Temperature-dependent changes in the dynamics and diversity of specific spoilage organisms in mackerel and trout fillets: a MALDI-TOF MS-based study.

Specific spoilage organisms (SSOs) are major contributors to the deterioration of fishery products and variations in their composition during fish storage deserve further investigation. In this study, we analysed the evolution of SSOs in fillets of Atlantic mackerel and rainbow trout during prolonged storage at 0 and 4 °C. SSOs were quantified and growth data were modelled to predict the shelf life of fillets, defined as the time to reach 6 log10 CFU/g for SSOs. Changes in the abundance of genera of SSOs were investigated using a culturomic approach, which involved the identification of colonies by MALDI-TOF MS. Storage temperatures influenced microbial growth, as the time to reach the critical threshold for SSOs was estimated at 8.8 (0 °C) and 3.4 days (4 °C) in mackerel, and 6.7 (0 °C) and 2 days (4 °C) in trout. Potentially histamine-producing bacteria (HPB), quantified only in mackerel samples, also reached higher levels earlier in samples stored at 4 °C. Temperature affected the complexity and succession of SSOs. In mackerel, Psychrobacter initially dominated at 0 °C, then declined with the increase of Pseudomonas and Shewanella. The same pattern occurred more rapidly at 4 °C. Regarding trout, an initial prevalence of Chryseobacterium and Acinetobacter was observed at 0 °C, but from the fifth day Pseudomonas became dominant. At 4 °C, nineteen genera, including bacteria not traditionally associated with spoilage (e.g. Buttiauxella), were detected during the experiment, compared with only thirteen genera for 0 °C samples. Storage at 0 °C remains a reliable method for limiting the growth of SSOs in fish. Culturomics is a valuable approach for capturing the evolution of SSOs during seafood storage and identifying emerging spoilage-associated genera. Further studies on different species are needed to design effective preservation strategies for fishery products.