What’s gallic acid?

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Gallic acid is a phytochemical found in many plants, with antioxidant, antimicrobial, and anticancer properties. It is part of larger polyphenolic compounds, such as EGCG in green tea. Gallic acid is also used to measure the concentration of phenolics in plant extracts.

Gallic acid is a phytochemical found in many plant tissues, both as a free compound and as a component of plant polymeric tannin. This phenolic molecule is an antioxidant and appears to have antimicrobial and anticancer activities in animal studies. Gallic acid is also part of the structure of other larger polyphenolic compounds, the molecules made up of multiple phenolic groups. One example is epigallocatechin-3-gallate (EGCG), a green tea phenol that appears to have strong anticancer abilities.

Thousands of phenolic compounds are known and many more are identified each year. These compounds are only made by plants and microorganisms, but many offer tremendous health benefits to humans. Phenolics are often powerful antioxidants and may have properties such as protection against oxidative damage. This can protect against diseases as diverse as dementia and cancer. Many of these compounds, including gallic acid, also have antimicrobial properties.

Many larger polyphenols contain gallic acid as part of their structure. When the compound is connected to another molecule by an ester bond, it is known as gallate. Examples include the green tea phenols EGCG and epicatechin gallate. These compounds are known as catechins. EGCG in particular is a powerful antioxidant and has been the subject of numerous studies on its ability to protect against heart disease and cancer.

ECGC is considered a green tea phenol due to its high concentrations in green tea. It is much less common in black tea because it is destroyed during the processing that produces black tea. The way green tea is prepared can greatly affect the concentration of available polyphenols. Adding milk will prevent them from being absorbed, and adding water that is too hot will cause them to chemically change. To get the most health benefits from green tea, it’s best to prepare it with water that hasn’t reached the boiling point and drink it without milk.

Gallic acid is common in plants. Some have particularly large concentrations, such as cranberries, witch hazel, oak bark, tea leaves, and grapes. The technical term for this compound is 3,4,5-trihydroxybenzoic acid.

One substance that has large amounts of this molecule is a type of tannin, a complex molecule made of phenolic compounds. When many gallate molecules are bound together, it forms a substance called hydrolyzable tannin. There are several kinds of this type of astringent polymer, once used to tan leather. This astringency gives the tea its bite. Tannin is found in plants and is also a component of some soils.

Gallic acid is also used in research laboratories as part of the standard test to measure the concentration of phenolics and polyphenols in plant extracts and other substances. A compound called the Folin-Ciocalteau reagent reacts with the phenol group but does not indicate the concentration of phenolic compounds. Varying amounts of gallic acid are prepared for analysis at the same time with the Folin-Ciocalteau reagent so that the number of molecules in the mixture can be measured. Results for phenolic samples tested are generally shown as gallic acid equivalents.




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