Tannins PDF

Pharmacognosy and Phytochemistry (Tannins) By Dr. Farah Al-Mamoori Tannins are generated through the following three pathways: the shikimic acid pathway, the phenylpropanoid pathway and the flavonoid pathway. The name tannin is derived from French “tanin”...

Pharmacognosy and Phytochemistry (Tannins) By Dr. Farah Al-Mamoori Tannins are generated through the following three pathways: the shikimic acid pathway, the phenylpropanoid pathway and the flavonoid pathway. The name tannin is derived from French “tanin” (tanning substances). They are able to combine with proteins of animal hides prevent their decomposition and convert them into leather.  Tannins are naturally occurring complex organic compounds possessing nitrogen free polyphenols of high molecular weight Compounds can be divided into two major groups on the basis of Goldbeater’s skin test. The goldbeater's skin (membrane prepared from the intestine of an ox) test is used to assess the tanning properties of a compound. A group of tannins showing the positive tanning test may be regarded as true tannins. whereas those, which are partly retained by the hide powder and fail to give the test, are called Goldbeater’s skin as pseudotannins. Most of the true tannins are high molecular weight compounds. These compounds are complex polyphenolics which are produced by polymerization of simple polyphenols Most of the true tannins are high molecular weight compounds. These compounds are complex polyphenolics which are produced by polymerization of simple polyphenols. They may form complex glycosides or remains as such Two major chemical classes of tannins are usually recognized based on this hydrolytic reaction and nature of phenolic nuclei involved in the tannins structure. The first class is referred to as hydrolysable tannins, whereas the other class is termed as condensed tannins. Hydrolyzable Tannins *Hydrolyzed by acid, alkali, enzymes and hot water and produce gallic acid or ellagic acid. The tannins derived from gallic acid are known as gallitannins and from that of ellagic acid are known as ellagitannins  Also called proanthocyanins Polymerized flavan-3-ols These tannins are resistant to hydrolysis. On treatment with acids or enzymes they are polymerised. Flavan-3-ols  They are phenolic compounds of lower molecular weight and do not show the goldbeater’s test. Examples: gallic acid in rhubarb and catechins in catechu  Antioxidant.  Antidiarrheal ( Astringent)  Antidote for heavy metals poisoning.  Treatment of burns (contract body tissue.  Astringent to stop bleeding (Haemorrhoids, Ulcers).  Anti-inflammatory  Anti-viral 9  Chemistry of Tannins *Astringency  Tannins bind carbohydrates and proteins and become insoluble *Antioxidants  Free-radical scavengers  Highly reactive phenols  Prevents oxidation  Prooxidants*  At high levels can act as a prooxidant (carcenogenic).  Both green and black tea are made from the leaves of the Camellia sinensis plant To make black tea, the leaves are first rolled and then exposed to air to trigger the oxidation process. This reaction causes the leaves to turn dark brown and allows the flavors to heighten and intensify On the other hand, green tea is processed to prevent oxidation and thus much lighter in color than black tea. Read about the role of black or green tea in weight loss. And does green tea act as magic on weight loss?  Tannins that are said to inhibit the absorption of iron. They bind with iron, specifically non-heme iron found in plant foods such as beans, peas, leafy green vegetables, and nuts *Can act as chelators, binding to minerals and inhibiting the body's ability to absorb them 23  The two forms of dietary iron are heme iron and non-heme iron: Heme iron is found only in meat, poultry, seafood, and fish, so heme iron is the type of iron that comes from animal proteins in our diet. Non-heme iron, by contrast, is found in plant- based foods like grains, beans, vegetables, fruits, nuts, and seeds 24 Different types of phytochemicals: One of the most important ones are TANNINS Condensed: Proanthocyanidins Hydrolyzables: ellagitannis and gallotannis Proanthocyanidins from blueberry act on striatum of the brain helping to keep the memory function while ageing. Ellagitannins from strawberry act on hippocampus of the brain reducing the effect of aging on spatial orientation. http://www.brainwaves.com/ Cranberries Have been medically proven to help prevent urinary tract infections in women by reducing the ability of the bacteria E. coli from adhering to cells lining the urinary tract. Proanthocyanidins from Cranberry have a protective effect against urinary track infections I. Is a source of tannin used in a number of skin care products. II. Witch hazel has been used to treat bee stings and skin abrasions III. Witch hazel tannins are also used in mouthwashes, eyewashes and for some bowel conditions. I. Unripened fruits are high in tannin content. The high tannin content discourages fruit eating animals from consuming the fruit until the seeds are mature and ready for dispersal. As the fruit ripens the tannin content lessens. II. Beside fruits, tannins are also contained in coffee, tea, red wine and beer. I. Tannins are also responsible for many of the enchanting colors seen in flowers and the final beauty of autumn leaves.