PCOG: Tannins

• What are tannins primarily composed of?

  A mixture of polyphenols
• Why are tannins difficult to separate?

  Because they do not crystallize
• What is the usual source of tannins?

  Barks and stems
• What are some uses of tannins?

  They are used as astringents and antidotes to alkaloidal poisoning
• How do tannins affect alkaloids and proteins?

  They can precipitate alkaloids and proteins
• What is a caution associated with tannins?

  They are carcinogenic, such as in the case of chewing betel nut
• What is the CNS stimulant found in betel nut?

  Arecoline
• What is the link between betel nut and cancer?

  It is linked to a high risk of esophageal cancer
• What are pseudotannins?

  Simpler phenolic substances
• What is the molecular weight of pseudotannins?

  They have a molecular weight of around $<1,000$
• How do pseudotannins differ from true tannins in terms of precipitation?

  Pseudotannins do not precipitate leather but can precipitate gelatin
• What is the molecular weight range of true tannins?

  They have a molecular weight of around $1,000 - 5,000$
• What must be the size of the polyphenol for it to be classified as a true tannin?

  It must be between $1,000$ and $5,000$
• What are the components of true tannins?

  Ellagic acid, gallic acid, catechins, chlorogenic acid, and sugar
• What are the tests used to identify tannins?

  • Goldbeater’s Test: Positive for true tannins, negative for pseudotannins
  • Gelatin Test: Positive for both true and pseudotannins
  • Phenazone Test: Positive for tannins
  • Matchstick Test: Positive for catechins
  • Chlorogenic Test: Positive for non-hydrolysable tannins
• What are the two classifications of true tannins?

  Hydrolyzable and non-hydrolyzable
• What are hydrolyzable tannins characterized by?

  They contain glucose and can be hydrolyzed to sugar and phenolic acids
• What are the two types of hydrolyzable tannins?

  Gallotannin and ellagitannin
• What is the structure of non-hydrolyzable tannins?

  They consist of flavonoids and do not contain sugar moiety
• What are some sources of non-hydrolyzable tannins?

  Cinnamon bark, hamamelis bark, cocoa, kola, and areca seed
• What is a complex tannin?

  A hybrid that contains both hydrolyzable and non-hydrolyzable tannins
• What is the scientific name of witch hazel?

  Hamamelis virginiana
• What are the uses of witch hazel?

  It has astringent and hemostatic properties
• What is the scientific name of nutgall?

  Quercus infectoria
• What causes the formation of nutgalls?

  It is caused by the puncture of the insect Cynips tinctoria
• How are nutgalls graded?

  Based on color: blue, green, white
• What is the scientific name of pomegranate?

  Punica granatum
• What is the primary constituent of pomegranate?

  28% ellagitannin, primarily punicalagin
• What is the use of cranberry?

  It is used for urinary tract infections
• What are the physical properties of tannins?

  They are soluble in water, alcohol, glycerol, dilute alkalis, and acetone
• What are the general uses of tannins?

  • Astringent for burns and minor ulceration
  • Protein precipitant
  • Antioxidant to trap free radicals
  • Enzymatic inhibitors to stop cancer and viral replication
  • Antidote for alkaloidal and heavy metal poisoning
• What are the dangers associated with tannins?

  They can cause severe central necrosis of the liver and are carcinogenic
• What is a potential benefit of condensed tannins?

  They have potential antitumor and anti-angiogenic properties