Characteristics of the Microbial Community in the Production of Chinese Rice-Flavor Baijiu and Comparisons With the Microflora of Other Flavors of Baijiu

High-Throughput Sequencing Analysis of Microbiota and Enzyme Activities in Xiaoqu from Seven Provinces in Southern China

Xiaoqu, a pivotal starter in baijiu fermentation, provides the most microflora and enzymes to initiate and maintain baijiu brewing. This study aims to explore the differences in microbiota and enzyme activities among Xiaoqu samples from seven provinces in southern China using high-throughput sequencing, plate isolation, and activity detection. The analyses revealed significant differences in bacterial and fungal communities across the samples. A total of 22 bacterial species and 17 target fungal species were isolated and identified. Predominant bacteria included Bacillus (Bacillus subtilis) and lactic acid bacteria (LABs), while the fungal communities were primarily composed of yeasts (Saccharomyces cerevisiae) and various molds. The activities of α-amylase and glucoamylase varied significantly among the samples, and samples from HN1 and GZ2 exhibited the highest activities. Correlation analyses highlighted the pivotal role of LABs in maintaining acidity and the importance of molds and yeasts in the saccharification and fermentation processes. These findings shed light on the microbial composition and diversity of Xiaoqu and the critical role of microbes in baijiu production. Moreover, they suggested potential microbial resources for developing artificial Xiaoqu via synthetic microbial community in the future, enhancing baijiu fermentation efficiency and overall product quality.

Effects of Saccharomyces cerevisiae and Cyberlindnera fabianii Inoculation on Rice-Flavor Baijiu Fermentation

Rice-flavor baijiu is a distilled Chinese spirit prepared from Xiaoqu culture. However, its dull taste may be a market limitation. In order to enhance the flavor profile of rice-flavor baijiu, two ester-producing yeast strains (Saccharomyces cerevisiae and Cyberlindnera fabianii) were inoculated for fermentation. At the end of the fermentation, the total alcohol and ester contents had also increased by 43.3% and 29.8%, respectively, and the number of ester species had increased by eight. Additionally, eleven flavor substances had significant contributions in the inoculated fermentation process, including several different esters and alcohols. A macrogenomic analysis revealed that the majority of the gene abundances associated with the alcohol, acid, and ester pathways were elevated by the third day of inoculated fermentation, and greater abundances of Saccharomyces cerevisiae, Cyberlindnera fabianii, Lichtheimia ramosa, Rhizopus delemar, and Rhizopus oryzaefive, annotated with these genes, were observed from either the pre-fermentation stage or post-fermentation stage. The results demonstrate that two added strains are associated with an increase in the content of the flavor substances. These findings may prove beneficial in enhancing the quality of rice-flavor baijiu through using inoculated fermentation with ester-producing yeast.

Effect of hydrolyzed soybean on the volatile flavors and microbial community in the traditional brewing process of chi-flavor Baijiu

Addition of soybean in raw materials could improve the flavor of chi-flavor Baijiu (CFB) in production. For investigating the mechanism of flavor improvement during fermentation, the changes of volatile flavors and their relationship with microbial community were analyzed. The results showed that the average contents of lactic and acetic acid in EG (added with hydrolyzed soybean) samples were higher those of CK (without hydrolyzed soybean) samples. The contents of main volatile esters, including ethyl acetate, ethyl palmitate, and ethyl benzoate, in EG samples were higher than those in CK samples at the end of fermentation. The content of alcohols in EG sample was 140.55 mg/L, higher than that in CK sample at the end of fermentation. Especially, the average content of characteristic flavor β-phenylethanol in EG samples increased 17.6% in comparison with that in CK samples during fermentation. Lactobacillus and Pediococcus were the dominant bacterial genera, whereas Saccharomyces, Mortierella, and Trichosporon were dominant fungal genera in both CK and EG samples. Lactobacillus and Weissella confusa showed strong positive correlation with β-phenylethanol, ethyl acetate, and ethyl benzoate. This study provides an in-depth analysis of the effects of hydrolyzed soybeans on the volatile flavor compounds and microbial communities of CFB and theoretical guidance for improving the quality of CFB.

Comprehensive analysis of spatial heterogeneity reveals the important role of the upper-layer fermented grains in the fermentation and flavor formation of Qingxiangxing baijiu

Different spatial positions lead to inconsistent fermentation effects and flavors, however, the spatial heterogeneity of Qingxiangxing (QXX) Baijiu remains unknown. We investigated the microbes, flavors, and physicochemical properties of different layers in fermented grains of QXX Baijiu using Illumina HiSeq sequencing, two-dimensional gas chromatography-mass spectrometry (GC × GC-MS) and ultra-high performance liquid chromatography-mass (UHPLC-MS). A total of 79 volatiles, 1596 metabolites, 50 bacterial genera, and 52 fungal genera were identified. The contents distribution followed the order: upper layer > bottom layer > middle layer. Organic acids and derivatives were the main differential metabolites across the three layers. Starch, pH, and reducing sugar levels increased from the upper to bottom layer. Saccharomyces and Lactobacillus were dominant microbes. Pediococcus, the biomarker of upper layer, showed positive correlations with formic acid, ethyl lactate, acetic acid, ethyl linoleate, and ethyl oleate. These findings deepen our understanding of the fermentation and flavor formation mechanisms of QXX Baijiu.

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.

Metagenomic analysis of core differential microbes between traditional starter and Round-Koji-mechanical starter of Chi-flavor Baijiu

Xiaoqu starter serves as the saccharifying and fermenting agent in the production of Cantonese soybean-flavor (Chi-flavor) Baijiu, and the complex microbial communities determine the flavor and quality of the product. Round-Koji-mechanical starter (produced by using an automated starter-making disk machine) is advantageous as it decreases operator influence, labor costs, and fermentation time, but the product quality is lower compared to traditional starter. Thus, two types of starters (traditional and Round-Koji-mechanical starter) from a Cantonese Baijiu factory were compared in a metagenomic analysis to investigate the differences in microbial community composition and core microbes. The results showed that several core microbes related to carbohydrate metabolism, amino acid metabolism and lipid metabolism, were differentially enriched in the traditional starter. Mucor lusitanicus and Rhizopus delemar were significantly positively correlated with the three key metabolic pathways. Saccharomyces cerevisiae, Cyberlindnera fabianii, Kluyveromyces marxianus, Lactobacillus fermentum, Mucor ambiguous, Rhizopus microspores, Rhizopus azygosporus, Mucor circinelloides, and Ascoidea rubescens were significantly positively correlated with two of the three key metabolic pathways. The results of this study provide a basis for understanding the differential core microbes in traditional and Round-Koji-mechanical starters of Chi-flavor Baijiu, and they also provide guidance for improving Round-Koji-mechanical starter.

Enhancing synthesis of ethyl lactate in rice baijiu fermentation by adding recovered granular cells

Ethyl lactate is the most abundant ester in semi-solid rice baijiu fermentation, affecting the flavor of baijiu to a great extent. The present study aimed to investigate the spatial distribution and formation contributor of ethyl lactate by removing the microorganisms and extracellular enzymes from the upper, middle, and lower fermentation broth during the later fermentation stage. The removal of suspended substances by centrifugation did not affect the ethyl lactate content in the top and middle fermentation broth containing free cells, enzymes, and starch particles. After day 5 of fermentation, only the lower fermentation broth containing granular cells attached to the starch could continue to accumulate lactic acid, thereby increasing the ethyl lactate content. The results showed that the chemical reactions were the main contributor to the increased ethyl lactate content at the anaphase of fermentation rather than enzymatic catalysis or microbial metabolism. Sequencing of granular cells revealed the main lactic acid producers at different fermentation stages. Lactobacillus helveticus showed the highest abundance of 94.45-95.40% on day 5, which decreased to 29.58-30.20% on day 15, while Lactobacillus acetotolerans showed the highest abundance of 47.93-49.72% at day 15. Additionally, the granular cells were recovered and used for supplementary inoculation in the next batch, which significantly increased the ethyl lactate content. This study provided a novel strategy for improving the ethyl lactate content in semi-solid baijiu fermentation.

A review on flavor of Baijiu and other world-renowned distilled liquors

The flavor characteristics of distilled liquors significantly affect consumer acceptance and adoption. Therefore, odorants that contribute to sensory properties have received more attention. The odorants depend on the operating parameters, such as raw materials and ingredients, manufacturing process and maturing circumstances. This review summarized the odorants in the Baijiu and other world-renowned distilled liquors. Especially, the contribution of the odorants to the dominant aroma attributes is given more attention. The variations in the constituents and contents of odorants among the liquors are discussed comprehensively. In general, further research is still needed on the interaction mechanism between the odorants and sensory properties of distilled liquors.

Comparison of fungal communities and flavour substances in surface and inner layers of fermented grains during stacking fermentation of sauce-flavour baijiu

The stacking fermentation process plays a vital role in the production of sauce-flavour baijiu. The aim of this paper is to elucidate the effects of environmental variables on the fungal communities of different layers of fermented grains (zaopei) during the sixth round of stacking and the changes in volatile flavour substances during this process. The composition of the fungal communities in different layers during the stacking fermentation process was analysed. Principal coordinate analysis (pCoA) showed that the dominant fungal communities in different layers differed significantly with the stacking fermentation process. The dominant fungal genera were Thermoascus, Thermomyces and Issatchenkia. The total content of flavouring substances in the surface layer of zaopei were higher, but the types of flavouring substances were less than in the inner layer. The relationship between temperature, moisture content, acidity, starch content and reducing sugar content and microbial community was analysed by Redundancy analysis. The results showed that the correlation between microbial communities and physicochemical indexes in different layers of zaopei varied. The core fungal genera in the surface layer were mainly influenced by acidity, and the microorganisms in the inner layer were more strongly correlated with temperature. Spearman correlation coefficient revealed the correlation between fungal community and volatile flavour substances, and the results showed that microorganisms in different layers of zaopei have different correlations with flavour substances. This study contributes to the understanding of the evolution of different layers fungal communities during the stacking of sauce-flavour baijiu and their relationship with volatile aroma substances.

Environmental Factors Affecting the Diversity and Composition of Environmental Microorganisms in the Shaoxing Rice Wine Producing Area

Shaoxing rice wine is a notable exemplar of Chinese rice wine. Its superior quality is strongly correlated with the indigenous natural environment. The results indicated that Firmicutes (75%), Actinobacteria (15%), Proteobacteria (5%), and Bacteroidetes (3%) comprised the prevailing bacterial groups. Among the main bacterial genera, Lactobacillus was the most abundant, accounting for 49.4%, followed by Lactococcus (11.9%), Saccharopolyspora (13.1%), Leuconostoc (4.1%), and Thermoactinomyces (1.1%). The dominant fungal phyla were Ascomycota and Zygomycota. Among the dominant genera, Saccharomyces (59.3%) prevailed as the most abundant, followed by Saccharomycopsis (10.7%), Aspergillus (7.1%), Thermomyces (6.2%), Rhizopus (4.9%), Rhizomucor (2.2%), and Mucor (1.3%). The findings demonstrate that the structure of the bacterial and fungal communities remains stable in the environment, with their diversity strongly influenced by climatic conditions. The continuous fluctuations in environmental factors, such as temperature, air pressure, humidity, rainfall, and light, significantly impact the composition and diversity of microbial populations, particularly the dominant bacterial community.

Exploration of microbiome diversity of stacked fermented grains by flow cytometry and cell sorting

Sauce-flavor baijiu is one of the twelve flavor types of Chinese distilled fermented product. Microbial composition plays a key role in the stacked fermentation of Baijiu, which uses grains as raw materials and produces flavor compounds, however, the active microbial community and its relationship remain unclear. Here, we investigated the total and active microbial communities of stacked fermented grains of sauce-flavored Baijiu using flow cytometry and high-throughput sequencing technology, respectively. By using traditional high-throughput sequencing technology, a total of 24 bacterial and 14 fungal genera were identified as the core microbiota, the core bacteria were Lactobacillus (0.08-39.05%), Acetobacter (0.25-81.92%), Weissella (0.03-29.61%), etc. The core fungi were Issatchenkia (23.11-98.21%), Monascus (0.02-26.36%), Pichia (0.33-37.56%), etc. In contrast, using flow cytometry combined with high-throughput sequencing, the active dominant bacterial genera after cell sorting were found to be Herbaspirillum, Chitinophaga, Ralstonia, Phenylobacterium, Mucilaginibacter, and Bradyrhizobium, etc., whereas the active dominant fungal genera detected were Aspergillus, Pichia, Exophiala, Candelabrochaete, Italiomyces, and Papiliotrema, etc. These results indicate that although the abundance of Acetobacter, Monascus, and Issatchenkia was high after stacked fermentation, they may have little biological activity. Flow cytometry and cell sorting techniques have been used in the study of beer and wine, but exploring the microbiome in such a complex environment as Chinese baijiu has not been reported. The results also reveal that flow cytometry and cell sorting are convenient methods for rapidly monitoring complex microbial flora and can assist in exploring complex environmental samples.

Mechanism of Enhancing Pyrazines in Daqu via Inoculating Bacillus licheniformis with Strains Specificity

Despite the importance of pyrazines in Baijiu flavor, inoculating functional strains to increase the contents of pyrazine in Daqu and how those interact with endogenic communities is not well characterized. The effects of inoculating Bacillus licheniformis with similar metabolic capacity on pyrazine and community structure were assessed in the Daqu complex system and compared with traditional Daqu. The fortification strategy increased the volatile metabolite content of Daqu by 52.40% and the pyrazine content by 655.99%. Meanwhile, results revealed that the pyrazine content in Daqu inoculated isolate J-49 was 2.35-7.41 times higher than isolate J-41. Both isolates have the almost same capability of 2,3-butanediol, a key precursor of pyrazine, in pure cultured systems. Since the membrane fatty acids of isolate J-49 contain unsaturated fatty acids, it enhances the response-ability to withstand complex environmental pressure, resulting in higher pyrazine content. PICRUSt2 suggested that the increase in pyrazine was related to the enzyme expression of nitrogen metabolism significantly increasing, which led to the enrichment of NH4⁺ and 2,3-butanediol (which increased by 615.89%). These results based on multi-dimensional approaches revealed the effect of functional bacteria enhancement on the attribution of Daqu, laid a methodological foundation regulating the microbial community structure and enhanced the target products by functional strains.

Analysis of the Microbial Community Structure and Volatile Metabolites of JIUYAO in Fangxian, China

JIUYAO is an important saccharification starter in the production of huangjiu and is also an important source of flavor. In this study, the microbial community structure of JIUYAO from Fangxian was studied by high-throughput sequencing (HTS) technology for the first time. The volatile flavor compounds of the JIUYAO metabolites were also analyzed by headspace solid-phase microextraction combined with full two-dimensional gas chromatography-mass spectrometry (HS-SPME-GC×GC/MS) for the first time. The results showed that there were 15 dominant bacterial genera, including Weissella, Pediococcus, unclasssified_k_norank_d_Bacteria, Lactobacillus, Leuconostoc, etc. Thirteen species of dominant fungi included Wickerhamomyces, Saccharomycopsis, Rhizopus, etc. The different samples of JIUYAO were similar in their microbial species, but the number of species was significantly different. A total of 191 volatile flavor compounds (VFCs) were detected, among which esters, alcohols, acids, and alkenes were the main flavor compounds, and 21 terpenoids were also detected. In addition, the functional prediction of micro-organisms in JIUYAO revealed that global and overview maps, amino acid metabolism, and carbohydrate metabolism were the dominant categories. Through correlation analysis, 538 potential correlations between the dominant micro-organisms and the different flavor compounds were obtained. This study revealed the interactions between the micro-organisms and the volatile metabolites in JIUYAO, which provided reliable data for the analysis of the microbial community structure of Fangxian JIUYAO and provided theoretical support for the quality evaluation of JIUYAO.

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.

Microbial succession and its effect on key aroma components during light-aroma-type Xiaoqu Baijiu brewing process

Light-aroma-type Baijiu is a Chinese distilled alcoholic beverage produced from fermented sorghum. Microbial composition and dynamics during Baijiu production have a great influence on the flavor and quality of Chinese Baijiu. However, the microbial changes that occur during brewing of Xiaoqu Baijiu are poorly understood. In this study, the microbial composition of light-aroma-type Xiaoqu Baijiu at the saccharification and fermentation stages was investigated to explore microbial dynamics and their effects on aroma components using high-throughput sequencing and gas chromatography-flame ionization detection (GC-FID). Rhizopus, Pichia, Wickerhamomyces, Saccharomyces, Acinetobacter, Lactobacillus, and Weissella constituted the core microbes for Xiaoqu Baijiu production. Microbial succession during brewing could be divided into two phases: at the saccharification and early fermentation stages (F-0d to F-4d), Rhizopus and Acinetobacter were identified as the predominant microbes, accounting for 78.2-90.8% and 53.9-89.5% of the fungal and bacterial communities, respectively, whereas at the middle and late stages of fermentation (F-5d to F-14d), the abundance of Pichia, Wickerhamomyces, Saccharomyces, and Lactobacillus increased. Redundancy analysis (RDA) and Mantel tests indicated that the water, amino acid nitrogen, acid, and reducing sugar contents were significantly correlated with the fungal and bacterial communities in grains (p < 0.05). Pichia, Rhizopus, Saccharomyces, and Wickerhamomyces, especially Saccharomyces, were closely related to the contents of major alcohols, esters and aldehydes, and these microbes had an important functional role in the formation of Xiaoqu Baijiu flavor. This work provides insights into the microbial succession that occurs during brewing of light-aroma-type Xiaoqu Baijiu and the microbial contribution to flavor, which have potential for optimizing production and enhancing the flavor of Baijiu.

Bacterial Diversity and Lactic Acid Bacteria with High Alcohol Tolerance in the Fermented Grains of Soy Sauce Aroma Type Baijiu in North China

Soy sauce aroma type baijiu (also known as Maotai-flavor baijiu) is one of the most popular types of baijiu in China. Traditionally, it is mainly produced in Southwest China. However, in recent decades, some other regions in China have also been able to produce high-quality soy sauce aroma type baijiu, but their microbial flora characteristics during fermentation are still unclear. Here, the bacterial microbial community structure of fermented grains in different rounds of Lutaichun soy sauce aroma type baijiu produced in North China was studied by high-throughput sequencing technology, and the potential probiotics strains with good characteristics (alcohol tolerance, etc.) were screened. The results showed that lactic acid bacteria were the main bacteria in the process of baijiu fermentation. However, as the number of repeated fermentation rounds increased, the proportion of lactic acid bacteria decreased. Firmicutes (96.81%) were the main bacteria in baijiu fermentation at the phylum level, and Lactobacillus (66.50%) were the main bacteria at the genus level. Finally, two strains with high resistance to alcohol stress, Lactiplantibacillus plantarum LTJ12 and Pediococcus acidilactici LTJ28, were screened from 48 strains of lactic acid bacteria in the fermented grains. The survival rates of L. plantarum LTJ12 and P. acidilactici LTJ28 under the 8% alcohol stress treatment were 59.01% and 55.50%, respectively. To the best of our knowledge, this study is the first to reveal the microbial succession of fermented grains in different rounds of soy sauce aroma type baijiu from North China, and has the benefit of explaining the deep molecular mechanism in the process of baijiu fermentation. In addition, the obtained lactic acid bacteria strains with high alcohol tolerance could be conducive to the development of new products such as active probiotic alcoholic beverages and may have important industrial development prospects also.

Chinese Baijiu: The Perfect Works of Microorganisms

Chinese Baijiu is one of the famous distilled liquor series with unique flavors in the world. Under the open environment, Chinese Baijiu was produced by two solid-state fermentation processes: jiuqu making and baijiu making. Chinese Baijiu can be divided into different types according to the production area, production process, starter type, and product flavor. Chinese Baijiu contains rich flavor components, such as esters and organic acids. The formation of these flavor substances is inseparable from the metabolism and interaction of different microorganisms, and thus, microorganisms play a leading role in the fermentation process of Chinese Baijiu. Bacteria, yeasts, and molds are the microorganisms involved in the brewing process of Chinese Baijiu, and they originate from various sources, such as the production environment, production workers, and jiuqu. This article reviews the typical flavor substances of different types of Chinese Baijiu, the types of microorganisms involved in the brewing process, and their functions. Methods that use microbial technology to enhance the flavor of baijiu, and for detecting flavor substances in baijiu were also introduced. This review systematically summarizes the role and application of Chinese Baijiu flavor components and microorganisms in baijiu brewing and provides data support for understanding Chinese Baijiu and further improving its quality.

The changes of microbial diversity and flavor compounds during the fermentation of millet Huangjiu, a traditional Chinese beverage

Huangjiu is a national alcoholic beverage in China. Millet has congenital advantages in development and utilization of nutrient. Brewing Huangjiu with millet can increase the value of millet. Microbial community plays crucial roles in millet Huangjiu fermentation. Flavor compounds reflect the quality and health function of Huangjiu. The flavor compounds of Huangjiu are complex and their formation is closely associated with microorganisms, but the relationship between them during fermentation has been unknown. In this research, this relationship during millet Huangjiu fermentation were deeply investigated. Totally 86 volatile compounds were detected. Bacillus, Weissella, Paenibacillus, Klebsiella, Prevotella was investigated as the dominant microbes through high-throughput sequencing. 537 correlations between major flavor compounds and microbes were established to reflect the dynamic change during millet Huangjiu fermentation. The top five dominant genus of flavor producing microbes were Chryseobacterium, Sporolactobacillus, Psychrobacter, Sphingobium and Anoxybacillus. The content of malic acid and citric acid was gradually improved all through the millet Huangjiu fermentation. Malic acid and citric acid generated from millet Huangjiu fermentation shows healthy properties as liver protection and eliminating fatigue. Our research provides essential information on microbial community succession and the flavor formation during millet Huangjiu fermentation, and beneficial for development of Huangjiu products.