Salt-free fermented fish of Northeast India: Microbial ecology, biochemical dynamics and comparative perspectives.

Salt-free fish fermentation systems, which likely evolved under conditions of high humidity and limited salt availability, are indigenous to Northeast India. Fermented fish products such as Ngari, Hentak, Shidal, and Napham exemplify this unique preservation strategy. Unlike conventional salt-based fermentation (15-30% NaCl), these systems rely on moisture reduction (10-30%), oxygen limitation, and spontaneous microbial succession rather than osmotic selection. Microbial consortia dominated by lactic acid bacteria, Bacillus, Micrococcus, and Staphylococcus, drive proteolysis and lipolysis, resulting in near-neutral pH, low titratable acidity, relatively high total volatile basic nitrogen (TVBN), and the accumulation of free amino acids and fatty acids while moderating lipid oxidation. These products are rich in protein (36-63%), essential amino acids (32-44%), omega-3 and omega-6 fatty acids (EPA and DHA), and essential minerals (Ca, K, Mg, and Zn), and exhibit antioxidant activity as well as potential probiotic properties. However, the occurrence of biogenic amines and foodborne pathogens (e.g., Staphylococcus aureus and Clostridium spp.) remains an important food safety concern. Integrative multi-omics approaches and controlled fermentation strategies are required to elucidate microbial functionality, improve process standardization, and enhance product safety. Collectively, these fermentation systems represent a distinct ecological paradigm in which the absence of salt governs microbial succession, biochemical transformations, and ultimately the nutritional quality, sensory characteristics, and functional potential of fermented fish, providing new opportunities for sustainable protein preservation and functional food development.