Antioxidant activities of the aqueous and ethanol extracts of pigeonpea [Cajanus
cajan (L.) Millsp.] leaves, as well as petroleum ether, ethyl acetate, n-butanol and water
fractions and the four main compounds separated from the ethanol extract, i.e.
cajaninstilbene acid (3-hydroxy-4-prenylmethoxystilbene-2-carboxylic acid), pinostrobin,
vitexin and orientin were examined by a DPPH radical-scavenging assay and a
β-carotene-linoleic acid test. In the DPPH system, the antioxidant activity of the ethanol
extracts was superior to that of the aqueous extracts, with IC50 values were 242.01 and
404.91 µg/mL, respectively. Among the four fractions, the ethyl acetate one showed the
highest scavenging activity, with an IC50 value of 194.98 µg/mL. Cajaninstilbene acid
(302.12 µg/mL) and orientin (316.21 µg/mL) showed more efficient radical-scavenging
abilities than pinostrobin and vitexin. In the β-carotene-linoleic acid test, the inhibition
ratio (%) of the ethyl acetate fraction (94.13%±3.41%) was found to be the highest, being
almost equal to the inhibition capacity of the positive control BHT (93.89%±1.45%) at 4
mg/mL. Pinostrobin (>500 µg/mL) and vitexin (>500 µg/mL) showed insignificant