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This work employed high-throughput sequencing technology to delve into the mechanism driving microbial community succession during the fermentation of black Daqu used for Jiangxiangxing Baijiu production, and it also applied flavoromics to analyze the change of volatile flavor compounds. Furthermore, this study performed an integrative analysis of the driving mechanisms for microbial community succession and the change of volatile flavor compounds. The results showed that temperature, moisture, and acidity were the key driving factors for microbial community succession. A large accumulation of pyrazines occurred during the transition from the first to the second turnover stage, indicating that this transition might be key to the synthesis and formation of flavor substances in black Daqu. The microbial community structure of black Daqu during the fermentation process was quite different from that of ordinary Daqu. Bacillus and Thermoascus predominated in the microbial community throughout the fermentation process, while biomarkers in different stages showed stage-by-stage succession patterns. It was also found that the bacterial community exerted a significant effect on the fermentation power of black Daqu, while the fungal community was the major contributor to the liquefaction power. For the bacterial community, Oceanobacillus, Virgibacillus and Kropentedtia positively contributed to the synthesis of various flavor compounds such as ethyl decanoate, 2-acrolein, benzyl alcohol, and benzyl alcohol. For the fungal community, Saccharomyces was positively correlated with various pyrazines. This study provides a theoretical basis for understanding the evolution of microbial community characteristics and flavor compounds during the fermentation process of black Daqu, thereby offering new insights into strengthening brewing production and product quality.

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.

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.

Ammonium polyphosphate (APP), pentaerythritol (PER) and melamine (MEL) were used as flame retardant systems in addition to titanium dioxide, zinc borate(ZB) and expandable graphite(EG) used as functional fillers to prepare the fireproof coatings. The effects of four matrix resins on the fire resistance and mechanical properties of fire-retardant coatings were studied. The thermal decomposition process of four matrix resins was analyzed, and the fire resistance, adhesion, flexibility and impact resistance of the four coatings were measured. The results show that the polyurethane coating has the longest fire resistance time. TGA analysis shows that the thermal decomposition temperature of polyurethane matches the carbonization and foaming temperatures of the intumescent flame-retardant system, and the fire resistance effect of the expanded carbon layer is better. Mechanical performance test shows that the polyurethane coating sample has the best adhesion, flexibility and impact resistance. [ABSTRACT FROM AUTHOR]