In this paper, bacterial floria and quorium sensing (QS) of specific spoilage bacteria of shrimp (Litopenaeus vannamei) during controlled freezing point storage were investigated. The regulations of quorium sensing and shrimp spoilage were also investigated by using quorum-sensing inhibitor. From the seafood preservation view point, this study provided a new way to prevent seafood spoilage and keep its favorable quality.This study included the following four parts:1. Changes of bacterial floria of shrimp during controlled freezing point storage were investigated. The results indicated that 463 strains were isolated and identified from fresh a shrimp by phenotypic, physical, chemical and 16SrDNA tests, and the Gram-negative bacteria was dominant bacteria in fresh and spoiled shrimps (almost 90%). The specific spoilage bacteria of shrimp were Acinetobacter spp.(about 50.6%) and Flavobacterium-cytophaga group (about 36.14%).2. The production of AHLs in shrimp specific spoilage bacteria Aci-1 and Aci-2 were investigated. The AHLs production of Aci-1 and Aci-2 strains were determined by Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136 (pCF218/pCF372) bacterial bio-sensors. The results showed that both strains Aci-1 and Aci-2 can produce AHLs, and the AHLs contents were increased with enhancing the concentration of bacteria strains. The production of AHLs in Aci-1 and Aci-2 were affected by pH, and the production of AHLs were totally destroyed by high pH value. The biofilm formation of Aci-1 were increased with the increasing of AHLs, and there is a positive relationship between biofilm formation and AHLs content, indicating that the biofilm formation of Aci-1 were regulated by the quorum-sensing system.3. The regulation of quorum sensing of Aci-1 and Aci-2 based on AHLs-mediated was investigated. The optimum extraction conditions of QS inhibitor from undaria pinnatifida were optimized by single factor experiments and orthogonal experiments, that is,75% ethanol concentration, extraction time 3h, solid-liquid ratio 1:6 (g/mL), extraction temperature 65℃. The production of AHLs and biofilm formation in Aci-1 and Aci-2 were inhibited by QS inhibitor, and there is a positive correlation between the inhibitory effect and the QS inhibitor concentration. 4. The regulation of the AHLs production and shrimp spoilage intervened by QS inhibitor were investigated.The AHLs concentration of shrimp treated with QS inhibitor was lower than that of control, and both of them increased to a peak on day 4 of storage. The shrimp qualities treated with QS inhibitor was better than those of control. The results indicated that QS inhibitor can effectively extend the shelf life of shrimp by inhibiting quorum sensing among bacteria. |