## 3 Results and Discussion
### Analysis of Microbial Community during Fermentation of BBP-Meju with Different Salt Concentrations
#### 3.6.2 Analysis of Microbial Community Structure
This explained the consistency of the differential succession of _Staphylococcus_ in BBP-meju at different salt concentrations with the trend of acid substances shown in Figure 5. Notably, three opportunistic pathogens, _Enterobacter_, _Pantoea_, and _Brevundomonas_, were also found among these genera. The relative abundance of all three bacterial genera showed a decreasing trend during BBP-meju fermentation and further decreased with increasing salt concentration (Figure 7c). This result suggested that high-salt conditions could effectively inhibit the propagation of pathogenic microorganisms. However, the salt-reduced fermentation of BBP will provide a favorable environment for the growth of opportunistic pathogens, posing a threat to human health and increasing the food safety risks of BBP products. To address this issue, researchers proposed inoculating competitive starter cultures, especially indigenous microorganisms, to antagonize opportunistic pathogens in low-salt fermented foods, thereby enhancing product quality. [PERSON] et al. [57] fermented Suanyu using a mixed starter culture consisting of _Lactobacillus plantarum_ 120, _Staphylococcus xylosus_ 135, and _Saccharomyces cerevisiae_ 31. It was found that adding this mixed starter culture could significantly enhance the sensory characteristics of Suanyu and effectively inhibit the growth of spoilage microorganisms. Furthermore, the addition of indigenous yeasts _Torulspora delbrueckii_ and _Pichia guilliermond_ during low-salt fermentation of soy sauce could effectively inhibit the growth of _Staphylococcus_ and _Enterococcus_ spp. while producing a richer flavor profile, thus improving the flavor impact caused by reduced-salt fermentation [58]. In terms of fungi, the 10 fungal genera with the highest relative abundance were Aspergillus, Mortierella, Fusarium, Acremonium, Thelonectria, unclassified_Basidiomycota, unclassified_Fungi, Nigrospor, Wickerhamomyces, and Cladosporium. Aspergillus and Mortierella constituted the dominant fungal communities in all BBP-meju samples (Figure 7d). The high levels of Aspergillus in BBP-meju were mainly due to its use as a starter for koji production. Aspergillus is known to secrete amylases, proteases, and other enzymes, leading to the formation and accumulation of numerous flavor compounds during BBP fermentation, while also creating suitable conditions for the growth of other microorganisms in the later stages of fermentation [59]. The results showed that the relative abundance of Aspergillus was relatively stable during fermentation, reaching 41.51-56.11% (L), 63.25-67.16% (M), and 72.49-87.42% (M), respectively, by day 35 (Figure 7d). This indicated that Aspergillus demonstrated good adaptability to the high-salt environment in BBP-meju. However, the metabolism of Aspergillus is closely linked to the development of musty and metallic off-flavors in BBP, along with the presence of mycelium in the final product, consequently affecting consumer acceptance [60]. Mortierella is capable of producing polyunsaturated fatty acids and exhibits inhibitory effects on some pathogens [61]. The relative abundance of Mortierella did not change significantly during fermentation, but decreased significantly with increasing salt concentrations, in contrast to Aspergillus (Figure 7d). This suggested that the high osmotic pressure under high-salt conditions exerted inhibitory effects on the growth of Mortierella, while salt-reduced fermentation provided suitable conditions for the accumulation of flavor compounds in BBP-meju. This result was consistent with the report of [PERSON] et al. [23]. _Bacillus, Staphylococcus, Aspergillus, and Mortierella_ were the predominant microbial communities during BBP-meju fermentation. Salt reduction promoted the growth of _Bacillus, Staphylococcus, and Mortierella_ while inhibiting the growth of _Aspergillus_. Therefore, salt-reduced fermentation facilitated the production of flavor compounds, such as amino acids and organic acids, while attenuating the musty taste of _Aspergillus_.