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ABSTRACT |
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Different classes of compounds found in tea are discussed:
polyphenols, amino acids, caffcinc, nucleoties, carbohydrates,
lipids, organic acids, chlorophyil, carotenoids, unsaponifiable
compounds, saponins, minerals, and volatile compounds. |
The apical schools of tea-consisting ideally of the terminal bud and
two adjacem leaves, and generally refered to as tea flush- make up
the raw material which is processed to black, green, oolong,
pouchong, or other forms of tea. Flush has been studied by several
workers(1-3), with particular emphasis being paid to the group of
polyphenolic compounds because the polyphenols and their
transformation products are responsible for the unique character of
tea. A generalized picture of the different classes of compounds and
their distribution throughout the tea bush (4,5) is presented in
Figure V.1.
POLYPHENOLS
The total content of polyphenols in tea flush is 25-35%
on a dry weight basis. These compounds are mainly flavanols,
together with flavonols and flavonol glycosides, flavones,
acids, and depsides, Table V. 1. Some structures of phenolic
comopounds listed in Table V. I are shown in Figure V.2.
During the processing of black tea, about 90-95%of the
flavanols [I-VIII] udergo cnzymatic oxidation to products which are
directly responsible for the characteristic color of tea brews,
their astringency, and unique taste. The chemistry and formation of
these oxidation products, named theaflayins and thearubigins, are
discussed in the next section of this issue, Process Biochemistry,
The flavonols and flavonol glycosides undergo
hardly any change during the processing of black tea. Early studies
(7) developed methods for the quantitative estimation of kaempferol
[X] and quercetin [IX] glycosides, and it was demonstrated that the
glycoside fraction had a beneficial effect in regulating the
permeability of capillary blood vessels. The presence of at least 14
glycosides of myricetin, quercetin, and kaemmpferol, has been
established (8,9), and two flavonol triglycerides have been added
(10,11). Flavonol glycosides
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