| Penaeus vannamei is one of the three major cultured shrimp in the world,rich in nutritional value,contains a variety of mineral elements,high protein and low fat,and has a good proportion of fatty acids and high edible value.Using low temperature drying,mild sterilization and vacuum packaging and other minor processing methods in production,ready-to-eat shrimp is not only high nutritional value but also easy to carry.However,the vacuum packaging ready-to-eat shrimp is easy to swell during processing,packaging and distribution,which affects the packaging appearance and reduces its commercial value.It is important to study the shelf-life and dominant spoilage bacteria of ready-to-eat shelled shrimp.In order to determine the shelf life and dominant spoilage bacteria characteristics of ready-to-eat shrimp,shelf-life of shrimp was determined by comprehensive physico-chemical and sensory evaluation.16S rRNA sequence identification and other methods were performed to identify the dominant spoilage bacteria.Biolog microplates was used to determine the metabolic capacity of dominant spoilage bacteria on four carbon sources.Finally,microwave sterilization technology was used to study the inactivation characteristics of Bacillus spores by microwave irradiation.The specific research results are as follows:1.Quality changes and shelf life of ready-to-eat shelled shrimp at ambient temperatureIn order to determine the quality and storage of shrimp and the dominant species of spoilage,the nutrient,quality and safety of shelf life were analyzed by sensory,physical and chemical,microbiological and electronic nose.The 16S rRNA sequencing method was used to identify the advantages of corruption bacteria.The results showed that there was no significant difference in water content,salinity,Aw,pH,color and texture between the first four months(p>0.05).After 4 months,the water content Content and Aw decreased,pH and salt increased;comprehensive sensory,chemical and microbiological determination of shelf life of 9 months,9months of storage at room temperature elasticity,adhesion,chewiness,hardness,shear,Sex and color exist volatility.The total number of colonies in the shrimp was less than30000CFU/g,and the TBA,TVBN and TVC were lower than limited standard.The dominant bacteria in Bacillus are Bacillus licheniformis and Bacillus subtilis.Through the preliminary study on the initial nutrition,quality and safety characteristics,the change of the storage quality and the shelf life of the freshly processed shrimp,the theoretical basis is provided to further optimize the product fence factor and target antibacterial2.Identification and carbon source metabolism kinetics of dominant spoilage bacteria isolated from cooked ready-to-eat shrimpIn order to determine the cooked ready-to-eat shrimp dominant spoilage bacteria and the differences of carbon source metabolism,the MIDI and 16 SrRNA sequencing method were adopted to identify dominant spoilage bacteria,and the uses of the BIOLOG system for its metabolism and metabolic dynamics of carbon source were studied.Results showed that the dominant spoilage bacteria are Bacillus licheniformis(S1)and Bacillus subtilis(S2).The overall carbon source metabolism ability of two dominant spoilage bacteria were not significantly different(P>0.05).However,the metabolism ability of sugar,acid,amino acid and fatty acid/ester were significantly different,meanwhile sugar metabolism ability was the strongest,followed by carboxylic acid.Amino acids of S1 metabolism was strongest in fatty acid/esters,amino acids of S2 was strongest in fatty acid/esters.S1 four-carbon sources metabolism ability was weaker than S2,esters/fatty acids and amino acids metabolism ability was significant different(P<0.05).There was significant difference in the kinetic study of the carbon sources metabolism of the two dominant spoilage bacteria.S1 sugar had low maximum specific growth rate(except for D-trehalose,sucrose,D-fructose)and low lag time(except for the D-trehalose and sucrose).S2 carboxylic acid had higher lag time and maximum specific growth rate(except for L-malic acid).The amino acid lag time(except for L-aspartate)and maximum specific growth rate of S2 were greater than the S1.In addition,the fatty acid ester lag time(except for twain 40)and the maximum specific growth rate of S2 were greater than the S1.Through the instant shrimp dominant spoilage bacteria identification and the analysis of carbon source metabolism,we aimed to optimize the product formula,inhibit the growth of corrupted bacteria,and extend the product shelf life.3.Inactivation characteristics of Bacillus subtilis spores from shrimp by microwave irradiationIn order to investigate sterilization effects and mechanisms of microwave irradiation on Bacillus licheniformis spores,we studied the the effects of different temperatures(80°C,85°C,90°C,95°C,100°C)and different treated time on the sterilization effects;water bath sterilization was used as a control.The changes of spore physico-chemical properties before and after water bath sterilization and microwave sterilization were analyzed.The results showed that at the same sterilizing temperature,microwave sterilization and water bath bactericidal effects were significantly different.The microwave and water bath both can finally kill the spores,but the microwave needed only 2 min,the water bath needed at least 5 min.R~2analysis showed that the weibull model could better fit the survival curves of the two sterilization methods,but the linear model was more intuitive.The time of protein and nucleic acid leakage in the spore suspension caused by the microwave treatment was earlier than that of the water bath.Compared with the water bath,the spore germination curve after microwave treatment had a longer lag phase.This research studied the sterilization effect of microwave sterilization by comparing with the water bath sterilization;it provided theoretical and practical basis for optimization of product sterilization technology,targeted sterilization and reduction of bag expansion rate. |
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