Tannins are polyphenols found principally in the bark, leaves and immature fruit of a wide range of plants. They form complexes with proteins and other plant polymers such as polysaccharides. It is thought that the role of tannins in nature is one of plant defence: they have an astringent, aversive taste that is off-putting to wannabe herbivores. As an animal or insect begins to munch on plant tissue, the tannins are released from cellular compartments and bind with the proteins and other cell components, making them taste unpleasant and rather indigestible.
==Special Precautions of Tannins==
* Tannins' numerous hydroxyl radicals confer them a strong avidity for metals such as Fe, Zn and Cu. This property makes them strong inhibitors for the gastrointestinal absorption of these metalsTannins can also impede the body’s ability to absorb iron which may adversely affect an otherwise balanced diet. If, for instance, you are in the habit of drinking coffee or tea while having your meal, the tannins in your drink can retard your body’s absorption of iron from the vegetables in your meal. There is a way though to counter the effect, or at least lessen it, through lemon or milk added to your brewed beverage. Another suggestion is to drink coffee or tea between meals – not during mealtime itself.
* Don't confuse with tannic acid : The main cause of confusion concerning tannins is that they're often mistakenly believed to be associated with tannic acid which is used for tanning leather, when this is not the case. Tannic acid is often extracted from oak leaves and has a completely different chemical makeup than polyphenols, so despite the fact that you may have heard that tea tannins (polyphenols) can be used for tanning leather, this simply is not true.
* Tannins can discolor teeth. This is one reason why dental specialists advise on limiting coffee and tea intake.
* Tannins can also impede the body’s ability to absorb iron which may adversely affect an otherwise balanced diet. If, for instance, you are in the habit of drinking coffee or tea while having your meal, the tannins in your drink can retard your body’s absorption of iron from the vegetables in your meal. There is a way though to counter the effect, or at least lessen it, through lemon or milk added to your brewed beverage. Another suggestion is to drink coffee or tea between meals – not during mealtime itself.
* Tannins are also believed to cause migraines in some people, although some medical experts strongly disagree with this, contending that the evidence from relevant researches is inconclusive.
* Treatment of bacterial infections : Ellagitannins (US20110105421A1)
* Inhibition or prevention of obesity, lipid storage (reducing blood triglyceride levels), hyperlipemia, arteriosclerosis and thrombosis : GA, EA, isoquercitrin, tellimagrandin I and II, pedunculagin, TGGs, PGG and di-galloyl-hexahydroxydiphenoyl-D-glucose (US7687085B2)
*Regulation of the synthesis and secretion of cytokines, including TNF-� alpha and IL-1 -Beta : Gallotannins and ellagitannins �(US20080070850A1)
* Anti-inflammatory or anti-allergic agent by the inhibition of histamine release from mast cells. Regular oral administration of product can ameliorate or prevent rhinitis, atopic dermatitis or asthmaEllagitannins (EP0727218A3)
* Inhibition of the propagation in human cells of a human retrovirus (HIV) : 1,3,4-tri-galloylquinic acid, galloylshikimic acid derivatives strictinin, corilagin, castalagin, vescalagin, chebulinic acid, chebulagic acid, punicalin, punicalagin, punicacortein C, cannamtannin B2 (CA2001898A1)
* Inhibition of Gram-positive bacteria (Staphylococcus aureus) growth, anti-inflammation and leukemia treatment : Tellimagrandin (US8975234B2)
===Table : Tannin-rich genera with some representatives and their tannin chemical profile, including major compounds andtheir reported bioactivities.===[[File:Tannins content table.jpg|thumb|Alt=Levisticum officinale|950px|left|]]
==References==
''By-Products of Agri-Food Industry as Tannin-Rich Sources: A Review of Tannins’ Tannins' Biological Activities and Their Potentialfor Valorization, María Fraga-Corral, Paz Otero, Javier Echave, Paula Garcia-Oliveira, Maria Carpena, Amira Jarboui, Bernabé Nuñez-Estevez, Jesus Simal-Gandara and Miguel A. Prieto''
[[Category:Treatments]]
[[Category:Astringent]]