Microbial Analysis Of Cucumber Spoilage Based On Three-dimensional Fluorescence

Cucumber is a t ypical perishable agricultural product,which is prone to qualit y deteriorati on and corruption after harvest and has a short shelf life.The species and quantit y of microorganisms on the surface of cucumber during storage are the key factors restricting the preservation of cucumber.This paper mainl y st udies the rapid qualitative and quantitative anal ysis of cucumber spoilage pathogenic microorganisms by using three-dimensional fluorescence spectrosc opy,explores the dynamic changes of fungal and bacterial communit y structure during cucumber storage,and carries out a series of related research.The main research contents and results are as follows:1.The fungal diversit y of fresh cucumber and rotten cucumber epidermis was anal yz ed by miseq high-throughput sequencing technology.During the storage of cucumber,the fungal communit y mai nl y includes three phyla:Ascom ycota,phragmoplastophyt a and Basidiom ycota,among which Ascom ycota is the dominant phyl a.With the progress of corruption,the abundance of Ascom ycetes increased,and the abundance of phrenic algae and basidiom ycetes decreased significantl y.The fungal communit y of cucumber during storage mainl y includes plectosphaerella,Cladosporium,Fusarium and Alternaria.With the increase of storage time,Cladosporium changed from dominant bacteria to inferior bacteria,and plectosphaerella changed from inferior bacteria to dominant bacteria.2.Using miseq high-throughput sequencing technology to analy ze the bacterial diversit y on the surface of cucum ber during cucumber corruption.The bacterial communit y of cucumber during storage mainl y includes five phyl a,namel y Proteobacteria,Firmicutes,Actinobacteria,Bacteroidetes and cyanobacteria.The dominan t phyla of fresh cucumber is Firmicutes.The dominant phylum of spoilage cucumber is Proteobacteria,while the abundance of Firmicutes decreased significantl y.A total of 16 genera of prokaryotic microorganisms have been annotated in the process of cucumbe r corruption.The dominant bacteria of fresh cucumber are weissella and Lactobacillus,and the dominant bacteria of rotten cucumber are Enterobacter and Enterococcus.3.Pseudomonas syringae pv.Lachrymans-8（PS L-8）and Fusarium graminearum-ACCC37687（Fusarium graminearum）were studied.By collecting the three-dimensional fluorescence spectrum data of gradient mixed bacterial solution samples,the second-order correction algorithms are used:Alternating Trilinear Decomposition（ATLD）,parallel factor anal ysis（PARAFAC）,self weighted alternating trilinear decomposition（SWATLD）Alternating penalt y trilinear decomposition（APTLD）and partial least squares regression coefficient method（PLS）are used to anal yze the data,extract the characteristic excitati on and emission wavelengths,and est ablish the concentration prediction model by multiple linear regression of the fluorescence intensit y data of the characteristic wavelength and the absorbance(OD₆₀₀)of the bacterial solution at the wavelength of 600 nm,Leave one out cross validation（LOOC V）is used to measure the prediction performance of the model,so as to realize the qualitative and quantitative anal ysis of single component in complex bacterial liquid mixture s ystem.The fluorescence characteristic peaks of Pseudomonas syringae are excitation/emission（E_x/E_m）=285nm/340nm,290nm/340 nm,285 nm/332.4 nm,280 nm/361.6 nm,295 nm/361.6 nm.The fluorescence characteristic peaks of Fusarium graminearum are excitation/emission（E_x/E_m）=380 nm/468 nm,390 nm/512 nm,340 nm/511.2 nm,415 nm/511.2 nm.The concentration prediction model of Pseudomonas syringae(R²_{c v}=0.92441191,RMSEP=0.005163633,R=0.961463421)is better than that of Fusarium graminearum(R²_{c v}=0.583953931,RMSEP=0.027653679,R=0.764168784).This paper uses three-dimensional fluorescence spectroscopy to quickl y identify the pathogenic microorganisms of plant fungal diseases and bacterial diseases,and explores the feasibilit y of three-dimensional fluorescence spectroscopy to quickl y identify plant fungal and bacterial diseases.The experimental method use d in this paper is valuable for the study of qualitative and quantitative anal ysis of bacteria and fungi by fluorescence spectroscopy.