Ferric iron availability and species identity jointly shape the metabolic profiles and spoilage potentials of grass carp spoilage bacteria: A combined metabolomic and physicochemical evaluation.

Ferric iron is essential for bacterial growth and spoilage-associated phenotypes, yet its specific influences on the metabolism and spoilage potential of fish spoilage bacteria remain unclear. Therefore, this study aimed to investigate the metabolic and spoilage potential changes of grass carp spoilage bacteria under varying ferric iron accessibilities, using combined metabolomic and physicochemical detection. The results showed that high ferric iron accessibility stimulated bacterial carbohydrate metabolism (glycolysis and tricarboxylic acid cycle) and fatty acid β-oxidation. Conversely, the low-ferric-mimicking condition partly hindered carbohydrate degradation and enhanced amino acid catabolism, evidenced by the increase in ammonia and a significant 29% decrease in glutamate level. As for spoilage potential, bacteria increased the accumulation of trichloroacetic acid (TCA)-soluble peptides (up to 2.17 μmol tyrosine/g) and biogenic amines (with histamine contents up to 19.32-30.04 mg/kg) under the low-ferric-mimicking condition, owing to possibly increased protease secretion, elevated siderophore synthesis, and decreased amine oxidase activity. Besides, the tested bacteria exhibited different characteristics, such as the potent activity of Pseudomonas putida in utilizing amino acids and carbohydrates, the high capacity of Shewanella putrefaciens in producing putrescine, cadaverine, and histamine, and the strong potential of Shewanella putrefaciens in degrading purine-related compounds. Taken together, this study revealed ferric-dependent metabolic and spoilage potential changes of grass carp bacteria, indicated the potential risk of ferric iron depletion on fish quality preservation, and thereby inspired the development of iron-based preservation strategies for aquatic products.