Everything about Tannin totally explained
Tannins are
astringent, bitter plant
polyphenols that either bind and
precipitate or shrink
proteins. The astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of red wine, strong tea, or an unripened fruit.. The term tannin refers to the use of tannins in
tanning animal
hides into
leather; however, the term is widely applied to any large
polyphenolic compound containing sufficient
hydroxyls and other suitable groups (such as
carboxyls) to form strong complexes with proteins and other
macromolecules. Tannins have
molecular weights ranging from 500 to over 3,000. Tannins are incompatible with alkalies, gelatin, heavy metals, iron, lime water, metallic salts, strong oxidizing agents and zinc sulfate.
Tannins are usually divided into
hydrolyzable tannins and condensed tannins (
proanthocyanidins).
Occurrence
Tannins are distributed all over the
plant kingdom. They are commonly found in both
gymnosperms as well as
angiosperms. In terms of location of the tannins in a plant, they're mainly located in the vacuoles or surface wax of the plants. These sites are where tannins don't interfere with plant metabolism, and it's only after cell breakdown and death that the tannins are active in metabolic effects. Tannins are found in leaf tissues, bud tissues, seed tissues, root tissues and stem tissues. An example of the location of the tannins in the stem tissue is that they're often found in the growth areas of trees, such as the secondary phloem and xylem and the layer between the cortex and epidermis. Tannins may help regulate the growth of these tissues. They are also found in the heartwood of conifers and may play a role in inhibiting microbial activity, thus resulting in the natural durability of the wood. However, there may be a loss in the bioavailability of tannins in plants due to birds, pests, and other pathogens. .
Hydrolyzable Tannins
At the center of a hydrolyzable tannin
molecule, there's a
carbohydrate (usually
D-glucose). The hydroxyl groups of the carbohydrate are partially or totally
esterified with phenolic groups such as
gallic acid (in gallotannins) or
ellagic acid (in ellagitannins). Hydrolyzable tannins are hydrolyzed by weak acids or weak bases to produce carbohydrate and phenolic acids.
Examples of gallotannins are the
gallic acid esters of
glucose in
tannic acid (
C76H52O46), found in the
leaves and
bark of many
plant species.
Condensed Tannins
Condensed tannins, also known as
proanthocyanidins, are polymers of 2 to 50 (or more)
flavonoid units that are joined by carbon-carbon bonds, which are not susceptible to being cleaved by
hydrolysis. While hydrolyzable tannins and most condensed tannins are water soluble, some very large condensed tannins are insoluble.
Foods with tannins
Tea
The
tea plant (
Camellia sinensis) is an example of a plant said to have a naturally high tannin content. When any type of tea leaf is steeped in hot water it brews a "tart" (
astringent) flavor that's characteristic of tannins. This is due to the
catechins and other
flavonoids. Tea "tannins" are chemically distinct from other types of plant tannins such as tannic acid and tea extracts have been reported to contain no tannic acid.
Black tea and peppermint tea are more inhibitory of iron than herb teas like chamomile, vercain, lime flower and pennyroyal. .
Wine
Tannins (mainly condensed tannins) are also found in
wine, particularly red wine. Tannins in wine can come from many sources and the tactile properties differ depending on the source. Tannins in
grape skins and
seeds (the latter being especially harsh) tend to be more noticeable in red wines, which are
fermented while in contact with the skins and seeds to extract the colour from the skins. The stems of the grape bunches also contain tannins, and will contribute tannins if the bunches are not de-stemmed before pressing and fermentation. Tannins extracted from grapes are condensed tannins, which are polymers of
proanthocyanidin monomers. Hydrolysable tannins are extracted from the oak wood the wine is aged in. Hydrolysable tannins are more easily oxidised than condensed tannins.
Modern
winemakers take great care to minimize undesirable tannins from seeds by crushing grapes gently when extracting their juice, to avoid crushing the seeds. Pressing the grapes further results in
press wine which is more tannic and might be kept separately. De-stemming is also widely practiced. Wines can also take on tannins if matured in oak or wood
casks with a high tannin content. Tannins play an important role in preventing
oxidation in aging wine and appear to
polymerize and make up a major portion of the sediment in wine.
Recently, a study in wine production and consumption has shown that tannins, in the form of
proanthocyanidins, have a beneficial effect on vascular health. The study showed that tannins suppressed production of the peptide responsible for hardening arteries. To support their findings, the study also points out that wines from the regions of southwest France and Sardinia are particularly rich in proanthocyanidins, and that these regions also produce populations with longer life spans.
Effects of tannins on the drinkability and aging potential of wine
Tannins in wine have been described, particularly by novice drinkers, as having the effect of making wine difficult to drink compared to a wine with a lower level of tannins. Tannins can be described as leaving a dry and puckered feeling with a "furriness" in the mouth that can be compared to a stewed tea, which is also very tannic. This effect is particularly profound when drinking tannic wines without the benefit of food.
Many
oenophiles see natural tannins (found particularly in varietals such as
Cabernet Sauvignon and often accentuated by heavy
oak barrel aging) as a sign of potential longevity and ageability. As tannic wines age, the tannins begin to decompose and the wine mellows and improves with age, with the tannic "backbone" helping the wine survive for as long as 40 years or more. A strongly tannic wine is also well-matched to very fatty food courses, in particular steaks; the tannins help break down the fat, with a salutary impact on both the wine and the steak. In many regions (such as in
Bordeaux), tannic grapes such as Cabernet Sauvignon are blended with lower-tannin grapes such as Merlot or Cabernet Franc, diluting the tannic characteristics. Wines that are vinified to be drunk young typically have lower tannin levels.
Fruits
Pomegranates
Pomegranates contain a diverse array of tannins, particularly hydrolysable tannins. The most abundant of pomegranate tannins are called
punicalagins. Punicalagins have a molecular weight of 1038 and are the largest molecule found intact in rat plasma after oral ingestion and were found to show no toxic effects in rats who were given a 6% diet of punicalagins for 37 days.. Punicalagins are also found to be the major component responsible for pomegranate juice's
antioxidant and health benefits
Several dietary supplements and nutritional ingredients are available that contain extracts of whole pomegranate and/or are standardized to punicalagins, the marker compound of pomegranate. Extracts of pomegranate are also
Generally Recognized as Safe (GRAS) by the United States
Food and Drug Administration.
It has been recommended to look for pomegranate ingredients that mimic the polyphenol ratio of the fruit, as potent synergistic effects have been observed in 'natural spectrum' extracts, especially pomegranate concentrate normalized to punicalagins.
Persimmons
Some
persimmons are highly astringent and therefore inedible when they're not extremely ripe (specifically the Korean, American, and Hachiya or Japanese). This is due to the high level of tannins, and if eaten by humans (and many other animals), the mouth will become completely dry, yet the saliva glands will continue to secrete saliva which can't affect the tannin-laced food. Areca Catechu also contains tannin which contributes to its antibacterial properties
Berries
Most berries, such as
cranberries,
strawberries and
blueberries, contain both hydrolyzable and condensed tannins.
Smoked foods
Tannins from the wood of mesquite, cherry, oak and other woods used in smoking are present on the surface of smoked fish and meat.
Beer
High amounts of tannins are in the hops of some beers, which contribute in part to the bitterness of some styles of beer.
Citrus,fruit juices
Although citrus fruits don't themselves contain tannins, orange-colored juices often contain food dyes with tannins. Apple juice, grape juices and berry juices are all high in tannins. Sometimes tannins are even added to juices and ciders to create a more astringent feel to the taste.
Condiments
Cloves, tarragon, cumin, thyme, vanilla, and cinnamon all contain tannins. .
Legumes
Not all, but most legumes contain tannins. Red-colored beans contain the most tannins, and white-colored beans have the least. Chickpeas also known as garbanzo beans have a smaller amount of tannins..
Chocolate
Tannin is also found in chocolate. The usual concentration is around 10mg per ml in the liquid form. You would have to eat 100 bars of chocolate to consume the equivalent amount found in a bottle of wine.
Nutrition
Tannins have traditionally been considered antinutritional but it's now known that their beneficial or antinutritional properties depend upon their chemical structure and dosage. The new technologies used to analyze molecular and chemical structures have shown that a division into condensed and hydrolysable tannins is far too simplistic . Recent studies have demonstrated that products containing chestnut tannins included at low dosages (0.15-0.2 %) in the diet can improve broiler chicken performance and wellbeing . Studies on chestnut tannins have shown beneficial effects on silage quality in the round bale silages, in particular reducing ammonia and NPN (non protein nitrogen) in the lowest wilting level . Improved fermentability of soya meal nitrogen in the rumen has also been reported by Mathieu F and Jouany JP (1993) . Studies by Gonzalez S. et al (2002) on in vitro ammonia release and dry matter degradation of soybean meal comparing three different types of tannins (quebracho, acacia and chestnut) demonstrated that chestnut tannins are more efficient in protecting soybean meal from in vitro degradation by rumen bacteria.
If ingested in excessive quantities, tannins inhibit the absorption of
minerals such as
iron which often leads to iron deficient
anemia, and
calcium which often leads to
osteoporosis. This is because tannins are metal ion
chelators, and tannin-chelated metal ions are not
bioavailable. This may not be bad for someone with an infection, as iron is mopped up by the immune system to keep microorganisms from properly multiplying. Tannins have been shown to precipitate proteins,
Tannins are phenolic compounds and interfere with iron absorption through a complex formation with iron when it's in the gastrointestinal lumen which decreases the bioavailability of iron. There is an important difference in the way in which the phenolic compounds interact with different hydroxylation patterns (gallic acid, catechin, chlorogenic acid) and the effect on iron absorption. The content of the iron-binding galloyl groups may be the major determinant of the inhibitory effect of phenolic compounds. However, condensed tannins don't interfere with iron absorption. .
In order to prevent these problems, it's advised to drink tea and coffee between meals, not during. Foods rich in vitamin C help neutralize tannin's effects on iron absorption. Adding lemon juice to tea will reduce the negative effect of tannins in iron absorption as well. Adding milk to coffee and tea has very little to no influence on the inhibitory effect of tannins..
In sensitive individuals, a large intake of tannins may cause bowel irritation, kidney irritation, liver damage, irritation of the stomach and gastrointestinal pain. With the exception of tea, long-term and/or excessive use of herbs containing high concentrations of tannins isn't recommended. A correlation has been made between esophogeal or nasal cancer in humans and regular consumption of certain herbs with high tannin concentrations.
Uses
Tannins are an important ingredient in the process of tanning leather.
Oak bark has traditionally been the primary source of
tannery tannin, though inorganic
tanning agents are also in use today.
Tannins may be employed medicinally in
antidiarrheal,
hemostatic, and
antihemorrhoidal compounds
The anti-inflammatory effect of tannins help control all indiccations of gastritis, esophagitis, enteritis, and irritating bowel disorders. Diarrhea is also treated with an effective astringent medicine that doesn't stop the flow of the disturbing substance in the stomach; rather, it controls the irritation in the small intestine.
Tannins not only heal burns and stop bleeding, but they also stop infection while they continue to heal the wound internally. The ability of tannins to form a protective layer over the exposed tissue keeps the wound from being infected even more. Tannins are also beneficial when applied to the mucosal lining of the mouth.
Tannins can also be effective in protecting the kidneys. Tannins have been used for immediate relief of sore throats, diarrhea, dysentary, hemorrhaging, fatigue, skin ulcers and as a cicatrizant on gangrenous wounds. Tannins can cause regression of tumors that are already present in tissue, but if used exessively over time, they can cause tumors in healthy tissue. Tannins are used indirectly as molluscicides to interrupt the transmission cycle of schistosomiasis. They have also reported to have anti-viral affects. When incubated with red grape juice and red wines with a high content of condensed tannins, the poliovirus, herpes simplex virus, and various enteric viruses are inactivated. .
Tannins can also be used to pull out poisons from poison oak or from bee stings, causing instant relief. The tannins help draw out all irritants from the skin because tannin is an astringent that tightens pores and pulls out liquids.
Tannins produce different colors with
ferric chloride (either blue, blue black, or green to greenish black) according to the type of tannin.
Iron gall ink is produced by treating a solution of tannins with
iron(II) sulfate.
Tannin is a component in a type of industrial
particleboard adhesive developed jointly by the Tanzania Industrial Research and Development Organization and Forintek Labs Canada.
Medical potential
Tannins have shown potential antiviral,, antibacterial and antiparasitic effects .
In the past few years tannins have also been studied for their potential effects against cancer through different mechanisms .
Tannins, including gallo and
ellagic acid (epigallitannins), are inhibitors of HIV replication.
- 1,3,4-Tri-O-galloylquinic acid
- 3,5-di-O-galloyl-shikimic acid
- 3,4,5-tri-O-galloylshikimic acid
- punicalin
- punicalagin
inhibited HIV replication in infected H9
lymphocytes with little cytotoxicity. Two compounds, punicalin and
punicacortein C, inhibited purified HIV
reverse transcriptase.
Further Information
Get more info on 'Tannin'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://tannin.totallyexplained.com">Tannin Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
