Microbiological Changes of Fresh Fish during/after Storage under Modified Atmospheres

关于气调贮藏鲜鱼在CO_2和/或N_2中的实际应用，人们已经进行了一些研究，但主要是以感官检验、化学分析和细菌总数作为评价贮藏鱼货架期的指标。人们认为有必要在MA储存期间/之后进行微生物学研究，以评估MA储存鱼类的防腐潜力和可能的微生物健康危害。本研究的主要目的是了解MA贮藏对沙丁鱼鱼片微生物发育的影响，以及MA对分离的微生物和指示菌/病原菌的影响。结果表明：(1)在MA(CO_2：N_2=20：80、50：50或70：30)条件下，沙丁鱼鱼片的货架期几乎是对照样品的3倍。好氧细菌和厌氧细菌的生长均受到CO2浓度的抑制。当MA储存的样品暴露在空气中时，细菌数量开始增加。(2)MA贮藏14d后，由弧菌、假单胞菌、莫拉氏菌等组成的鱼片初始菌群转变为气单胞菌(70-95%)，而对照样品中以假单胞菌和弧菌(20%)为主。在MA中放置4d后转移到空气中的样品以假单胞菌(85%)和气单胞菌(10%)为主。(3)在含有CO_2的MA下，MA贮藏前和贮藏期间的对照样品中的假单胞菌、弧菌、莫拉氏菌和不动杆菌的生长受到抑制，而MA贮藏14天的样品中的菌株(气单胞菌和乳杆菌)没有受到明显的影响。(4)副溶血性弧菌、金黄色葡萄球菌、鼠伤寒沙门氏菌和大肠埃希氏菌等指示菌和病原菌在含有CO_2的MA条件下接种于沙丁鱼肉末后，指示菌和病原菌的数量迅速减少。

Several studies have been carried out on the practical application of modified atmosphere (MA) storage of fresh fish in CO_2 and/or N_2. Most of them, however, dealt mainly with the organoleptic inspection, chemical analyses and total bacterial counts as an index to evaluate the shelflife of the stored fish. Microbiological studies during/after MA storage have been thought necessary to evaluate both the preservative potential and the possible microbiological health hazard of MA storage of fish. The main objective of the present study was to obtain the informations about the effects of MA storage on the microbial development of sardine fillet, and the effects of MA on the isolated microorganisms and indicator/pathogenic bacteria. The results were as follows :(1) Sardine fillets packed under MA (CO_2 : N_2=20 : 80, 50 : 50 or 70 : 30) showed nearly thrice the shelflife of the control samples with air. Both aerobic and anaerobic bacterial growth were retarded depending on the enriched CO_2 concentration. When MA stored samples were exposed to air, the bacterial counts started to increase. (2) Initial microflora of fillets consisting of Vibrio, Pseudomonas, Moraxella etc. changed to Aeromonas (70-95%) after MA storage for 14 days, while Pseudomonas and Vibrio (20%) became dominant in the control samples. Samples stored in MA for 4 days and then transferred to air were dominated by Psedomonas (85%) and Aeromonas (10%). (3) The growth of the isolates (Pseudomonas, Vibrio, Moraxella, and Acinetobacter) from the control samples before/during MA storage were inhibited under the MA containing CO_2, while the isolates (Aeromonas and Lactobacillus) from the samples under MA for 14 days were not significantly affected. (4) The number of indicator and pathogenic bacteria such as Vibrio parahaemolyticus, Staphylococcus aureus, Salmonella typhimurium and Esherichia coli which were inoculated on the minced sardine meat rapidly decreased under MA containing CO_2.