Exploring the controllability of the Baijiu fermentation process with microbiota orientation

Machine learning-enhanced flavoromics: Identifying key aroma compounds and predicting sensory quality in sauce-flavor baijiu

The quality of Sauce-flavor baijiu hinges on sensory characteristics and key aroma compounds, which traditional methods struggle to evaluate accurately and effectively. This study explores the sensory characteristics and aroma compounds of Sauce-flavor baijiu across different rounds using flavoromics and machine learning, constructing quality grade prediction models. Sensory characteristics shift from acid in the early stages BJ1-BJ2 rounds to sauce in the mid-stages BJ3-BJ5 rounds and caramel in the late stages BJ6-BJ7 rounds. Employing AEDA and OAV analyses, 18 key odor-active compounds were identified, such as ethyl butyrate, ehyl isovalerate, and phenethyl acetate. Additionally machine learning models combined with clustering algorithms achieved high accuracy in predicting quality grades: 85 % (MLP+ HCA), 97 % (XGBoost+ K-means), and 84 % (Random Forest+ GMM). The SHAP model identified 20 key aroma compounds, including diethyl succinate, Tetramethylpyrazine, and Acetaldehyde, determining quality concentration thresholds. This study offers robust methods for baijiu flavor control and quality evaluation.

Effect of Saccharomyces cerevisiae inoculation on the co-fermentation of Clostridium kluyveri and Clostridium tyrobutyricum: A strategy for controlling acidity and enhancing aroma in strong-flavor Baijiu

Microbial synergistic fermentation plays a vital role in the intelligent brewing and industrial upgrading of the Chinese traditional Baijiu fermentation industry. In this study, a chain-elongating microbial assemblages consisting of Clostridium and varying proportions of S. cerevisiae was applied to a solid-state simulated fermentation system to validate its functionality during strong-flavor Baijiu fermentation. The addition of S. cerevisiae promoted the hydrolysis of fermented grains and reduced the acidity compared with Clostridium biofortification (Group CFE; P < 0.05). The most significant enhancement in volatile flavor substances was achieved by the addition of S. cerevisiae at a high proportion (Group SFB), where the yields of ethyl hexanoate, phenylethyl alcohol, and ethanol increased by 191.2 %, 109.8 %, and 59.7 %, respectively. The OPLS-DA model (R2X = 0.976, Q2 = 0.992) identified seven volatile flavor substances that effectively distinguished the different co-fermented grains (VIP > 1, P < 0.05). S. cerevisiae accelerated the enrichment of Lentilactobacillus, Lactiplantibacillus, Loigolactobacillus, and Clostridium_sensu_stricto_12. Metabolic pathway and correlation analysis revealed that S. cerevisiae provides endogenous ethanol to chain-elongating microorganisms, and this fungal-bacterial synergistic fermentation enhances the reverse β-oxidation pathway, ultimately contributing to the production of volatile flavor substances. Overall, the microbial assembly pattern of chain-elongating microbial assemblages will help achieve quality enhancement and intelligent control by increasing the production of flavor ethyl esters and ethanol for Baijiu solid-state fermentation system.

The discrepancy in amino acids within high-temperature Daqu: A novel metabolic marker for the quality evaluation of Daqu

Mechanical pressing in Daqu production has introduced quality-affecting variations. Up to now, clear elucidation has not yet been applied to the mechanisms behind this phenomenon, and the determinants of Daqu quality are not yet completely excavated. For this reason, the physicochemical factors, enzyme activity, metabolites, and microbial communities were compared between the mechanical Daqu (MDQ) and traditional Daqu (TDQ) in this paper. The results showed significant differences in amino acids between MDQ and TDQ, with arginine being the key differentiator. High temperature, high moisture, and low acidity were crucial to Daqu's amino acid richness. Additionally, mechanical pressing affected core community stability. Bacillus was the primary biological factor for the discrepancy in amino acids. Further investigation indicated that arginine contributed to the reduction of lactic acid and higher alcohols in Jiupei, confirming that amino acids were potential novel markers affecting the quality of Daqu.

Assembly of a lignocellulose-degrading synthetic community from the strong-flavor Daqu by a stepwise method

The lignocellulose in Daqu plays an important role during the Baijiu fermentation, such as providing energy for microbial metabolism and precursors for flavor compounds. However, due to the complexity of the Daqu microbial community and the fermentation environment, the regulation of lignocellulose degradation efficiency is limited. In such cases, artificial intervention can be achieved through the application of synthetic communities. Here, we studied the structure of the lignocellulose-degrading microbial communities in Daqu. Based on the characteristics of lignocellulose composition, we developed three high-throughput screening methods and used a stepwise assembly approach to construct a synthetic community composed of Bacillus stercori, Bacillus paramycoides, Klebsiella pneumoniae, and Cyberlindnera fabianii. After fermentation, 54.71 % of the bran was degraded and 11 substances were uniquely produced. 4-vinylguaiacol and 2-ethyl-3,5(6)-dimethylpyrazine were considered to be the key aroma compounds of the synthetic community. This synthetic community offers a new approach to control Daqu fermentation.

Application of indigenous Saccharomycopsis fibuligera for light-flavor Baijiu fermentation: Changes of microbial community and flavor metabolism

Ethyl acetate, a characteristic flavor compound in light-flavor Baijiu (LFB), plays a pivotal role in defining its sensory profile. Insufficient concentrations in fermented grains may diminish the quality of Baijiu. Indigenous microbial bioaugmentation has proven effective in improving Baijiu quality by reshaping microbial community and modulating flavor metabolism within fermentation ecosystems. This study investigated the effects of Jiuqu fortified with an indigenous Saccharomycopsis fibuligera Y162 on the microbial community, physicochemical parameters, and volatile compound profiles throughout the fermentation of LFB. Results demonstrated a significant increase in ethyl acetate content in both original Baijiu and fermented grains, alongside pronounced fungal community restructuring. PacBio single-molecule real-time (SMRT) sequencing analysis showed that Lactobacillus helveticus, Rhizopus sp., Saccharomyces cerevisiae, and Issatchenkia orientalis became the dominant species at the end of fermentation. Correlation network analysis revealed that ethyl acetate was significantly related (P < 0.05, |ρ| > 0.7) to the I. orientalis and Rhizopus sp. (the main fungal biomarkers), which was driven by the functional S. fibuligera. Mantel test further highlighted acidity, temperature, and moisture as critical environmental factors influencing the microbial community (P < 0.05, |ρ| > 0.7). To summarize, biofortification with S. fibuligera exhibited positive effects in enhancing typical flavor metabolites by influencing fungal community structure in LFB. These findings imply that the indigenous strains have great application potential in improving the quality of Baijiu.

Identification of the saccharifying microbiota based on the absolute quantitative analysis in the batch solid-state fermentation system

The fermentation process of Chinese baijiu, a distinctive example of batch solid-state fermentation (BSSF), involves the recurrent use of the same raw material to optimize starch utilization. However, it is unclear which microorganisms are able to metabolize low concentration starch effectively. In this study, we successfully identified the key saccharifying microbiota that degraded low-concentration starch in the BSSF system by absolute quantification techniques. The results indicated a 61.93 % enhancement in the efficient utilization of starch, absolute quantification combined with correlation analysis revealed that Geotrichum, Aspergillus, Bacillus, Candida, and Kroppenstedtia were the saccharifying microbiota, with relative abundances exceeding 10 % during fermentation. In the KEGG metabolic pathway, these five saccharifying microbiota had a complete metabolic pathway for degrading starch to d-glucose-1p and d-glucose, including eight related enzymes: maltose phosphorylase, α-amylase, glucoamylase, oligo-1,6-glucosidase, α-glucosidase, pullulanase, α-glucosidase, and maltogenic α-amylase. These studies showed that the saccharifying microbiota can co-degrade starch by multiple saccharifying enzymes, thus improving the utilization of starch substrates.

Two new arthroconidial yeast species from bark and pit mud in China

A study on yeast species from the genera Geotrichum and Magnusiomyces in southwest and central China was conducted based on morphological and molecular phylogenetic analyses using the ITS region and the D1/D2 domain of the LSU rRNA gene. The research identified two new yeast species: Geotrichumhubeiense and Magnusiomycespitmudophilus. The study contributed to understanding arthroconidial yeast diversity in fermentation and natural environments and paved the way for future taxonomic and ecological studies. Descriptions, illustrations, and phylogenetic analysis results of the two new taxa are provided.

Identification of Oligopeptides in the Distillates from Various Rounds of Soy Sauce-Flavored Baijiu and Their Effect on the Ester-Acid-Alcohol Profile in Baijiu

Endogenous peptides in Baijiu have primarily focused on finished liquor research, with limited attention given to the peptides in base liquor prior to blending. Liquid chromatography-tandem mass spectrometry (LC-MS) was employed to identify endogenous peptides in the distillates from the first to seventh rounds of soy sauce-flavored Baijiu. Two hundred and five oligopeptides were identified from these distillates, all of which had molecular weights below 1000 Da and were composed of amino acid residues associated with flavor (sweet, sour, and bitter) and biological activity. Furthermore, full-wavelength scanning, content determination of the main compounds, and molecular docking were performed to analyze these oligopeptides' effect on the ester-acid-alcohol profile in Baijiu. This determination revealed a negative correlation between the peptide content and total ester content (r = -0.691), as well as the total acid content (r = -0.323), and a highly significant negative correlation with ethanol content (r = -0.916). Notably, the screened peptides (TRH, YHY, RQTQ, PLDLTSFVLHEAI, KHVS, LPQRHRMVYSLL, and NEWH) had specific interactions with the major flavor substances via hydrogen bonds, including esters (ethyl acetate, ethyl butanoate, ethyl hexanoate, and ethyl lactate), acids (acetate acid, butanoate acid, hexanoate acid, lactate acid), and alcohols (ethanol, 1-propanol, 1-butanol, and 1-hexanol). These findings elucidate the distribution and dynamic changes of endogenous peptides in the distillates from various rounds of soy sauce-flavored Baijiu, providing a theoretical foundation for further investigation into their interaction mechanisms associated with flavor compounds.

Metagenomic and metabolomic profiling analyses to unravel the formation mechanism of n-propanol during the first and second round of Jiangxiangxing Baijiu fermentation

N-propanol is one of the higher alcohols, a moderate amount of n-propanol is beneficial for the harmony of the liquor body, whereas excessive or repeated intake will lead to discomfort and pose significant harm to human health. In actual production process of Jiangxiangxing Baijiu, the n-propanol content of the base baijiu in first round (FR) is far higher than that of second round (SR). Nevertheless, the formation mechanism and the key n-propanol producing microbials remain unclear and this limits the quality control of baijiu fermentation. Here, we combined metagenomics and metabolomics to verify the biosynthesis pathway of n-propanol and to identify characteristic microorganisms in FR and SR. The results showed that the preliminary period of pit fermentation was critical for the accumulation of n-propanol. FR was enriched in Lactobacillus plantarum, Lactobacillus ponits, Lactobacillus brevis and Lactobacillus panis, while it was harbored greater abundances of Pichia kudriazevii, Saccharomyces cerevisiae and Lactobacillus acetotolerans in SR. Function analysis combined with KEGG providing comprehensive evidence for the main synthetic pathways of n-propanol in Jiangxiangxing baijiu, and L. panis was key microbial. In addition, the experiments of inoculating L. panis and L. acetotolerans in situ indicated L. panis was mainly responsible for n-propanol production while L. acetotolerans not conducive to the production of n-propanol. Besides, the bioturbation effect on microbiota and flavor compounds were also analyzed. These results are useful for elucidating the mechanism of flavor formation in baijiu fermentation and promoting the further application of bioturbation technology in the traditional fermentation industry.

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.

Improving the Quality of Low-grade Tobacco by Enzymatic Treatment and Co-fermentation with Yeast and Lactic Acid Bacteria

Enzymatic treatment is a promising method to modulate the chemical composition, flavoring substances and to enhance the sensory quality of cigarettes. This study investigates the feasibility of enzymatic treatment in conjunction with co-fermentation with yeast and lactic acid bacteria to improve the quality of low-quality cigarettes. Amylase, flavourzyme, glucoamylase, protease, and their combinations were used for the enzymatic treatment of tobacco-sorghum by using the liquid-state fermentation method. The biochemical components and flavor substances of the fermented products were analyzed. The findings show that amylase and glucoamylase can effectively degrade starch into fermentable reducing sugars, facilitate microbial growth and proliferation, and significantly enhance the levels of flavoring alcohols and esters. Flavourzyme and glucoamylase, either individually or combined with amylase, achieved a more balanced distribution of flavor substances in the products. Additionally, flavourzyme was capable of increasing the content of guaiacol, solanesol, and 2-acetylpyrrole in the fermented products, thereby improving the richness and depth of the cigarette flavor. While the protease treatment group showed fewer flavor substances and higher nicotine content, which was detrimental to the quality of cigarettes. When integrating the fermentation products into low-quality cigarettes, flavourzyme and glucoamylase combined with amylase treatment received higher scores in sensory quality evaluations. This study provides a beneficial strategy for effectively improving the quality of low-quality cigarettes.

Machine learning discrimination and prediction of different quality grades of sauce-flavor baijiu based on biomarker and key flavor compounds screening

The quality grade of base Baijiu directly determines the final quality of sauce-flavor Baijiu. However, traditional methods for assessing these grades often rely on subjective experience, lacking objectivity and accuracy. This study used GC-FID, combined with quantitative descriptive analysis (QDA) and odor activity value (OAV), to identify 27 key flavor compounds, including acetic acid, propionic acid, ethyl oleate, and isoamyl alcohol etc., as crucial contributors to quality grade differences. Sixteen bacterial biomarkers, including Komagataeibacter and Acetobacter etc., and 7 fungal biomarkers, including Aspergillus and Monascus etc., were identified as key microorganisms influencing these differences. Additionally, reducing sugar content in Jiupei significantly impacted base Baijiu quality. Finally, 11 machine learning classification models and 9 prediction models were evaluated, leading to the selection of the optimal model for accurate quality grade classification and prediction. This study provides a foundation for improving the evaluation system of sauce-flavor Baijiu and ensuring consistent quality.

Characteristic aroma compounds during the fermentation of Chinese steamed bread fermented with different starters

The characteristic aroma compounds of Chinese steamed bread (CSB) fermented with different starters were studied using HS-SPME-GC/MS, aroma recombination and omission experiments. The dynamic changes of the microbiota and their function and metabolites during fermentation were analyzed using metagenomics and non-targeted metabolomics. Forty-nine volatile flavor compounds were identified, while 5 characteristic aroma-active compounds were investigated in CSB fermented with commercial dry yeast (AQ-CSB), and 10 were investigated in CSB fermented with traditional starter (NY-CSB). Microbial structure and function analysis showed that Saccharomyces cerevisiae dominated during AQ-CSB fermentation and contributed >95% to its KEGG pathways, while Pediococcus pentosaceus, unclassified Pediococcus, Lactobacillus plantarum, Lactobacillus brevis and unclassified Lactobacillus were predominant in NY-CSB and together had an ~96% contribution to these pathways. NY-CSB showed higher metabolic activity during fermentation, and the characteristic metabolites were mainly involved in carbohydrate, amino acid and lipid metabolism. The characteristic aroma compounds were identified and increased the understanding of the contributions of the microbiota. This may be useful for designing starter cultures that produce CSB with desirable aroma properties.

Unraveling the core microorganisms and metabolic pathways related to off-flavor compounds formation during Jiang-flavor Baijiu fermentation

Off-flavor is one of the most frequent and serious causes for the aroma deterioration in Jiang-flavor Baijiu. However, the key compounds and their formation mechanism responsible for off-flavor are still unclear. This study identified 271 volatile compounds from 1 normal and 5 types of off-flavor fermented grains (putrid, rancidity, mud, musty, and burnt) by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry. Using VIP and OAV analysis, 47 key flavor compounds including indole, phenol, isoamyl alcohol, diacetyl, acetic acid, isobutyric acid, and isovaleric acid were found to distinguish normal and off-flavor fermented grains. Furthermore, 40 microbial genera (mainly Monascus, Enterococcus, Dyadobacter, Ottowia, Pseudoxanthomonas, Stenotrophomonas, Pseudomonas, and Xanthomonas) were significantly (p < 0.05, Pearson correlation) related to these 47 compounds. Finally, metabolic pathways for off-flavor compounds formation were constructed. This study provides comprehensive information on the off-flavor compounds and their potential formation mechanism during Jiang-flavor Baijiu fermentation.

Microbial community assembly patterns at the species level in different parts of the medium temperature Daqu during fermentation

Medium-temperature Daqu (MT-Daqu) serves as a crucial saccharifying and fermentation agent in the production of strong-flavor Baijiu. Due to the spatial heterogeneity of solid fermentation, significant differences occurred in the fermentation state and appearance features in different parts of Daqu during fermentation. Currently, the understanding of the underlying mechanism behind this phenomenon remains limited. Here, we analyzed the microbial succession and assembly models and driving factors in different parts of MT-Daqu at the species level based on the PacBio single-molecule real-time sequencing technology. The results showed significantly different bacterial and fungal community compositions, successions, and interaction patterns in different parts of MT-Daqu. The bacterial community composition and succession model in the middle layer were similar to those in the core layer, whereas the fungal community composition and succession model in the surface layer were similar to those in the middle layer. The co-occurrence network analysis showed that microbial interaction is stronger in the middle and core layers than in the surface layer. Analyses based on both niche theory and neutral theory models indicated that deterministic processes predominantly governed the microbial community assembly and these processes played an increasingly important role from the surface to the core layer. Random forest analysis revealed that temperature was the primary endogenous factor driving the bacterial and fungal community assembly. The results of this study contribute to a better understanding of the microbial community in MT-Daqu and are helpful for the quality control of MT-Daqu fermentation.

Exploring Community Succession, Assembly Patterns, and Metabolic Functions of Ester-Producing-Related Microbiota during the Production of Nongxiangxing baijiu

Esters are vital flavor compounds in Chinese Nongxiangxing baijiu and greatly affect the quality of baijiu. Microbial communities inhabiting fermented grains (FGs) have a marked impact on esters. However, the specific microorganisms and their assembly patterns remain unclear. This study utilized high-throughput sequencing and a culture-based method to reveal ester-producing microorganisms. A total of 33 esters were detected, including 19 ethyl esters, 9 linear chain esters, and 2 branched chain esters. A correlation analysis indicated that the bacterial genus Lactobacillus (relative abundance in average: 69.05%) and fungal genera Pichia (2.40%), Aspergillus (11.84%), Wickerhamomyces (0.60%), Thermomyces (3.57%), Saccharomycopsis (7.87%), Issatchenkia (0.96%), and Thermoascus (10.83%) were dominant and associated with esters production and their precursors. The numbers of esters positively correlated with them were 1, 17, 3, 2, 1, 1, 1, and 1, respectively. The modified stochasticity ratio (MST) index and Sloan neutral model revealed that bacteria were predominantly governed by deterministic processes while fungal assemblies were more stochastic. Saturnispora silvae and Zygosaccharomyces bailii were isolated and identified with ester synthesis potential. PICRUSt2 analysis showed that fungi in FG had a high potential for synthesizing ethanol, while 14 enzymes related to esters synthesis were all produced by bacteria, especially enzymes catalyzing the synthesis of acyl-CoA. In addition, ester synthesis was mainly catalyzed by carboxylesterase, acylglycerol lipase and triacylglycerol lipase. These findings may provide insights into ester production mechanism and potential strategies to improve the quality of Nongxiangxing baijiu.

Synthetic microbial communities: A gateway to understanding resistance, resilience, and functionality in spontaneously fermented food microbiomes

This review delves into the intricate traits of microbial communities encountered in spontaneously fermented foods (SFF), contributing to resistance, resilience, and functionality drivers. Traits of SFF microbiomes comprise of fluctuations in community composition, genetic stability, and condition-specific phenotypes. Synthetic microbial communities (SMCs) serve as a portal for mechanistic insights and strategic re-programming of microbial communities. Current literature underscores the pivotal role of microbiomes in SFF in shaping quality attributes and preserving the cultural heritage of their origin. In contrast to starter driven fermentations that tend to be more controlled but lacking the capacity to maintain or reproduce the complex flavors and intricacies found in SFF. SMCs, therefore, become indispensable tools, providing a nuanced understanding and control over fermented food microbiomes. They empower the prediction and engineering of microbial interactions and metabolic pathways with the aim of optimizing outcomes in food processing. Summarizing the current application of SMCs in fermented foods, there is still space for improvement. Challenges in achieving stability and reproducibility in SMCs are identified, stemming from non-standardized approaches. The future direction should involve embracing standardized protocols, advanced monitoring tools, and synthetic biology applications. A holistic, multi-disciplinary approach is paramount to unleashing the full potential of SMCs and fostering sustainable and innovative applications in fermented food systems.

Source and succession of microbial communities and tetramethylpyrazine during the brewing process of compound-flavor Baijiu

Pyrazines are important flavor components and healthy active components in Baijiu, which including tetramethylpyrazine (TTMP). During the brewing process, the traceability of microbial communities and the content distribution characteristics of TTMP are important for improving the quality and style characteristics of compound-flavored Baijiu (CFB). However, the traceability analysis of microorganisms in fermented grains (FG)-used in the production of CFB-lacks quantitative and systematic evaluation. In this study, the microbial communities and TTMP content of Jiuqu (JQ), Liangpei (LP), FG, and pit mud (CP) used in CFB production were characterized; further, coordinate and discriminant analyses were employed to determine differences in microbial communities. Additionally, traceability and correlation analyses were performed to reveal the origin of microbial communities in FG. The source, content, and distribution characteristics of TTMP based on the brewing process have also been discussed. The results showed that most of the bacterial and fungal communities at different levels of FG came from other sources, and the microorganisms of Cladosporium, Acetobacter, Aspergillus, Methanosarcina, and Bacillus were considered have a osculating correlations with TTMP content of FG. Taken together, this study provides insights into the origin of microbial communities in FG and the distribution characteristics of TTMP based on the CFB brewing process. The current findings are conducive for optimizing the fermentation process and improving the quality and style characteristics of CFB.

Targeted microbial collaboration to enhance key flavor metabolites by inoculating Clostridium tyrobutyricum and Saccharomyces cerevisiae in the strong-flavor Baijiu simulated fermentation system

Ethyl hexanoate and ethyl butyrate are indispensable flavor metabolites in strong-flavor Baijiu (SFB), but batch production instability in fermenting grains can reduce the quality of distilled Baijiu. Biofortification of the fermentation process by designing a targeted microbial collaboration pattern is an effective method to stabilize the quality of Baijiu. In this study, we explored the metabolism under co-culture liquid fermentation with Clostridium tyrobutyricum DB041 and Saccharomyces cerevisiae YS219 and investigated the effects of inoculation with two functional microorganisms on physicochemical factors, flavor metabolites, and microbial communities in solid-state simulated fermentation of SFB for the first time. The headspace solid-phase microextraction-gas chromatography-mass spectrometry results showed that ethyl butyrate and ethyl hexanoate significantly increased in fermented grain. High-throughput sequencing analysis showed that Pediococcus, Lactobacillus, Weissella, Clostridium_sensu_stricto_12, and Saccharomyces emerged as the dominant microorganisms at the end of fermentation. Co-occurrence analysis showed that ethyl hexanoate and ethyl butyrate were significantly correlated (|r| > 0.5, P < 0.05) with a cluster of interactions dominated by lactic acid bacteria (Pediococcus, Lactobacillus, Weissella, and Lactococcus), which was driven by the functional C. tyrobutyricum and S. cerevisiae. Mantel test showed that moisture and reducing sugars were the main physicochemical factor affecting microbial collaboration (|r| > 0.7, P < 0.05). Taken together, the collaborative microbial pattern of inoculation with C. tyrobutyricum and S. cerevisiae showed positive results in enhancing typical flavor metabolites and the synergistic effects of microorganisms in SFB.

Organic-Acid-Sensitive Visual Sensor Array Based on Fenton Reagent-Phenol/Aniline for the Rapid Species and Adulteration Assessment of Baijiu

Baijiu is an ancient, distilled spirit with a complicated brewing process, unique taste, and rich trace components. These trace components play a decisive role in the aroma, taste, and especially the quality of baijiu. In this paper, the redox reaction between the Fenton reagent and four reducing agents, including o-phenylenediamine (OPD), p-phenylenediamine (PPD), 4-aminophenol (PAP), and 2-aminophenol (OAP), was adopted to construct a four-channel visual sensor array for the rapid detection of nine kinds of common organic acids in baijiu and the identification of baijiu and its adulteration. By exploiting the color-changing fingerprint response brought by organic acids, each organic acid could be analyzed accurately when combined with an optimized variable-weighted least-squares support vector machine based on a particle swarm optimization (PSO-VWLS-SVM) model. What is more, this novel sensor also could achieve accurate semi-quantitative analysis of the mixed organic acid samples via partial least squares discriminant analysis (PLSDA). Most importantly, the sensor array could be further used for the identification of baijiu with different species through the PLSDA model and the adulteration assessment with the one-class partial least squares (OCPLS) model simultaneously.

Probiotic Bacillus as fermentation agents: Status, potential insights, and future perspectives

Probiotic Bacillus strains can solve the problems of single flavor and long fermentation time of fermented products caused by the lack of certain functional genes and insufficient metabolism ability of fermenter strains (Lactobacillus and Bifidobacterium) at the present stage. There is a lack of systematic evaluation and review of probiotic Bacillus as food fermentation agents. In this paper, it is observed that probiotic Bacillus strains are involved to varying degrees in liquid-state, semi-solid state, and solid-state fermentation and are widely present in solid-state fermented foods. Probiotic Bacillus strains not only produce abundant proteases and lipases, but also effective antifungal lipopeptides and extracellular polymers, thus enhancing the flavor, nutritional value and safety of fermented foods. Bacillus with probiotic qualities is an underutilized group of probiotic food fermentation agents, which give a potential for the development of fermentation technology in the food business and the integration of ancient traditional fermentation techniques.

Bacterial composition and physicochemical characteristics of sorghum based on environmental factors in different regions of China

The fermentation process for Jiang-flavored baijiu using sorghum as the raw material involves a variety of microorganisms. However, the specific physicochemical characteristics of sorghum and microbial composition on its surface have not been fully elucidated. We aimed to perform a comprehensive comparative analysis of the variations in physicochemical properties and surface microflora in waxy sorghum samples from three prominent production regions in China (Renhuai, Jinsha, and Duyun). Multivariate statistical assessments were conducted that incorporated local soil and climate variables. The results showed that Cyanobacteria, unclassified bacteria, Proteobacteria, Firmicutes, and Bacteroidota were the dominant bacteria in these regions. These bacteria were associated with ethyl acetate, ethyl caprylate, ethyl lactate, and butyl groups, which synergistically produce flavorful compounds. The surface bacterial communities were affected by soil total phosphorus, altitude, diurnal temperature range, monthly mean temperature, precipitation, and effective accumulated temperature. The findings of this study provide a new perspective on microorganisms related to Jiang-flavored baijiu and can help establish a reference for the stability of liquor quality.

Strategies and Challenges of Microbiota Regulation in Baijiu Brewing

The traditional Chinese Baijiu brewing process utilizes natural inoculation and open fermentation. The microbial composition and abundance in the microecology of Baijiu brewing often exhibit unstable characteristics, which directly results in fluctuations in Baijiu quality. The microbiota plays a crucial role in determining the quality of Baijiu. Analyzing the driving effect of technology and raw materials on microorganisms. Elucidating the source of core microorganisms and interactions between microorganisms, and finally utilizing single or multiple microorganisms to regulate and intensify the Baijiu fermentation process is an important way to achieve high efficiency and stability in the production of Baijiu. This paper provides a systematic review of the composition and sources of microbiota at different brewing stages. It also analyzes the relationship between raw materials, brewing processes, and brewing microbiota, as well as the steps involved in the implementation of brewing microbiota regulation strategies. In addition, this paper considers the feasibility of using Baijiu flavor as a guide for Baijiu brewing regulation by synthesizing the microbiota, and the challenges involved. This paper is a guide for flavor regulation and quality assurance of Baijiu and also suggests new research directions for regulatory strategies for other fermented foods.

Unveiling the microbiota of sauce-flavor Daqu and its relationships with flavors and color during maturation

This study investigated the microbial community in three-color sauce-flavor Daqu (black, yellow, and white) throughout their maturation processes, together with their physicochemical factors, culturable microbes, flavor components, and fermenting vitalities. Results from high-throughput sequencing revealed distinct microbial diversity, with more pronounced variations in bacterial community than in fungal community. Firmicutes and Ascomycota emerged as the most dominant bacterial and fungal phyla, respectively, during maturation. Genus-level analysis identified Kroppenstedia, Virgibacillus, and Bacillus as dominant bacteria in black Daqu, yellow Daqu, and white Daqu, severally, while Thermoascus was shared as the core dominant fungi for these Daqu. Physicochemical factors, particularly acidity, were found to exert a significant impact on microbial community. Kroppenstedtia was the key bacteria influencing the color formation of these Daqu. Furthermore, correlations between dominant microbes and flavor compounds highlighted their role in Daqu quality. Molds (Aspergillus, Rhizomucor, and Rhizopus), excepting Bacillus, played a crucial role in the formation of pyrazine compounds. Consequently, this study offers innovative insights into the microbial perspectives on color and pyrazine formation, establishing a groundwork for future mechanized Daqu production and quality control of sauce-flavor baijiu.

Comparative characterization and contribution of key aroma compounds in the typical base liquor of Jiang-flavor Baijiu from different distributions in the Chinese Chishui River basin

The characteristic of typical base liquor is crucial in controlling ultimate quality of Jiang-flavor Baijiu. This study investigates the flavor compounds of three typical base liquors (Jiangxiang, Chuntian, and Jiaodixiang) by LLE/LLME/HS-SPME, gas chromatography-mass spectrometry (GC-MS), gas chromatography-flame ionization detection (GC-FID), sensory analysis, and odor activity value (OAV). Of the 201 main volatile compounds identified, 37 significant compounds distinguished the three typical base liquors. Acid (441.72 ± 0.17 mg/L), alcohol (5388.88 ± 0.55 mg/L), and ester compounds (8181.64 ± 0.15 mg/L) were respectively marked in Jiangxiang, Chuntian, and Jiaodixiang typical base liquors. Orthogonal partial least squares discriminant analysis (OPLS-DA), correlation analysis, and aroma recombination showed that butyric acid (OAV: 102.23), butyl 2-methylbutyrate (OAV: 6045.59), and ethyl caproate (OAV: 418.37) were significantly correlated with sweet, fruity, pit mud, jiang, and ethanol aromas. It identifies the primary constituents that affect flavor variations in the three typical base liquors and provides guidance for investigations on the flavor formation of Jiang-flavor Baijiu.

Synergistic Fermentation with Functional Microorganisms Improves Safety and Quality of Traditional Chinese Fermented Foods

Traditional fermented foods are favored by people around the world for their positive health and taste advantages. Many of the fermented foods, including Chinese traditional fermented foods, are produced through mixed-culture fermentation. Apart from reducing the formation of harmful compounds such as ethyl carbamate (EC) and biogenic amines (BAs) during food fermentation, it is also difficult to precisely control and regulate the fermentation process based on the control of environmental conditions alone, due to the complex microbiota and an unclarified fermentation mechanism. In this review, key microorganisms involved in Chinese fermented foods such as baijiu, soy sauce, and vinegar production are elaborated, and relations between microbial composition and the aroma or quality of food are discussed. This review focuses on the interpretation of functions and roles of beneficial (functional) microorganisms that participate in food fermentation and the discussion of the possibilities of the synergistic use of functional microorganisms to improve the safety and quality of Chinese fermented foods. Conducting work toward the isolation of beneficial microorganisms is a challenge for modern food fermentation technology. Thus, methods for the isolation and mutagenesis of functional microbial strains for synergistic food fermentation are summarized. Finally, the limitations and future prospects of the use of functional microorganisms in traditional Chinese fermented foods are reviewed. This review provides an overview of the applications of synergistic fermentation with functional microorganisms in the improvement of the safety or sensory qualities of fermented foods.