The Effect Of Ultra-high Pressure Treatment On The Structure Of Spoilage Bacteria In Oysters During Cold Storage And The Lethal Mechanism Of Typical Strains

Oyster,regarded as an economical and nutritional shellfish,was a kind of seafood with unique flavor.However,because of the physiological characteristics of the filter,it was prone to enrich the microorganisms in environment.So the capture of oyster had a short shelf life,which was not conducive to the circulation and sale of products.In order to investigate the effects of ultra-high pressure processing on the structure of oyster flora and the change of microbial community structure during cold storage,Illumina Mi Seq high throughput sequencing technology and traditional plate incubation method were applied.According to the sequencing results,the dominant bacteria,Shewanella putrefaciens,Vibrio parahaemolyticus and Pseudoalteromonas,in oysters were selected as objects.And the survival rate,extracellular alkaline phosphatase activity and extracellular reducing sugar content were used as the index to discuss the mechanism of UHPP on typical spoilage strains in oyster by electron microscope observation.The results showed that:(1)Illumina Mi Seq high throughput sequencing technology and traditional plate incubation method were applied.Results showed that the dominant bacteria belonged to Proteobacteria(77.5%)in phylum level and Gammaproteobacteria(72.3%)in class level.In the order level,Vibrionales(49.3%)and Alteromonadales(12.2%)were dominant.In the family level,Vibrionaceae(36.8%),Shewanellaceae(10.3%)and Pseudoalteromonadaceae(7.2%)were dominant.In the genus level,the proportion of Vibrio(28.3%),Shewanella(10.3%)and Pseudoalteromonas(7.2%)were relatively high.The results of traditional incubation method were consistent with those of high throughput sequencing technology in the genus level,although the proportions were different.(2)During storage,Vibrio decreased rapidly and then tended to be stable.Shewanella decreased firstly and then increased.While the proportion of Pseudoalteromonas in the whole cold storage period increased rapidly,and the proportion of total corruption was up to32.2% at last.Psychrobacter turned to be dominant bacteria after ultra-high pressure processing,as up to 42%.However,the proportion of Pseudoalteromonas was only 0.8%,and the ratio of Shewanella was less than 0.1%,which indicated that the UHPP changed the bacterial community structure in oyster.(3)The result of antibacterial mechanism showed that the bacteria decreased rapidly after UHPP.The mortality rates of Vibrio parahaemolyticus and Pseudoalteromonas were about 84.18% and 67.1% when treated by 350 MPa,respectively,while viable bacteria couldis not detected for Vibrio parahaemolyticus after 400 MPa treatment.Furthermore,the rate of the later increased up to 73.54%.The survival rate of Shewanella putrefaciens,the representative strain,had no significant change under 100 MPa pressure treatment(P>0.05),then decreased rapidly with the increase of treatment pressure.There was no viable bacteriadetected after 400 MPa and above pressure processing.And extracellular alkaline phosphatase activity and reducing sugar content were significantly changed under lower pressure treatment conditions(<100 MPa),then to be stable.After ultra-high pressure treatment,the cells adhered to each other and appeared clusteredly.With the pressure further increasing,the boundaries between each other bacterial cells has been blurred,until the loss of the original form,and ultimate death.