| In order to inhibit the process of putrefaction and melanosis of Litopenaeus vannamei during storage, the storage features, the characterisation of partly purified extracts of polyphenol oxidase, and the phase ofmicroflora were studied. Based on the results, a kind of effective bio-preservative was developed, the main content and conclusion are as followed:1.The effects of decapitating and peeling on sensory score, odor, pH, total volatile basic nitrogen (TVB-N), enzyme activity of phenoloxidase (PO) and total viable count (TVC) of Litopenaeus vannamei stored under refrigeration (0±0.5℃) were studied. Results showed that changes in quality of whole, decapitated and peeled prawns were different. Sensory scores of the three lots decreased during storage. However, the reasons that caused the decrease were different. PO activity was different among the three lots, and the higher activity could be detected in whole prawns while no activity was detected in peeled form. E-Nose analysis showed that odors were different among the three lots at the end of shelf-life. Changes of TVB-N were in good agreement with APC when indicating the shelf-life of different form of prawns, while sensory score delayed. Shelf-life of whole, decapitated and peeled prawns stored under refrigeration (0±0.5℃) could be expected to be 7,9 and 11 days, respectively.2.Tissue distribution of melanosis and characterisation of partly purified extracts of polyphenol oxidase were studied in Litopenaeus vannamei post mortem. The resultes showed that marked melanosis developed in the head followed by that in the junction between abdomen exoskeleton and telson, moreover, different tissues inordinately showed evidence of black spots Further characterisation was carried out in extracts partly purified using 40-70% ammonium sulfate fractionation whose activity increased to 1.82 times. The enzyme had the highest activity at 30℃and pH 5.0.4-HR was the strongest inhibitor which made the enzyme lost 69.81% activity, followed in turn by sodium hydrogensulfite, sodium metabisulfite, ascorbic acid, and L-homocysteine.3.Seven strains (5 Gram-negative bacteria,2 Gram-positive bacteria) were.isolated from the spoiled shrimp, and they were identified based on biochemical methods. In order to observe the impact of microoganisim during storage, TVC,TVB-N and odor were studied on the special shrimp paste which were inoculated the 7 strains respectively. All strains bred well and released gas with sulfur originating except for Sphingomonas paucimobili s. Virgibacillus proomii producted low TVB-N compared with the others.4.4-Hexylresorcinol (4-HR) was determined as the primary component in the presupposed bio-preservative to inhibit melanosis and its application amount was reduced by added ascorbic acid and L-cysteine. Chitosan and Nisin were used as antibacterial composition. The result showed that the appropriate ingredient was made up by 4-HR 0.01 g/L, 1-cysteine 0.3 g/L, VC 1.0 g/L, Nisin 0.5 g/L and Chitosan 1.0 g/L. After being immersed the shelf life of shrimp is prolonged by 3 days and melanosis was effectively inhibited. |
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