Integrated Assessment of Shelf Life Evolution in Small Marine Fish from the Northwestern Spanish Coast: Microbial, Chemical, and Sensory Changes During Chilled Storage

An integrated study was conducted to evaluate quality loss in small marine fish—sardine (Sardina pilchardus), horse mackerel (Trachurus trachurus), and megrim (Lepidorhombus whiffiagonis)—during a 9-day chilled storage. A progressive increase in microbial counts was observed in all species; aerobic mesophiles exceeded the spoilage limit (7 log CFU·g−1) only in horse mackerel by day 9 (7.02 log CFU·g−1), while remaining below this threshold in sardine (4.49 log CFU·g−1) and megrim (5.42 log CFU·g−1). Lipid oxidation showed species-specific behaviour, with sardine and horse mackerel exhibiting higher peroxide values (up to 19.73 and 10.73 meq O2·kg−1 lipids, respectively) and TBARS formation, whereas megrim showed limited primary and secondary oxidation but a marked increase in tertiary products (ca. six-fold). Lipid hydrolysis increased significantly, with free fatty acids rising by factors of approximately 4.1 (sardine), 13.7 (horse mackerel), and 18.6 (megrim). Similarly, trimethylamine formation increased markedly, with values rising by factors of about 13.1, 19.0, and 51.8, respectively. Sensory evaluation indicated that all species remained acceptable up to day 6 but were unacceptable by day 9, establishing a shelf life of approximately 6 days. Overall, horse mackerel showed the fastest deterioration, highlighting the need for species-specific shelf life assessment strategies.