Abstract Secondary metabolites present in the plants are predominantly responsible for treating various ailments. Secondary metabolites are also called as plant constituents or natural compounds which exert significant pharmacological and toxicological effects in humankind. The chemical compounds present in the plant sources are categorized as primary and secondary metabolites based on the chemical structure and biosynthetic derivation. These substances are called plants secondary metabolites. One of the most important of secondary metabolites is Tannins. Tannins are phenolic compounds, secondary metabolites of plants widespread in terrestrial and aquatic natural environments. As they can be found in plenty of plants and herbs, they have been traditionally used for medicinal and other purposes, such as the leather industry. This fact is explained by the fact that they exert plenty of different biological activities and, thus, they entail a great potential to be used in the food, nutraceutical, and pharmaceutical industry.
Among the biological activities of tannins, the most relevant ones are antioxidant, anti-inflammatory, anti-diabetic, cardioprotective, healing and antimicrobial (antiviral and antibacterial)
Consequently, this review article is directed towards the description of the biological activities exerted by tannins as they could be further extracted from by-products of the agri-food industry to produce high-added-value products.