Effects of modernized fermentation on the microbial community succession and ethyl lactate metabolism in Chinese baijiu fermentation

Bioturbation analysis of microbial community and organic acid metabolism in the enriched liquid of pit mud by Daqu, HuangShui, and ZaoPei

In this study, the traditional fermentation starter (Daqu), a fermentation by-product (Huangshui) and fermentation grains (Zaopei) were combined with pit mud to provide the initial bacterial source, using a single pit mud bacterial inoculation source as the control group. Changes in metabolite accumulation and microbial community were assessed over six rounds of enrichment. Results showed that the addition of exogenous microorganisms (Daqu, Huangshui and Zaopei) better enhanced the quality of the enriched pit mud liquid compared to the use of multiple rounds of enrichment. The quality enhancement of the enriched pit mud liquid could be ranked in descending order as follows: Zaopei > Huangshui > Daqu. The quality of the enriched pit mud liquid was found to be highest in rounds 2-3 of the addition of Zaopei. These results provide theoretical guidance and technical support for the development of pit mud maintenance systems and techniques for the rapid aging of artificial pit mud.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-025-01824-z.

Unraveling the multiple interactions between phages, microbes and flavor in the fermentation of strong-flavor Baijiu

The fermentation process of strong-flavor Baijiu represents a complex and unique ecosystem, characterized by the involvement of various microorganisms that drive intricate biochemical reactions, ultimately contributing to the distinct flavor profile of the Baijiu. Viruses may affect the succession of microorganisms and thus affect the style and quality of the product. However, the interaction between viruses and microorganisms during the fermentation of Baijiu is still unclear. Here we combined viral metagenomics and amplicon sequencing, physicochemical analysis, and GC-MS detection with temporal sampling to study the dynamics of viral and microbial communities, physicochemical properties, and flavor compounds during strong-flavor Baijiu fermentation. Viral metagenomic analysis revealed 513 viral operational taxonomic units (vOTUs), encompassing 34 viral families. Principal coordinates analysis (PCoA) demonstrated significant differences in vOTUs at different fermentation stages. Notably, the microbial community exhibited distinct succession patterns at various fermentation stages; it changed rapidly during the initial five days, with similarities observed between days 10 and 20. Volatile profile analysis identified 38 flavor components in fermented grains, comprising 16 ester compounds, 11 alcohols, and 8 acids, with the majority formed between days 10 and 30. The Spearman's rank correlation analysis revealed that Peduoviridae exhibited a negative correlation with Gluconobacter. Genomoviridae showed a negative correlation with Issatchenkia, Penicillium, and Monascus. These findings highlight the potential for complex interactions between viruses and microbial communities during Baijiu fermentation, underscoring the importance of considering viral communities in studies of the microbial ecology of fermented foods.

Research progress on the diversity, physiological and functional characteristics of lactic acid bacteria in the Nongxiangxing baijiu microbiome

Nongxiangxing baijiu (NXXB) is one of the main types of Chinese Baijiu. Its unique flavor is formed during fermentation by the combined action of various microorganisms, with lactic acid bacteria (LAB) making a great contribution. Lactate fermentation produces the precursors of key flavor compounds, such as lactic acid, acetic acid, and other flavor compounds, which combine to produce the unique sensory characteristics of NXXB. This review focuses on the diversity of LAB species and their physiological and metabolic characteristics. These characteristics include key species involved at different fermentation stages, metabolite biosynthesis, acid-tolerance mechanisms, interactions with yeasts, and factors influencing LAB community composition. It also discusses current challenges and future research directions for LAB in relation to NXXB production, aiming to advance understanding and potential future applications of these bacteria.

Effects of pits of different ages on ethyl acetate and its metabolism-related microorganisms during strong-flavor Baijiu fermentation

The esters are the most important flavor components in Baijiu as their species and content decide the style of Baijiu. During the formation of esters, pits play important roles. In this study, the main esters and their related microorganisms in different years of pits (5, 35 and 100 years) of strong-flavor Baijiu were comprehensively researched by headspace solid-phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS) and amplicon sequencing. A total of 690 bacterial genera and 155 fungal genera were detected. The microbial composition of ZPs (fermented grains) from 100 years pit was the most abundant at the genus level. A total of 177 volatile flavor components were observed, including 80 esters, 42 alcohols, 21 acids, 10 ketones and 11 aldehydes. Ethyl acetate was the lowest and ethyl caproate was relatively high in 100 years pit. 15 genera, including Lactobacillus, Pichia, Issatchenkia, Saccharomyces, and Aspergillus, were positively related to the formation of four major esters and their precursors. The research demonstrated that 100 years pit was benefit for maintaining microbial diversity and controlling ethyl acetate. This study is helpful for understanding the microbial composition and succession in the fermentation process of strong-flavor Baijiu, and revealing the complex relationships between dominant genera, physicochemical properties and volatile flavor components.

Exploring the impact mechanisms on different mechanized airing approaches during second round heap fermentation of sauce-flavor Baijiu: From physicochemical parameters, microbial diversity to volatile flavor compounds

The airing process of sauce-flavor Baijiu is a critical operation that serves the functions of cooling, homogenizing, and facilitating microbial proliferation and metabolism. Comprehensive analysis of physicochemical parameters, bacterial and fungal community of fermented grains, and volatile flavor compounds of soy-sauce (Jiangxiang) and mellow-sweet (Chuntian) typical base liquors among traditional (CT) and two different mechanized (JXA and JXB) airing operations were investigated. The results indicated that the dynamic variation patterns of moisture content, total titratable acidity, starch content, lactic acid, acetic acid, pH, and dominated microbial composition among CT, JXA, and JXB were similar, while minor bacterial genera with relative abundance including unclassified Micrococcineae, unclassified Rhizobiales, etc, and dominated fungi such as Torulaspora, Hyphopichia, Candida, Pichia, and Penicillium were profoundly influenced by mechanized airing operations, especially by JXB. A total of 100 and 101 volatile flavor compounds were qualitatively and quantitatively detected from soy-sauce (Jiangxiang) and mellow-sweet (Chuntian) typical base liquors. Mechanized airing operations were more consistent with CT for mellow-sweet (Chuntian) typical base liquors, but 2,3-dimethyl-5-ethylpyrazine, 2,3-dimethylpyrazine, tetramethylpyrazine and ethyl benzoate etc. were more abundant in soy-sauce (Jiangxiang) typical base liquors by mechanized airing operations, which were mainly associated with Leuconostoc, Acetoanaerobium, Limnohabitans and Bradyhizobium etc. This study provides a theoretical evidence for understanding the relationships among physicochemical parameters, microbial communities and volatile flavor compounds during second round heap fermentation of sauce-flavor Baijiu, laying a foundation for further elucidating the mechanized brewing mechanisms.

Initial abiotic factors as key drivers in core microbe assembly: Regulatory effects on flavor profiles in light-flavor Baijiu

Instability in initial abiotic factors of open solid-state fermentation systems can significantly alter Baijiu's flavor profile, but the mechanisms governing microbial interactions and flavor formation remain unclear. This study comprehensively monitored changes in abiotic factors, microbial communities, and flavor profiles across two distinct fermentation processes in a Baijiu distillery, which differed significantly in their management of initial abiotic factors. Our results revealed significant differences in abiotic factors between the two groups, including moisture, ethanol, acidity, glucose, and organic acid levels. The assembly of microbial communities in fermented grains was primarily driven by deterministic processes. The moisture content in the fermented grains positively affected the growth and metabolism of core microbiota. The rapid proliferation and metabolism of core microbes led to a rapid increase in the acidity of the fermented grains, alongside a significant accumulation of ethyl lactate. This study provides technical support and theoretical guidance for Baijiu production.

Effects of Lactiplantibacillus plantarum on Metabolites and Flavors in Synthetic Microbiota During Baijiu Fermentation

The distinctive flavor and aroma of Chinese baijiu are closely linked to the microorganisms involved in the fermentation process. Lactiplantibacillus plantarum, a dominant species in the fermentation of Chinese baijiu, has become a prominent research focus. In this study, we selected well-characterized pure cultures of microorganisms to construct diverse chassis microflora. The primary objective was to investigate the effects of L. plantarum on the fermentation process of Chinese baijiu and its association with metabolites produced by different chassis microflora. Our results demonstrated that the concentrations of ethyl lactate and other volatile aromatic compounds increased in all fermentation protocols where L. plantarum was added. The addition of L. plantarum also significantly increased the concentration of total organic acids, particularly lactic acid, which rose by 17 to 123 times. Furthermore, L. plantarum helped maintain the stability of ethanol concentration during the middle and late stages of fermentation. Notably, among the three different chassis microbial fermentation protocols involving L. plantarum, the protocol with the highest microbial diversity exhibited a greater capacity to produce lactic acid (1.56 ± 0.19 mg/g), ethanol (5.74 ± 0.47 mg/g), and reducing sugars (6.39 ± 0.31 mg/g). These findings provide valuable insights into the potential of L. plantarum for modulating the flavor of Chinese baijiu.

Effect of Organic Acid Addition Before Fermentation on the Physicochemical and Sensory Properties of Cherry Wine

Lack of acidity is the main reason for the spoilage of cherry wine, and for insufficient aroma and mouthfeel. In this study, the initial acidity of cherry purees was adjusted to 3.50, 4.15, 4.80 and 5.45 g/kg by using malic acid, lactic acid and a mixture of the two before fermentation. And the effects of different organic acid additions on the physicochemical profiles and sensory properties of cherry wines were investigated. Our findings suggest that organic acid addition can inhibit the formation of volatile acid and enhance ethanol production, while having a negative effect on their polyphenol contents. These additions can be utilized as carbon sources during cherry wine fermentation and affect its metabolism. Among them, the application of malic acid with lactic acid was shown to have more metabolically active effects on non-volatile compounds, and enhanced the total volatile organic compounds by 14.04%-66.92%. MC-4.80 and MLC-4.80 had the highest total VOC content and odor score in the sensory evaluation. However, the addition of large amounts of acids reduced the acidity score and overall acceptability of cherry wine. In conclusion, adjusting the initial acid content to 4.15 g/kg before fermentation significantly improved the quality of cherry wines, and the combination of malic acid and lactic acid was more effective for cherry winemaking. This finding evidenced that organic acid addition could be an effective strategy for improving the quality of cherry wines.

Succession of microbial community structure in fermented grains during the fermentation of strong-flavor Baijiu and its impact on the metabolism of acids, alcohols, and esters

The study clarified the succession of microbial community structures in fermented grains (FG) and their association with flavor compounds, along with their potential metabolic functions. The community diversity, functional genera and metabolites in FG were investigated by polyphasic detecting approaches. There are 13 dominant microorganisms in FG (relative abundance > 1%). Moisture and acidity are the key indicators driving the succession of microbial communities in FG. Eight kinds of microorganisms were involved in the metabolism of acid, higher alcohols and ethanol in FG and the abundance of pyruvate dehydrogenase and lactate dehydrogenase were significantly higher than other enzymes (P < 0.05). The results showed that 23 main flavor compounds were the results of the interaction of dominant microorganisms in FG. This study provides a basis for the formation of flavor substances in strong-flavor Baijiu.

Difference between traditional brewing technology and mechanized production technology of jiangxiangxing baijiu: Micro ecology of zaopei, physicochemical factors and volatile composition

Mechanized production of Jiangxiangxing Baijiu (JB) stands as a pivotal trend in today's Baijiu industry. This study, employing high-throughput sequencing and headspace solid phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) technology, comprehensively analyzed the micro ecology, physicochemical factors, and volatile components during pit fermentation, comparing traditional fermentation Zaopei (TZP) and mechanized fermentation Zaopei (MZP). According to the research findings, the dominant microorganisms in the fermentation process of ZP comprise Lactobacillus, Monascus, Issatchenkia, and Zygosaccharomyces. In addition, functional microorganisms like Zygosaccharomyces, Monascus, Issatchenkia, Leiothecium, Candida, Pichia, and others exhibited differences on day 0 and throughout the fermentation process. These differences are attributed to the effects of distinct fermentation environment and physicochemical factors. Furthermore, comprehensive analysis detected 87 volatile compounds in TZP and MZP, with 56 showing significant differences, primarily including alcohols, aldehydes, ketones, acids, esters, and aromatics. Additionally, fermentation can be classified into two phases based on ethanol and volatile compounds production: the initial phase (0-12 days, P1) primarily focuses on alcohols production, while the subsequent phase (12-30 days, P2) concentrates on volatile compounds generation. The subsequent correlation analysis indicates that variations in volatile compounds primarily arise from shifts in microbial composition, with notable differences observed in fungi, specifically Monascus, Zygosaccharomyces, and Issatchenkia, which drive the disparities in volatile compounds. This study provides an important theoretical basis and practical guidance for the realization of mechanized high-quality production of JB.

Microbial interactions in mixed-species biofilms on the surfaces of Baijiu brewing environments

Environmental microorganisms commonly inhabit dense multispecies biofilms, fostering mutualistic relationships and co-evolution. However, the mechanisms underlying biofilm formation and microbial interactions within the Baijiu fermentation microecosystem remain poorly understood. Hence, the objective of this study was to investigate the composition, structure, and interactions of microorganisms residing in biofilms on environmental surfaces in Baijiu production. The results revealed a shift in the bacteria-fungi interaction network following fermentation, transitioning from a cooperative/symbiotic relationship to a competitive/antagonistic dynamic. Core microbiota within the biofilms comprised lactic acid bacteria (LAB), yeast, and filamentous fungi. From the environmental surface samples, we isolated two strains of LAB (Lactiplantibacillus pentosus EB27 and Pediococcus pentosaceus EB35) and one strain of yeast (Pichia kudriavzevii EF8), all displaying remarkable biofilm formation and fermentation potential. Co-culturing LAB and yeast demonstrated a superior capacity for dual-species biofilm formation compared to mono-species biofilms. The dual-species biofilm displayed a two-layer structure, with LAB in the lower layer and serving as the foundation for the yeast community in the upper layer. The upper layer exhibited a dense distribution of yeast, enhancing aerobic respiration. Metabolic activities in the dual-species biofilm, such as ABC transporter, oxidative phosphorylation, citric acid cycle, sulfur metabolism, glycine, serine, threonine metabolism, lysine degradation, and cysteine and methionine metabolism, showed significant alterations compared to LAB mono-species biofilms. Moreover, bacterial chemotaxis, starch, and sucrose metabolism in the dual-species biofilm exhibited distinct patterns from those observed in the yeast mono-species biofilm. This study demonstrated that a core microbiota with fermentation potential may exist in the form of a biofilm on the surface of a Baijiu brewing environment. These findings provide a novel strategy for employing synthetic stable microbiotas in the intelligent brewing of Baijiu.

Seasonal dynamics of the microbial community in a strong-flavor baijiu fermentation

BACKGROUND

The microbial community plays a crucial role in Chinese strong-flavor baijiu (SFB) fermentation. However, the seasonal dynamics of the microbial community in the SFB fermentation system and its contribution to the unique flavor of SFB have not been fully elucidated. In this study, we investigated the seasonal dynamics of the microbial community through 16S rRNA and ITS gene sequencing.

RESULTS

The results revealed significant temporal dynamics of microbial communities and environmental variables throughout the four seasons. The influence of seasons on fungal communities was found to be more significant than on bacterial communities. The diversity of bacteria was higher during the winter and summer, whereas fungal diversity was more prominent in summer and autumn. Stochastic processes maintained their dominance in microbial assembly throughout all four seasons but the significance of heterogeneous selection increased during summer for both bacteria and fungi, whereas homogeneous selection became more pronounced during winter for fungi. The pH and environmental temperature were important drivers of microbial community assembly across different seasons, primarily impacting the core genera responsible for the production of major volatile flavor compounds (VFCs), especially ethyl caproate.

CONCLUSION

These findings provide new insights into the impact of seasons on microbial communities and hold promise for improving the quality-control measures for SFB brewed in different seasons. © 2024 Society of Chemical Industry.

Screening of a Saccharomyces cerevisiae Strain with High 3-Methylthio-1-Propanol Yield and Optimization of Its Fermentation Conditions

3-Methylthio-1-propanol (3-Met) is an important flavor compound in various alcoholic beverages such as Baijiu and Huangjiu. To maintain the content of 3-Met in these alcoholic beverages, it is necessary to screen a micro-organism with high yield of 3-Met from the brewing environment. In this study, the ability of yeast strains from the Baijiu brewing to produce 3-Met was analyzed, aiming to obtain yeast with high-yield 3-Met, and its fermentation conditions were optimized. Firstly, 39 yeast strains were screened using 3-Met conversion medium. The results showed that the majority of the strains from Baijiu brewing sources could produce 3-Met, and nearly half of the strains produced more than 0.5 g/L of 3-Met. Among these, yeast F10404, Y03401, and Y8#01, produced more than 1.0 g/L of 3-Met, with yeast Y03401 producing the highest amount at 1.30 g/L. Through morphological observation, physiological and biochemical analysis, and molecular biological identification, it was confirmed that yeast Y03401 was a Saccharomyces cerevisiae. Subsequently, the optimal fermentation conditions for 3-Met production by this yeast were obtained through single-factor designs, Plackett-Burman test, steepest ascent path design and response surface methodology. When the glucose concentration was 60 g/L, yeast extract concentration was 0.8 g/L, L-methionine concentration was 3.8 g/L, initial pH was 4, incubation time was 63 h, inoculum size was 1.6%, shaking speed was 150 rpm, loading volume was 50 mL/250 mL, and temperature was 26 °C, the content of 3-Met produced by S. cerevisiae Y03401 reached a high level of 3.66 g/L. It was also noteworthy that, in contrast to other study findings, this yeast was able to create substantial amounts of 3-Met even in the absence of L-methionine precursor. Based on the clear genome of S. cerevisiae and its characteristics in 3-Met production, S. cerevisiae Y03401 had broad prospects for application in alcoholic beverages such as Baijiu.

Screening, Identification, and Fermentation Condition Optimization of a High-Yield 3-Methylthiopropanol Yeast and Its Aroma-Producing Characteristics

A high-yield 3-methylthiopropanol (3-Met) yeast Y1402 was obtained from sesame-flavored Daqu, and it was identified as Saccharomycopsis fibuligera. S. fibuligera Y1402 showed a broad range of growth temperatures and pH, as well as the maximum tolerance to glucose, NaCl, nicotine, and 3-Met at 50% (w/w), 15% (w/v), 1.2 g/L, and 18 g/L, respectively. After optimization using single-factor experiments, a Plackett-Burman design, a steepest ascent test, and a Box-Behnken design, the 3-Met yield reached 4.03 g/L by S. fibuligera Y1402 under the following optimal conditions: glucose concentration of 40 g/L, yeast extract concentration of 0.63 g/L, Tween 80 concentration of 2 g/L, L-methionine concentration of 5 g/L, liquid volume of 25 mL/250 mL, initial pH of 5.3, fermentation temperature of 32 °C, inoculum size of 0.8%, shaking speed of 210 rpm, and fermentation time of 54 h. The fermentation was scaled up to a 3 L fermenter under the optimized conditions, and the yield of 3-Met reached 0.71 g/L. Additionally, an aroma analysis revealed that the flavor substances produced by S. fibuligera Y1402 in sorghum hydrolysate medium was mainly composed of compounds with floral, sweet, creamy, roasted nut, and clove-like aromas. Therefore, S. fibuligera has great potential for application in the brewing of Baijiu and other fermented foods.

Comparison of the Correlations of Microbial Community and Volatile Compounds between Pit-Mud and Fermented Grains of Compound-Flavor Baijiu

The microbial composition and volatile components of fermented grains (FG) and pit mud (PM) are crucial for the quality and flavor of compound-flavor baijiu (CFB). The physicochemical indices, culturable microorganisms, microbial communities, and volatile components of FG and PM were analyzed and correlated in our research. Considering FG and PM, amplicon sequencing was used to analyze the microbial community and the volatile components were detected by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME). For FG, redundancy analysis and correlation perfume Circos were used to clarify the correlations between the dominant microbial community and volatile components. The results showed that Aspergillus, Pichia, and Rhizopus were the main fungal microflora in FG and PM, whereas Lactobacillus and Bacillus were the dominant bacteria in FG, and Methanosarcina and Clostridium sensu stricto 12 were the dominant bacteria in the PM. The microbial community and volatile compounds in the CB sampled from the bottom layers of the FG were greatly affected by those in the PM. There were 32 common volatile components in CB and PM. For FG, most of the volatile components were highly correlated with Lactobacillus, Bacillus, Aspergillus, Pichia, and Monascus, which includes alcohols, acids and esters. This study reveals correlations between microbial composition, volatile components, and the interplay of FG and PM, which are conducive to optimizing the fermentation process and improving the quality of CFB base.

Synthesis of an autochthonous microbial community by analyzing the core microorganisms responsible for the critical flavor of bran vinegar

Traditional bran vinegar brewing unfolds through natural fermentation, a process driven by spontaneous microbial activity. The unique metabolic activities of various microorganisms lead to distinct flavors and qualities in each batch of vinegar, making it challenging to consistently achieve the desired characteristic flavor compounds. Therefore, identifying the critical microbial species responsible for flavor production and designing starter cultures with improved fermentation efficiency and characteristic flavors are effective methods to address this discrepancy. In this study, 11 core functional microbial species affecting the fermentation flavor of Sichuan shai vinegar (Cupei were placed outside solarization and night-dew for more than one year, and vinegar was the liquid leached from Cupei) (SSV), were revealed by combining PacBio full-length diversity sequencing based on previous metagenomics. The effects of environmental factors and microbial interactions on the growth of 11 microorganisms during fermentation were verified using fermentation experiments. Ultimately, the microbial community was strategically synthesized using a 'top-down' approach, successfully replicating the distinctive flavor profile of Sichuan shai vinegar (SSV). The results showed that the interaction between microorganisms and environmental factors affected microorganism growth. Compared with traditional fermentation, the synthetic microbial community's vinegar-fermented grains (Cupei) can reproduce the key flavor of SSV and is conducive to the production of amino acids. In this study, the key flavor of SSV was reproduced through rational design of the synthetic microbial community. This achievement holds profound significance for the broader application of microbiome assembly strategies in the realm of fermented foods.

Exploring the impact of initial moisture content on microbial community and flavor generation in Xiaoqu baijiu fermentation

Moisture is essential in microbiota succession and flavor formation during baijiu fermentation. However, it remains unknown how moisture content affects microbiota, metabolism, and their relationship. Here, we compared the difference in volatiles, microbiota characteristics, and potential functions with different initial moisture contents (50 %, 55 %, 60 %, 65 %, 70 %). Results showed that the ratio of ethyl acetate to ethyl lactate and total volatile compounds content increased as the moisture content was elevated from 50 % to 70 %. As increasing moisture content, fermentation system microbiota dominated by Lactobacillus was formed more rapidly. Lactobacillus, Dekkera, and Pediococcus were positively correlated with moisture, promoting the production of propanol, acetic acid, butyric acid, and 2-butanol. The complexity and stability of ecological networks enhanced as moisture content increased (R2 = 0.94, P = 0.004). Our study revealed that moisture-drive microbiota was a critical contributor to flavor formation, providing the theoretical basis for moisture control to regulate flavor compounds.

Exploring the Role of Active Functional Microbiota in Flavor Generation by Integrated Metatranscriptomics and Metabolomics during Niulanshan Baijiu Fermentation

Active functional microbiota for producing volatile flavors is critical to Chinese baijiu fermentation. Microbial communities correlated with the volatile metabolites are generally explored using DNA-based sequencing and metabolic analysis. However, the active functional microbiota related to the volatile flavor compounds is poorly understood. In this study, an integrated metatranscriptomic and metabolomics analysis was employed to unravel the metabolite profiles comprehensively and the contributing active functional microbiota for flavor generation during Niulanshan baijiu fermentation. A total of 395, 83, and 181 compounds were annotated using untargeted metabolomics, including LC-MS, GC-MS, and HS-SPME-GC-MS, respectively. Significant variances were displayed in the composition of compounds among different time-point samples according to the heatmaps and orthogonal partial least-square discriminant analysis. The correlation between the active microbiota and the volatile flavors was analyzed based on the bidirectional orthogonal partial least squares discriminant analysis (O2PLS-DA) model. Six bacterial genera, including Streptococcus, Lactobacillus, Pediococcus, Campylobacter, Yersinia, and Weissella, and five fungal genera of Talaromyces, Aspergillus, Mixia, Rhizophagus, and Gloeophyllum were identified as the active functional microbiota for producing the volatile flavors. In summary, this study revealed the active functional microbial basis of unique flavor formation and provided novel insights into the optimization of Niulanshan baijiu fermentation.

Unravelling Metabolic Heterogeneity of Chinese Baijiu Fermentation in Age-Gradient Vessels

Fermentation vessels affect the characteristics of food fermentation; however, we lack an approach to identify the biomarkers indicating fermentation. In this study, we applied metabolomics and high-throughput sequencing analysis to reveal the dynamic of metabolites and microbial communities in age-gradient fermentation vessels for baijiu production. Furthermore, we identified 64 metabolites during fermentation, and 19 metabolites significantly varied among the three vessels (p < 0.05). Moreover, the formation of these 19 metabolites were positively correlated with the core microbiota (including Aspergillus, Saccharomyces, Lactobacillus, and Bacillus). In addition, ethyl lactate or ethyl acetate were identified as the biomarkers for indicating the metabolism among age-gradient fermentation vessels by BP-ANN (R2 > 0.40). Therefore, this study combined the biological analysis and predictive model to identify the biomarkers indicating metabolism in different fermentation vessels, and it also provides a potential approach to assess the profiling of food fermentations.

Effect of lactic acid bacteria on the structure and potential function of the microbial community of Nongxiangxing Daqu

OBJECTIVES

The microbial community structure of the saccharifying starter, Nongxiangxing Daqu(Daqu), is a crucial factor in determining Baijiu's quality. Lactic acid bacteria (LAB), are the dominant microorganisms in the Daqu. The present study investigated the effects of LAB on the microbial community structure and its contribution to microbial community function during the fermentation of Daqu.

METHODS

The effect of LAB on the structure and function of the microbial community of Daqu was investigated using high-throughput sequencing technology combined with multivariate statistical analysis.

RESULTS

LAB showed a significant stage-specific evolution pattern during Daqu fermentation. The LEfSe analysis and the random forest learning algorithm identified LAB as vital differential microorganisms during Daqu fermentation. The correlation co-occurrence network showed aggregation of LAB and Daqu microorganisms, indicating LAB's significant position in influencing the microbial community structure, and suggests that LAB showed negative correlations with Bacillus, Saccharopolyspora, and Thermoactinomyces but positive correlations with Issatchenkia, Candida, Acetobacter, and Gluconobacter. The predicted genes of LAB enriched 20 functional pathways during Daqu fermentation, including Biosynthesis of amino acids, Alanine, aspartate and glutamate metabolism, Valine, leucine and isoleucine biosynthesis and Starch and sucrose metabolism, which suggested that LAB had the functions of polysaccharide metabolism and amino acid biosynthesis.

CONCLUSION

LAB are important in determining the composition and function of Daqu microorganisms, and LAB are closely related to the production of nitrogenous flavor substances in Daqu. The study provides a foundation for further exploring the function of LAB and the regulation of Daqu quality.

Stochastic Processes Drive the Assembly and Metabolite Profiles of Keystone Taxa during Chinese Strong-Flavor Baijiu Fermentation

Multispecies communities participate in the fermentation of Chinese strong-flavor Baijiu (CSFB), and the metabolic activity of the dominant and keystone taxa is key to the flavor quality of the final product. However, their roles in metabolic function and assembly processes are still not fully understood. Here, we identified the variations in the metabolic profiles of dominant and keystone taxa and characterized their community assembly using 16S rRNA and internal transcribed spacer (ITS) gene amplicon and metatranscriptome sequencing. We demonstrate that CSFB fermentations with distinct metabolic profiles display distinct microbial community compositions and microbial network complexities and stabilities. We then identified the dominant taxa (Limosilactobacillus fermentum, Kazachstania africana, Saccharomyces cerevisiae, and Pichia kudriavzevii) and the keystone ecological cluster (module 0, affiliated mainly with Thermoascus aurantiacus, Weissella confusa, and Aspergillus amstelodami) that cause changes in metabolic profiles. Moreover, we highlight that the alpha diversity of keystone taxa contributes to changes in metabolic profiles, whereas dominant taxa exert their influence on metabolic profiles by virtue of their relative abundance. Additionally, our results based on the normalized stochasticity ratio (NST) index and the neutral model revealed that stochastic and deterministic processes together shaped CSFB microbial community assemblies. Stochasticity and environmental selection structure the keystone and dominant taxa differently. This study provides new insights into understanding the relationships between microbial communities and their metabolic functions. IMPORTANCE From an ecological perspective, keystone taxa in microbial networks with high connectivity have crucial roles in community assembly and function. We used CSFB fermentation as a model system to study the ecological functions of dominant and keystone taxa at the metabolic level. We show that both dominant taxa (e.g., those taxa that have the highest relative abundances) and keystone taxa (e.g., those taxa with the most cooccurrences) affected the resulting flavor profiles. Moreover, our findings established that stochastic processes were dominant in shaping the communities of keystone taxa during CSFB fermentation. This result is striking as it suggests that although the controlled conditions in the fermentor can determine the dominant taxa, the uncontrolled rare keystone taxa in the microbial community can alter the resulting flavor profiles. This important insight is vital for the development of potential manipulation strategies to improve the quality of CSFB through the regulation of keystone species.

Screening of Yeasts Isolated from Baijiu Environments for Producing 3-Methylthio-1-propanol and Optimizing Production Conditions

3-Methylthio-1-propanol (3-Met) is widely used as a flavoring substance and an essential aroma ingredient in many foods. Producing 3-Met by microbial transformation is green and eco-friendly. In the present study, one strain, YHM-G, which produced a high level of 3-Met, was isolated from the Baijiu-producing environment. Strain YHM-G was identified as Hyphopichia burtonii according to its morphological properties, physiological and biochemical characteristics, and ribosomal large subunit 26S rRNA gene D1/D2 domain sequence analysis. The optimal conditions for 3-Met production by YHM-G were obtained by single factor design, Plackett-Burman design, steepest ascent path design and response surface methodology as follows: 42.7 g/L glucose, pH 6, 0.9 g/L yeast extract, 6 g/L L-methionine (L-Met), culture temperature 28 °C, shaking speed 210 rpm, loading volume 50 mL/250 mL, inoculum size 0.5% (v/v), culturing period 48 h and 2.5 g/L Tween-80. Under these optimal conditions, the 3-Met production by strain YHM-G was 3.16 g/L, a value 88.1% higher than that before optimization. Strain YHM-G can also produce a variety of flavor compounds that are important for many foods. This strain thus has the potential to increase the abundance of 3-Met in some fermented foods and enhance their aroma profiles.