Have you ever borne to bite a still unripe fruit and immediately feel the language that dries, almost crashing? That rough feeling and tosometimes a little unpleasant, it’s not just a feeling of the palate, but it is the signal that there are gods tannins. The tannins they are natural compounds with antioxidant abilitiesand which are found not only in the fruits (especially kaki, melagran or grapes), but also in the bark, in the seeds, in wine, in tea, and in some woods. There are different types, some solubles and others more complex, and each with different roles. For example, plants help a defend yourself from external attacks – insects, mushrooms, herbivores – and to respond to unfavorable climatic conditions. The production of tannins is not accidental, but due to hormonal mechanisms internal to the plant.
What is a tannin
From a chemical point of view, the tannins are polyphenols: large, complex molecules, rich in aromatic rings and obshydrile groups (–OH). But what makes them really special is their ability to bind to proteins and “rush them”, that is to make them insoluble. This is what causes that astringent sensation in the mouth, typical of a non -mature persimmon, of a green banana, or a full -bodied red wine.
Not all tannins are the same. Some are hydrosoluble (they melt in the water), others form more complex and resistant structures. In general, they are divided into two large families: i condensed tannins (or proantocianidine), derived from flavonoids and hydrolyzable tanninswhich include Gallannini and Ellagitannini, derived from Gallic acid.
Where tannins are in nature and what functions they have
The short answer? A little everywhere. But here are some concrete examples, the tannins are present in the bark of oaks, chestnuts and acacies; in the fruits such as pomegranate, persimmons, grapes, strawberries and berries; in the seeds and in the leavesas in green and black tea, cocoa, coffee, and cola; in roots, pods, shells and wood. Curiously, tannins are often more abundant in the fruits not yet mature. A smart move: make the fruit unpleasant on the palate until the seeds are ready for diffusion. Only when it is the right time, the astringency is reduced and the fruit becomes sweet, attractive for the animals that will bring the seeds away.
For plants, tannins are like a sort of multifunction shield. Have numerous effects, including: antiebivoresbecause they make the leaves harder to digest; antimicrobialuseful against bacteria and mushrooms; protectivein difficult situations such as drought, salinity or excess of light. All this does not happen at random, in fact the Synthesis of the tannins is activated by precise hormonal signals. Hormones such as salicylic acid or jasmonate can “turn on” the production of tannins in response to an infection or an invasion of insects. In some species, such as red fir, it has been observed that the application of salicylic acid significantly increases tannins in the cortex – making it more resistant to the attacks of the beetles.
Understanding the adjustment of the synthesis of the tannins is now a central theme also for the genetic improvement of crops. Some varieties of lives, kaki and strawberry are selected precisely due to their optimal content in tannins, capable of balanced taste and nutritional benefits. In the future, studying the genes involved in the production of tannins will allow to obtain more resistant fruits to diseases, but also healthier and tastier for us.
What tannins and effects on human health are used for
In addition to being fundamental for the survival of plants, the tannins play a key role in our relationship with fruit, drinks and spices. Are responsible for astringency And bitterness in wine, tea, coffee, cocoa, unripe apples, persimmons and berries; of color and stability of wine, particularly in ripe reds; from the food conservationbecause, thanks to their antioxidant power, they slow down oxidation.
Also In the industrial field they are widely used In the tanning of the skins, such as natural additives in foods and feed, and even in craft beer to improve flavor and foam.
The tannins arouse contrasting opinions. On the one hand, thanks to theirs antioxidant activityare associated with benefits For human health, such as, for example, cardiovascular protection, neurodegenerative, anticancer and antibacterial the antibacterial; But also the prevention of oxidative stress and inflammation. On the other, excessive consumption of tannins can have side effectsas the reduction of intestinal absorption of iron and proteins, and gastrointestinal disorders in sensitive subjects. The key, as often happens, is in the quantity and in the variety of the diet.
