Tannins

Dear Colleagues,

Tannins are a widely distributed group of compounds, found throughout the plant kingdom. There are two distinct types of tannins, the hydrolyzable tannins, which are polymers of ellagic or gallic acid esterified to a carbohydrate (usually glucose), and condensed tannins (proanthocyanidins), which are polymers of flavan-3-ols. Tannins can be high molecular weight, have very heterogeneous structures, and can form complexes with a number of other molecules (especially proteins and carbohydrates). All of these characteristics of tannins can influence their biological properties.

Tannins are astringent defense compounds that serve as predator feeding deterrents, and are produced by plants in times of stress, acting as antimicrobials. They may also play a role in fruit ripening and plant growth regulation. Tannins have a number of industrial uses, including dying and preserving, converting animal hides to leather, and the precipitation of proteins in wine and beer.

Historically, ingestion of tannins has been associated with anti-nutritional effects, especially on protein digestibility in ruminant animals. However, recent research on tannins has focused on their potential to positively impact human health, when consumed in the proper dosage and structural form. Tannins have demonstrated a host of potent biological activities, including bacterial anti-adhesion activity, anti-parasitic, antioxidant, anti-inflammatory and anti-proliferative activities, as well as influencing cell signaling and gut health.

This special issue of Molecules will consider submissions related to all characteristics of tannins (both hydrolyzable and condensed), including biological and chemical properties and potential human health effects.

Dr. Amy B. Howell
Guest Editor