Anti-fungal activity, mechanism studies on α-Phellandrene and Nonanal against Penicillium cyclopium

Essential oils from plants have been reported to have wide spread antimicrobial activity against various bacterial and fungal pathogens, and these include α-Phellandrene, Nonanal and other volatile substances. However, biological activities of α-Phellandrene and Nonanal have been reported only in a few publications. Further investigations are necessary to determine the antimicrobial activity of these compounds, especially for individual application, to establish the possible mechanism of action of the most active compound.

The results are shown that α-Phellandrene and Nonanal have a dose-dependent inhibition on the mycelial growth of Penicillium cyclopium. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) are 1.7 and 1.8 mL/L for α-Phellandrene, 0.3 and 0.4 mL/L for Nonanal, respectively. The volatile compounds altered the morphology of P. cyclopium hyphae by causing loss of cytoplasmic material and distortion of the mycelia. The membrane permeability of P. cyclopium increased with increasing concentrations of the two volatile compounds, as evidenced by cell constituent release, extracellular conductivity and induced efflux of K⁺. Moreover, the two volatile compounds induced a decrease in pH and in the total lipid content of P. cyclopium, which suggested that cell membrane integrity had been compromised.

The results demonstrated that α-Phellandrene and Nonanal could significantly inhibit the mycelia growth of P. cyclopium by severely disrupting the integrity of the fungal cell membrane, leading to the leakage of cell constituents and potassium ions, and triggering an increase of the total lipid content, extracellular pH and membrane permeability. Our present study suggests that α-Phellandrene and Nonanal might be a biological fungicide for the control of P. cyclopium in postharvest tomato fruits.