Gallic Acid
Gallic acid is a colorless powder in its pure form, and it can be found in plants alone or as a part of tannins. It is a phenol, which is an aromatic ring of carbons, a compound that is only synthesized in plants. Phenols also have a hydroxyl (-OH) attached to at least one of the carbons. Gallic acid has 3 hydroxyls and one carboxyl (-COOH) attached to it. These units have an "extra" electron that they want to get rid of, and that is what makes this type of compound such a great antioxidant.
One source of gallic acid is gall nuts, which are small, hard lumps found on the outside of wood. They are commonly spotted on oak trees, and are formed when insects drill into them to deposit their eggs. The plant's reaction is to surround the eggs with a substance that is rich in tannins and gallic acid, which then hardens into the lump. Gall nuts were used in the past to produce ink, dyes and pigments because of their rich resins and tannins. Most plants produce some gallic acid, but other especially good sources are sumac, witch hazel, tea leaves, grapes, hops, Tulare walnuts and oak bark.
Gallic acid has antifungal and antiviral properties which protect the plant. When scientists found that a variety of walnuts called Tulare was remarkably resistant to the aflatoxin fungus, tests showed that it was gallic acid in the walnut itself which was inhibiting the production of aflatoxin. You can read about this research at the Agricultural Research Service web site.
Like all the phenolic compounds gallic acid is a powerful antioxidant, neutralizing free radicals that can damage cells. Several studies have shown it can induce apoptosis (the cell death signal) in cancer cells, while not harming normal cells. Gallic acid has astringent properties and can be been used to treat hemorrhage, especially in chronic condition such as stomach ulcers. It can be used as a gargle to cure inflammed mucous membranes or bleeding gums, or bleeding following the extraction of teeth. Some ointments that are used to treat psoriasis and external haemorrhoids contain gallic acid.
In the 1830's Henry Fox Talbot developed a process of developing photos which used a negative to produce positive prints. He used a solution of silver nitrate and gallic acid for this process. He patented this process, called the calotype, in 1841. Gallic acid is used in the pharmaceutical industry in the production of various drugs, and can also be used to synthesize the hallucinogenic alkaloid mescaline.
Angelo Mai, an Italian philologist who was born in the 1700's, worked with palimpsests in several Italian libraries, including the Vatican library. A palimpsest is an ancient parchment that has been scraped and reused, so that there are layers of text. Mai found that applying gallic acid to the pages would remove the top layers and allow him to read the lower text, and he restored many ancient documents in this way.
An herbal supplement called NT combines rhubarb, ginger, astragulus, red sage and turmeric with gallic acid, and is marketed with claims that it can reduce food intake and cause weight loss. Researchers at Pennington Biomedical Research Center, Baton Rouge, Louisiana studied this herbal supplement to see how effective it was, and the results were published in the Journal of Medicinal Food in March of 2007. The study found that there were no ill effects from the supplement, but it had no effect on appetite or weight loss. They reasoned that the gallic acid was poorly absorbed into the system when taken orally, since blood plasma amounts never rose above a certain level even though dosage was increased.
A homeopathic remedy is made from oak bark and is used in the treatment of disorders of the spleen and gall bladder. Apparently oak seeds, which are high in gallic acid, can also be ground and eaten, but they are extremely bitter if you don't take steps to remove the tannins.
The information on this page is not meant to be used in treatment of medical conditions. Please seek the advice of a physician about any medical condition or symptom. Those with medical conditions should consult a medical professional about the appropriateness of taking dietary supplements or diet therapy, and how these methods will interact with their medications.