ABSTRACT
Tannic acid is a special commercial form of tannin, a type of polyphenol. It is a weak acid (pKa ≈ 6) due to the numerous phenol groups in the structure. The chemical formula for commercial tannic acid is often given as C76H52O46 (Scheme 10.1), which corresponds with decagalloyl glucose. But, in fact, it is a mixture of polygalloyl glucoses or polygalloyl quinic acid esters with the number of galloyl moieties per molecule ranging from 2 up to 12, depending on the plant source used to extract the tannic acid. The structure of gallic acid is given in Scheme 10.2. Commercial tannic acid is usually extracted from the following plant parts: tara pods (Caesalpinia spinosa, a small leguminous tree), gall nuts from Rhus semialata and Quercus infectoria, or Sicilian Sumac leaves (Rhus coriaria, a deciduous shrub to small tree). Tannic acid hydrolyzes into glucose and gallic or ellagic acid units. Tannic acid is odorless but has a very astringent taste. Pure tannic acid is a light yellowish and amorphous powder.
