Modelling microbial growth in modified-atmosphere-packed hake (Merluccius merluccius) fillets stored at different temperatures

Market globalization and changes in purchasing habits pose a challenge to the fishery industry because of the short shelf life of fish products. In view of this scenario, it would be very helpful if tools capable of predicting the shelf-life of fish could be developed. Thus, the objective of this study was to employ a modelling approach capable of predicting the evolution of the microbiota of hake fillets packaged under a modified atmosphere (MAP) rich in CO2 (50% CO2 / 50% N-2) when stored at temperatures ranging between 1 and 10 degrees C. Growth curves of ten microbial groups were obtained at four different temperatures and fitted with the Baranyi model. Photobacterium showed high growth rates in hake fillets (0.99 days(-1) at 4 degrees C), similar to those of Shewanella, lactic acid bacteria, and non-specific microbial groups investigated, and significantly higher than those of Pseudomonas. Furthermore, no lag phase was observed for Photobacterium regardless of the temperature investigated. On the other hand, Enterobacteriaceae and moulds and yeasts displayed low growth fitness, and their counts increased by < 1.5-2 Log(10) cycles along the incubation period regardless of storage temperature. The influence of storage temperature on growth parameters (lambda, mu(max) and Y-end)was subsequently studied, and secondary models were developed for the eight most relevant microbial groups. All of the final equations developed in this study showed R-2 values >= 0.90, and RMSE values <= 0.50. In addition, results obtained in this investigation strongly suggest that Photobacterium would be the main responsible microorganism for the spoilage of hake fillets stored under MAP conditions (50% CO2/50% N-2) along the entire range of temperatures investigated (1-10 degrees C).