Analysis of bacterial communities in pit mud from Zhijiang Baijiu distillery using denaturing gradient gel electrophoresis and high- throughput sequencing

Yeast diversity in pit mud and related volatile compounds in fermented grains of chinese strong-flavour liquor

Chinese strong-flavour liquor is produced via a traditional solid-state fermentation strategy facilitated by live microorganisms in pit mud-based cellars. For the present analysis, pit mud samples from different spatial locations within fermentation cellars were collected, and the yeast communities therein were assessed via culture-based and denaturing gradient gel electrophoresis (DGGE) approaches. These analyses revealed significant differences in the composition of yeast communities present in different layers of pit mud. In total, 29 different yeast species were detected, and principal component analyses revealed clear differences in microbial diversity in pit mud samples taken from different cellar locations. Culture-dependent strategies similarly detected 20 different yeast species in these samples. However, while Geotrichum silvicola, Torulaspora delbrueckii, Hanseniaspora uvarum, Saturnispora silvae, Issatchenkia orientalis, Candida mucifera, Kazachstania barnettii, Cyberlindnera jadinii, Hanseniaspora spp., Alternaria tenuissima, Cryptococcus laurentii, Metschnikowia spp., and Rhodotorula dairenensis were detected via a PCR-DGGE approach, they were not detectable in culture-dependent analyses. In contrast, culture-based approaches led to the identification of Schizosaccharomyces pombe and Debaryomyces hansenii in these pit mud samples, whereas they were not detected using DGGE fingerprints profiles. An additional HS-SPME-GC-MS-based analysis of the volatile compounds present in fermented grains samples led to the identification of 66 such compounds, with the highest levels of volatile acids, esters, and alcohols being detected in fermented grains from lower layer samples. A canonical correspondence analysis (CCA) suggested they were significant correlations between pit mud yeast communities and associated volatile compounds in fermented grains.

The microbial diversity and flavour metabolism of Chinese strong flavour Baijiu: a review

Strong flavour Baijiu is widely consumed in China and is produced by the fermentation of grains using microbial starters. However, a comprehensive understanding of the diversity and metabolic characteristics of microbial communities involved in the solid-state fermentation of Baijiu is important for determining the relationship between microbial composition, flavour metabolism and understanding Baijiu fermentation conditions. Although studies have examined the metabolic pathways and impact of major processes on flavour compounds in strong flavour Baijiu, aspects of the fermentation process remain unexplored. In this review, methods are discussed for the optimisation of microbial diversity in strong flavour Baijiu and associated effects on the flavour of Baijiu. Recent studies are reviewed on starters (Daqu), fermented grains (Jiupei), and pit mud together with the effects of microbial composition on the quality of strong flavour Baijiu. The challenges of Baijiu research and production are discussed, including the role of the microbial diversity of Daqu and Jiupei in the flavour composition of strong flavour Baijiu. This review contributes to the current understanding of processing strong flavour Baijiu and serves as a reference for screening flavour related microorganisms, which is valuable for improving the quality of strong flavour Baijiu.

Comparing the differences of prokaryotic microbial community between pit walls and bottom from Chinese liquor revealed by 16S rRNA gene sequencing

This study aims to explore the prokaryotic microbial community structures and diversity in pit mud from different depths, and provide a theoretical basis for the liquor production and further study of pit mud. The fermented pit muds of strong-flavor liquor from Yun distillery were taken as samples. The high-throughput sequencing approach, followed by bioinformatics analyses, was used to compare the differences in the prokaryotic microbial community between pit walls and bottom represented by samples. A total of 31 bacteria phyla and 2 archaea phyla were detected. The dominant phyla in YJ-S, YJ-Z, and YJ-X (sample name) were Proteobacteria and Firmicutes, while the dominant genera in them were Acinetobacter, Aminobacterium, and Lactobacillus. YJ-Z and YJ-X were the closest in species diversity. In species richness analysis, YJ-X was the highest, followed by YJ-Z, and YJ-S was the lowest; in species uniformity analysis, YJ-S was the highest, followed by YJ-Z, and YJ-X was the lowest. The function predicted by 16S rRNA genome showed that prokaryotic microbial function in pit mud was mainly concentrated in "Carbohydrate transport and metabolism" and "Amino acid transport and metabolism." Significant differences in prokaryotic microbial community and gene function prediction between pit walls and bottom were found in YJ-S, YJ-Z, and YJ-X (p < 0.05).

A new method for screening and culture of Clostridium from pit mud under non-anaerobic conditions

Strong-flavor Baijiu (SFB) is produced in complex fermentation in pits under ground. Clostridium producing hexanoic acid plays a key role in the flavor formation of SFB. The screening and culture for Clostridium are very difficult because of its strict anaerobic characteristics. In this study, electric field assisted screening (EFAS) was used to screen Clostridium from pit mud, and electric culture (EC) was used to cultivate Clostridium under non-anaerobic conditions. A strain with a high yield of hexanoic acid was screened and named as Clostridium sp. EFAS6. Under non-anaerobic conditions, it grew rapidly only near the cathode end in the EFAS device because of the low oxidation-reduction potential of that electrode. In the experiment of high-density culture in the EC device, the cell concentration reached 10⁶-10⁷. After energy consumption was calculated, the optimal loading voltage was found to be 10 V. In the application, the broth of Clostridium sp. EFAS6 increased the content of ethyl hexanoic in SFB. Under non-anaerobic conditions, the anaerobe was screened by EFAS and cultivated in high density by EC. The EFAS and EC could also be used for the screening and culture of other anaerobes under non-anaerobic conditions.

Analysis of microbial community structure and volatile compounds in pit mud used for manufacturing Taorong-type Baijiu based on high-throughput sequencing

In this study, the pit mud used in manufacturing Taorong-type Baijiu was collected from the upper, middle, lower and bottom layers of pits at Henan Yangshao Liquor Co., LTD. High-throughput sequencing (HTS) technology was used to analyze the microbial community structure of the pit mud. In addition, the volatile compounds in the pit mud were subjected to preliminary qualitative analysis through headspace-solid phase microextraction and gas chromatography-mass spectrometry (GC-MS). The HTS results demonstrated that there were 5, 3, 5 and 5 dominant bacterial phyla (including 11, 11, 9 and 8 dominant bacterial genera) and 3, 3, 3 and 3 dominant fungal phyla (including 4, 7, 7 and 5 dominant fungal genera) in the pit mud from the F-S (upper), G-Z (middle), H-X (lower) and I-D (bottom) layers, respectively. In the qualitative analysis of the volatile compounds, a total of 77types of volatile compounds were detected in the pit mud, including 46, 45, 39 and 49 types in the pit mud from layers F-S, G-Z, H-X and I-D, respectively. Esters and acids were the two main components of the pit mud. The correlation between the microorganisms present and the main volatile compounds in the pit mud was analyzed. Lentimicrobium, Syner-01 and Blvii28_wastewater-sludge groups were found for the first time in pit mud used for manufacturing Taorong-type Baijiu. The findings of this study could provide a theoretical foundation for improving the quality of pit mud and the flavor of Taorong-type Baijiu.

Culturing Bacteria From Fermentation Pit Muds of Baijiu With Culturomics and Amplicon-Based Metagenomic Approaches

The Baijiu-making microbiota has an important role in the alcohol production, flavor, and character of Baijiu. 16S rRNA gene sequencing revolutionized the understanding of Baijiu-making microbiota. In this study, nine phyla, 23 classes, 49 orders, 99 families, and 201 genera were detected in pit muds (PMs) by 16S rRNA gene sequencing. Firmicutes and Bacteroidetes predominated (>99%). At the order level, Clostridiales, Bacteroidales, and Bacillales predominated (>92%). At the genus level, Hydrogenispora, Petrimonas, Proteiniphilum, and Sedimentibacter predominated. The pure culture of Baijiu-making prokaryotes was essential to elucidating the role of these microbes in the fermentation of Baijiu. According to the theory of microbial culturomics, a culturing approach with multiple culture conditions was adopted, combining 16S rRNA gene sequencing. We identified 215 prokaryotic strains, which were assigned to 66 species, 41 genera, four phyla, and 19 potential new species. Gas conditions were key factors in culturomics. In addition, culturomics significantly increased the number of species isolated from the fermentation PM compared with previous reports. With culturomics, the diversity spectrum of culturable bacteria in the PM was increased 273.33% at the genus level. This study confirms the complementary role of culturomics in the exploration of complex microbiota.

Effect of Pit Mud on Bacterial Community and Aroma Components in Yellow Water and Their Changes during the Fermentation of Chinese Strong-Flavor Liquor

As the main by-product of Chinese strong-flavor liquor, yellow water plays an important role in the formation of flavor components. Yellow water from different fermentation periods (30th day, 45th day, 60th day) was selected to analyze the aroma components by Headspace solid phase micro-extraction Gas Chromatography–Mass Spectrometry, and the microorganism community was evaluated by high-throughput sequencing technology and bioinformatics analysis of DNA. As the fermentation time was prolonged, the main flavor components significantly increased, and the amount of the common microbial population between yellow water and pit mud increased gradually. Among the common microorganisms, Lactobacillus accounted for the largest proportion, at about 56.96%. The microbes in the yellow water mainly belonged to Firmicutes. The abundance of Bacilli (the main bacteria) gradually decreased with time, at 87.60% at the 30th day down to 68.87% at the 60th day, but Clostridia gradually increased from 10.29% to 27.48%. At the genus level, some microbes increased significantly from the 30th day to 60th day, such as Caproiciproducens, which increased from 2.65% to 6.30%, and Sedimentibacter, increasing from 0.47% to 2.49%. RDA analysis indicated that the main aroma components were positively correlated with Clostridia and negatively correlated with Bacilli.