Tannins are condensed and hydrolyzed plant chemicals or polyphenolic compounds very common in plants.
There are different types according to their chemical composition, which can be used for various functions such as wine making, tanning leather for shoes and clothing, or using them as antioxidants. Some of them, the «condensed tannins,» are part of the flavonoids.
The first time they were isolated or discovered was in 1922 by the German chemist Karl Johann Freudenberg.
Contents
Types of tannins
- Condensed tannins.
- Hydrolyzable tannins.
Condensed tannins
This type of plant chemical compound is a class of flavonoid. Its origin, synthesis, and obtaining are from plants. Condensed tannins serve to give color to the flowers, leaves, and seeds of plants.
They are considered the best natural origin pigments, also being able to be used to dye clothing or provide the dark red color to wine.
The condensed are formed from anthocyanidins or anthocyanins, a class of flavonoids widely distributed throughout the plant kingdom. They can be found mostly in flowers and fruits, and can be consumed by humans as they have anti-inflammatory, antioxidant properties, and benefits for the immune system.
Hydrolyzable tannins
They are another class of pigments that, as their name suggests, can be broken down in the presence of water.
Hydrolyzable tannins are heterogeneous polymers and, unlike condensed tannins, their formation is from phenolic acids, very common to find simple sugars, gallic acid, and ellagic acid in their composition. This makes it possible to differentiate them as gallotannins and ellagitannins.
Gallotannins or tannins from gallic acid are obtained from tree galls and plants such as Rhus semisalata, Rhus coriaria, Quercus infectoria, and Caesalpinia spinosa.
Ellagitannins or tannins from ellagic acid are extracted from oak wood such as Quercus alba, Quercus robur, Quercus petraea. It is also common to use chestnut wood (Castanea sativa) and myrobalan wood (Terminalia chebula).
In both cases (gallotannins and ellagitannins), they can be obtained from other plant species.
The hydrolyzable ones have a smaller size than the condensed ones. Due to their small size, hydrolyzable tannins can be hydrolyzed much more easily when mixed with water or a diluted acid in H2O.
Often, hydrolyzed ones are known as proanthocyanidins.
Functions and properties of tannins
- Act as pigments that give color to organic and inorganic tissues.
- Protect against herbivores when present in plants.
- Reduce intestinal inflammation.
- Provide a bitter taste.
- Provide astringent property, which dries.
- Possess dark colors, red, orange, yellow, violet, brown, black…
One of the uses of tannins is to function as a dye in vegetables. Plants synthesize them naturally, using them to express colors that would otherwise be unattainable (phenotype).
Also, their function is to repel herbivores that want to feed on forage grasses. When animals ingest them, they feel less appetite.
An important aspect is that, besides producing rejection for ingestion, when they penetrate the intestines, they have anti-inflammatory properties, somewhat similar to the properties of flavonols, reducing the characteristic swelling of ruminant animals. In this sense, tannins are also considered as antinutrients or natural compounds that modify the absorption of nutrients.
Given all the properties of tannins, they are highly sought after by pharmacognosy, a science that studies the benefits of natural substances, although they are generally used for other purposes even though they belong to the group of flavonoids like natural flavones, being used for different purposes than chalcone.
Side Effects
- Headache.
- Rash.
- Gastrointestinal discomfort.
- Difficulty breathing.
- Vomiting.
- Dizziness.
- Allergy symptoms.
Allergy and Headache
Some people feel discomfort when drinking wine. This is mostly caused by the natural compounds that this beverage contains. Although problems related to wine intake can arise from many substances, those most frequently causing a reaction are sulfites and sulfur derivatives.
However, it is common for the tannins in wine to cause headaches, drowsiness, and discomfort, something that, although in many cases these discomforts appear, they also do not have effects on weight gain just like soy isoflavones do not make you gain weight just like isoflavones for menopause don’t either.
In the face of these symptoms, it is best to avoid consuming them. A severe allergic reaction is not common since their intake is usually moderate in these individuals. However, by insisting on consuming them when they do not feel well to the human body, a greater hypersensitivity could occur. In this case, the symptomatology could worsen, requiring measures to alleviate the adverse effects.
The best thing in these cases is to avoid them. Some people only notice their side effects with red wine. When drinking white wine, they do not feel discomfort or headaches, which may be because white wines contain much fewer tannins.
Tannins in Red and White Wine
Their presence is widespread as wine is made from grapes, a fruit with a high amount of tannins, so, unless they are isolated and mechanically extracted, all types of red and white wine contain tannins.
This means that during tasting, they can be appreciated, producing a series of organoleptic properties in the taster. Additionally, their presence is also due to the content of the wood. When wine matures in barrels, it obtains a large amount of them.
To prevent the wine from having too many tannins, it must be matured and cured with extreme care. If the production process is not adequate, the final flavor will be less pleasant, causing dryness in the mouth. The best wines undergo a much more careful manufacturing process to eliminate or partly reduce the properties of tannins.
Tannins in red wine are more numerous than in rosé or white wine. The darker it is, the more anthocyanins or anthocyanidins it contains, also providing the body with other natural antioxidants that correspond to the group of bioflavonoids with effects on hemorrhoids and tinnitus.
The evolution of tannin varies over time, being able to group together over the months and in the presence of oxygen that penetrates through the wood or through small cracks in the barrels. When this happens, it is called a process of polymerization. After a certain time, the tannin reaches a larger size, weighing more than the liquid it is contained in and falling to the bottom as sediment. It is common to visualize them at the end of the bottle or as sediment in the jugs.
Although in many cases they can be seen as a defect in the wine, in reality, they are a fundamental part of the taste and texture of the wines produced by wineries. The difference between them lies in their quality. Noble tannins are those that time makes more pleasant, improving the taste of the wine. On the other hand, green tannins are those that over time maintain the unpleasant sensation on the palate, drying the gums.
Tannins in Leather
They are widely used in the textile industry as they can convert raw animal hide into leather.
The original name of «tanning» comes from the English denomination «tanning», which means tanning in Spanish.
To produce quality leather suitable for making jackets, pants, and clothing, tannins from leather must be hydrolyzed (mixed with water) and alcohol added.
Subsequently, decantation must be carried out, that is, separating the mixture to obtain the final product, leather, which must be allowed to dry to obtain all the wonderful properties we know.
When the tannins used for leather are exposed to air, they lose their potential, losing all their value for tanning the hides. Their degradation can be detected when they turn a dark color.
The function of tannin in leather is to modify the skin extracted from the animal. It reacts with collagen proteins, binding them and making them stronger. Untanned skin is weak against friction and the passage of time. In contrast, leather is very resistant, able to last many years in perfect condition.
Another characteristic of tannins is that they increase resistance against microbes that feed on biological tissues. They also inhibit the putrefaction of proteins with moisture, water, or increased temperature.
Plants with Tannins
Tannins in plants are very common. Plant species use them for various functions such as pigment to give color and as a repellent against ruminal animals, the herbivores that feed on them.
The most common plants with tannins are:
- Agrimony (Agrimonia eupatoria).
- Sweet alyssum (Lobularia maritima).
- Bistort (Polygonum bistorta).
- Raspberry (Rubus idaeus).
- Strawberry (Fragaria).
- Walnut (Juglans regia).
- Burnet (Sanguisorba minor).
- Oak (Quercus) (highly used for their extraction).
- Tormentil root.
- Tormentil (Potentilla erecta) root.
- Sumac (Rhus) (its wood is widely used to obtain them).
- Grape vine (Vitis vinifera).
To obtain vegetable tannins and not synthetic ones, you have to mix pieces of wood with water and alcohol and then dry the liquid or decant the raw materials to obtain a quality final product.
Foods with Tannins
Most fruits and vegetables contain them, making it difficult to choose a natural food for people who have hypersensitivity or allergy to tannins.
Although it is more common for the immune system to provoke a response when they have been added, for example, in wine or beer, below we indicate the foods with tannins.
List of foods and spices
- Almonds.
- Blueberries.
- Coffee.
- Cinnamon.
- Beer.
- Dark chocolate.
- Clove.
- Pomegranates.
- Beans.
- Quince.
- Blackberries.
- Tea.
- Grapes.
Tannins in foods are very common in fruits and vegetables.
Tea
It is very common for green tea to leave dryness or roughness in the mouth. These effects are mostly due to the amount of tannins it contains.
Like many medicinal plants, herbs, and infusions, tannin is present in this stimulating beverage.
It can also be found in large concentrations in black tea. The rougher and more bitter it is, the more tannins it contains.
Coffee
Another widely consumed food worldwide is coffee, which also contains different plant compounds due to its origin.
The tannins in coffee are either appreciated or denigrated. Like red wine, their presence marks the organoleptic properties of this beverage. The higher the amount of tannins in coffee, the greater its astringent characteristic, with a bad coffee being compared to the proportion of these plant compounds it contains.
When coffee beans are harvested unripe, very green, it is common for them to produce displeasure on the palate. They leave the mouth dry and with a bitter sensation, the opposite of roasted and ground beans that have been harvested at the right time and have obtained excellent roasting.
Coffee comes from the coffee plant and, as with grapes, it uses the plant compound to express its color and protect itself from animals. Therefore, it is important to care for the quality and production process so that the taste of coffee is authentic and without the undesired effects of tannins.
Beer
Tannins make beer cloudy, bitter, and astringent. Tannins in beer are usually a product of poor quality. They come from barley grains, malt, or the cereal with which the drink has been made, as well as being present in hops.
It is essential to control their quantity from almost the first moment of their production.
For good beer quality, it is necessary to control the doses of gallotannins (tannin of gallic acid). Although these are necessary for fermentation to produce its characteristic flavor and organoleptic properties that drinkers desire, poor control of the dose can ruin the entire production.
When turbidity appears, it means that there are suspended particles that reflect light, many of these particles being tannins.
Other Uses of Tannins
In addition to the mentioned applications (wine industry, leather tanning), tannins have uses for hair.
Indeed, tanninoplasty is a branch of aesthetics that uses these natural compounds for
Tannins for Hair
Another characteristic of this type of polyphenolic compound is that, when applied to the hair, it produces a natural straightening effect. Tannins for hair are a smoothing treatment against curls and wavy hair, eliminating frizz or frizzy hair.
Through the application of tannin on the hair, a treatment known as tanninoplasty, it is possible to tame difficult-to-comb hair.
Today, many stylists and hairdressers use them as an alternative to keratin and for hair straightening. It is a natural and ecological solution, much safer than chemical dyes, which often cause allergies and pollute the environment.
References
- Taiz, Lincoln, and Eduardo Zeiger. «Secondary Metabolites and Plant Defense«. «Plant Physiology, Fourth Edition. Sinauer Associates», 2006.
- Morris P, Robbins M P. 1997. «Manipulating condensed tannins in forage legumes«.
- Kersie, DCW Brown. «Biotechnology and the improvement of Forage Legumes«, CAB International, Wallingford, Oxon, UK.
- Real Academia Española y Asociación de Academias de la Lengua Española (2014). «tanino«. Diccionario de la lengua española (23.ª edición). Madrid: Espasa.
- Corder, JA Douthwaite, DM Lees. 2001. «Endothelin-1 synthesis reduced by red wine«. Nature.
- GW Felton, K Donato, RJ Del Vecchio, SS Duffey. 1989. «Activation of plant foliar oxidases by insect feeding reduces nutritive quality of foliage for noctuid herbivores«. Journal of Chemical Ecology.
- Butler, L. G. 1989. «Effects of condensed tannin on animal nutrition«. RW Hemingway y JJ Carchesy. «Chemistry and significance of condensed tannins«, Plenum, New York.