The composition and change of the microbial community during the fourth round of heap fermentation of Jiang-flavor baijiu were explored using traditional culture-dependent approaches and high-throughput sequencing, and flavor compounds from fermented grains were analyzed by gas chromatography. The correlation among physicochemical parameters, flavor compounds and the microbial community was also analyzed. The results showed that the dominant bacteria were Bacillus amyloliquefaciens, B. licheniformis, uncultured Kroppenstedtia sp., K. eburnea, Sphingobium yanoikuyae and Lactobacillus sp., and the dominant fungi were Pichia kudriavzevii, Kazachstania humilis, Thermomyces languginosus, Byssochlamys spectabilis, Zygosaccharomyces parabilii and Aspergillus sp. The microbial community had a complex relationship with physicochemical parameters and flavor compounds. The water content was positively correlated with yeasts like P. kudriavzevii, negatively correlated with filamentous fungi such as T. lanuginosus, B. spectabilis and A. costiformis, while the starch and reducing sugar contents were positively correlated with Bacillus sp., and negatively correlated with P. kudriavzevii. Meanwhile, yeasts were positively correlated with alcohols such as propanol, isobutanol, isoamyl alcohol and β-phenylethanol (P < 0.01), while filamentous fungi and bacteria were positively correlated with acids and esters, such as acetic acid, propionic acid, isobutyric acid, ethyl lactate, ethyl oleate and butyl caproate (P < 0.01). This study may provide a theoretical basis for further clarifying the mechanism of heap fermentation of Jiang-flavor 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.