| Botrytis cinerea is the most important pathogenic bacteria in grape postharvest diseases. SO2 insecticides mainly used in production for preventing grape gray mold occurrence during cold storage, but can not be completely killed. With the extension of the use of time, the bacteria produce resistance. It is bound to increase dosage, resulting in grape phytotoxicity and SO2 residues increased, leading to food safety risk. Natamycin is a new type of microorganism preservative, which can efficiently suppresses the yeast and the mildew. Natamycin low solubility in itself would lead to drug effects can not fully play its role. Therefore, how to improve the solubility of the natamycin to achieve the efficient and safe application of grape refrigeration, in order to reduce the application of SO2 like grape preservative has important practical significance. Therefore, the experiment is carried out to study the inhibition of Botrytis cinerea by considering the good solubility and the emulsifier as the carrier of the drug diffusion. On the basis of the above, the experiment of the isolated and in vivo antibacterial activity of the gray mould is carried out. and the effect of the preservation of grape is studied.The results of emulsification and dissolution system show that the best emulsifier is sodium oleate, and the best proportion is added to the same mixture of sodium oleate with natamycin. The natamycin best solubility of pH is 6, and the temperature range is 0-30℃.The effect of ultraviolet exposure and fluorescent lamp irradiation on natamycin water solubility is greater. Ultraviolet irradiation 90min, natamycin decrease from 289.95mg/L degradation to 145.49mg/L. Fluorescent light 10d, natamycin decrease from 287.07mg/L degradation to 198.38mg/L. Orthogonal test show that 1.5g/L natamycin with the same amount (0.15%) of sodium oleate mixed at pH 6,without fluorescent under ultraviolet light and irradiation conditions is satisfied natamycin dissolve in water, natamycin solubility is 291.14mg/L.The mass fraction of 0.10%.0.15% and 0.20% natamycin with an equal amount of sodium oleate mixed use to inhibit Botrytis cinerea. The results indicate that the inhibition of emulsification of natamycin on the Botrytis cinerea is far greater than that of the two.The MIC of natamycin in the Botrytis cinerea is 10mg/L.0.20% natamycin combine with equal amount of sodium oleate have the best effect.The inhibition rate of mycelium growth rate reach 50.09%. The conidial germination is as low as 30.65%.The dry weight of mycelium decreased by 0.23g. Cell membrane relative permeability increase 6.00%.An amount of soluble protein exudation higher 106.03μg/g.In vivo antibacterial activity of the gray mould grape spore, grapes inoculation don’t appear mycelium growth at 0℃ under the storage of 30d, for 25℃ vivo vaccination Botrytis cinerea 7d.Cell inhibition rate is as high as 97.40%.And pure sodium oleate does not have any inhibition on Botrytis cinerea.Natamycin emulsified water solution can significantly prolong fruit postharvest storage period, of which 0.20% natamycin with equal amount of sodium oleate is best of refrigeration on grape storage. At the end of the cold storage, the number of gray mold isolate from grape is 19.95% less than that of pure natamycin. The fruit dropping rate is 7.80% less than that of the simple natamycin solution treatment, and decreased by 20.50% compare with the blank control. The hardness is increased by 1.03kg/cm2 compare with the simple natamycin treatment, and the increase is 1.99kg/cm2 compare with the blank control. Soluble solids content increased by 0.80% compare with that of pure natamycin, and increased by 1.50% compare with the blank control. Titratable content increased by 0.014% compare with the simple natamycin treatment, and the increase is 0.076% compare with the blank control. The content of reducing sugar is increased by 2.56% compare with that of the pure natamycin, and the reducing sugar content increased by 8.78% compare with the blank control. Respiratory intensity is reduced by 0.88mg/(kg·h) compare with the simple treatment of the natamycin, and decreased by 1.40mg/(kg·h) compare with the blank control. The electrical conductivity of the fruit stem is decreased by 2.80% compare with that of the simple natamycin, and decreased by 11.60% compare with that in the blank control group. The pectin content is increased by 0.03% compare with that of pure natamycin, and the content of pectin increased by 0.13% compare with that in the blank control group. Pectinase content is 1.40mg/(g·h) less than that of the simple natamycin solution treatment, and decreased by 1.90mg/(g·h) compare with the blank control. The activity of PPO compare with the pure natamycin solution increased by 0.121U/g, compare with the control increased by 0.202U/g. The activity of POD compare with the pure natamycin solution increased by 0.024U/g, compare with the control increased by 0.508U/g. The activity of PAL compare with the pure natamycin solution increased by 5.29U/g, compare with the control increased by 8.50U/g. At the end of storage, the relative residual amount of the grape is 0.38mg/kg, which is lower than that of the national standard. The results show that the mixture of natamycin and sodium oleate is effective in preventing the deterioration of grape gray mould and delaying the quality of grape in cold storage.Based on the above results, in the natamycin concentration does not exceed 2.0g/L under the premise, adding the same amount of sodium oleate to promote natamycin best solution, of which 0.20% natamycin with equal amount of sodium oleate to inhibit the gray mold grape spore and the grape refrigeration effect is best. |
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