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.
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.
[Hirose, Masao, et al.. "Modification of carcinogenesis by α-tocopherol, t-butylhydro-quinone, propyl gallate and butylated hydroxytoluene in a rat multi-organ carcinogenesis model." Carcinogenesis 14.11 (1993): 2359-2364.]
A 2009 study found that propyl gallate acts as an estrogen antagonist.
Propyl gallate has many biological activities, including:
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Enzyme inhibition
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Antimicrobial activity
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Inhibition of nitrosamine formation
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Anticarcinogenesis
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Antitumorigenesis
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Anesthesia
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Anti-nociceptive
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Inhibition of biosynthetic processes
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Ionizing/ultraviolet (UV) radiation protection
Safety
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Propyl gallate is an irritant to the skin and eyes, and it can be inhaled. Some studies have reported that propyl gallate is toxic, while others have reported therapeutic benefits.
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The FDA recognizes propyl gallate as being generally safe, but in other countries, it's either been used on a very limited basis or completely banned. This is because some preliminary studies have suggested that propyl gallate may cause cancer (in several organs) in rats and be an endocrine disrupter.
