###### Abstract  
Alkali is an indispensable additive in Chinese steamed bread (CSB) production. This work aimed to evaluate the key roles of alkali in the microbial community of dough fermented using Chinese traditional starter (CTS) and the aroma profiles of CSB. The dominant fungi in CTS and fermented dough were members of the phylum Ascomycata and the genus _Saccharomyces_. _Peliococcus_, _Companilactobacillus_, and _Weissella_ were the dominant bacterial genera in CTS and fermented dough. Adding alkali could retain the types of dominant yeasts and LAB derived from CTS, decrease the relative abundance of _Companilactobacillus crustorum_ and _Weissella cibiratia_, and increase that of _Peliococcus pentosaccus_, in fermented dough. Principal component analysis (PCA) indicated that adding alkali decreased the content of sourness-related volatiles in CSB fermented by CTS. Correlation analysis showed that _Peliococcus_ and _Weissella_ in fermented dough were positively correlated with the lipid oxidation flavor-related compounds in CSB, and _Lactobacillus_ was positively correlated with sourness-related aroma compounds. Synthetic microbial community experiments indicated that CSB fermented by the starter containing _P. pentosaccus_ possessed a strong aroma, and adding alkali weakened the flavor intensity. Alkali addition could promote the formation of ethyl acetate and methyl acetate with a pleasant fruity aroma in _W. cibiratia_-associated CSB. microbial composition; aroma compounds; traditional fermented wheat flour food; alkali addition; high-throughput sequencing; synthetic microbial community +
Footnote †: journal: _foods_  
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Na\({}_{2}\)CO\({}_{3}\), provided a reliable solution [5]. It rapidly replaced the ancient neutralizers and is widely used in cereal foods on a global scale, such as in wheat noodles [6], corn tortillas [7], and pretzels [8]. Alkali has even become a primary additive in the manufacture of CSB. Some recent reports have revealed that adding alkali could improve the specific volume and texture properties with increased crumb hardness and resilience of buckwheat CSB [9], and Na\({}_{2}\)CO\({}_{3}\) could improve the flavor of CSB by inhibiting aroma-negative compounds [10]. CTSs are complex and stable biological ecosystems, containing bacteria, yeasts, and molds. The microbial composition and main strains have been the subject of many studies. The yeasts possess superior gas generation capacity and make CSB spongy and fluffy. The reported relevant yeast species include _Saccharomyces cerevisiae_, _Kazachstania humilis_, _Pichia kudriavzweii_, and so on [3,11]. The lactic acid bacteria (LAB) in CTSs include _Fructilactobacillus sanfranciscensis_, _Pediococcus pentosaccus_, _Companilactobacillus crustorum_, _Weissella cibaria_, _Lactiplantiobacillus plantarum_, etc. [2,12]. CTS-derived yeasts and LAB are considered to have a vital role in improving the flavor of wheat flour products because of their high metabolic activity in producing flavor compounds and their precursors [13]. [PERSON] et al. [4] reported that _Pediococcus_ was the predominant genus in CTS by high-throughput sequencing, and there were far more flavor compounds in CSB compared with commercial yeast-based CSB. [PERSON] et al. [14] used a synthetic microbial community technique that was the combination of LAB with yeast strains derived from sourdoughs as new starter cultures for wheat flour dough fermentation, and found that the doughs inoculated with _L. plantarum_ and _S. cerevisiae_ cultures could replace naturally fermented doughs and improve the specific volume, texture, and aroma of bread. The combination of high-throughput sequencing and synthetic microbial community techniques could provide convenience for the study on the relationship between the microorganisms in CTSs and the aroma profiles of CSBs.