6. TANNINS
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Transcript of 6. TANNINS
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T NN NS
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Definition of Tannins
(Cantoria, 1990)
Tannins are amorphous, polyhydroxy phenolic
compounds with molecular weights in the
range of from about 1,000 to 5,000 which
possess an astringent taste and the ability tocombine with hide to form leather.
TANNIN CELL
IN
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Characteristics of Tannins
Widely distributed in plants and many are
glycosides ex. Glucogallin
Occur in solution in cell sap
Usually found in great quantities
in dead or dying cells
Exert inhibitory effect on enzymes by proteinprecipitation, thus becoming a protectant for
barks and heartwoods.
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GALLOTANNIN or Tannic Acid usually occurs in
the bark and fruit of a large number of plants,such as:
1. dried beans of Coffea arabica L.(Rubiaceae)-Arabica Coffee,
Arabian Coffee, Abyssinian Coffee
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2. fresh forage (fodder) of
Equisetium arrense L. (Equisetaceae)
3. Roots of Glycyrrhiza glabra L. (Fabaceae)
-Common Licorice, Licorice Root,
Spanish Licorice Root
4. juice of the plant of Rhamnus
purshianus DC. (Rhamnaceae)-
Cascara Sagrada, Cascara
buckthorn
5. flowers and plants of Verbena officinalis L.
(Verbenaceae)-Vervain, Verbena.
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GALLOTANNIN or Tannic Acid
Identification Tests
1. Tannic acid, when heated to 210-215C, gets
decomposed to yield pyrogallol and CO2. The
evolution of CO2 may be confirmed when it turns
freshly prepared lime-water milky.
Tannic Acid heated at 210215C Pyrogallol + CO2
2. It instantly gives rise to insoluble precipitates with
albumin, starch, gelatin and a host of alkaloidal and
metallic salts.
3. It readily forms a bluish-black color or precipitate
with ferric salts e.g., FeCl3.
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GALLOTANNIN or Tannic Acid
Uses
1. Tannic acid with ferric salts are invariably used in themanufacture of inks.
2. It is used for tanning i.e., making leather from hides ofcow, goat, sheep and buffalo skin.
3. It is employed as a pharmaceutical aid due to its
astringent and antiseptic actions.4. It is used as a mordant in dyeing.
5. It is invariably employed to clarify beer and wine.
6. It is employed as a coagulant in the manufacture of
rubber.7. It is used in the large scale production of gallic acid andpyrogallol.
8. It is employed as a reagent in analytical chemistry.
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ELLAGITANNINSThey may be derived by the oxidative
coupling of two molecules of gallic acid
which are esterified to glucose orprobably by the condensation of
hydroaromatic precursors.
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COMPLEX TANNINS
This has been applied by Okuda to anewly-discovered group of tanninswhich are biosynthesized from both a
hydrolyzable tannin (mostly C-glucosideellagitannin) and a condensed tannin.
The union through a C-C bondbetween the C1 of the glucose unit of
the ellagitannin and the C8 or C6 of theflavan-3-ol derivative.
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Main Classes of Tannins
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HYDROLYZABLE TANNINS (also referred to as
pyrogallotannins)
1. When treated with acids or enzymes, they yieldphenolic acids, such as gallic and ellagic acids, and
carbohydrates usually glucose.
2. Their solution turn bluish black with FeCl3 TS
3. On dry distillation, gallic acid and similar
components are converted into pyrogallol.
Main Classes of Tannins
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CONDENSED TANNINS (PHLOBATANNINS,
FLAVOLANS OR CATECHOL TANNINS)
1. They are more resistant when treated with acidsor enzymes as compared to hydrolyzable tannins.
They are decomposed to red insoluble compounds
known as phlobaphenes or tanners red.
2. Their solution turn greenish black with FeCl3 TS
3. On dry distillation, gallic acid and similar
components are converted into catechol.
Main Classes of Tannins
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PSEUDOTANNINS are compounds of lower molecular
weights than true tannins and they do not respond
to the goldbeaters skin test.
Examples:
Depsides formed by ether linkages between two or
more molecules of phenolic acids (ex. m-gallic acid
in galls , chlorogenic acid in coffee)Derivatives of flavan or phenyl-2-benzodihydropyran
(ex. Catechins or catechols in gambir and kremeria)
Main Classes of Tannins
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Tannin Formation
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Tannin Formation
Polygalloylgiucose is the parent compound of many, if
not all, of the hydrolyzable tannins.
Catechins and flava-3,4-diols appear to be the
intermediate In the biosynthesis of condensed tannins
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Useful Tests for Tannins
1. Goldbeaters skin test. a brown or black color on the skindenotes the presence of tannins
Golbeaters skin is a membrane prepared from the intestine ofthe ox and behaves similarly to an untanned hide.
2. Gelatin test. Gallic acid and other pseudotanninsprecipitate gelatin if the solutions are sufficientlyconcentrated.
3. Phenazone test. All tannins are precipitated, the precipitatebeing bulky and often colored.
4. Test for Catechin. The phlorogloucinol produced turns thewood pink or red.
5.Test for chlorogenic acid. Development of a green color.
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TANNIN APPLICATIONS
Has the property of precipitating proteins,thusact therapeutically as astringent, both on theGIT and skin abrasions
Tanning leather Precipitates alkaloids, thus used for their
detection and antidotal treatment of toxic
overdoses of these substances Forms deep colored compounds with iron
salts, thus used in the manufacture of inks
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PART USED LOCAL NAME BOTANICALORIGIN
LEAF Hamamelis Hamamelis virginiana
Fam. Hamamelidaceae
Bayabas Psidium guajava L.
Fam. Myrtaceae
Dried aqueous extract Gambir Uncaria gambir(Fam. Rubiaceae)
Excrecence Nutgall Formed on young twigs of Qurcus
infectoria (Fam. Fagaceae) by the gall
wasp,Adleria gallaetinctoriae
Bark Duhat Syzygium cumini(L.) Skeels
Fam. Myrtaceae
Kamachile Pithecolobium dulce (Roxb.) Benth.
Fam. Fabaceae