| The infection of Penicillium italicum Wehmer and Penicillium digitatum Sacc caused by Penicillium spp was the most serious postharvest diseases of citrus fruit. More and more research suggests that the essential oil of citrus fruits and their potential antimicrobial substances can be inhibited P. italicum and P. digitatum and so many kinds of fruit and vegetables pathogen growth, however, research on its anti fungal mechanism is not clear. This study intended to P. italicum and P. digitatum as the research object, by GC-MS analysis of different ripening stage Ponkan (C. reticulala Blanco) essential oil, and contrast the change of antibacterial performance, the sitting potential antimicrobial components, and is verified through experiments. By scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observed the effects of ponkan essential oil (November) and the main antibacterial components of citral, octanal, a-terpineol on cell surface morphology and ultrastructure features of P. italicum and P. digitatum, respectively; The effects of ponkan essential oil (November) and the main antibacterial components of citral, octanal, a-terpineol on P. italicum and P. digitatum of the cell constituents’ release, the extracellular conductivity and extracellular pH, ions leakage and lipid content in cells. The process and antifungal mechanisms of the essential oil was to explore and clarify.The main results were shown as below:1. By GC-MS analysis. Fifty terpenes compounds such as limonene, γ-terpinene, β-linalool,β-myrcene, α-pinene, β-pinene and octanal were identified. Citrus essential oils mainly comprisd terpenes, including terpene olefins compounds (80.26%～88.91%), alcohol (4.88%～13.26%), aldehyde (4.51%～5.80%), and ether (0.10%～0.33%), respectively; where in the highest content was limonene (47.28%-60.11%), accounts for about half of the total content.2. We also investigates the inhibitory effect of citrus essential oils of different developmental stages and their potential antibacterial components (citral, Octanal, nonanal, decanal, β-linalool and α-terpilenol) on the mycelial growth of P. italicum and P. digitatum, using agar dilution culture method, and screened the inhibitory effect. The results showed that the citrus essential oils had better inhibitory effect on P. italicum and P. digitatum. Compared with others, the citrus essential oils obtained in November had the best inhibitory effect on P. italicum, the MIC was2.50μL/mL, the inhibition effect of ponkan essential oil (July～October) on P. italicum is similar, MIC is5.00μL/mL. While the MIC values of citrus essential oils of all months (from July to November) on P. digitatum was40.0μL/mL.From comparing the MIC and MFC, we can found that Octanal had the best inhibitory effect on P. italicum and P. digitatum, while a-terpilenol and P-linalool had the weakest inhibition effect; citral and nonanal had the stronger inhibitory effect on P. italicum and P. digitatum, while the inhibition of the other four to two kinds of penicillium were similar. So, we elect citral, Octanal and a-terpilenol these the three kinds of terpene compounds to study their antibacterial mechanisms.3. Scanning electron microscopy (SEM) observations found that the cells of P. italicum and P. digitatum were treated with MIC and MFC shows irregular changes of hyphal structure, the loss of linear form; the spore structure distortion, surface apparent bump, shrinking or even death.4. The cell constituents’release:measured at260nm absorbance values found that after the essential oils joining to supernatant, as the essential oil increased concentration and the extension of processing time, cell composition to release a quantity to larger and larger, And the most evident in30min to release.5. Effect of cell membrane permeability:Determination of extracellular conductivity and extracellular pH studies have found that the different concentrations ponkan essential oil (November) and the main antibacterial components of citral, octanal, a-terpineol can destroy cell membrane permeability of P. italicum and P. digitatum, lead to leakage of intracellular substances. Therefore, cell membrane is the ponkan essential oils and terpene compounds inhibiting P. italicum and P. digitatum one of the targets.6. Determination of ions leakage:The cells of P. italicum and P. digitatum were treated with citral concentration of MIC and MFC, which the rate of K+leakage leakages was higher than Mg2+and Ca2+, a significant of K+leakage, Mg2+has a small amount of leakage, while Ca2+has no leakage.This result illustrate that the citral can change the plasma membrane of P. italicum resulting in the ion leakage and inhibition of cell growth, and the leakage of K+was significantly higher than that of Mg2+and Ca2+leakage.7. Determination of lipid content in cells:It was found that the treated cells of P. italicum and P. digitatum and its lipid content in cells have decreased significantly, and the influence of octanal on P. italicum and P. digitatum lipid content in cells was more serious than that the influence of citral and a-terpineol. Among, the MFC of citral, octanal and a-terpineol treated P. italicum and P. digitatum and its lipid content in cells compared with the control to reduce quantity is235.2mg/g,250.1mg/g and213.4mg/g;218.6mg/g,205.8mg/g and112.9mg/g, respectively. |
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