Tea is the hot water infusion of the leaves of Camellia sinensis L.
with a worldwide annual production of approximately 20% green,
2% oolong and the 78% black tea leaves (McKay & Blumberg, 2002).
Other plant infusions have become very popular such as rooibos
(Aspalathus linearis), rose hip (Rosa spp.) and chamomile (Matricaria
recutita L.) however it is important to highlight that the terms “herbal
teas” or tisanes are best applied to this variety of beverages.
Fig. 1 illustrates the main groups of compounds present in tea
leaves and infusions beyond flavan-3-ols. The main classes of compounds
are represented by flavonoids (flavan-3-ols, flavonols and
proanthocyanidins), phenolic acids such as gallic acid, non-proteic
amino acids such as GABA (gamma-aminobutyric acid) and L-theanine,
alkaloids such as methylxanthines (e.g. caffeine) and polyamines
(e.g. spermidine and spermine).
Compounds derived of flavan-3-ols such as theaflavins (dimeric
forms) and thearubigins (oligomeric/polymeric forms) are formed
during the oxidative processing (“fermentation”) involved in the
manufacturing of oolong and black teas. Thearubigins are the major
compounds present in black tea however the exact chemical structure
has not been fully elucidated yet.