Metabolomic Profiling of Antioxidant Compounds in Five Species.

The genus , previously known as Acacia, belongs to the family Fabaceae, subfamily Leguminosae, which are flowering plants, commonly known as thorn trees. They are traditionally used medicinally in various countries including South Africa for the treatment of ailments such as fever, sore throat, Tuberculosis, convulsions and as sedatives. The aim of this study was to determine biochemical variations in five species and correlate their metabolite profiles to antioxidant activity using a chemometric approach. The antioxidant activity of five aqueous-methanolic extracts were analyzed using three methods: 2,2-di-phenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) analysis and the ferric reducing antioxidant power (FRAP) assay by means of serial dilution and bioautography with the thin-layer chromatography (TLC) method. Amongst the extracts tested, , and demonstrated the highest DPPH, ABTS and FRAP inhibitory activity. The antioxidant activities of DPPH were higher than those obtained by ABTS, although these values varied among the species. Proton nuclear magnetic resonance (H NMR), coupled with multivariate statistical modeling tools such as principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA), were performed to profile metabolites responsible for the observed activity. The OPLS-DA categorized the five species, separating them into two groups, with , and demonstrating significantly higher radical scavenging activity than and which clustered together to form another group with lower radical scavenging activity. Annotation of metabolites was carried out using the ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-qTOF-MS), and it tentatively identified 23 metabolites of significance, including epigallocatechin ( = 305.0659), methyl gallate ( = 183.0294) and quercetin ( = 301.0358), amongst others. These results elucidated the metabolites that separated the species from each other and demonstrated their possible free radical scavenging activities.