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. Propyl gallate (PG) is a white to nearly white odorless crystalline powder that has slightly bitter taste and darkens in the presence of iron salts. It is an irritant that can cause skin dryness, dermatitis, and sensitization. Inhalation may cause chemical pneumonia

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. Propyl gallate is an antioxidant that neutralizes free radicals, which are unstable molecules that can damage cells, proteins, and DNA. 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. Propyl gallate has many biological activities, including:

Safety