Tea polyphenols: from the leaf to the cup
The leaves of the tea plant, Camellia sinensis, and tea are rich in bioactive compounds.
More than 4000 molecules have been found in the beverage.
Approximately one third of these compounds are polyphenols, the most important molecules in determining nutritional value and health benefits of the beverage.
Tea polyphenols are mostly flavonoids, such as catechins in green tea (e.g. EGCG), and thearubigins and theaflavins in black tea.
Other bioactive compounds present in tea are:
- alkaloids, such as caffeine, theophylline and theobromine;
- amino acids, and among them, theanine (r-glutamylethylamide), that is also a brain neurotransmitter and one of the most important amino acids in green tea;
- volatile organic molecules, that is, compounds that easily produce vapors and contribute to the odor of the beverage;
- fluoride, aluminum and trace elements.
These molecules provide the nutritional value of the tea, affecting human health in many ways. Their composition is highly influenced by processing of tea leaves.
Biological activities of polyphenols
Polyphenols, both in vivo and in vitro, have a broad spectrum of biological activities such as:
- antioxidant properties;
- reduction of various types of tumors;
- inhibition of inflammation;
- protective effects against hyperlipidemia and diabetes.
Therefore, they have a protective role against the development of many diseases.
Thanks to the abundance of tea polyphenols, there has been a growing interest in recent years about the possible preventive effects of beverage against several diseases, particularly cardiovascular disease, for example in the development and progression of atherosclerosis.
Mechanisms of action of tea polyphenols
Currently, there is limited information on how tea polyphenols exert their effects at cellular level.
It seems, at least in vitro, that catechins in green tea, and theaflavins and thearubigins in black tea are the bioactive compounds responsible for the physiological effects and health benefits of tea.
And among the observed mechanisms by which tea polyphenols act at the cellular level, in addition to the antioxidant effect, it has been observed, as a consequence of polyphenol binding to specific receptors on the cell membrane, changes in the activity of various protein kinases, and growth and transcriptional factors.
Moreover, it seems that these molecules, or at least EGCG, may enter the cell and directly interact with their intracellular specific targets.
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