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Sunny with a high of 75
Join Date: Mar 2004
Location: OK
Posts: 1,007
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COMPOSITION OF GREEN TEA
Tea derives from the leaves of the plant Camellia sinensis,
and is reported to contain nearly 4,000 bioactive chemical
compounds, one-third of which are polyphenols.36
EGCG, the major catechin in tea, accounts for 10% of
the total weight (Fig. 1).3 Camellia sinensis is indigenous
to India and the Far East countries, primarily China and
Japan.36 Three different types of tea: green (no “fermentation”),
oolong (moderate “fermentation”), and black
(complete “fermentation”) tea can be derived from this
plant.7 When tea leaves at harvest are withered and immediately
steamed or heated, the polyphenol oxidase
that is present in the leaves is inactivated, yielding green
tea. If the leaves are harvested, withered, rolled, and
crushed, the polyphenol oxidase is liberated and is biochemically
oxidized, which in turn leads to polymerization
of the polyphenols. Polyphenols are converted to
dimers and polymers, mainly theaflavins and thearubigins.
These products are responsible for the characteristic
yellowish-orange to reddish-brown color of these teas
and for physiologic and biochemical properties comparable
with those of catechins, but with considerably less
antioxidant effects (Table 2). This process is stopped by
drying the product in a stream of hot air. Oolong tea is
produced when this reaction time is about 30 minutes,
and black tea is the result of a 60- to 90-minute reaction
time.36
Polyphenols are bonded benzene rings with multiple
hydroxyl groups (Fig. 1). Polyphenols are categorized by
structure into flavonoids and nonflavonoids, with the
chemicals found in tea being mainly flavonoids. All
three types of teas contain compounds called catechins;
which are currently thought to be primarily responsible
for the beneficial effects of tea.23-26,37 Green tea has the
highest concentration of catechins per gram of dried
leaves compared with black and oolong teas and is the
best dietary source of this compound. In green tea, catechins
represent 80% of flavonoids, although in black
tea they only represent 20% to 30% (Fig. 1).4 Each tea
contains primarily four different types of catechins including:
(-)-epicatechin, (-)-epicatechin-3-gallate, (-)-epigallocatechin,
and (-)-epigallocatechin-3-gallate (EGCG).38 Other important
dietary sources of catechins are red wine, black grapes,
apples, and chocolate.39-41Themost important flavonols in
tea are quercetin, kaempferol, and rutin. They are more
widely distributed and can also be found in red wine,
black grapes, apples, onions, cherries, berries, grapefruits,
and cruciferous vegetables.19,40-42Tea also contains
phenolic acids, including mainly caffeic, gallic, and
quinic acids, and is an excellent source of methylxanthines,
containing approximately one-third the amount of
caffeine compared with coffee.3 A cup of tea contains 40 to
55 mg of caffeine, and a cup of coffee contains 125 to 150
mg.36
I did a quick search to see what I could find out about the concentration of methylxanthines/caffeine in standardized green tea extract. What I found was many brands say they are 'lightly caffeinated' while others do not specify. It seems to me that their might be some caffeine in the standardized extract.
Here is a snippet of a quote: "Because caffeine occurs naturally in green tea extract, it has been difficult to separate the effects of green tea from caffeine in humans."
[taken from Herbal Preparations for Obesity Are they Useful? David Heber, MD, PhDUCLA Center for Human Nutrition. Heber D - Prim Care - 01-JUN-2003; 30(2): 441-63]
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