The capacity to reduce ferric ions was determined using the Ferric
Reducing Antioxidant power (FRAP) assay as described by
Benzie and Strain (1996). Briefly, an aliquot of 8.5 ll of tea (1% or
2% water extracts) was added to 275 ll of diluted FRAP reagent
using a microplate and the plates were incubated at 37 C for
30 min before measuring the absorbance at 395 nm using a plate
reader. The working FRAP reagent was prepared by mixing 10 volumes
of 300 mmol/l acetate buffer, pH 3.6, with 1 volume of
10 mmol/l TPTZ (2,4,6-tripyridyl-s-triazine) in 40 mmol/l hydrochloric
acid and with 1 volume of 20 mmol/l ferric chloride. A
standard curve was prepared using different concentrations
(200–2000 lmol/l) of FeSO4 7H2O. The antioxidant capacity
based on the ability to reduce ferric ions of the extract was
expressed as micromole FeSO4 equivalents per litre of aqueous
extracts. All solutions were used on the day of preparation and
all determinations were performed in triplicate