Antioxidant Potential of Green and Black Tea Determined Using the Ferric Reducing Power (FRAP) Assay by Langley-Evans SC.
Tea is one of the most commonly consumed beverages in the world
and is rich in polyphenolic compounds collectively known as the tea
flavonoids. Tea flavonoids possess antioxidant properties in vitro
and have been proposed as key protective dietary components,
reducing risk of coronary heart disease and some cancers. The
present study aimed to evaluate the possible effects of different
preparation methods on the antioxidant properties of green and
black tea. Antioxidant potentials of tea infusates were assessed
using an assay based upon the reduction of ferric chloride linked
to a chromophore. Green tea, black leaf tea and black tea in tea
bags were infused with water at 90 degrees C for time periods
ranging from 0.25 to 15 min. Green tea infusates possessed
approximately 2.5-fold greater antioxidant capacity than both types
of black tea infusates. Both green and black teas released
significant levels of antioxidants into the hot water within 2 min
of infusion. Preparation of teas across a range of temperatures
between 20 and 90 degrees C revealed that although antioxidants
were liberated from the leaves into the water in cooler infusions,
increasing the temperature could increase antioxidant potential by
4 to 9.5-fold. Black tea prepared using tea bags had significantly
lower antioxidant capacity than black leaf tea at temperatures
between 20 and 70 degrees C, suggesting that tea bag materials may
prevent some extraction of flavonoids into the tea solution. The
addition of milk appeared to diminish the antioxidant potential of
black tea preparations. This effect was greatest where whole cow's
milk was used and appeared to be primarily related to the fat
content of the added milk. These experiments have considered the
effects of commonly used domestic methods of preparation on the in
vitro antioxidant potential of tea. It is concluded that maximum
antioxidant capacity and hence maximal health benefit may be
derived from green tea or from black leaf tea prepared by infusion
with water at 90 degrees C for up to 2 min and taken with the
addition of either fat-free milk, or without milk addition. Further
studies are required to assess the antioxidant actions of tea
flavonoids in vivo.
University College Northampton, UK.
PMID: 10945114 [PubMed - indexed for MEDLINE]
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