7. DPPH radical scavenging activity
The DPPH radical scavenging activity of kumquat extracts was
measured according to a slightly modified method of Yamaguchi,
Takamura, Matoba, and Terao (1998). After 0.5 mL of kumquat
extract was mixed with 0.5 mL of 0.5 mM DPPH in methanol for
30 min, the mixture was subjected to HPLC analysis with reverse
phase column (Thermo ODS-2 Hypersil, 250 mm 4.6 mm, 5 lm)
under photodiode array (PDA) detection at 517 nm. The mobile
phase was methanol/water (7/3, v/v) and the flow rate was 1 mL/
min. The change in peak area of DPPH was determined after the
reaction. Radical scavenging activity was expressed as percent
inhibition and was calculated using the following formula: