| The samples of Penaeus vannamei which were cultured90d and120d respectively were taken from thefreshwater (0.5‰), the saltwater (6.9‰) and the seawater (18.5‰). The physical indexes, the textuer andthe biochemical indexes of Penaeus vannmei. The total number of bacterial colonies were measured underthe condition of different salinity. The dominant spoilage bacteria were isolated and identified of Penaeusvannmei. The inhibitory effects of the chitosan, the nisin and the lysozyme on the isolated dominantspoilage bacteria were studied by the oxeford cup dispersion method. The processing technology ofproducts and during the storage stability of shrimp were studied. The main conclusion were as followed:1. The body length and weight of prawns which were breeded for90d in the saltwater were significantlyhigher than that of other two groups (P<0.05), the shell weight showed no obvious difference amongsamples under different salinity (P>0.05). Thickness of the shell of prawns in the seawater weresignificantly higher than that of prawns in the freshwater (P<0.05), the contents of crude protein of prawnsin the saltwater were significantly higher than that of prawns in the freshwater and the seawater (P<0.05),the contents of the water of prawns in the freshwater were significantly higher than that of prawns in thesaltwater and seawater (P<0.05). The body length and the weight of prawns which were breeded for120din the freshwater and the seawater were significantly higher than that of prawns in the saltwater (P<0.05).The shell weight of prawns which were breeded for120d in the freshwater were significantly higher thanthat of other two groups (P<0.05), thickness of the shell of prawns in the freshwater were significantlyhigher than that of prawns in the seawater (P<0.05), the contents of crude protein of prawns in thefreshwater were significantly higher than that of prawns in the seawater (P<0.05),the water content ofprawns in the freshwater and the saltwater were significantly higher than that of prawns in the seawater(P<0.05). The body length, weight, shell weight and thickness of the shell of prawns among samples whichwere breeded for120d under different salinity were significantly higher than that were breeded for90d.The contents of the crude fat showed no obvious differences between samples which were breeded for90d and120d (P>0.05). The total amino acids, the essential amino acid and the delicious amino acid showedno difference among samples, and the contents of the glutamic acid was the highest among17kinds ofamino acids under different salinity. The hardness, the springiness, the cohesiveness and the chewiness ofprawns which were breeded for90d in the saltwater were significantly higher than freshwater(P<0.05),thespringiness of prawns which were breeded for120d in the freshwater were significantly higher thansaltwater (P<0.05). The contents of the hardness, the cohesiveness and the chewiness showed no obviousdifferences between samples which were breeded for120d (P>0.05).2. The results indicated that Bacillus and Marinococcus were the dominant spoilage bacteria of Penaeusvannmei.The two kinds of strains were highly senstitive to the chitosan of which concentration was15.0g/100ml. The two kinds of strains were insenstitive to the nisin and the lysozyme.3. Two products of Penaeus vannmei which were semi-dry and high-moisture were developed, thetechnology for high-moisture was as follows:head, the intestinal glands of live shrimps were removed, andthen the shrimps were washed and soaked in70%edible alcohol for3mins,heated in the salt water (1%w/w) for3mins, dried and soaked in seasoning for1h, and then soaked in the chitosan solution(15.0mg/100ml) for10mins after drying. After the treatment of the hot-air (60℃,2hours),then vacuumpackaged (0.095MPa). After the bacillus germinated (60℃,20minutes) and sterilized at120℃for5mins.The semi-dry of shrimps products were not soaked in seasoning and chitosan solution,and driedbymicrowave with medium-low for5mins,packed and sterilized at115℃for5mins.All other technology forsemi-dry was the same as the high-moisture of Penaeus vannmei products.4. In the process of storage for the semi-dry of shrimps products, the pH value which were around6.7to7.4increased after the first decreasing, the Aw and the sensory evaluation declined gradually, the aerobicplate count increased slowly. The shelf-life were54,42,36and18d respectively at25℃,30℃,35℃,40℃.During storage of high-moisture of shrimps products at4℃, the hardness decreased after the firstincreasing,and the TVB-N value increased slowly. The springiness and Aw reduced. These treatmentsabove that were non-drying which were115℃for10mins and120℃for5mins and the hot air drying(60℃,2hours),the sterilation at115℃for10mins and120℃for5mins,the shelf-life with4treatmentsabove were45,60,75,75d respectively. |
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