Staphylococcus nepalensis Enhanced the Flavor Quality of Low-Salt Fish Sauce through Regulating the Microbial Community during Fermentation

Staphylococcus nepalensis 7MR-3, a salt-tolerant strain having a strong ability to produce enzymes and degrade biogenic amines, was utilized as a starter culture in the production of low-salt fish sauce. This study investigated the impact of inoculated fermentation on the physicochemical properties, including pH, amino acid nitrogen (AAN) and biogenic amines (BAs), as well as the microbial community structure and the generation of flavor compounds in low-salt fish sauce. Inoculated fermentation significantly increased the AAN content in low-salt fish sauce, reaching 0.65 g/100 mL after three months, which was higher than that (0.60 g/100 mL) of naturally fermented fish sauce. It also markedly inhibited the formation of BAs such as cadaverine, histamine, putrescine, and cadaverine, with their concentrations at the end of the fermentation period being reduced by 20.29%, 39.23%, 32.04%, and 18.74%, respectively, when compared to naturally fermented fish sauce. 16S rRNA sequencing indicated that inoculated fermentation significantly affected the richness and evenness of the microbial community, with distinct differences in the microbial community being observed between inoculated and naturally fermented fish sauces. Analysis by gas chromatography-mass spectrometry (GC-MS) identified a total of 118 volatile compounds in the two fish sauces. Out of these compounds, 16 and 19 differential flavor compounds were identified by partial least square-discriminant analysis (PLS-DA) in non-inoculated and inoculated low-salt fish sauces at three different fermentation stages, respectively. Furthermore, the constructed correlation network revealed that the key flavor compounds in the inoculated low-salt fish sauce were primarily produced by Halobacillus, Psychrobacter, Anaerococcus, Tetragenococcus, Bacteroides, Staphylococcus, Corynebacterium, and Bacillus, with Staphylococcus showing significant positive correlations with 3-methylbutyric acid, phenylethyl alcohol, benzyl methyl ketone, and 3-ethyl-2,5-dimethylpyrazine, indicating its central role in the production of flavor compounds in low-salt fish sauce. In conclusion, S. nepalensis 7MR-3 can be used as a starter culture the industrial production of fish sauce to improve the flavor and safety of rapidly fermented low-salt fish sauce.