Antioxidant activity
Total phenolic content
The TPC of each herbal tea infusion was measured using the
method described by K¨ahk¨onen et al.14 The herbal tea infusion
(3 mL) was added to 1.5 mL of Folin–Ciocalteu’s phenol reagent
(10% v/v) and was allowed to react for 5 min. Next, 1.2 mL of 7.5%
w/v sodium carbonate was added to the reaction mixture and
incubated for 30 min. The resulting blue complex was measured
at765 nm,andTPCwasexpressed asmg g−1 gallic acid equivalents
(GAE). Measurements were performed in triplicate.
Total flavonoid content
The total flavonoid content (TFC) was assayed as described by
Zhishen et al.15 In brief, 0.5 mL of herbal tea infusion was mixed
with 2 mL of distilled water and 0.15 mL of 20% w/v sodium
nitrite and was left to stand for 5 min. Then 0.3 mL of 10% w/v
aluminium chloride was added to this mixture. After 6 min, 2 mL
of 1 mol L−1 sodium hydroxide and 0.2 mL of distilled water were
added. The absorbance was read at 510 nm. The results were
expressed as mg g−1 quercetin equivalents (QE). Measurements
were performed in triplicate.
Total proanthocyanidin content
The total proanthocyanidin content (TAC) of each of the herbal
tea infusions was measured using the method described by Sun
et al.16 First, 2.5 mL of 1% (w/v) vanillin in methanol and 2.5 mL
of 9.0 mol L−1 hydrochloric acid in methanol were added to 1 mL
of herbal tea infusion. After incubation at 30 ◦C for 20 min, the
absorbance was measured at 500 nm using a spectrophotometer
(Shimadzu UV 1240; Shimadzu,) and expressed as mg g−1
catechine equivalents (CE). Measurements were performed in
quintuplicate.
1,1-Diphenyl-2-picrylhydrazyl free radical scavenging activity
The DPPH free radical scavenging activity of each herbal tea
infusion was determined according to the method described by
Leong and Shui.17 A 0.1 mmol L−1 solution of DPPH in methanol
was prepared. An aliquot of 0.1 mL of herbal tea infusion was