Synergistic antimicrobial effect and mode of action of palmarosa oil-loaded nanoemulsion and citric acid against Pectobacterium carotovorum

The synergistic antimicrobial activity of palmarosa oil ( Cymbopogon martini , PO)-loaded nanoemulsion (PO-NE) and citric acid (CA) against Pectobacterium, the major pathogen for soft-rot disease, was evaluated. The combination of PO-NE and CA (PO-NE + CA) significantly improved the storage stability of PO-NE at 30 °C. Compared to the anti- Pectobacterium activity of alone, PO-NE + CA reduced the minimum inhibitory concentration (MIC) by 1/4 and 1/2, respectively. Bactericidal efficacy of PO-NE + CA against P. carotovorum PCC3 was similar of PO-NE alone in the MIC in time-kill kinetic assay. PO-NE treatment mainly influenced membrane integrity, while CA treatment strongly stimulated intracellular ATP depletion. This synergistic combination effectively reduced the use of PO-NE, imparting a strong flavor note without sacrificing the antimicrobial efficacy against Pectobacterium.