Tannins

What Are Tannins?

Tannins are nitrogen-free polyphenols found in many medicinal plants, characterized by a bitter taste. Historically used for tanning leather, their role in leather production has diminished, replaced by inorganic salts. However, their importance in health and cosmetics remains significant. Recent advancements in isolation and spectroscopic methods have identified over a hundred new tannin compounds, clarifying their biological activity and specific effects.

Types and Chemical Properties

Tannins are weakly acidic, water-soluble, or form colloids, creating insoluble complexes with proteins. They are classified into hydrolyzed tannins (gallotannins, ellagitannins, and some caffeic acid esters) and condensed tannins (proanthocyanidins). Gallotannins are esters of gallic acid with simple sugars or sugar alcohols, while ellagitannins are esters of hexahydroxydiphenic acid, typically with glucose, yielding ellagic acid upon decomposition. Condensed tannins, or proanthocyanidins, consist of flavan units, with procyanidins formed from catechin and epicatechin. Other compounds, like chlorogenic acid, rosmarinic acid, and phlorotannins, partially exhibit tannin properties.

During drying and storage, water-soluble catechin tannins convert to insoluble, less effective phlobaphenes. For example, oak bark loses half its water-soluble tannins after 15 months, turning reddish and less valuable. Tannins are poorly soluble in hot water, so teas intended to minimize tannin content are prepared by pouring hot water over the plant material. Avoid sweetening tannin-rich teas with honey, as its proteins cause tannins to coagulate, clouding the tea. For a milder taste, prepare teas with cold water or add milk.

Health Benefits and Applications

Tannins primarily affect the skin and mucous membranes, binding to collagen fibers in a reversible process called astringency, which reduces swelling and enhances resistance. Excessive tannin incorporation can permanently alter collagen fibers. Tannins exhibit antibacterial and antiviral properties, with those from true tea preventing dental plaque and caries. Procyanidins may lower blood pressure, while ellagitannins neutralize free radicals, aiding conditions like poor organ blood flow, vascular calcification, Parkinson’s disease, joint rheumatism, and aging.

Medicinal plants rich in tannins are used to treat gastric and intestinal catarrh, acting as astringents against bacteria and excessive mucus secretion while slowing intestinal peristalsis by constricting capillaries. For oral and pharyngeal inflammation, tannin solutions are used for rinsing or gargling. Aqueous tannin solutions relieve pain and prevent blisters from sunburns or minor burns. In baths, they help with cracked skin, frostbite, itchy skin, or inflammation of the genitals and anus. Tannins reduce excessive sweating of hands and feet by narrowing sweat gland outlets and preventing odor through antibacterial action. In cosmetics, small amounts of tannins enhance skin resilience against environmental damage.

Safety Considerations

When used internally in permitted amounts, tannins are harmless, as healthy intestinal mucosa minimally absorbs them. However, they should not be applied to open skin lesions or major burns to avoid adverse effects.