TANNINS

 Tannins are a diverse group of high-molecular-weight polyphenolic compounds found in many plants. 

Their primary function in plants is to provide defense against herbivores and pathogens, antioxidant protection, and ensure structural support.

• Bark & wood: Oak, chestnut, quebracho, Wattle (Acacia) 
• Leaves: Tea, oak leaves, eucalyptus 
• Fruits & seeds: Grapes, pomegranates, persimmons, berries 
• Nuts & legumes: Walnut, pecan, tamarind 
• Herbs & spices: Cloves, cinnamon 

Tannins are abundant in wine (especially red), tea, and unripe fruits (responsible for astringency).

 Tannins are polymers or oligomers of polyphenolic units. 

• Solubility: Water-soluble and soluble in some organic solvents. 
• Key property: Ability to precipitate proteins and alkaloids. 

Two major classes: 

1. Hydrolyzable tannins – based on gallic acid or ellagic acid esters of glucose.
   • Examples: Gallotannins, ellagitannins. 

1. Condensed tannins (proanthocyanidins) – polymers of flavan-3-ol units (like catechin). 
   • Found in cocoa, grape seeds, bark.

• Antioxidant: Protects against oxidative stress. 
• Astringent: Binds salivary proteins → dry, puckering sensation in mouth. 
• Antimicrobial: Inhibits bacterial, fungal, and viral activity. 
• Metal chelation: Can bind iron and other metals, reducing availability to microbes. 
• Cardiovascular health (from polyphenol action) 
• Cancer prevention (antioxidant, anti-proliferative effects in cell studies) 
• Antimicrobial and anti-inflammatory potential.

• Leather tanning – classic use, stabilizes collagen in hides. 
• Wine & brewing – controls flavor, color, and stability. 
• Textiles & dyes – acts as a mordant to fix natural dyes. 
• Animal feed – can reduce parasite load but may lower protein digestibility. 
• Biotechnology – antioxidant additives, enzyme inhibitors, pharmaceutical excipients.