Study On The Preservation Of Litopenaeus Vannamei By Low-voltage Electrostatic Field And Modified Atmosphere Packaging

Litopenaeus vannamei is an important aquaculture shrimp with abundant resources and huge yield in China.It is easy to deteriorate rapidly after death due to bacterial invasion in the process of fishing,transportation,processing and storage.Effective shelf life extension of this kind of products is always the most important thing.In order to meet the increasing demand of consumers for high-quality materials,improve the existing preservation technology and make better use of the resources of Litopenaeus vannamei,this paper studied the preservation technology of Litopenaeus vannamei in different low-voltage electrostatic fields during controlled freezing-point storage,and studied the freezing-point of Litopenaeus vannamei in different packaging materials,gas-material ratio and CO₂-N₂ ratio.The quality changes of Litopenaeus vannamei during storage period were studied.The quality changes and water molecular stability of Litopenaeus vannamei under the combination of low-voltage electrostatic field,modified atmosphere packaging and ice temperature were studied.The dominant spoilage bacteria at the end of storage under three conditions were isolated and identified.The main research contents were as follows:1)Using fresh Litopenaeus vannamei as raw material,the effects of different electrostatic field intensities?1.5,2.5,3.5 kV?on the quality of Litopenaeus vannamei during controlled freezing-point storage[?-1±1??]were compared.The results showed that the PPO activity of Litopenaeus vannamei treated by electrostatic field was inhibited,and the sensory color was better than that of pure ice temperature samples.The total number of colonies in shrimp meat was inhibited by the action of electric field;TVB-N value and K value were slowed down in varying degrees at anaphase storage.Meanwhile,the juice loss rate of shrimp meat was also maintained at a low level,and the softening of shrimp meat was also delayed.Overall,2.5kV electrostatic field treatments has more effective in controlling quality changes in shrimp meat,which can extend the shelf life of Litopenaeus vannamei to 8 days.2)The effects of packaging materials,gas-to-material ratio on fresh-keeping effect of fresh Penaeus vannamei were studied.The experiment confirmed that the packaging material was aluminum foil bag,and the ratio of gas to material was 6:1?v:w?.On this basis,the effects of different ratios of CO₂ to N₂?common air,25%CO₂/75%N₂,50%CO₂/50%N₂,75%CO₂/25%N₂?combined with ice temperature on the quality of Litopenaeus vannamei during storage were studied.The results showed that75%CO₂/25%N₂ had the best fresh-keeping effect and could prolong the shelf life of Litopenaeus vannamei at ice temperature for 10 days.3)The effects of low-voltage electrostatic field?LVEF,2.5KV,50Hz?combined with modified atmosphere packaging?MAP,75%CO₂/25%N₂?on the fresh-keeping of Litopenaeus vannamei during ice-temperature storage and the mechanism of water molecular stability were studied.The results showed that low-voltage electrostatic field combined with modified atmosphere packaging had a positive effect on Litopenaeus vannamei.The shelf life could extend to 14 days,which was longer by about 8 days than that of blank group.It can significantly inhibit the spoilage and deterioration caused by microorganisms,maintains the sensory quality,and delays the degradation of nucleolus to some extent.The sample color and sensory score were good,drip loss rate Was less than3%,and help to delay the softening of shrimp during storage.At same time,the water migration of shrimp meat was enhanced,and the difference of water change could be clearly distinguished by NMR pseudo-color image from the 3rd day of storage.Low-voltage electrostatic field combined with air conditioning could better retard the water migration and loss rate of shrimp meat to the 12th day of storage.4)The species of dominant spoilage bacteria after combined treatment of ice temperature,low-voltage electrostatic field and modified atmosphere packaging were studied.The main spoilage bacteria of shrimp meat were isolated and purified by aerobic plate culture,the dominant spoilage bacteria were classified and identified by combining morphological characteristics with 16S rDNA sequence.The putrefaction ability of spoilage bacteria was verified.The results showed that the spoilage bacteria of shrimp meat at storage end point were Chryseobacterium indologenes,Chryseobacterium indologenes sp,Roseomonas gilardii,Pseudomonas lutea,Pseudomonas fluorescens,and Shewanella putrefaciens.The specific spoilage organisms?SSO?were Pseudomonas flavus,Pseudomonas fluorescens and Shewanella putrefaciens,with the proportions of 17.02%,25.53%and 22.34%,respectively.