Phytosterol-Rich Delonix regia Seed Oil Exhibits Antimicrobial, Antibiofilm, Radical-Scavenging and Pancreatic Lipase-Inhibitory Activities: Integrated GC-MS Profiling and Molecular Docking of Stigmasterol

Natural products may address infection, oxidative stress and metabolic disorders. This study used gas chromatography-mass spectrometry (GC-MS), bioassays and molecular docking to characterize Delonix regia seed oil and evaluate its antimicrobial, antibiofilm, radical-scavenging and pancreatic lipase-inhibitory activities. The most abundant tentatively identified peaks in the GC-MS total ion chromatogram were β-sitosterol (26.35%), stigmasterol (14.57%), linoleic acid (10.39%), and oleic acid (5.82%). Minimum inhibitory concentrations (MICs) were 15.62 µg/mL for Listeria monocytogenes, Salmonella typhi, and Candida albicans, and 62.5 µg/mL for methicillin-resistant Staphylococcus aureus. The corresponding inhibition zones were 28 ± 0.7, 21 ± 0.3, 31 ± 0.1, and 15 ± 0.5 mm, respectively. At 75% of the minimum bactericidal/fungicidal concentration, the oil inhibited biofilm formation by 94.95% for both L. monocytogenes and C. albicans. DPPH and ABTS radical-scavenging IC50 values were 17.04 ± 0.25 and 13.17 ± 0.40 µg/mL, respectively, while the pancreatic lipase IC50 was 26.29 ± 0.08 µg/mL. Time-kill assays demonstrated ≥3 log10 CFU/mL reductions, with no recoverable colonies for any of the five tested pathogens within 3 h. Docking predicted stronger stigmasterol binding to L. monocytogenes Sortase A (−6.60 kcal/mol) than to C. albicans lanosterol 14α-demethylase (CYP51; −3.41 kcal/mol), involving hydrogen bonds with Met63 and Arg381, respectively, and hydrophobic contacts. These findings identify a phytosterol-enriched GC-MS-detectable fraction of Delonix regia seed oil with in vitro activities warranting further mechanistic and in vivo investigation.