Page 123 - Phytochemistry 2 (06-PG 605)

Polyphenols as antioxidants
Polyphenols are the biggest group of phytochemicals, and many of them
have been found in plant-based foods.
Polyphenol-rich diets have been linked to many health benefits.
Tannins
Tannins are polyphenols which have the ability to precipitate
protein. These compounds have been used for decades to convert
raw animal hides into leather. In this process, tannin molecules
crosslink the protein and make it more resistant to bacterial and
fungal attack. Today, however, many substances considered to be
tannins by virtue of their structure and biosynthetic origin have
limited, if any, ability to make leather]. There are two major types
of tannins: hydrolyzable tannins and condensed tannins.
Hydrolyzable tannins are formed from several molecules of
phenolic acids such as gallic and hexahydroxydiphenic acids,
which are united by ester linkages to a central glucose molecule.
Two principal types of hydrolysable tannins are gallotannins and
ellagitannins, which are, respectively, composed of gallic acid and
ellagic acid units. Ellagitannins found in plants of medicinal interest
and for which structures have been elucidated include geraniin
(isolated from Geranium robertianum (Herb Robert) and Geranium
maculatum (American cranesbill) and tellimagrandins 1 and 2
(isolated from Quercus alba (Oak bark), Punica granatum
(pomegranate) and Filipendula ulmaria (Meadowsweet)) .

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