Utilization of Pinus pumila seed scales as forestry residues: Green microwave-assisted hydrodistillation for essential oil extraction and its antibacterial activity.

Pinus pumila seed scales, a commonly discarded forestry residue, were utilized in this study as a raw material for essential oil (PSEO) extraction using microwave-assisted hydrodistillation (MAH). Compared with conventional hydrodistillation (HD), MAH increased the PSEO yield (1.119 and 0.886%), while reducing energy consumption (0.5004 and 2.2257 kWh/g) and CO₂ emissions (0.4003 and 1.7806 kg/g), respectively. GC-MS analysis showed that the terpenoid content in PSEO extracted by the MAH method (96.20%) was 7.93% higher than that obtained by the HD method (88.27%). Antibacterial assays demonstrated that the PSEO extracted by MAH exhibited stronger inhibitory activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria monocytogenes than that extracted by the HD method. Mechanistic studies further indicated that PSEO caused structural damage to the cell wall and membrane of E. coli, leading to the leakage of alkaline phosphatase (AKPase), nucleic acids, and proteins, as well as an increase in extracellular conductivity. PSEO obtained by the MAH method caused more significant cellular disruption than that obtained by the HD method. In addition, molecular docking analysis showed that the active compounds abundant in PSEO extracted using the MAH method exhibited strong binding affinity for the OmpF protein through van der Waals forces and hydrogen bonds. These findings supported the green and effective utilization of P. pumila seed scales as a bioactive and eco-friendly antibacterial agent.