| China is one of important countries in the world’s fisheries production, which isalso a country of the world’s first-aquaculture and aquatic products trade. Total output ofaquatic production has ranked first for23years in the world. Freshness and safety arethe most important indexes on the quality of the aquatic products. Turbot (Scophthalmusmaximus) is a type of marine flatfish naturally distributing along the coastal area ofEuropean. Now it is an economically important fish in China for its good taste. Largescale turbot cultures have been performed off the northern coast of China in recent yearsbecause of high market value. However, the circulation is limited by its short shelf-life.In this research, the turbot was studied under refrigerated storage to evaluate thequalities by the microbial, physicochemical and sensory parameters as well as textureindex. The key factors such as the concentration of bio-preservative, processing timeand refrigerated temperature were optimized systematically for extending the shelf-lifeof the refrigerated turbot. Furthermore, the microbiological changes during therefrigerated storage were researched. The spoilage reason caused by Specific SpoilageOrganisms (SSO) was discussed, and the mechanism of bio-preservative was pointedout preliminarily. The main conclusions were shown as follows:1. The results showed that, the moisture, ash, crude fat and protein content ofturbot were75.30%,1.01%,5.42%and22.26%, respectively, so the fish has a verygood edible value.2. During the storage at-2℃and4℃, the pH value, thiobarbituric acid (TBA)value might not be the suitable indicators for evaluating quality changes of turbot duringthe storage, but microorganisms, total volatile basic nitrogen (TVB-N), the content ofIMP and K value had significant linear relationships with the storage time. Besides, thechanges of texture and color were not obvious. The research suggested that storage atlower temperature could keep the fish quality, and storage at-2℃was better than the4℃.3. The turbot was treated by0.3%tea polyphenols solution. The results showed that the changes of physical and chemical parameters were delayed. After treatment, thebacteria growth slowed significantly, TVB-N value reduced, and the K value remainedat low levels at the end of storage. To a certain extent, tea polyphenols could extend theshelf life of turbot about4-6days.4. Selective culture methods and PCR technology were applied in turbot’s storage.Based on sequencing method, the SSO were Pseudomonas sp. and shewanella sp. Bycomparing the Genbank, suggested bacterium A as Pseudomonas sp. for its homologyaccorded with the gene pool of Pseudomonas sp. BG2; and bacterium B as shewanellasp. for its homology accorded with the gene pool of S. putrefaciens ATCC8071.5. The antibacterial mechanism of tea polyphenols has been studied preliminary.The results showed that tea polyphenols had a great effect on the bacterium growthcurve. The conductivity of the bacteria culture increased significantly, and theultraviolet absorption also increased. With the extension of processing time, the proteinelectrophoresis showed that most of the band disappeared. The results of SEM exhibitedthat the morphology and structure of the bacteria changed constantly, bacteria shrinkedgradually and appeared bending deformation phenomenon, cytoplasm decreasedgradually, cell walls began to collapseand its surface bubbles appeared abnormal. Teapolyphenols could destroy the integrity of the cellular structure. Its antibacterialmechanism might be accomplished by destroying the cell wall or inhibiting thesynthesis of biological macromolecules. Tea polyphenols could damage the cell walland cell membrane, leading to the form of surface holes, causing somatic cell contentsleaked and finally leading to death. |
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