THE Effect of vacuum and modified atmosphere packaging on growth of listeria in rainbow trout (oncorhynchus mykiss) fillets

Rainbow trout (Oncorhynchus mykiss) fillets stored at 4 ± 1C were analyzed with respect to properties of microbiological (Listeria monocytogenes, total aerobic mesophilic count, psychrotrophic bacteria and Enterobacteriaceae) and chemical (pH, total volatile bases nitrogen) under air (control), vacuum and modified atmosphere packaging (MAP) with various gas mixture (50% CO₂ : 50% N₂, 80% O₂ : 20% CO₂ and 2.5% O₂ : 7.5% N₂ : 90% CO₂). The minimum L. monocytogenes counts were determined in the samples packaged with MAP, and no significant differences were found among them. It was determined that the effect of different atmosphere conditions and storage time on total aerobic bacteria count, psychrotrophic bacteria count and Enterobacteriaceae count were significantly different (P < 0.01). The maximum total volatile bases nitrogen value was determined from the control group. The effects of atmosphere condition on pH values were significant (P < 0.05). Fresh fish are highly susceptible to spoilage due to postmortem microbial growth and biochemical reactions under refrigerated storage conditions. Therefore, the fish-processing industry has been motivated to investigate methods for maintaining products freshness. Modified atmosphere packaging (MAP) has become a useful preservation technique for prolonging the shelf time of perishable products. MAP is capable of inhibiting aerobic and anaerobic microbial growth and can be explained by the growth profiles of aerobes and anaerobes. Despite the advantages of modified atmosphere packaging, caution should be taken since improper handling and or extended storage might pose a public health hazard due to survival microorganisms, such as Listeria monocytogenes. Considering this fact, the establishment of the gas mixtures related to the target product is very important. Thus, the present study was undertaken to determine the effects of air (control), vacuum and MAP with various gas mixtures on microbiological and chemical changes of rainbow trout (Oncorhynchus mykiss) fillets during storage at 4 ± 1C.