Study On Preparation Of Compound Preservative Of Ready-to-eat Crayfish And Its Preliminary Antibacterial Mechanisms

Crayfish is nutritious and tasty,which is currently one of the best-selling freshwater shrimp in our market.However,crayfish is affected easily by season and territory because most of them are sold in a fresh way.Moreover,crayfish is composed of high moisture and protein,which results in the infection of different microorganisms.Thus,it is difficult to preserve crayfish.In this study,ready-to-eat crayfish was prepared by frying,cooking,sterilization and packaging technology,which used the fresh shrimp as material.Combining with the processing technology and characteristics of spoilage organism in shrimp product,the way to solve the problem of decomposition was studied.The research provides an important practical significance for the preservation of ready-to-eat crayfish.The results completed are reported as follows:(1)The colonies isolated from ready-to-eat crayfish at the end of the shelf life were classified by morphological observation,staining and microscopy.And they were identified by morphological identification,physiological and biochemical experiments and 16 S rRNA molecular biology identification.The results showed that 186 strains of colony were isolated from the crayfish,which were classified into four categories and the dominant spoilage bacterium was Citrobacter murliniae Y3,accounting for 86.02% of the total number of colonies.(2)Based on the minimum inhibitory concentration(MIC)and single factor experiment,the optimal proportion of compound preservative was obtained by the experiment of response surface design,which using total number of colonies as evaluation index.The results showed that the effect of potassium sorbate,sodium dehydroacetate,?-polylysine and chitosan on the preservation of crayfish was better,and the best concentration was 0.50 g/L,0.31 g/L,0.21 g/L and 2.84 g/L.Treatment of ready-to-eat crayfish with the compound preservative can effectively reduce the decrease of sensory quality of crayfish,significantly reduce the number of microorganisms,pH value,TVB-N content,TBA value and K value.The compound preservative contributes to the preservation of ready-to-eat crayfish,which extends the shelf life from 6 to 30 days.(3)Strain Citrobacter murliniae Y3 was used to study the antibacterial mechanisms of compound preservative.The MIC of compound preservative was determined by the method of enzyme-labeled plate.The antibacterial mechanisms of compound preservative were explained by bacterial growth curve,cell wall permeability,cell membrane permeability and the change of microbial morphology of the bacteria observed with scanning electron microscopy(SEM).The results showed the MIC of the compound preservative was 0.483 g/L for Citrobacter murliniae Y3.After treated with compound preservative,the growth of strain was inhibited obviously.The permeability of cell wall increased,resulting in the increase of AKP content in the bacterial fluid.The conductivity,UV absorbance,soluble sugar and protein of the bacteria were significantly increased,which indicated the permeability of cell membrane was also increased.Under the scanning electron microscope,the microscopic morphology of the cells was seriously damaged,the edges were blurred,the cells were seriously damaged and broken,the cell wall was dissolved,and the cytoplasm was leaking from the cells.Those results showed that the compound preservative damage cell wall and cell membrane by destroying the integrity of cell structure,which inhibited bacterial growth and even killed bacteria.