Antibacterial Effect And Mechanism Of Compound Yeast M_3-1,Preparation And Application In Keeping Yellow Peach Fresh

Yellow peach is a kind of fruit with high nutritional value and economic value,but it is easy to be infected and rotted by pathogenic bacteria after harvest,which causes great economic loss.The experiment proved that antagonistic yeast could effectively inhibit the growth and reproduction of fruit and vegetable diseases,and antagonistic yeast was also proved to be a harmless strain.In this study,in order to improve the biocontrol effect of antagonistic yeast,two antagonistic yeast were combined into compound bacteria in a certain proportion,and the compound bacteria were prepared into active lyophilized powder by freeze-drying technology and applied to yellow peach.At the same time,part of biocontrol mechanism of yeast was studied.The structure and content of this paper are as follows:（1）Two strains of yeast were obtained from our laboratory,which were Kloeckera apiculata Y23 and Candida intermedia C17,of which Y23 had a good inhibitory effect on anthrax of peach fruit and C17 had a good inhibitory effect on brown rot of peach fruit.Through affinity test,it was found that the two kinds of yeast did not have obvious inhibitory effect and could be co-cultured.The results showed that when the ratio of Y23 to C17 was 3:1,the compound bacterial liquid M_3-1had the best inhibitory effect on C.gloeosporioides.M_3-1was inoculated on the fruit of yellow peach to further confirm that it had certain biocontrol ability.Through the analysis of yeast antibacterial spectrum experiment,it was proved that M_3-1had certain antagonistic effect on a variety of pathogenic bacteria,and had broad spectrum bacteriostasis.Through the study on the stress resistance of M_3-1,it was found that M_3-1had strong stress resistance to the environment,among which the tolerance to low temperature environment was the best,and the tolerance to high temperature environment,high oxygen environment and high acid environment were all good.（2）In vivo experiments of yellow peach showed that the optimal inhibitory concentration of M_3-1was 1×10⁸cells/m L.When Y23,C17 and M_3-1were co-cultured with C.gloeosporioides spores in PDB medium,they could inhibit the germination of C.gloeosporioides spores effectively.At the same time,it was observed that Y23,C17 and M_3-1could adsorb to C.gloeosporioides mycelia well and inhibit the growth of mycelia.GC-MS analysis showed that the volatile substances of M_3-1and Y23 both contained antimicrobial substances.M_3-1could increase the activity of resistant enzymes such as catalase,peroxidase and phenylalanine ammonia-lyase and the content of total phenols and flavonoids in yellow peach fruits,thus enhancing the disease resistance of fruits.（3）The transcriptomics analysis of C.gloeosporioides response to volatile substances of yeast strain Y23 showed that the number of differentially expressed genes of C.gloeosporioides treated by Y23 was as high as 1307,among which the number of differentially expressed genes was 717up-regulated and 590 down-regulated.These differentially expressed genes were studied using GO functional annotation and KEGG enrichment analysis,and the results showed that volatile substances produced by Y23 had a significant effect on the metabolic pathway of C.gloeosporioides.Genes involved in carbohydrate metabolism,such as BGL1B and MAE1,genes involved in amino acid metabolism such as mms B and amds,and genes involved in lipid metabolism such as FUM6and PED1,were selected for RT-q PCR verification,and the verification results were consistent with the basic trend of sequencing results.（4）In order to obtain the optimal conditions for preparation and storage of M_3-1bacterial agent,the centrifugal parameters,the ratio of protective agent,storage temperature and other parameters were studied.Finally,the optimal centrifugation parameters were set as 8000 r/min,10 min.A single protective agent with good effect was obtained by single factor test,and the optimal composite protective agent ratio was obtained by response surface center composite design:xylo-oligosaccharide 17 g/100m L+sodium glutamate 11 g/100m L+xylitol 3 g/100m L;The optimal storage temperature was-20℃by contrast test.At the same time,the biocontrol effect of the obtained M_3-1bacterial agent was also studied in this chapter.（5）After the M_3-1was rehydrated,the pretreated yellow peaches were treated by soaking and spraying respectively,and it was analyzed whether the M_3-1bactericidal agent could effectively resist the infection of postharvestal pathogenic bacteria of yellow peaches,so as to achieve a certain freshness preservation effect.The experiment showed that the M_3-1inoculant could reduce the decay rate of postharvest yellow peaches during storage,and maintain the physiological indexes of postharvest yellow peaches such as total TA content and cell membrane permeability,indicating that this biocontrol agent has the value of being promoted to the first line of production.