Protocatechuic acid and proanthocyanidins are types of polyphenols commonly referred to as condensed tannins. Protocatechuic acid is a type of hydrolyzed catechin and a derivative of catechin. Proanthocyanidins are a subclass of procyanidins and are made up of 2 or more interlinked flavan-3-ol units. Procyanidins can be made up of 2 to over 10 flavan-3-ol units and can also contain other types of flavonoids besides catechin. Procyanidins can be hydrolyzed to release catechins, including epicatechin, catechin, and gallocatechin.
Protocatechuic acid is a kind of natural organic acid, which is often used as raw material of medicine. It has anti-inflammatory, antibacterial, antiviral, anti-tumor and other biological activities, widely used in medicine, cosmetics, food and other fields. However, research on protocatechuic acid is still in its early stages, and further proof of its safety and efficacy is needed.