The method is based on the reduction
of the relatively stable radical, DPPH, to the formation of a non
radical form in the presence of hydrogen donating antioxidant. The
tea samples showed antioxidant activity by the reduction of purple
colored DPPH to the yellow colored diphenylpicrylhydrazine derivatives.
DPPH radical scavenging capacity was estimated according to
Brand-Williams, Cuvelier, and Berset (1995) and Shyu and Hwang
(2002) with slight modifications. In the assay, 1 mL of diluted extract
was mixed with 2 mL of 0.1 mmol/L solution of DPPH in methanol.
The mixture was incubated in the dark at room temperature for
30 min, and the absorbance at 517 nm was measured. All tests were
performed in triplicate. The scavenging capacity was calculated as:
(1 − As/Ac) × 100%, where Ac is the absorbance of the control and As
is the absorbance of the tested sample after 30 min. Trolox was used
as standard. Free radical scavenging capacities of tea samples were
expressed as mM Trolox equivalent and IC50 values (concentration of
samples required to scavenge 50% of DPPH radicals).