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Tea is an infusion
of flavorful leaves that has been consumed for centuries.
The tea shrub (genus Camellia, family Theaceae) is a
perennial evergreen with its natural habitat in the
tropical and subtropical forests of the world. Cultivated
varieties are widely grown in its home countries of
South and South East Asia as well as parts of Africa
and the Middle East. The young shoots or flushes are
plucked and processed into green (unfermented), black
(fermented) oolong (red, partially fermented) or yellow
(partially fermented) teas. n fermented teas, the action
of leaf oxidizing enzymes (mainly polyphenol oxidase)
converts tannins and catechins in tea leaves into brown/red
colored products1,5.
Catechin levels of Different
Types of Tea1
Green tea
|
30-42 wt% |
Oolong tea |
8-20 wt% |
Black tea |
3-10 wt% |
(Catechins
are expressed as wt% of extract solids.) |
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Green tea (Camellia sinensis) has been acclaimed for
its medicinal properties which include:
- Antioxidant action on edible fats and oils,
- Antibacterial action against foodborne or phytopathogenic
bacteria and infectious disease,
- Protection against tooth decay,
- Protection against atherosclerosis and hypertension,
and
- antimutagenic effects.
Green tea’s therapeutic properties have been
attributed to the antioxidant activities of the catechins,
the active constituents of tea2.
Tea catechins include (-)-epicatechin (EC), (-)-epicatechin
gallate (ECg)(-)-epigallocatechin (EGC) and (-)-epigallocatechin
gallate (EGCg).4
A recent study3 focused on
catechin intake and heart health. Dr. Ilja C.W.Arts
and fellow researchers from the National Institute of
Public Health and Environment (RIVM) in the Department
of Chronic Diseases Epidemiolgy located in Bilthoven,
Netherlands evaluated the association between high catechin
intake (mainly from black tea, apples, and chocolate)
and the incidence of mortality from ischemic heart disease
and stroke. They used data from the Zutphen Elderly
Study, a prospective cohort of 806 men aged 65-84 years
old in 1985.
It was determined that elderly men who consumed the
most catechins , were 51% less likely to develop ischemic
heart disease over 10 years compared to men who consumed
lesser amounts. (Ischemic heart disease is characterized
by reduced amounts of oxygen and blood getting to heart
due to narrowed arteries.)
The average catechin intake was 72 milligrams, and
black tea was the major source of these compounds in
the study. Although men who consumed more catechins
also tended to exercise more, not smoke, drink less
coffee, and consume more fiber and vitamin C, the research
did not find these factors to influence the overall
results3.
The mechanism by which catechins guard against certain
diseases is not clear; however, Dr. Arts the study’s
lead author, suggested they may work by preventing LDL
("bad") cholesterol from damaging cells by
recycling other antioxidants (e.g. vitamin E) or by
reducing the risk of inflammation associated with heart
disease. More studies in other countries and populations
should be conducted to confirm the results3.
Sources:
- Graham, H.N. (1992) Prev. Med. 21, 334-350.
- Prophylactic functions of tea catechins : Information
brochure, Food Research Laboratories, Mutsui Norin
Co. Ltd., Japan.
- Reuters Health Report based on Arts et al. (2001)
Am. J. Clin. Nutr. 74(2), 227-232.
- Chu, D.C. (1997) Green tea-its cultivation, processing
of the leaves for drinking materials, and kinds of
green tea,in Chemistry and applications of green Tea,
Yamamato, T., Juneja, I.R., Chu, D.C. and Kim, M.
eds.CRC Press LLC Boca Raton, FL.
- Bokuchava, M.A. and Skobeliva, N.J. (1980). Crit.
Rev. Food Sci.& Nutr. 12, 303-370.
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