Studies On The Isolation And Purification Of Mold From Prunus Mume And The Mechanism Of Ozone Bacteriostatic

Prunus mume has high moisture content,rich nutrition,and thin peel.During picking,transportation,storage,fresh sale,and processing,due to mechanical damage to the peel,diseases and insect pests,it is particularly susceptible to contamination by fungal pathogenic microorganisms,which is not easy to store but easy to cause rot and deterioration.Thus it greatly shortens the storage period of the fruit and affects its market share.The development of its related deep processing industry will also be restricted,and it cannot effectively increase its added value,which seriously restricts the upgrade and development of the Prunus mume industry.Because of the above reasons,this paper through the separation and purification of post-harvest rot fungi,researched on the bacteriostatic mechanism of ozone on the main rot fungi,ozone preservation method and modified atmosphere packaging,and optimized the ozone preservation conditions,which innovated the preservation method of Prunus mume.It has laid an experimental foundation for the processing and storage of Prunus mume.?1?Isolated and purified the microorganisms in the moldy part of the postharvest Prunus mume storage process;by observing the colony morphological characteristics,mycelial microstructure and molecular biological identification,and studying the biological characteristics of the pathogenic bacteria,we obtained three strains of fungus were finally identified:Aspergillus japonicus,Penicillium crustosum and Aspergillus oryzae.Biological characteristics studies have shown that Aspergillus japonicus has a wider adaptability than the other two molds.Combined with the separation rate was 83.3%and the pathogenicity rate was more than 90%,Aspergillus japonicus was identified as the predominant pathogenic mold for Prunus mume storage.?2?Under in vitro conditions,using three molds as experimental strains,the inhibitory effect of ozone treatment with different concentrations and different times were explored.The results show that ozone treatment can significantly inhibit the germination rate and mycelial growth rate of the three mold spores?p<0.05?,and increase the conductivity and protein dissolution rate of the mold spore suspension?p<0.05?.Observed by scanning electron microscope?SEM?the obvious difference between the control group and the treatment group,ozone treatment caused not only the rough surface of the mold cells and twisted hyphae but also affected the spore morphology and size.Overall,when the ozone treatment concentration was 15¹8 ppm,and treatment time was 75⁹0 min could achieve a good in vitro suppression effect.?3?Under living conditions,the Prunus mume fruits inoculated with Aspergillus japonicus were treated with ozone under different conditions.The results show that all treatments can reduce the incidence of fruit,suppress the diameter of the lesion,the decrease of soluble solids?TSS?content,and the deterioration of fruit color?p<0.05?.At the same time,it induced the increase of polyphenol oxidase?PPO?and peroxidase?POD?activities?p<0.05?,and reduced the accumulation of malondialdehyde?MDA?in the fruit.Based on the experimental results,the concentration 9-12 ppm with a duration of 60 to 90 minutes ozone treatments increased the resistance of the fruit to pathogenic bacteria,inhibited the reproduction of Aspergillus japonicus,and delayed the time of onset and reduce the incidence of disease.?4?Through the BGISEQ-500 sequencing platform,transcriptome sequencing analysis was performed on Aspergillus japonicus with and without ozone treatment.The differentially expressed genes were screened,and 499 differentially expressed genes were screened by FPKM method,including 433 up-regulated genes and 66 down-regulated genes.Through GO enrichment analysis,it was found that the differential genes were enriched into the molecular functional ontology with the most entries.In the first 20 significantly enriched differential GO Term,enriched to the cell-specific membrane-related intrinsic components,compositional components and Membrane;enriched to biological processes related to transmembrane transport,transportation,localization establishment;enriched to molecular functions related to catalytic activities including oxidoreductase activity,glutamate decarboxylase activity.The KEGG enrichment analysis found that the significantly enriched Pathway has the amino acid metabolism process in the metabolic pathway,mainly including taurine and subtaurine metabolism,lysine degradation,etc;biosynthesis of indole diterpene alkaloids,steroid bio Synthesis;Starch and sucrose metabolism in carbohydrate metabolism and degradation of other glycans,interconversion of pentose and glucuronate;?-linolenic acid metabolism in lipid metabolism.?5?After the ozone treatment of different concentrations?0,9,15 ppm;60 min?and different time?0,45,75 min;9 ppm?,using fresh-keeping box packaging and modified atmosphere packaging?MAP;5%O₂,10%CO₂ and 85%N₂?,with no ozone treatment as a control group,a total of 10 groups;all experimental groups were stored in a 4±1?fresh-keeping store for 25 days.The results showed that:ozone and ozone+MAP treatment induced increased peroxidase?POD?activity,while polyphenol oxidase?PPO?activity was inhibited?p<0.05?,ozone+MAP treatment was significantly better than ozone alone treatment?p<0.05?;compared with the control group,the MDA content of all treatment groups was lower than that of the control;when combined with ozone and MAP treatment,it could significantly inhibit weight loss,hardness reduction,color changes?p<0.05?,enhance POD activity and inhibit PPO activity,which shows Ozone and MAP have a synergistic effect.