Rusip, a traditional Indonesian fermented anchovy fish: Microbial changes, biochemical transformation, and functional prediction during the fermentation

Fermentation improves food safety, shelf life, sensory attributes, and bioactivity by harnessing the enzymatic actions of various microbes. Rusip is a traditional Indonesian fermented anchovy product that undergoes spontaneous fermentation driven by indigenous microorganisms. However, its microbial dynamics and functional potential are not well understood. The aim of this study was to examine the physicochemical properties of rusip during fermentation and used a metagenomic approach to characterize bacterial succession and predict microbial functions. The results showed that fermentation significantly altered rusip's biochemical composition, increasing titratable acidity, TVBN, soluble protein, and key amino acids (glycine, arginine, and lysine), as well as beneficial fatty acids, such as methyl myristate and methyl cis-11.14-eicosadienoate. Microbial analysis revealed a shift toward halophilic and salt-tolerant bacteria, particularly Tetragenococcus halophilus and Salinivibrio kushneri, as well as a reduction in microbial diversity. Functional predictions showed enrichment in metabolic pathways related to amino acid metabolism, steroid degradation, and aromatic compound breakdown. This indicates microbial contributions to flavor development and bioactivity. In conclusion, these findings underscore the pivotal role of microbial metabolism in shaping rusip's nutritional and sensory qualities and provide a scientific foundation for enhancing traditional fermentation processes through targeted microbial management in future research and food production practices.