Green Tea is rich in Antioxidants
All types of tea are brewed from the dried leaves of the Camellia Sinensis bush and the level of oxidation of the leaves determines the type of tea. Green tea is one of the less processed types of tea and it contains the most antioxidants and beneficial polyphenols since it is obtained from unoxidized leaves. Fresh tea leaf is unusually rich in the flavanol group of polyphenols known as catechins which may constitute up to 30% of the dry leaf weight.
Caffeine is present at an average level of 3% along with very small amounts of the other common methylxanthines, theobromine and theophylline. The amino acid theanine (5-N-ethylglutamine) is also unique to tea, as has been discussed later. Polyphenols present in black tea can be due to many factors. Theaflavins are the most important one. Whereas, other type is thearubigens, a large group of polymeric polyphenols (structure of these compounds are not properly known till date). Presence of these groups mainly contributes towards the orange-red colouration of tea, in addition to the taste. Tea accumulates aluminum and manganese.
In addition to the normal complement of plant cell enzymes, tea leaf contains an active polyphenol oxidase which catalyzes the aerobic oxidation of the catechins when the leaf cell structure is disrupted during black tea manufacture. The various quinones produced by the enzymatic oxidations undergo condensation reactions which result in a series of compounds, including bisflavanols, theaflavins, epitheaflavic acids, and thearubigens, which impart the characteristic taste and colour properties of black tea. Most of these compounds readily form complexes with caffeine.
There is no tannic acid in tea. Thearubigens constitute the largest mass of the extractable matter in black tea but their composition is not well known. Proanthocyanidins make up part of the complex. Tea peroxidase may be involved in their generation. The catechin quinones also initiate the formation of many of the hundreds of volatile compounds found in the black tea aroma fraction. Green tea composition is very similar to that of the fresh leaf except for a few enzymatically catalyzed changes which occur extremely rapidly following plucking. New volatile substances are produced during the drying stage. Oolong tea is intermediate in composition between green and black teas.
