Green tea

Green tea contains mainly flavanols or catechins of epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC). In black tea, the major polyphenols are thearubigins and theaflavins.The major theaflavins of black tea are theaflavin, theaflavin 3-gallate, theaflavin 3’-gallate, and theaflavin 3,3’-gallateTheaflavins are orange-red compounds responsible for the astringent taste and coppery color of black tea. Although thearubigins are most abundant in black tea, their chemical nature and structure are largely unknown. They are water-soluble, acidic, and often rust-brown with structures ranging from dimeric and trimeric to tetrameric, and with molecular weights of 700–2000.

Tea polyphenols are well-known for their antioxidant properties. Green tea has greater antioxidant potential than oolong and black teas.Tea polyphenols are also known for their antibacterial activity. In general, antibacterial activity decreases when the extent of tea fermentation is increased, implying stronger activity in green tea than black tea.Green tea catechins, particularly EGCG and ECG, have antibacterial activity against both Gram-positive and Gram-negative bacteria. Green tea can prevent tooth decay by inhibiting oral bacteria.The antibacterial activity of black tea has also been reported.