## 1 Introduction  
Douchi is a traditional Chinese fermented soybean product with a pleasant flavor and is rich in nutrition. Depending on the fermentation's main microorganism, it can be categorized into four different types [1, 2, 3], including _Mucor_-type douchi, _Aspergillus_-type douchi, bacterial-type douchi, and _Rhizopus_-type douchi. In China, _Mucor_-type douchi is predominantly produced in southwest areas, with typical products being Yongchuan douchi and Tongchuan douchi. Traditional douchi has been made by steeping, stewing, cooling, zhiqu, stirring salt and post-fermentation and is produced via traditional natural fermentation, with most of the microorganisms derived from the natural environment and raw materials, and its post-fermentation time takes more than 10 months. In addition, because _Mucor_ grows only at low temperatures, traditional douchi can be produced only from November through February [1; 4; 5]. As a result, traditional natural zhiqu douchi was unable to satisfy the market's needs; thus, the industrialized _Mucor_- and _Apergillus_-type douchis could develop. Aroma determination has become a hot research topic. Headspace solid-phase micro extraction (HS-SPME), stir bar sorptive extraction (SBME), and supercritical fluid extraction (SFE) are mainly extraction methods for sample pretreatment [6; 7]. The advantages of SPME are its simplicity, ease of automation, and robustness, and it is used for determining the flavors of volatile and semi-volatile compounds [6]. [PERSON] [8] et al. chose six types of commercially available silica SPME fibers and found that divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber had the highest extraction efficiency for the analytes released into the headspace. Also, other researchers used DVB/CAR/PDMS to evaluate the flavor quality [9; 10]. Researchers have been investigating the roles of different starter cultures in a range of fermented foods and how they can affect the sensory quality of fish sauces [11] and Chinese fermented soybeans, such as douchi and sufu [12; 13], and how the components of these foods can affect the human microbiota. Most recent research has focused on the roles of microorganisms in the quality of fermented products. For instance, [PERSON] [14] conducted a study on the association between microorganisms and flavor formation in _Apergillus_-type douchi through 165 rRNA sequencing and SPME-GC-MS and found that bacteria were the dominant microorganism. The researchers evaluated the key model of bacteria and flavor components by O2 PLS analysis and found that the main volatile flavor components were aldehydes, ketones, and acids for _Staphylococcus_, ketones and pyrazines for _Bacillus_, and acids and aldehydes for _Lactobacillus_. A study by [PERSON] [15] explored the relationship between the top 10 microorganisms in bacteria and fungi and flavor components during the natural fermentation of red sufu from Chaling and found that _Leuconostoc_, _Lactobacillus_, _Weissella_, _Debargomyces_, _Tusonia_, and _Pichia_ were the main microorganisms responsible for the flavor formation of sufu. [PERSON] [1] compared the quality and microbial communities between natural-type and artificial-type douchis and found that the microflora of the natural-type douchi were more abundant and diverse. [PERSON] [13] et al. investigated the effect of the microbial community on the volatile aromatic substances of _Mucor racemosus_ during sufu fermentation. They found that _Lactobacillus_, _Pseudomonas_, and so on primarily influenced the synthesis of acids and alcohols. In this study, seven different types of douchi were used as raw materials from Sichuan-Chongqing. High-throughput sequencing, flavor chemistry, and correlation analysis were used to establish the correlation between the microbiota and flavor substances in douchi and to screen out potential flavor-related microorganisms.