Nowadays, developing effective preservation methods to extend the shelf-life of fish is essential for reducing waste and enhancing consumption. Additionally, it is important to improve the organoleptic qualities of fish. Given that fish is a highly perishable product, special precautions are necessary throughout the stages from fishing to consumption to prevent rapid deterioration caused by chemical reactions, physical damage, and microbial proliferation.

This study aimed to evaluate the effects of different preservation techniques—vacuum (50%), modified atmosphere (80%N₂ + 20%CO₂), and refrigeration (control)—on the physicochemical and microbiological properties of Atlantic bonito fillets over 15 days of refrigeration storage at 4°C. The physicochemical properties, including peroxide index and Thiobarbituric Acid Reactive Substances (TBARs), were measured, and microbiological analysis was conducted according to Regulation nº2073/2005 and Health Protection Agency (HPA) guidelines.

The results indicated that the peroxide value increased gradually over time for all preservation methods, with refrigeration showing the highest values and modified atmosphere showing the lowest, at 23,40±0,08 and 1,10±0,05mEq./kg by day 15, respectively.

TBARs values also increased over time, with a slight increase for modified atmosphere and vacuum, at 1,29±0,06 and 0,78±0,06mgMDA/kg by day 15, respectively, and a more significant increase for refrigeration, at 7,32±0,10mgMDA/kg.

Both methods quantify primary oxidation compounds, revealing an increase in lipid oxidation over the storage period. Among the techniques, modified atmosphere packaging yielded the lowest oxidation values.

Microbiological analysis demonstrated that Atlantic bonito fillets preserved in a modified atmosphere met satisfactory microbiological quality standards after 15 days, outperforming other techniques in maintaining microbial safety. The parameters analysed included total viable count at 30°C, moulds, yeasts, Enterobacteriaceae, Coagulase Staphylococci (+), Listeria monocytogenes, Salmonella spp., Sulphite-reducing Clostridium spores, Lactic Acid Bacteria, and Vibrio Parahaemolyticus.

In conclusion, modified atmosphere preservation is recommended for extending the shelf-life and maintaining the quality of Atlantic bonito fillets, offering a lower peroxidation activity and microbiological quality compared to vacuum and refrigeration methods.