Gallatsyrer

Gallatsyrer, commonly referred to in English as gallic acids, are a class of phenolic carboxylic acids. The principal member is gallic acid, or 3,4,5-trihydroxybenzoic acid. They occur naturally in many plants and are released upon hydrolysis of hydrolyzable tannins known as gallotannins. The name derives from gall nuts, historic sources of these compounds, and from the plant tissues in which they accumulate.

Gallic acid consists of a benzoic acid core bearing three phenolic hydroxyl groups. It is a colorless or white crystalline solid with acidic properties; it forms esters with alcohols and phenols, known as gallates, such as methyl gallate and propyl gallate. These derivatives are widely used as antioxidants and stabilizers in foods, cosmetics and polymers. Gallic acid itself is also a building block in the synthesis of various polyphenolic compounds and in leather tanning, where gallotannins and related esters are hydrolyzed to release gallic acid during processing.

In plants, gallatsyrer are produced as part of secondary metabolism, notably within gallotannins that can be hydrolyzed to gallic acid and glucose. They are found in gallnuts from oak trees, as well as in tea, grapes, sumac, and many berries. They can chelate metals and interact with proteins, contributing to astringent taste and antimicrobial properties.