| Penaeus vannammei has been more and more popular for its excellent nutritions and delicious, however, the criculation is limited by its short shelf-life. In this research, the optimum composition of combined natural preservative was based on the research of total bacteria count, physicochemical index and sensory evaluation, and the bacterial species and volume changes during cold storage were also studied. The results were gotten as follows:1. Prawns (Penaeus vannammei) were coating by chitosan with Vc and Phytic acid, compared to the un-coated prawns. After treatments the prawns were stored at 4℃, in order to study the effects of chitosan on the shelf life extension, the sensory changes, TVB- N, the total count of bacteria colonies and pH were regularly evaluated as guideline. The result of the experiment indicated that prawns coated with chitosan could maintain better sensory characterisitics than those uncoated ones. The chitosan with the addition of 0.5% Vc and 0.1% Phytic acid could extend the melanosis 1～2 days, the self-life of prawns could extend 3～4 days,and prolonged to 8 days.2. To solve the spoilage of prawn and food safety issues which caused by abuse of chemical preservatives, a safe and non-residual complex natural preservative with chitosan, tea polyphenols and Nisin was developed. The effect of preservation on penaeus vannammei was verified. According to the results of orthogonal experiment L9 (33), the optimum composition of combined natural preservative was as follows, chitosan 1.5%, tea polyphenols0.1% and Nisin 0.02%. It was found that complex preservative treatment slowed down the increase of the total volatile basic nitrogen (TVB-N) and total count of bacteria colonies (TBC) and sensory quality was kept effectively during storage at (4±1)℃. Shelf-life of Penaeus vannammei treated by the combined natural preservative was extended from 4 days to 7～8 days. The cost of processing one kilogram prawns was only 0.17Yuan. 3. Application of combined natural preservative on prawn (penaeus vannammei) anti-melanosis and preservation. A safe complex natural preservative with chitosan, phytic acid and Vc was developed. The effects of the combined natural preservative on Penaeus vannammei preservation and anti-melanosis were verified. According to the results of orthogonal experiment L9 (34), the optimum composition of chitosan 1.5%, phytic acid 0.05% and Vc2.0 g/L was determined. The preservative can restrain prawn melanosis effectively, and also slow down the increase of total count of bacteria colonies (TBC) and total volatile basic nitrogen (TVB-N) of Penaeus vannammei significantly. Shelf-life of Penaeus vannammei treated by the complex natural preservative was extended 2～3 days, the cost of processing one kilogram prawns was only 0.11 Yuan make its application easily.4. Identification of microorganism strain was performed by using the physiology and biological test, and 16SrDNA sequence analysis. Combined with physiological and biochemical test results and phylogenetic tree analysis, the result demonstrated that there were eight typical microorganism strains in the Penaeus vannammei under cold storage. In the end of shelf life the proportion respectively of these eight microorganism strains was as follows, Shewanella putrefaciens (36%), Aeromonas hydrophila(26%), Pseudomonas putida (15%),Bacillus cereus(7%),Psychrobacter sp.(10%), Acinetobacter (2%), Staphyloccocus aureus(2%), Microbacterium(1%). Shewanella putrefaciens could be considered as dominated strains during Penaeus vannammei cold storage.5. Study on antibacterial action and mechanism of combined biological preservative. For the purpose of identifying the antibacterial effects and mechanism of combined biological preservative, Shewanella putrefaciens was selected for the reseach of the antibacterial effects of combined natural preservative which was made of chitosan, tea polyphenols and Nisin. First determine the minimum inhibitory concentration was determined to 0.5 mg/ml. Then the mechanism was investigated by cell morphology and the physiology and biological test. It was shown that the bacterial deformation, bubble-like structure formed on the bacteria surface and the injury of the structure of cell wall and cell membrane could be caused by the combined biological preservative. |
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