Propyl gallate

Propyl gallate, or propyl 3,4,5-trihydroxybenzoate, is an ester formed by the condensation of gallic acid and propanol. Since 1948, this antioxidant has been added to foods containing oils and fats to prevent oxidation. As a food additive, it is used under the E number E310.

Description
Propyl gallate is an antioxidant. It protects against oxidation by hydrogen peroxide and oxygen free radicals. It appears as a white to creamy-white crystalline odorless solid.

Production
Propyl gallate does not occur naturally, and is prepared either from reactions with gallic acid and 1-propanol, or by enzyme catalysis of tannic acid. Syntheses with gallic acid have been the most prominent methods of production, and include Steglich esterification with N,N'-diisopropylcarbodiimide and 4-dimethylaminopyridine, anhydrous addition of thionyl chloride, and Fischer esterification with various catalysts.

Uses
Propyl gallate is used to protect oils and fats in products from oxidation; it is used in foods, cosmetics, hair products, adhesives, biodiesel, and lubricants. It is often used interchangeably with octyl gallate and dodecyl gallate in these applications.

It is used as a triplet state quencher and an antioxidant in fluorescence microscopy.

Biological effects
A 1993 study in fat rodents found little or no effect on carcinogenesis by propyl gallate.

A 2009 study found that propyl gallate acts as an estrogen antagonist.