A hydrolysable tannin or pyrogallol-type tannin is a type of tannin that, on heating with hydrochloric or sulfuric acids, yields gallic or ellagic acids.[1]
At the center of a hydrolysable tannin molecule, there is a carbohydrate (usually D-glucose but also cyclitols like quinic or shikimic acids). The hydroxyl groups of the carbohydrate are partially or totally esterified with phenolic groups such as gallic acid in gallotannins or ellagic acid in ellagitannins. Hydrolysable tannins are mixtures of polygalloyl glucoses and/or poly-galloyl quinic acid derivatives containing in between 3 up to 12 gallic acid residues per molecule.[2]
Hydrolysable tannins are hydrolysed by weak acids or weak bases to produce carbohydrate and phenolic acids.
Examples of gallotannins are the gallic acid esters of glucose in tannic acid (C76H52O46), found in the leaves and bark of many plant species.
Hydrolysable tannins can be extracted from different vegetable plants, such as chestnut wood (Castanea sativa), oak wood (Quercus robur, Quercus petraea and Quercus alba), tara pods (Caesalpinia spinosa), gallnuts (Quercus infectoria and Rhus semialata), myrobalan (Terminalia chebula), sumac (Rhus coriaria) and Aleppo gallnuts (Andricus kollari).[3][4]