Antioxidant and radical-scavenging carbazole alkaloids from the oleoresin of curry leaf (Murraya koenigii Spreng.)

Oleoresin of curry leaves (Murraya koenigii Spreng.), obtained using acetone, was evaluated for its antioxidant activity using a β-carotene–linoleic acid model system along with the other extracts obtained using methanol, water and volatile oil. The oleoresin showed maximum activity of 83.2% at 100 ppm among all other extractives in comparison to a synthetic antioxidant, namely, butylated hydroxy anisole which exhibited 90.2% activity at the same concentration. The methanol and water extracts showed activities of 16.7% and 11.3%, respectively, at the same concentration. The volatile oil showed negligible (<10%) activity at 100 ppm concentration. Therefore, the oleoresin was fractionated on a silica gel column to obtain five compounds. Among the five, two compounds with maximum antioxidant activity were identified by 1H and 13C NMR spectra as mahanimbine and koenigine. Koenigine also showed a high degree of radical-scavenging activity.