This study investigated the association of cellar microbial communities with the differences in the flavor of base Baijiu obtained after the 2nd to 4th rounds of fermentation during the mechanized production of Jiangxiangxing Baijiu. It systematically analyzed the variations in physicochemical indicators of fermented grains, the succession pattern and assembly mechanism of microbial communities, and the flavor components of base Baijiu. The core microbial community in each fermentation round was identified and differential flavor compounds among fermentation rounds were selected. Furthermore, correlation analysis was performed to elucidate the mechanism underlying the differences in the flavor of base Baijiu across fermentation rounds. The results showed that the moisture and total titratable acidity in fermented grains exhibited a similar increasing trend with increasing fermentation rounds. Meanwhile, the dynamic changes and succession patterns of the microbial communities revealed that Candida and Geotrichum were detected only in the 2nd round, while Lactobacillus and Pichia were common dominant microorganisms in each fermentation round. The top 13 bacterial genera and the top 17 fungal genera identified by the random forest algorithm were considered as core microorganisms across all rounds. The Mantel test results showed that the total titratable acidity, moisture, and starch content of fermented grains drove microbial community succession. In total, 11 differential flavor compounds were identified by orthogonal partial least square-discriminant analysis (OPLS-DA) with their contents in base Baijiu varying among all fermentation rounds and among the upper, middle, and bottom layers of fermented grains. The Spearman correlation analysis between differential flavor compounds and core microbiota indicated that Planococcus, Kazachstania, and Zygosaccharomyces might influence the formation of ethyl acetate and acetal in base Baijiu. Through neutral community model analysis, it was found that the contribution of the random processes (e.g., random migration, birth-death events, environmental disturbances, and probabilistic dispersal) to shaping the microbial communities decreased with increasing fermentation rounds, while that of the deterministic factors (e.g., fermentation temperature, humidity, and pH) exhibited a reverse trend. The research results can provide a theoretical basis and technical support for the high-quality mechanized production and quality and flavor regulation of Jiangxiangxing Baijiu.

An ultra-high performance liquid chromatography-high resolution mass spectrometric (UPLC-HRMS) method was developed, optimized and applied to analyze the bitter compound trihydroxyoctadecenoic acid in Chinese baijiu. The samples were diluted and filtered through a 0.22 μm membrane before analysis. Acetonitrile was selected as the organic phase and 0.1% formic acid as the aqueous phase with a flow rate of 0.3 mL/min and an injection volume of 2 μL. The analyte was separated on a Hypersic Gold (100 mm × 2.1 mm, 1.9 μm) column by gradient elution, and qualitative analysis was achieved by comparison of secondary daughter ions and theoretical simulation of molecular ion fragment structures using the Mass Frontier 8.0 software, which could avoid false positive results. This method had the advantages of simple pretreatment, fast analysis, low detection limit (0.2 ng/mL) and high accuracy, and could meet the requirements for the detection of baijiu samples. This method was used to study the change in the content of trihydroxyoctaenoic acid during the production process of Maotai-flavor baijiu. The results showed that with the prolongation of fermentation time, a large amount of linoleic acid in the raw materials was likely to be oxidized and decomposed into trihydroxyoctadecenoic acid, and then transferred into the base liquor by distillation. The content of trihydroxyoctadecenoic acid in the base liquor did not obviously change during storage, indicating that it was affected little by storage time. The content of trihydroxyoctadecenoic acid in Maotai-flavor base liquor was lowest among the three typical bodies of Maotai-flavor baijiu, so Maotai-flavor base liquor could be used as one of the major base liquors for packaged products.

This study investigated the physicochemical properties, enzyme activities, volatile flavor components, microbial communities, and sensory evaluation of high-temperature Daqu (HTD) during the maturation process, and a standard system was established for comprehensive quality evaluation of HTD. There were obvious changes in the physicochemical properties, enzyme activities, and volatile flavor components at different storage periods, which affected the sensory evaluation of HTD to a certain extent. The results of high-throughput sequencing revealed significant microbial diversity, and showed that the bacterial community changed significantly more than did the fungal community. During the storage process, the dominant bacterial genera were Kroppenstedtia and Thermoascus. The correlation between dominant microorganisms and quality indicators highlighted their role in HTD quality. Lactococcus, Candida, Pichia, Paecilomyces, and protease activity played a crucial role in the formation of isovaleraldehyde. Acidic protease activity had the greatest impact on the microbial community. Moisture promoted isobutyric acid generation. Furthermore, the comprehensive quality evaluation standard system was established by the entropy weight method combined with multi-factor fuzzy mathematics. Consequently, this study provides innovative insights for comprehensive quality evaluation of HTD during storage and establishes a groundwork for scientific and rational storage of HTD and quality control of sauce-flavor Baijiu.

A rapid and accurate qualitative and quantitative method based on ultra-high performance liquid chromatography-high-resolution mass spectrometry (UPLC-HRMS) was established for the determination of various trace aroma and flavor substances and their derivatives in baijiu. Samples were centrifuged at high speed, filtered and separated on a Hypersil Gold C₁₈ (150 mm × 2.1 mm, 1.9 μm) column before analysis. The results showed that the pretreatment process allowed multi-component analysis of baijiu without extraction using ethanol or other organic solvents within 16 minutes. The calibration curves established using a mixed standard solution of 17 amino acids, 4 bioamines and 11 non-volatile organic acids exhibited good linearity (R² > 0.990), and the detection limits and quantitation limits were relatively low for all analytes, which meet the requirements of the compositional analysis of baijiu. The average recoveries for all analytes were 71.92%–117.45%, with relative standard deviations (RSDs) of 0.46%–5.48%. The developed method had good recovery, precision, and stability for all analytes. Therefore, this method has the advantages of simple operation, high sensitivity, and good repeatability, and is of reference significance for the analysis of the types and contents of other non-volatile flavor substances in baijiu.