatertoanaqueousextractofthedrug.
-Condensedtanninsgivesabuff-coloredprecipitate
-Hydrolysabletanninsdonotformanyprecipitate.
•Testforcatechin:
Catechinsonheatingwithacidsformphloroglucinolandtheycanbe
detectedbyamodificationofthewell-knowntestforlignin.
Dipamatchstickintheplantextractcontainingcatechin,dry,moistenwith
concentratedHClandwarmnearaflameapinkorredisproduced.
•Testforchlorogenicacid:
Addaqueousammoniatoanextractcontainingchlorogenicacid,exposeto
airagreencolorgraduallydevelops.

26. Quantitativedetermination
1.Hidepowdermethod:
Thisisthemostwidelyusedoncommercialscale.
Aknownamountofareferencesampleofhidepowderisaddedtothe
drugextract.
Thedifferenceinthedryweightoftheextractbeforeandaftertreatment
withhidepowderisameasureforthetannincontent.
1.Copperacetatemethod:
Tanninisprecipitatedquantitativelywithcopperacetatesolution.
Theprecipitateofcoppertannateiscollectedonanashlessfilterpaper,
washedwithwatertillfreefromcopperionsandignited.
Theresidueofcopperoxideobtainediscompletelyoxidizedbyaddinga
fewdropsofnitricacid.
Tannincontentiscalculatedonthebasisthat1partofcopperoxideis
equivalentto1.305partsoftannins.

27. •Agglutinationmethod
Thisdependsonthatasuspensionofredbloodcellsisagglutinated
withtannins,buthaemolysisdoesnotoccur(c.f.saponins).The
erythrocytesareagglutinated(sticktogether)duetoformationofasticky
membraneontheirsurfaceincontactwithtannins.
Thequantityofredbloodcellsprecipitatedisproportionaltothe
amountof"astringent"tanninpresent.
Theendpointisreachedwhenredbloodcellsarecompletely
precipitatedi.e.thesolutioniscolorlessonshaking.Reactionisstopped
whenthefiltrategivesnoprecipitatewithferricchloride(thisindicates
absenceoftannins).
Theastringencyvalueoftheextractiscomparedwiththatoftannicacid
usedasreferencestandard,recordedaspercentagetannicacidand
referredtoas"tanninnumber".
Allthesolutionsusedshouldbeisotonic.
Catechinisinactive.
•Iodometricdetermination
Tanninsandpseudotanninsquantitativelyconsumeiodinefromalkaline
mediumduetotheirphenolicnature.
Excessiodineisdeterminedbytitration,afteracidification,withstandard
sodiumthiosulphatesolutionusingstarchasindicator.
Truetanninscanberemovedfromtheextractbyprecipitationwithgelatin.
Thiscanpermitthedeterminationofeachgroupofconstituentsalone.

28. Medicinalandbiologicalproperties
Tannin-containingdrugsprecipitateproteinsandhavebeentraditionally
usedasstyptics(stophemorrhage)andinternallyfortheprotectionof
inflamedsurfacesofmouthandthroat.
Theyplayanimportantroleinthetreatmentofburns.Theyformamild
antisepticprotectivelayeronthesurfaceoftheinjuredskinbelowwhich
regenerationofnewtissuetakesplace.
Theyactasanti-diarrheals,althoughnotrecommendedinthisrespectas
theyusuallydelayeliminationofbacterialtoxinsfromthebody.
Tanninshavebeenemployedasantidoteinpoisoningbyheavymetals,
alkaloidsandcertainglycosidesduetotheirprecipitationas
tannates.
Recentlytanninsasmostpolyphenolswereprovedtohaveapotent
antioxidanteffect.

29. Studiesontheantitumoreffectoftanninsprovedthatastrong
activityisobtainedwithellagitanninshavinggalloylgroupsattheO-
2andO-3positionsoftheglucosecore(s),asinthe
tellimagrandins.
Certaintanninswereprovedtohaveanti-HIVactivities
TellimagrandinII (Anti herpes virus)

30. Economicimportance
Tanninsareusedinleatherindustrytotransformrawanimalskinto
leatherduetotheirabilitytocross-linkwithproteins.Tobeeffectivefor
tannage,thepolyphenolmoleculemustbeneithertoolargeasitwill
beunabletoentertheintersticesbetweenthecollagenfibrilsofthe
animalskinnortoosmallasitwillbeunabletocross-linkbetweenthe
proteinmoleculesofadjacentfibrilsatseveralpoints.
Tanninsareusedinthemanufactureofinksbasedonthedarkcolored
complexestheyformwithironsalts.
Tanninsareusedinfoodindustriestoimproveacceptanceofmany
beveragesandfoodswhenadegreeofastringencyisrequired.

31. Summary:
1.Definition
2.Classification
3.General characters
4.Distribution and physiological role
5.Tests for identification
6.Quantitative determination
7.Medicinal and biological properties
8.Economic importance