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Study on the Effect of Three Volatile Flavor Compounds Against Geotrichum Citri-aurantii of Postharv

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Tutor: TaoNengGuo
School: Xiangtan University
Course: Chemical Engineering and Technology
Keywords: Geotrichum citri-aurantii,Ponkan essential oil,Flavor compounds,antifungal activ
CLC: S436.661
Type: Master's thesis
Year:  2013
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Sour disease is a serious citrus postharvest disease. In recent years, after mostplaces strengthened control of blue, green mold disease, the incidence of sour diseasesin citrus gradually increased and had the trend of outbreak. A pathogenic fungus wasisolated and indentified. GC-MS analysised citrus essential oils of different storagetime and we explored the inhibitory effect and mechanism of the above essential oilsand potential antibacterial component agaist sour bacteria. The results are as follows:(1) Pathogencity measurement and biological characteristics of G. citri-aurantiiA pathogenic fungus was isolated from the surface of natural rotten MiyagawaWase (Citrus unshiu Marc) fruit£¬ and it was indentified by the way of themorphological characterization and rDNA-ITS analysis. To further study thepathogenic fungus, we investigated its basic biological characteristics. Results of thepathogencity measurement showed that the time for rotten of the full citrus fruitinoculated with GC was11d. The basic biological characteristics of GC were asfollows: the optimal temperature for the mycelium growth was28¡ãC, the myceliumgrowth flourish at pH4.0, the lethal temperature was85¡ãC. In addition, the myceliumgrowth of GC was unaffected by lighting.(2) Pokan essential oil stored different days and the chemical composition wasanalyzed GC-MS and their antifungal activityThe essential oil of pokan extracted by steam distillation and the chemicalcomposition was analyzed by GC-MS. The results of GC-MS showed that the majorcomponents of the essential oil of pokan stored different days were terpenes(89.18%~90.82%), alcohols (4.89%~5.54%), aldehydes (4.22%~5.28%) and ether(0.10%~0.33%) respectively; where in the highest content was limonene (62.50%¡«63.33%), respectively; accounts for two-thirds of the total content. The results ofantifungal activity of the essential oil of pokan revealed that the essential oil of pokanstored5¡¢10and15d promoted the growth of mycelium at a low concentration(¡Ü10¦ÌL/mL), while the effect of promotion was gradually reduced with increasing ofconcentration. When the essential oil of pokan stored10d show the lowest promoteraction (0.71%). When the essential oil of pokan stored5d show the highest promoteraction (42.22%). While the essential oil of pokan stored20d show the inhibitionaction (7.06%).(3) Antifungal activity of six volatile flavor compounds against G. citri-aurantii Citral, octanal, nonanal, decanal, ¦Á-terpineol, linalool, ¦Â-pinene were initiallyscreened against G. citri-aurantii using agar disc diffusion. Citral and octanal showedhigher efficacy in aldehydes£¬while ¦Á-terpineol showed higher efficacy in alcohols.The results of the antifungal activity of citral£¬octanal and ¦Á-terpineol againstGeotrichum citri-aurantii were listed as follows: the minimal inhibitory concentration(MIC) and the minimal fungicidal concentration (MFC) were0.50¦ÌL/mL and1.00¦ÌL/mL of citral in Potato Dextrose Agar medium, respectively. While the MIC andMFC of the octanal and ¦Á-terpineol were0.50¦Ìl/ml and2.00¦ÌL/mL£¬2.00¦ÌL/ml and4.00¦ÌL/mL. So, we elect citral, octanal and ¦Á-terpilenol these the three kinds ofvolatiles to study their antibacterial mechanisms.(4) Mechanisms of the antifungal activity of citral¡¢octanal and ¦Á-terpineolagainst G. citri-aurantiiAfter G.citri-aurantii cells treated with citral, octanal and ¦Á-terpineol at MIC andMFC, the result of scanning electron microscopy show considerable alterations in themorphology of the hyphae and the massive loss of cytoplasm was observed; the cellconstituents¡¯ release in the tested fungus suspensions increased visibly with theincreased concentration. The maximum cell constituents¡¯ release was observed in theG. citri-aurantii cell suspensions treated with citral at MFC, showing an absorbanceof0.636; the increasing of extracelluar conductivity and the change of pH mean anincreasing in the permeabilization of the cells; the decreasing of the total lipids ofcells revealed that the three volatiles could disrupt lipid structures of the cells.
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