| Green mold caused by Penicillium digitatum lead to80%of citrus postharvestrot. At present, postharvest pathogens are controlled mainly by synthetic fungicides,which usually results in serious environmental problems due to their residual natureand the fact that those strains are showing resistance to synthetic fungicides day byday. Therefore, seeking for the biological control strategy using some naturalsubstances to give more acceptable and less environmental damage to agriculture is ahot spot of academic attention.The objectives of our investigation were to investigate the effects of citral,octanal, and eight mixtures composed by citral, octanal, α-terpineol, and β-linalool onPenicillium digitatum fungi, as well as the effects on qualities of citrus fruit, such asVc content, chromatic index, pH value, and soluble solids content. We also studied theeffects of these aromatic compounds on oxidation resistance enzyme activities, suchas catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) activities andcompounds related to senescence, such as polyphenol oxidase (PPO), phenylalanineammonialyase (PAL) activities and malondialdehyde (MDA) content. The mainresults were listed as follows:(1) Citral, octanal, and eight mixtures composed by citral, octanal, α-terpineol,and β-linalool all had antifungal effects on Penicillium digitatum fungi in vitro.Among them, the minimum inhibitory concentration of citral against P. digitatum is2.0μL/mL, and the minimum fungicidal concentration is4.0μL/mL; the minimuminhibitory concentration of octanal against P. digitatum is0.5μL/mL, and theminimum fungicidal concentration is1.0μL/mL; among the combinations composedby two compounds, the minimum inhibitory concentration of citral+octanal (v/v:4:1) mixture against P. digitatum in vitro is2.5μL/mL, and the minimum fungicidalconcentration is2.5μL/mL; the minimum inhibitory concentration of citral+α-terpineol (v/v:1:1) mixture against P. digitatum is4.0μL/mL, and the minimumfungicidal concentration is4.0μL/mL; the minimum inhibitory concentration of citral+β-linalool (v/v:1:1) mixture against P. digitatum is4.0μL/mL, and the minimumfungicidal concentration is8.0μL/mL; the minimum inhibitory concentration ofoctanal+α-terpineol mixture (v/v:1:4) mixture against P. digitatum is2.5μL/mL,and the minimum fungicidal concentration is5.0μL/mL; the minimum inhibitory concentration of octanal+β-linalool (v/v:1:4) mixture against P. digitatum is2.5μL/mL, and the minimum fungicidal concentration is5.0μL/mL; the minimuminhibitory concentration of α-terpineol+β-linalool (v/v:1:1) mixture against P.digitatum is8.0μL/mL, and the minimum fungicidal concentration is16.0μL/mL;among the combinations composed by three compounds, the minimum inhibitoryconcentration of citral+octanal+α-terpineol (v/v/v:4:1:4) mixture is2.25μL/mL,and the minimum fungicidal concentration is5.0μL/mL; the minimum inhibitoryconcentration of citral+octanal+β-linalool (v/v/v:4:1:4) mixture is2.25μL/mL, andthe minimum fungicidal concentration is5.0μL/mL. Then we selected citral, octanal,and citral+octanal mixture to experiment below.(2) The results in vivo showed that the antifungal effect of citral at theconcentration of1×MFC was not obvious. But when the concentration was increasing,the antifungal effect was more obvious. The antifungal effect of citral was best whenthe concentration was equal to10×MFC, with only67%of decay rate compared tocontrol group after6d of storage. The data in vivo experiment also showed that theantifungal effects of octanal were not satisfactory when the concentration is too highor too low. Only when the concentration was2×MFC, octanal performed perfectly,with only33%of decay rate compared to that of control group after6d of storage.Treated citrus fruits by citral+octanal mixture in vivo experiments, it showed thatcitral+octanal (v/v:4:1) mixture could only decrease decay rate to73%in the early4d of storage. Then we selected samples treated by citral (10×MFC) and octanal(2×MFC) to study qualities of citrus fruit and enzyme activities experiments.(3) By measuring the effects of citral (10×MFC) on the qualities of citrus fruit, itshowed that citral (10×MFC) can effectively increase the Vc content of citrus fruits,but have insignificant influence on the color index, pH value, and the soluble solidscontent; By measuring effect of octanal (2×MFC) on the qualities of citrus fruit, itshowed that octanal (2×MFC) treatment had insignificant effects on qualities of citrusfruit, such as Vc content, chromatic index, pH value, and soluble solids content.(4) Through the enzyme experiments, it can be measured that, citral (10×MFC)treatment had induced the oxidation resistance enzyme activities, such as CAT, SOD,and POD activities. And it also has obvious inhibitory effect on the compoundsrelated to senescence, such as PPO, PAL activities and MDA content, particularly onthe3d day. Octanal (2×MFC) treatment had increased the CAT, SOD, and PODactivities, and reduced the production of H2O2, as well as reduced PAL activity and MDAcontent, which were related to senescence.(5) Observing the mycelium treated by citral+octanal (v/v:4:1) mixture withscanning electron microscopy (SEM), it was found that the mycelium was deformedand dried. Through determination the leak of nucleic acid, pH value and extracellularconductivity, it was found that samples treated with citral+octanal mixture had muchhigher OD260values, pH values, and extracellular conductivity values after30min,indicating that material intracellular was leaked, and the membrane permeability wasdamaged. |
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