The variation in microbiota during pit fermentation is the main reason for the distinct characteristics of the 7 types of base Baijiu in jiang-flavor Baijiu (JFB) brewing. However, the specific structure, succession, and functional differentiation of microbial communities across different fermentation rounds remain unclear. Therefore, this study compared the differences in microbiota structure, environmental factors driving community assembly, and functional differentiations throughout 1–7 rounds (JC1–JC7) of pit fermentation in JFB production. Results showed that Lactobacillus dominated all rounds and complied with declining relative abundance from rounds JC1–JC7. The mould composition was similar in JC3–JC5 while the yeast structure in JC4 was found intermediate between JC3 and JC5. LEfSe analysis unveiled aroma-producing microorganisms as prominent biomarkers in JC1, strong enzyme-producing attributes in JC2, JC6, and JC7 biomarkers, and an enzyme and aroma-producing focus with robust tolerance in JC3–JC5 biomarkers. Acidity mainly regulated the microbial community in the first 4 rounds, with nutrient limitation drove microbial succession from the fifth round onward. Functional predictions underscored enriched amino acid metabolism enzymes in JC6 and JC1, while carbohydrate degradation exhibited predominant enzymatic profiles in JC2, JC6, and JC7. This study laid a foundation for comprehending community composition, succession, and flavor regulatory mechanisms throughout JFB brewing.

The sensory flavor characteristics and characteristic flavor composition of Baijiu are an important basis for recognizing different aroma types of Baijiu and identifying Baijiu quality. However, at present, there are few studies on the sensory quality and flavor compounds of different aroma types of Baijiu. In this study, the major volatile compounds of four aroma types of Baijiu, Jiangxiangxing, Nongxiangxing, Qingxiangxing and Qingjiangxiangxing, were determined by sensory evaluation and headspace-solid phase microextraction/liquid-liquid microextraction coupled to gas chromatographymass spectrometry (HS-SPME/LLME-GC-MS) and gas chromatography-flame ionization detector (GC-FID), and their characteristic volatile compounds were identified by their odor activity values (OAV). Besides, a correlation evaluation model was developed using partial least squares regression (PLSR). The results showed that there were significant differences in the flavor profiles of the aroma types of Baijiu. A total of 251 volatile compounds were detected across all samples, including 54 characteristic flavor compounds. Ethyl isovalerate, dimethyl trisulfide, ethyl butyrate, furfural, 2,3,5-trimethylpyrazine, 2,3,5,6-tetramethylpyrazine contributed significantly to the flavor of Jiangxiangxing Baijiu. The key flavor compounds of Nongxiangxing Baijiu were ethyl hexanoate, p-cresol and γ-nonolactone. Nonanal, ethyl decanoate and phenylethanol were the characteristic flavor compounds in Qingxiangxing Baijiu. The most significant contributors to the characteristic flavor of Qingjiangxiangxing Baijiu were dimethyl trisulfide, phenethyl acetate, phenethyl alcohol, nonanal, decanal, ethyl laurate and 3-methyl-1-butanol.

To identify the green off-flavor compounds in Moutai-aroma type Baijiu, a method involving sensory-guided fractionation and metabolomics was developed for analyzing its characteristic off-flavor compounds. The samples were separated into volatile and non-volatile compounds by vacuum rotary evaporation. Liquid-liquid extraction and sensory analysis were performed on the volatile components with an intense green off-flavor, and the results showed that the green off-flavor compounds mainly existed in the neutral/alkaline components. A total of 94 flavor compounds were qualitatively and quantitatively identified in the volatile components by gas chromatography-mass spectrometry (GC-MS), the predominant ones being esters, alcohols and aromatic compounds. There were significant differences between normal and defective Baijiu as determined by Venn diagram and clustered heatmap analysis. Furthermore, a total of 15 major differential compounds with variable importance in the projection (VIP) > 1 were identified by orthogonal partial least-squares discriminant analysis. Among them, alcohol and ester compounds showed the most significant difference between the two Baijiu samples. Esters including ethyl lactate, ethyl 2-furoate and ethyl DL-2-hydroxycaproate, as well as higher alcohols including isoamyl alcohol, isobutanol and furfural were identified as the major green off-flavor compounds, and also important contributors to the bitterness and astringency of Baijiu. It is worth noting that ethyl 2-furoate and ethyl DL-2-hydroxycaproate were identified in Baijiu with green off-flavor for the first time; however, their flavor characteristics have yet to be further investigated. The results of this study provide a scientific basis for improving the quality of Moutai-aroma type Baijiu and also provide a reference for the analysis of characteristic flavor compounds in foods in the future.

The bacterial community structure in different fermentation rounds in Maotai town was analyzed by MiSeq high-throughput sequencing combined with SPSS statistical software 26.0 and the environmental effect on it was evaluated. A total of 33 bacterial classes, 153 families and 396 genera were identified, among which, the dominant classes were Gammaproteobacteria, Bacilli, Sphingobacteriia, Alphaproteobacteria, Actinobacteria, Flavobacteriia and Betaproteobacteria. Totally 19 dominant families were found, including Enterobacteriaceae, Sphingobacteriaceae, Bacillaceae, Flavobacteriaceae, Thermoactinomycetaceae, and Planococcaceae. Among them, Flavobacteriaceae, Planococcaceae, Bacteroidales_S24-7_group, Microbacteriaceae and Brucellaceae were considered as the dominant bacterial families for the first time in baijiu-making environments. A total of 22 dominant genera were identified, including Sphingobacterium, Enterobacter, Pantoea, Acinetobacter, Oceanobacillus and Pseudomonas. The correlation of environmental factors (temperature, humidity, precipitation, sunlight and atmospheric pressure) with the alpha diversity and the 48 dominant bacterial classes, families and genera was analyzed by t-test combined with Spearman correlation analysis. The results showed that the alpha diversity was significantly correlated with environmental factors, and the environmental bacterial communities in the 2nd and 3rd rounds of fermentation had a significant correlation with temperature and humidity. In addition, 35 dominant bacteria had a significant correlation with environmental factors; among them, Gammaproteobacteria and Bacilli as well as their respective subclasses were significantly correlated with the five environmental factors, especially temperature, humidity and sunlight. Alphaproteobacteria and its subclasses had a significantly positive correlation with environmental temperature. Sphingobacteriia, and its Sphingobacterium genus had a significant correlation with temperature and precipitation. Actinobacteria and its subclasses were significantly positively correlated with light duration. Betaproteobacteria and Flavobacterium as well as their respective subclasses were almost not affected by environmental factors. The results of this study provide a basic theoretical and disciplinary basis for the in-depth understanding of the microbial community structure characteristics in the brewing environment of Maotai town and their correlation with environmental factors.

In this study, the microbial community structure in fermented grains from the upper middle and lower layers of the cellar in the first and second rounds of fermentation of Maotai-flavor was analyzed by high-throughput sequencing, and the acid composition by ultra-high performance liquid chromatography (UPLC). Moreover, the correlation between them was investigated. The results showed that the total acid content of fermented grains was greater in the second round than the first round of fermentation. The radial distribution patterns of seven acidic compounds in different times and spaces of the cellar were different. The contents of lactic acid and acetic acid accounted for a large proportion in the two rounds of fermentation. For both rounds, the absolutely dominant bacterial genus was Limosilactobacillus, and the dominant fungal genera were Saccharomyces and Candida. As the fermentation time extended, there was a significant difference in the microbial community structure. The contents of total and individual acids were positively correlated with the relative abundance of Limosilactactacillacus, Schizosaccharomyces, Zygosaccharomyces, Candida and Kazachstania, and negatively correlated with the relative abundance of Lactobacillus, Saccharomyces, Paecilomyces and Torulaspora. This study provides a theoretical basis for further elucidating the fermentation mechanism of Maotai-flavor Baijiu cellar.

In this study, liquid-liquid microextraction coupled with gas chromatography with hydrogen flame ionization detection (LLME-GC-FID) and orthogonal partial least squares-discriminant analysis (OPLS-DA) were integrated to track and monitor the contents of furfural and furfuryl alcohol in the raw materials, Daqu, stacking fermented grains, pit fermented grains, upper and lower steamer fermented grains, and distillates, which were collected at the key steps of the brewing process of sauce-flavor Baijiu. The results showed that the spatial and temporal distribution of furfural and furfuryl alcohol during the brewing process of sauce-flavor Baijiu varied significantly. The contents of furfural and furfuryl alcohol increased at first and then decreased at the Daqu-making stage. The contents of furfural and furfuryl alcohol showed an upward trend at the stacking fermentation stage. During the pit fermentation stage, the content of furfural decreased while the content of furfuryl alcohol increased. During the distillation process, the content of furfural increased, while the content of furfuryl alcohol decreased from the upper steamer to the lower steamer. The contents of furfural and furfuryl alcohol showed an increasing trend at the alcohol extraction stage. The distribution of furfural during the brewing process was generally lower layer > middle layer > upper layer. The distribution of furfuryl alcohol was middle layer > lower layer > upper layer at the stacking fermentation stage, and lower layer > middle layer > upper layer at the cellar fermentation stage and the distillation stage. Traceability analyses showed that furfural and furfuryl alcohol were mainly derived from Daqu powder, rice husk, and the late distillation stage. The formation mechanism of furfural during the brewing process of sauce-flavor Baijiu was attributed to microbial action, sugar degradation, and Maillard reaction under high temperature and acidic conditions. This study provides theoretical guidance for the reduction and control of furfural and furfuryl alcohol during the brewing of Baijiu, and provides a scientific basis for regulating the quality and safety of Baijiu.