Tannins are polyphenols found in different plant species. They are
often found in the bark, root leaf, wood, seed and fruit of plants. These
molecules are able to form complexes with proteins, digestive
enzymes, starch and minerals. As a result, tannins are characterized as
toxic, anti-nutritional agents that reduce digestibility and protein
availability in ruminants. In general, tannins can be separated in two
major groups: condensed tannins and completed tannins. The former
is difficult to hydrolyze while the latter is not. Hydrolysable tannins
are composed by a polyol (mainly glucose) as a central core esterified
by gallic acid, digallic acid (gallotannins), or ellagic acid (ellagitannins)
[1].