## 3 Results and Discussion
### Analysis of Aroma Compounds in CSB Prepared with Synthetic Microbial Community Starter  
To further analyze the effects of different dominant LAB and alkali addition on the aroma profiles of CSB, referring to the microbial community analysis described above, _P. pentosacea_, _C. crustorum_, and _W. cibaria_ were combined with _S. cerevisiae_ as synthetic microbial community starters, respectively. The contents of aroma compounds in CSBs are shown in Table S4 and were subjected to heatmap analysis (Figure 6). Hierarchical clustering of CSBs prepared with synthetic microbial community starters showed that alkali-added CSBs and alkali-free CSBs fermented by the same starters were clustered together, indicating that adding alkali retained the original aroma characteristics of alkali-free CSBs. Notably, \(>\)50% of the aroma compounds in CSB fermented by _P. pentosaceus_ were more abundant than those in CSB fermented by _C. crustorum_ or _W. cibaria_, such as phenylethyl1 alcohol, 3-methyl-1-butanol (balsamic), and ethanol. Phenylethyl alcohol and 3-methyl-1-butanol are typical higher alcohols in fermented dough. Higher alcohols are converted by the corresponding branched-chain amino acids via Ehrlich pathway in an anaerobic environment; for example, phenylethyl1 alcohol is generated from phenylalanine [42]. Ethanol is a marker of the Embden-Meyerhof-Parnas (EMP) pathway in _S. cerevisiae_ metabolism under anaerobic conditions [43]. We found that CSB fermented by _P. pentosaceus_ had a strong aroma with high concentrations of Ehrlich volatiles and ethanol, which indicated that _P. pentosaceus_ might be better at promoting Ehrlich and EMP pathways in  
Figure 6: Comparison of volatile compounds in alkali-added and alkali-free CSBs fermented using synthetic microbial community starters. Pearson correlation with hierarchical clustering among the CSB samples was applied. WC-FB, CC-FB, and PP-FB indicate alkali-free CSBs fermented by synthetic microbial community starters containing _Weissella cibaria_, _Companilatobacillus crustorum_, and _Pediococcus pentosaceus_, respectively. WC-AB, CC-AB, and PP-AB symbolize alkali-added CSBs fermented by synthetic microbial community starters containing _W. cibaria_, _C. crustorum_, and _P. pentosaceus_, respectively. \({}^{*}\)_p_\(<\)0.05. S. cerevisiae_ metabolism than _C. crustorum_ and _W. cibaria_, in the dough ecosystem. With the addition of alkali, the content of 17 compounds such as pentanoic acid, hexanoic acid, heptanoic acid, hexanal, octanal, 1-hexanol, and 1-octen-3-ol significantly decreased in CSB, suggesting that adding alkali could weaken the aroma profile of CSB fermented by _P. pentosaceus_. Similarly to the results of aroma compound analysis of CSB fermented by CTS, the addition of alkali decreased almost all of the volatile acids in CSB fermented by synthetic microbial community starter. Pentanoic acid, hexanoic acid, and heptanoic acid showed significant decreases in CSBs fermented by _W. cibaria_ and _P. pentosaceus_, and only pentanoic acid displayed a significant decrease in CSB fermented by _C. crustorum_, which might be related to the higher tolerance of _C. crustorum_ to alkali than _W. cibaria_ and _P. pentosaceus_ in the dough ecosystem. Acetic acid has been demonstrated to impact the aroma of wheat flour bread negatively at high concentrations [31]. The concentration of acetic acid in CSB fermented by _W. cibaria_ was the highest (average 15.92 mg/kg), >1.5-fold that in _C. crustorum_-fermented CSB (average 9.45 mg/kg). The heterofermative fermentation property of _W. cibaria_ might be responsible for the accumulation of acetic acid in the fermented dough [44].Heterofermative _W. cibaria_ directly converts glucose to lactic acid and acetic acid via the pyruvate metabolism pathway, but lactic acid is the only byproduct of glucose in homofferentiative _C. crustorum_, in the dough ecosystem. Heteroformation can also produce esters that impart a pleasant and fruity odor in bread [45].