Tannins, compounds present in different plants, are complex molecules made up of about 12 to 16 phenolic groups, which gives them the great capacity to interact with other molecules of biological interest. For the most part, they are divided into hydrolyzable tannins and condensed tannins.

Tannins have defensive functions in plants, as they possess astringent and anti-nutritional (interfering with nutrient absorption) properties, such as the ability to bind to dietary proteins, preventing their absorption, which gives the plant protection against herbivores and insects.

These characteristics are also of interest to the food and health sectors; it has been reported that, under adequate doses of 1.5 to 2.5 grams per day, tannins present beneficial properties without being anti-nutritional. Some of the foods in which tannins are present are grapes, apples, berries, blueberries, sorghum, cocoa, hazelnuts, walnuts, cinnamon, and beverages such as red wine.

Different studies attribute beneficial properties to tannins, such as their antioxidant capacity, reduction of oxidative stress, prevention of cellular aging, as well as an antiproliferative, reducing factor, or with the capacity to stop the multiplication of cancer cells.

It has also been reported that they also have anti-inflammatory properties and help regulate the expression of certain genes (Nf-kb) related to this process, thus preventing other types of damage in the organism due to inflammation. Similarly, their great capacity to regulate glucose levels by promoting an increase in its uptake in the cell has also been associated.

Speaking of specific tannins, we can mention epicatechin, which has the capacity to reduce blood glucose by promoting the regeneration of pancreatic β-cells; the molecule epigallocatechin gallate, on the other hand, reduces the absorption of glucose ingested in the diet and also regulates glucose absorption by hepatocytes, possibly by regulating the redox state (reduction of oxidation), thus preventing cell damage due to oxidative stress.

One of the common sources of tannins is black tea, in which it has been reported that catechins inhibit enzymes related to carbohydrate digestion such as α-glucosidase and, thus, regulate their availability and absorption at the intestinal level.

Another attraction of tannins is at the industrial level, since they also contribute to the flavor and palatability (taste enjoyment) of wines and foods due to their astringent properties, to the tanning of skins in the textile industry, and in the production of inks and dyes, as well as in the pharmaceutical industry, where they are part of the formulation of antidiarrheal, antibacterial, antiviral, enzyme inhibitors, hepatoprotectors, and vasodilators, among others.

In conclusion, it is important to highlight that, although tannins have anti-nutritional potential, if they are consumed in doses below 2.5 grams, the beneficial contributions are preserved without reaching the negative effect. Some of the foods that have a higher concentration of tannins are fruits with bright colors in their skin, such as berries, grapes, blueberries, etc.

That is why the consumption of foods containing tannins (not exceeding 2.5 grams) can bring health benefits in the prevention of diseases related to oxidative stress and some chronic diseases such as diabetes, obesity, and metabolic syndrome.

It is also essential to continue with research that provides scientific bases on the different properties of tannins and their possible uses in daily life, as well as the types of tannins present in foods and their concentration in their different parts.

Sources and bibliography: Luis Aurelio Montoya Inzunza, science graduate student, and Erick Paul Gutiérrez Grijalva, Conacyt Chairs researcher assigned to the Regional Coordination of CIAD in Culiacán.