Online HPLC-DPPH screening method for evaluation of radical scavenging phenols extracted from Moringa oleifera leaves

In this work the phenolic profile of Moringa oleifera leaves from trees located in Oued Souf and Tamanrasset, desert region south Algeria, was characterized by a real-time HPLC coupled to the DPPH assay, together with high resolution mass spectrometry (HPLC-DAD-ESI-MSn) studies. The contribution of single component to the overall radical scavenging capacity was evaluated for water, hydroalcoholic and hydroacetonic extracts of M. oleifera leaves. Hydroacetonic extracts (70% acetone) exhibit the highest amount of phenolic compounds (57 ± 3 mg GAE/g), as well as the highest flavonoid content (9.12 ± 0.01 mg QE/g). Twelve compounds, mainly phenolics, were identified by high-resolution orbitrap mass spectrometry. Among these, chlorogenic acids (3-caffeoylquinic acid and 4-caffeoylquinic acid) and quercetin glycosides (quercetin-3-O-glucoside, quercetin-3-O-galactoside and quercetin 3-O-(6′′-malonyl) glucoside) are the most potent quenchers of DPPH radical both for hydroethanolic and hydroacetonic extracts. Aqueous extracts exhibit a quite different behaviour, with citric acid and quinic acid, arising from the oxidation of the chlorogenic acids, acting as the unique antioxidants.