Tannins

• Tannins


  A large group of complex substances that are widely distributed in the plant kingdom
• Tannins


  • Usually localized in specific plant parts such as leaves, fruits, barks or stems
  • Usually occur as mixtures of polyphenols that are difficult to separate because they do not crystallize
  • Precipitate proteins from solutions and can combine with proteins, rendering resistant to proteolytic enzymes
• Use of tannins


  Astringent
• Types of tannins


  • Hydrolyzable tannins
  • Non-Hydrolyzable tannins
• Hydrolyzable tannins


  • Consist of gallic acid (3,4,5,trihydroxy benzoic acid) and hexahydroxydiphenic acid or related polyphenol or related polyhydric compounds esterified with glucose
  • Gallic acid when heated result to the formation of pyrogallol
  • Hydrolyzed to yield the phenolic acids and sugar
  • Give a bluish or black color with ferric chloride
  • Yield no precipitate with bromine water TS
  • Pyrogallol give soluble compound with lead acetate
• Non-Hydrolyzable tannins


  • Also known as proanthocyanidins
  • Contain only phenolic nuclei but frequently are linked to carbohydrates or proteins
  • Treated with hydrolytic agents they tend to polymerize yielding insoluble, usually red colored products known as phlobaphenes
  • Give a dark green color with ferric chloride
  • Usually contain phloroglucinal nucleus in part
  • Usually precipitated by bromine water TS
  • Yield cathecol when heated
  • Most results from the condensation of 2 or more flavans-3-ols or flavan 3,4-diols
• Hamamelis leaf (witch hazel) contains hamamelitannin and tannin derived from gallic acid, a hexose sugar, a volatile oil, a bitter principle, gallic acid and calcium oxalate
• Uses of Hamamelis leaf

  Astringent and hemostatic properties
• Nutgall is the excrescence obtained from the young twigs of Quercus infectoria
• Composition of nutgall


  Tannic acid, chief source of tannic acid
• Uses of nutgall


  Used in tanning and dying industry, formerly in the manufacture of ink
• Tannic acid


  Also known as gallotannic acid or tannin, usually obtained from nutgall
• Uses of tannic acid

  Astringent, treatment of bed sores, minor ulcerations, alkaloidal precipitant
• Kamachile (Pithecolobium dulce) contains tannins and is used for contusions and other injuries, headache, noninflammatory hemorrhoids
• Duhat (Syzgium cumini) contains tannins and is used for diarrhea, gum gingivitis, wounds
• Guava (Psidium guajava) contains tannins and is used to halt gastroenteritis, diarrhea and dysentery, wounds, ulcers, toothache
• Tangal (Ceriops candolleana Arn., Ceriops boivianiana Tul.) contains tannins and is used as astringent, haemostatic & quinine substitute to cure malaria