Enhanced Phenolic Content and Bioactivity of <i>Moringa oleifera</i> Leaf Extracts Obtained by Ultrasound-Assisted Extraction: Antioxidant and Antibacterial Evaluation

Moringa oleifera leaves were processed to obtain an aqueous crude extract (CE) via ultrasound-assisted extraction and a purified extract (PE) derived from CE. Phenolic composition was characterized by HPLC-TOF/QTOF-MS, while antioxidant activity was assessed using ABTS•+ (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and DPPH (2,2-diphenyl-1-picrylhydrazyl). Antibacterial activity was evaluated through minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against Escherichia coli, Staphylococcus aureus, and Enterococcus faecalis. PE exhibited higher phenolic (147.91 mg GAE/g) and flavonoid (81.06 mg QE/g) contents, superior antioxidant capacity (IC50: 0.91 mg/mL for ABTS•+, 1.41 mg/mL for DPPH•+), and stronger antibacterial effects (MIC: 0.39 mg/mL for E. coli and S. aureus, 12.5 mg/mL for E. faecalis) than CE. Quercetin 3-O-(6″-malonylglucoside) and kaempferol 3-O-rutinoside were the main antibacterial contributors. This study reports the first identification of dihydro-p-coumaric acid and the acetylated flavonoid spinacetin 3-O-(2”-feruloylglucosyl)(1→6)-[apiosyl(1→2)]-glucoside compounds with potential antioxidant and bioactive properties in M. oleifera extracts.