One such prominent
phenolic acid is gallic acid which is found in a wide variety of vegetables,
fruits, tea, coffee and wine. It occurs in plants in the form of free acids,
esters, catechin derivatives and hydrolysable tannins. It also occur
as methylated gallic acids e.g., syringic acid or galloyl conjugates of
catechin derivatives, i.e., flanvan-3-ols, or polygalloyl esters of glucose,
quinic acid or glycerol [3,4].