2.7. Determination of oxygen radical absorbance capacity (ORAC)
Oxygen radical absorbance capacity (ORAC) was determined according to Ou et al. (2001). Fluorescein (100 μL, 500 mM) and 25 μL of diluted Pelargonium sidoides extracts were added into each working well in a microplate (96 well) preincubated at 37 °C. Thereafter, 25 μL of 250 mM AAPH was quickly added and the microplate was shaken for 5 s in a microtiter plate fluorometer Multiskan Ascent instrument (Labsystems, Helsinki, Finland). The fluorescence (Ex. 485 nm, Em. 510 nm) was read every 3 min over 90 min. The net area under the curve was used to calculate antioxidant capacity which was expressed in trolox equivalents (TE).