Polyphenols are a large number of compounds with one or more aromatic rings and also there are one or more hydroxyl groups on the rings. They are the most abundant secondary metabolites found in plants. The structures of more than 8,000 phenolic are presently known, including simple molecules like phenolic acids and highly polymerized compounds like tannin. They are broadly distributed in all plant organs and are therefore an essential part of the human diet. Polyphenols are widespread components of plant foods (cereals, vegetables, fruits, olive, chocolate and so on) and beverages (coffee, tea, beer, wine and so on).