LC-MS–MS characterisation of curry leaf flavonols and antioxidant activity

Curry leaf (Murraya koenegii) is a common flavouring agent in Indian foods. This study characterised the flavonol profile of curry leaf extracted with different solvents and the relative antioxidant capacity of these extracts by quantifying phenolic constituents. Flavonols were extracted using ethanol, methanol, or acetone prior to identification and quantification using liquid chromatography coupled to atmospheric pressure chemical ionisation (APCI) mass spectrometry in tandem mode (LC-MS–MS) with negative ion detection. Major curry leaf flavonols included myricetin-3-galactoside, quercetin-O-pentohexoside, quercetin-3-diglucoside, quercetin-3-O-rutinoside, quercetin-3-glucoside, quercetin-3-acetylhexoside, quercetin-O-xylo-pentoside, kaempferol-O-glucoside, and kaempferol-aglucoside. Lag-time and TBARS tests demonstrated that curry leaf phenolics prevent cupric-ion induced oxidation of LDL. The best extraction yield was obtained with 80% ethanol. Acetone extracts provided better antioxidant activity expressed as increased lag-time formation, than did ethanol or methanol extracts. Curry leaf is a rich source of flavonols that have biological activity in vitro and further studies are warranted in regards to the potential health benefits and identification of the novel flavonols whose identities remain unknown.