Aqueous leaves’ extract of Sonneratia alba: secondary metabolites with antibacterial activity for functional food applications

This study investigates the secondary metabolites and antibacterial activity of boiling water extract from Sonneratia alba leaves using in vitro and in silico approaches. The use of boiling water as an extraction solvent ensures safety for consumer applications in functional foods. Six extraction times (5, 10, 15, 20, 25, and 30 min) were evaluated. The 30-minute extraction yielded the highest flavonoid (20.22 ± 1.41 mg quercetin equivalent/g) and tannin (2.63 ± 0.34 mg tannic acid equivalent/g) contents. This extract exhibited strong antibacterial activity against Escherichia coli, Staphylococcus aureus, Streptococcus mutans, and Pseudomonas aeruginosa, with the highest activity against S. mutans (inhibition zone: 18.17 ± 0.29 mm), comparable to ciprofloxacin (21.17 ± 0.29 mm). Gas chromatography-mass spectrometry identified 65 compounds. Molecular docking analysis revealed three compounds with favorable binding to Glucan-Binding Protein C (GbpC) of S. mutans: 2-acetonyl-9-[3-deoxy-β-D-ribofuranosyl]hypoxanthine, paromomycin, and melezitose. Melezitose showed optimal binding conformation with key active site residues (Glu A:360 and Asn A:349). These findings demonstrate the potential of S. alba leaf extract as a natural antibacterial agent for functional food development, though further in vivo validation is required.