CHAPTER 4

• Tannin - was first applied by Seguin in 1796 to

  denote substances present in plant extracts which were able to combine with protein of animal hides, prevent their putrefaction and convert them into leather.
• Tannin - Is a substance which is detected qualitatively by a tannin Test (Goldbeater’s Skin Test) and is determined quantitatively by its absorption on standard hide powder.
• tannin - many are glycosides
• tannin - are source of fruit acids (Glycolic, Lactic, Mandelic, Malic, Tartaric and Citric acid)
• Properties of tannins:

  ❑ Are source of fruit acids (Glycolic, Lactic, Mandelic,

  Malic, Tartaric and Citric acid)

  ❑ Found in immature fruits

  ❑ Found in specific plant parts (leaves, fruits, barks or stems)

  ❑ Found in great quantities in dead or drying cells.

  ❑ Occur in solution in cell sap, often in distinct vacuoles.

  ❑ Plant polyphenols

  ❑ “Tannin Extracts”

  ❑ Non-crystallizable

  ❑ Complex substance– a mixture of polyphenols and

  non-crystallizable compounds

  ❑ Precipitate proteins

  ❑ Sharp “puckering” taste
• Complex substance– a mixture of polyphenols and

  non-crystallizable compounds
• Classifications of tannins:

  1. hydrolysable tannins
  2. non hydrolysable tannins
  3. pseudotannins
• Hydrolysable Tannins – This may be hydrolyzed by acids or enzymes such as Tannase.
• Hydrolysable tannins - They form several molecules of phenolic acids as Gallic acid and Hexahydroxy-diphenic acid which are united by ester linkages to a central glucose molecules.
• Hydrolysable tannin - formerly known as pyrogallol tannins.
• Progallol tannin - is a phenolic compound produced/derived from either Gallic acid and other similar compounds within tannins during dry distillation
• Hydrolysable tannins - when treated with acids/enzymes produced phenolic acids such as gallic acid, ellagic acid, and glucose.
• Non Hydrolysable Tannins (condensed tannins) - also called proanthocyanidins
• Pseudo tannins - not true tannins but have properties that resemble those of tannins.
• Hydrolysable tannins - are classified to Polyhedric phenol from which they derived: gallitannins and ellagitannins
• Gallitannins - derived from gallic acid
• Ellagitannins - derived from hexahydroxy-diphenic acid units
• Hydrolysab tannins - produced blue color when tested with ferric chloride
• Hydrolysa Tannins - do not form a precipitate when treated with bromides
• Non Hydrolysable tannins - specifically known as condensed tannins
• Terms of condensed tannins based on differerent aspects of their chemical structure or properties:

  1. Proanthocyanidins tannins
  2. Polyflavonoid
  3. Catechol-type
  4. Pyrocatecollic-type tannins
• Non Hydrolysable tannins - Are not readily hydrolyzed to simpler molecules and they do not contain a sugar moiety.
• Non Hydrolysable tannins - Are related to the Flavonoid pigments and have polymeric Flavan-3-ol structures.
• Catechins - also occur with the tannins and Flavan in the biosynthesis of the molecules..
• Non Hydrolysable Tannin - when treated with enzymes/acids converted into red insoluble compounds known as phlobaphenes
• Phlobaphenes– give the characteristic color to many drugs (red cinchona bark)
• non hydrolysable tannins - produced greenish color when subjected to ferric chloride, indicating the presence of non hydrolysable tannins in substances
• Non Hydrolysable tannins- precipitated with bromides
• Pseudotannins - are compounds of lower molecular weight than true tannins and they do not respond to the Goldbeater’s skin test
• Pseudotannins - can form through linkages between two or more phenolic acids such as digallic acids and chlorogenic acids. Also derived from flavan such as catechins/catehols
• Example of pseudotannins;

  1. gallic acid
  2. catechins
  3. chlorogenic acid
  4. ipecacuanha acid
• Gallic acid - found in rhubarb and most materials which contain gallitannins
• Catechins - flavan (pseudotaninin) compounds found in catechu, acacia cutch, kino, cocoa, guarana
• Chlorogenic acid - found in unroasted coffee and nux vomica
• Ipecacuanha acid - found in Ipecacuanha plant
• subtype of catechol tannins

  1. pyrocatechol
  2. phlobatannin
• Pyrocatechol/phlobatannins - when heated, generates catechol as a results of thermal decomposition
• pyrocatechol/phlobatannins - when boiled with HCI, formed insoluble red compounds known as phlobaphenes, precipitated red color in the sol. or material being treated
• Pyrocatecho/phlobatannins - when treated with FeCl3 Test solution exhibits green color change
• Pyrocatecho/phlobatannins- when treated with bromine test sol. formed precipite