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

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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.