Microbial communities, functional, and flavor differences among three different-colored high-temperature Daqu: A comprehensive metagenomic, physicochemical, and electronic sensory analysis

High-temperature Daqu (HTD) is the starter for producing sauce-flavor Baijiu, with different-colored Daqu (white, yellow, and black) reflecting variations in fermentation chamber conditions, chemical reactions, and associated microbiota. Understanding the relationship between Daqu characteristics and flavor/taste is challenging yet vital for improving Baijiu fermentation. This study utilized metagenomic sequencing, physicochemical analysis, and electronic sensory evaluation to compare three different-colored HTD and their roles in fermentation. Fungi and bacteria dominated the HTD-associated microbiota, with fungi increasing as the fermentation temperature rose. The major fungal genera were Aspergillus (40.17%) and Kroppenstedtia (21.16%), with Aspergillus chevalieri (25.65%) and Kroppenstedtia eburnean (21.07%) as prevalent species. Microbial communities, functionality, and physicochemical properties, particularly taste and flavor, were color-specific in HTD. Interestingly, the microbial communities in different-colored HTDs demonstrated robust functional complementarity. White Daqu exhibited non-significantly higher α-diversity compared to the other two Daqu. It played a crucial role in breaking down substrates such as starch, proteins, hyaluronic acid, and glucan, contributing to flavor precursor synthesis. Yellow Daqu, which experienced intermediate temperature and humidity, demonstrated good esterification capacity and a milder taste profile. Black Daqu efficiently broke down raw materials, especially complex polysaccharides, but had inferior flavor and taste. Notably, large within-group variations in physicochemical quality and microbial composition were observed, highlighting limitations in color-based HTD quality assessment. Water content in HTD was associated with Daqu flavor, implicating its crucial role. This study revealed the complementary roles of the three HTD types in sauce-flavor Baijiu fermentation, providing valuable insights for product enhancement.

Microbial communities and their correlation with flavor compound formation during the mechanized production of light-flavor Baijiu

Light-flavor Baijiu fermentation is a typical spontaneous solid-state fermentation process fueled by a variety of microorganisms. Mechanized processes have been increasingly employed in Baijiu production to replace traditional manual operation processes, however, the microbiological and physicochemical dynamics in mechanized processes remain largely unknown. Here, we investigated the microbial community succession and flavor compound formation during a whole mechanized fermentation process of light-flavor Baijiu using the conventional dilution plating method, PacBio single-molecule real-time (SMRT) sequencing and headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry. The results showed that largely different fungal and bacterial communities were involved in the soaking and fermentation processes. A clear succession from Pantoea agglomerans to Bacillus (B.) smithii and B. coagulans in dominant bacterial species and from Cladosporium exasperatum to Saccharomyces cerevisiae and Lichtheimia ramosa in dominant fungal species occurred in the soaking processes. In the fermentation process, the most dominant bacterial species was shifted from Pantoea agglomerans to Lactobacillus (La.) acetotolerans and the most dominant fungal species were shifted from Lichtheimia ramose and Rhizopus arrhizus to Saccharomyces cerevisiae. The bacterial and fungal species positively associated with acidity and the formation of ethanol and different flavor compounds were specified. The microbial species exhibited strong co-occurrence or co-exclusion relationships were also identified. The results are helpful for the improvement of mechanized fermentation process of light-flavor Baijiu production.

Probiotic Properties Including the Antioxidant and Hypoglycemic Ability of Lactic Acid Bacteria from Fermented Grains of Chinese Baijiu

In this study, lactic acid bacteria (LAB) strains were isolated from fermented grains of traditional Chinese Baijiu, and their probiotic properties were characterized. Eleven out of 29 LAB strains showed good tolerance to the gastrointestinal tract and bile salts. The surface characteristics (auto-aggregation, co-aggregation, hydrophobicity), safety (hemolytic and antibiotic sensitivity), antibacterial activity against three foodborne pathogens, and antioxidant and hypoglycemic properties of the 11 LAB strains were investigated. Principal component analysis (PCA) was used to comprehensively evaluate LAB strains and their probiotic properties. It was found that Weissella cibaria (OP288150), Pediococcus acidilactici (OP288151), Pediococcus pentosaceus (OP288154), Pediococcus pentosaceus (OP288156) and Levilactobacillus brevis (OP288158) showed high probiotic properties, with potential for commercial development. The results also demonstrated that fermented grains of Chinese Baijiu can be used as a source of high-quality probiotics.

RETRACTED: Unraveling the composition and succession of microbial community and its relationship to flavor substances during Xin-flavor baijiu brewing

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the authors. The authors reported unauthorized use of several figures in this paper of copyrighted material from the Daohuaxiang Liquor Co., Ltd. Therefore, the authors are retracting the paper in its entirety. They apologize for any inconvenience this may have caused.

Metatranscriptomics Unravel Composition, Drivers, and Functions of the Active Microorganisms in Light-Flavor Liquor Fermentation

The microbial community in the fermented pit determines the quantity and quality of light-flavor liquor. Genetic diversity and the potential functions of the microbial community are often analyzed by DNA-based omics sequencing. However, the features of the active microbial community have not been systematically studied. Here, metatranscriptomic analysis was performed to elucidate the active microbial composition, drivers, and their functions in light-flavor liquor fermentation. Bacterial genera, Lactobacillus, Streptococcus, Pediococcus, Thermotoga, and Faecalibacterium, and fungal genera, Saccharomyces, Talaromyces, Aspergillus, Clavispora, Rhizophagus, Cyberlindnera, and Wickerhamomyces, were the dominant active microorganisms during the fermentation process. Additionally, they dominated the three-stage fermentation successively. Redundancy analysis showed that pH, ethanol, moisture, and starch were the main driving forces of microbial succession. Among the genes for the respective carbohydrate-active enzyme families, those for the glycoside hydrolase family 23, the glycosyltransferase family 2, the carbohydrate-binding module family 50, the polysaccharide lyase family 4, the auxiliary activity family 1, and the carbohydrate esterase family 9 showed the highest expression level. Additionally, the highly expressed enzymes and their contributed microorganisms were found in the key KEGG pathways, including carbohydrate metabolism, energy metabolism, lipid metabolism, and amino acid metabolism. Based on these data, a functional model of carbohydrate hydrolysis, ethanol production, and flavor generation were proposed. Taken together, Saccharomyces, Lactobacillus, Wickerhamomyces, Pediococcus, Candida, and Faecalibacterium were suggested as the core active microorganisms. Overall, our findings provide new insights into the composition, drivers, and functions of the active microorganisms, which is crucial for improving the quality of light-flavor liquor. IMPORTANCE There is an urgent need for discovering the diversity and functions of the active microbial community in solid-state fermentation, especially in the pit of Chinese distilled liquor fermentation. Although the genetic composition of the microbial community has been clarified frequently by DNA-based sequencing, the composition and functions of the active microbial community have not been systematically revealed so far. Therefore, analysis of RNA-based data is crucial for discovering the functional microbial community. In this study, we employed metatranscriptomic analysis to elucidate the active microbial composition, successive drivers, and their functions in light-flavor liquor fermentation. The strategy can be broadly useful for discovering the active microbial community and exploring their functions in other types of flavor distilled liquor or other ecosystems. This study provides new insights into the understanding of the active microbial community composition and its functions.

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.

Bacterial Diversity, Organic Acid, and Flavor Analysis of Dacha and Ercha Fermented Grains of Fen Flavor Baijiu

Fen flavor Baijiu needs two rounds of fermentation, which will obtain Dacha after initial fermentation and Ercha after secondary fermentation. The quality of Baijiu is closely related to the microbes within fermented grains. However, the bacterial diversity in Dacha and Ercha fermented grains of Fen flavor Baijiu has not been reported. In the present study, the structure and diversity of bacteria communities within fermented grains of Fen flavor Baijiu were analyzed and evaluated using MiSeq platform's HTS with a sequencing target of the V3-V4 region of the 16S rRNA gene. Through the analysis of physical and chemical indexes and electronic senses, the relationship between bacterial flora, organic acid, taste, and aroma in fermented grains was clarified. The results indicated that Lactobacillus was the main bacteria in Dacha, and the mean relative content was 97.53%. The bacteria within Ercha samples were Pseudomonas and Bacillus, mean relative content was 37.16 and 28.02%, respectively. The diversity of bacterial communities in Ercha samples was significantly greater than that in Dacha samples. The correlation between Lactobacillus and organic acids, especially lactic acid, led to the difference between Dacha and Ercha organic acids, which also made the pH value of Dacha lower and the sour taste significantly higher than Ercha. Lactobacillus was significantly positively correlated with a variety of aromas, which made Dacha the response value of aromas higher. In addition, Bacillus had a significant positive correlation with bitterness and aromatic compounds, which led to a higher response value of bitterness in Ercha and made it present an aromatic aroma. This study provides an in-depth analysis of the difference between different stages of Fen flavor Baijiu, and theoretical support for the standard production and improvement in quality of Fen flavor Baijiu in the future.

Effects of ultra-long fermentation time on the microbial community and flavor components of light-flavor Xiaoqu Baijiu based on fermentation tanks

Microbial structure and succession of fermented grains play a significant role in Baijiu's flavor and quality. In this study, high-throughput sequencing (HTS) coupled with headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) were used to analyze the microbial community structures and flavor components in the fermented grains at the end of fermentation from different fermentation time of light-flavor Xiaoqu Baijiu. HTS results showed that Lactobacillus acetotolerans, Lactobacillus helveticus, Lactobacillus buchneri, Wickerhamomyces, Saccharomyces, and Condenascus were identified as the dominant microbes, but Lactobacillus (96.28%) exhibited obvious advantages at the end of ultra-long fermentation time (day 98). HS-SPME-GC-MS analysis revealed that esters and alcohols had the most abundance in fermented grains of day 98, containing high concentrations of ethyl acetate, diethyl succinate, phenylethyl alcohol, isoamyl alcohol, and n-propanol, which were related to the succession of Lactobacillus and yeast communities. Interestingly, the content of n-propanol in the ultra-long fermentation time samples (day 98) was 6 times of that in normal fermented grains (day 14), which may be caused by higher abundance of Lactobacillus in day 98 samples. Monte Carlo permutation test showed residual starch, acidity, and amino nitrogen (p < 0.05) were important factors affecting the microbial community. Together, these results shed light on the physicochemical changes, microbial dynamics, and key flavor components of fermented grains at the end of fermentation from different fermentation time and provide a strategy for further improvement of Baijiu quality.

Detection of viable and total fungal community in zaopei of Chinese strong-flavor baijiu using PMA combined with qPCR and HTS based on ITS2 region

Background

Chinese strong-flavor baijiu (CSFB), one of the three major baijiu types, is the most popular baijiu type among consumers in China. A variety of microbes are involved in metabolizing raw materials to produce ethanol and flavor substances during fermentation, which fundamentally determined the quality of baijiu. It is of great importance to study microbial community of fermented grains (zaopei) during baijiu brewing process for improving its quality. In this study, we firstly used propidium monoazide (PMA) to treat zaopei samples from 5-year pit and 20-year pit for removing the interference of non-viable fungi, and analyzed the diversity of total fungi and viable fungi by quantitative PCR (qPCR) and high-throughput sequencing (HTS) based on ITS2 gene.

Results

The results showed that total fungi and viable fungi displayed no significant differences at OTU, phylum, or genus levels during fermentation within two kinds of pits. A total of 6 phyla, 19 classes, and 118 genera in fungi were found based on OTUs annotation in zaopei samples from 5-year pit and 20-year pit. Besides, non-viable fungi had little effect on the fungal community diversity during the fermentation cycle. It was found that the most dominant viable fungi belonged to Saccharomyces, Kazachstania, Naumovozyma, and Trichosporon, and Naumovozyma was firstly detected in zaopei samples of CSFB. Moreover, based on the variation of flavor substances in zaopei samples, the quality of CSFB produced from older pit was better than that produced from younger pit.

Conclusion

The non-viable fungi had little effect on the fungal diversity, structure, and relative abundance in zaopei samples of CSFB, and Naumovozyma was firstly detected in zaopei samples of CSFB. Our findings can be applied as guidance for improving the quality and stability of CSFB.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02334-8.

Microbial composition and dynamic succession during the Daqu production process of Northern Jiang-flavored liquor in China

The microbial community structure and succession regularity of six key periods during high-temperature Daqu production were revealed using high-throughput sequencing to explore the factors affecting the flavor formation of Northern Jiang-flavored Baijiu technology. The results showed that among the six Daqu samples, the bacteria mainly included Firmicutes, Actinobacteriota, and Proteobacteria, of which Proteobacteria was the most dominant. The primary fungus was Ascomycota. At the genus level, the primary bacterial groups were Lactobacillus, Weissella, Bacillus, Delftia, Achromobacter, Saccharopolyspora, Thermoactinomyces, Scopulibacillus, Pseudomonas, and Stenotrophomonas. The main fungal groups in the Daqu were Wickerhamomyces, Saccharomycopsis, Thermoascus, and Thermomyces. During the initial stage of Daqu production, the dominant bacteria were Lactobacillus (20.07%) and Weissella (48.30%). As the fermentation temperature of the Daqu increased, Achromobacter, Stenotrophomonas, and Delftia became the dominant bacteria during the first Daqu flipping period, the second Daqu flipping period, and the dry-fire period. During these three periods, many bacteria were eliminated, decreasing the bacterial diversity, while a decline in temperature was evident during the Daqu exit period. After adapting to the high-temperature environment, the accumulation of Saccharopolyspora (22.07%), Thermoactinomyces (16.73%), Scopulibacillus (27.13%), Kroppenstedtia (9.03%), and Bacillus (6.97%) increased the bacterial diversity during the Daqu exit period. Wickerhamomyces (83.47%) represented the main dominant fungus during the initial production stage but were eliminated with increased temperature. Furthermore, a higher temperature increased the abundance of Saccharomycopsis and Thermoascus, while Thermomyces gradually accumulated in the D, E, and F samples. Thermomyces (79.90%) and Thermoascus (13.83%) became the dominant fungi during the Daqu exit period. In this study, high-throughput sequencing technology was used to reveal the microbial diversity during the high-temperature Daqu production process of Northern Jiang-flavored Baijiu. This provided a scientific basis for improving the production process of this product in the future. Therefore, understanding the formation of the flavor substances and the related microorganisms in Northern Jiang-flavored Baijiu can provide guidance for using them to manipulate the preparation process while implementing microbial control and improving the production procedures.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02779-8.

Effect of frozen storage on the inhibition of microbial population, chemical and sensory characteristics of coconut neera

AIM

In this study, the effect of frozen storage on the inhibition of microbial population in coconut neera for shelf life extension was analysed.

METHODS AND RESULTS

The aliquots of fresh neera were frozen at -6 and -20°C. The microbial reduction and chemical qualities were analysed during storage days, and were compared with the control. The highest reduction in microbes was obtained at -20°C for lactic acid bacteria, yeast and total viable count. Moreover, the fluorescence cell staining and cell density analysis exhibited a decline at -20°C, however it showed higher at -6°C. At the end of 28 days, neera exhibited a pH of 5·37, total soluble solid of 14·0 °Brix and total acidity of 0·82 mg l^-1 at -20°C. Besides, color, viscosity, total protein and ethanol showed a less difference with control and better sensory attribute up to 21 days at -20°C.

CONCLUSIONS

Frozen storage at -20°C resulted in a better inhibition of lactic acid bacteria, which preserves neera from the metabolic conversion. The physicochemical qualities of neera were preserved for a longer period when stored at -20°C than at atmospheric storage.

SIGNIFICANCE AND IMPACT OF THE STUDY

Frozen storage reduced microbial population and preserves the chemical properties with acceptable sensory attributes and increases the shelf life of coconut neera, making it fit for consumption.

The deletion of Schizosaccharomyces pombe decreased the production of flavor-related metabolites during traditional Baijiu fermentation

The microbiota in traditional solid-state fermentation is a complex microbiota that plays a key role in the production of feed, fuel, food and pharmaceutical products. The function of microbiota is an important factor dictating the quantity and quality of products. Core functional species play key metabolic roles in the microbiota, and their disappearance could result in the abnormal fermentation process. In this work, we combined Baijiu production and laboratory experiments to explore the keystone microbes and their metabolites. We found the deletion of core functional microbe resulted in the loss of multiple metabolites involved many alcohols and acids. In the traditional Baijiu production, the absence or appearance of Schizosaccharomyces pombe caused the content divergence in 227 flavor-related metabolites, especially in ethanol, butanol and pentanoic acid between abnormal and normal group (each content > 1 mg/kg and the content ratio of normal/abnormal group > 2). Schi. pombe increased the expression level of related genes involving alcohol dehydrogenase (ADH), acyl-CoA oxidase (ACOX) and trans-2-enoyl-CoA reductase (TER). Moreover, in the verification experiment of laboratory, the absence or appearance of Schizosaccharomyces pombe C-11 caused the content divergence in 136 flavor-related metabolites, especially in ethanol, butanol and pentanoic acid between Sp- and Sp+ group (each content > 1 mg/kg and the content ratio of Sp+/Sp- group > 2). Our results identified specific member that were essential for the function of fermentation microbiota. This study also suggests species deletions from fermentation microbiota and synthetic consortium could be a useful approach to illustrate relevant microbe-metabolites association and defining metabolic roles in the traditional solid-state fermentation.

Composition and Metabolic Functions of the Microbiome in Fermented Grain during Light-Flavor Baijiu Fermentation

The metabolism and accumulation of flavor compounds in Chinese Baijiu are driven by microbiota succession and their inter-related metabolic processes. Changes in the microbiome composition during Baijiu production have been examined previously; however, the respective metabolic functions remain unclear. Using shotgun metagenomic sequencing and metabolomics, we examined the microbial and metabolic characteristics during light-flavor Baijiu fermentation to assess the correlations between microorganisms and their potential functions. During fermentation, the bacterial abundance increased from 58.2% to 97.65%, and fermentation resulted in the accumulation of various metabolites, among which alcohols and esters were the most abundant. Correlation analyses revealed that the levels of major metabolites were positively correlated with bacterial abundance but negatively with that of fungi. Gene annotation showed that the Lactobacillus species contained key enzyme genes for carbohydrate metabolism and contributed to the entire fermentation process. Lichtheimia ramosa, Saccharomycopsis fibuligera, Bacillus licheniformis, Saccharomyces cerevisiae, and Pichia kudriavzevii play major roles in starch degradation and ethanol production. A link was established between the composition and metabolic functions of the microbiota involved in Baijiu fermentation, which helps elucidate microbial and metabolic patterns of fermentation and provides insights into the potential optimization of Baijiu production.

Understanding the Biosynthetic Changes that Give Origin to the Distinctive Flavor of Sotol: Microbial Identification and Analysis of the Volatile Metabolites Profiles During Sotol (Dasylirion sp.) Must Fermentation

In northern Mexico, the distilled spirit sotol with a denomination of origin is made from species of Dasylirion. The configuration of the volatile metabolites produced during the spontaneous fermentation of Dasylirion sp. must is insufficiently understood. In this study, the aim was to investigate the composition of the microbial consortia, describe the variation of volatile metabolites, and relate such profiles with their particular flavor attributes during the fermentation of sotol (Dasylirion sp.) must. Ascomycota was the phylum of most strains identified with 75% of total abundance. The genus of fermenting yeasts constituted of 101 Pichia strains and 13 Saccharomyces strains. A total of 57 volatile metabolites were identified and grouped into ten classes. The first stage of fermentation was composed of diesel, green, fruity, and cheesy attributes due to butyl 2-methylpropanoate, octan-1-ol, ethyl octanoate, and butanal, respectively, followed by a variation to pungent and sweet descriptors due to 3-methylbutan-1-ol and butyl 2-methylpropanoate. The final stage was described by floral, ethereal-winey, and vinegar attributes related to ethyl ethanimidate, 2-methylpropan-1-ol, and 2-hydroxyacetic acid. Our results improve the knowledge of the variations of volatile metabolites during the fermentation of sotol must and their contribution to its distinctive flavor.