Salt as a Master Regulator of Microbial Assembly and Metabolic Pathways in Fermented Fish: From Preservation to Flavor Innovation

Fermented fish constitutes a complex biotechnological system wherein fish substrates are transformed into value-added products via the synergistic metabolic interactions of microbial metabolism and enzymatic hydrolysis. Currently, the industry faces a critical trade-off-preserving traditional sensory heritage while addressing the urgent public health mandate for sodium reduction. This review critically examines salinity as the dominant abiotic factor governing microbial assembly rules and metabolic trajectories. High-salt environments (> 18%) impose rigorous osmotic filters, selecting for halophilic consortia (e.g., Tetragenococcus, Halobacterium) that drive deep proteolysis and characteristic umami formation. Conversely, in low-salt systems (5%-18%), osmotic constraints are alleviated, shifting the metabolic landscape toward carbohydrate-driven acidification by lactic acid bacteria (LAB) and yeast-mediated esterification, distinct sour-fruity profiles. Furthermore, the salt reduction paradox is analyzed, wherein the biological hurdle effect is compromised by lowered salinity, increasing risks of biogenic amine accumulation and pathogen survival. To address this, a paradigm shift from empirical processing to precision metabolic regulation is proposed. By integrating multi-omics with synthetic biology, robust microbial networks can be reconstructed to ensure safety and flavor complexity even in reduced-sodium matrices, paving the way for the sustainable modernization of fermented fish.