Identification of microorganisms producing lactic acid during solid-state fermentation of Maotai flavour liquor

Transcriptomics to evaluate the influence mechanisms of ethanol on the ester production of Wickerhamomyces anomalus with the induction of lactic acid

Wickerhamomyces anomalus is one of the most important ester-producing strains in Chinese baijiu brewing. Ethanol and lactic acid are the main metabolites produced during baijiu brewing, but their synergistic influence on the growth and ester production of W. anomalus is unclear. Therefore, in this paper, based on the contents of ethanol and lactic acid during Te-flavor baijiu brewing, the effects of different ethanol concentrations (3, 6, and 9% (v/v)) combined with 1% lactic acid on the growth and ester production of W. anomalus NCUF307.1 were studied and their influence mechanisms were analyzed by transcriptomics. The results showed that the growth of W. anomalus NCUF307.1 under the induction of lactic acid was inhibited by ethanol. Although self-repair mechanism of W. anomalus NCUF307.1 induced by lactic acid was initiated at all concentrations of ethanol, resulting in significant up-regulation of genes related to the Genetic Information Processing pathway, such as cell cycle-yeast, meiosis-yeast, DNA replication and other pathways. However, the accumulation of reactive oxygen species and the inhibition of pathways associated with carbohydrate and amino acid metabolism may be the main reason for the inhibition of growth in W. anomalus NCUF307.1. In addition, 3% and 6% ethanol combined with 1% lactic acid could promote the ester production of W. anomalus NCUF307.1, which may be related to the up-regulation of EAT1, ADH5 and TGL5 genes, while the inhibition in 9% ethanol may be related to down-regulation of ATF2, EAT1, ADH2, ADH5, and TGL3 genes.

Unraveling the correlations between microbial communities and metabolic profiles of strong-flavor Jinhui Daqu with different storage periods

Daqu is a saccharification agent required for fermenting Baijiu, a popular Chinese liquor. Our objective was to investigate the relationships between physicochemical indices, microbial community diversity, and metabolite profiles of strong-flavor Jinhui Daqu during different storage periods. During different storage periods of Jinhui Daqu, we combined Illumina MiSeq sequencing and non-target sequencing techniques to analyze dynamic changes of the microbial community and metabolite composition, established a symbiotic network and explored the correlation between dominant microorganisms and differential metabolites in Daqu. Fungal community diversity in 8d_Daqu was higher than that in 45d_Daqu and 90d_Daqu, whereas bacterial community diversity was higher in 90d_Daqu. Twelve bacterial and four fungal genera were dominant during storage of Daqu. Bacillus, Leuconostoc, Kroppenstedtia, Lactococcus, Thermomyces and Wickerhamomyces decreased as the storage period increased. Differences of microbiota structure led to various metabolic pathways, and 993 differential metabolites were found in all Daqu samples. Differential microorganisms were significantly related to key metabolites. Major metabolic pathways involved in the formation of amino acids and lipids, such as l-arogenate and hydroxyproline, were identified. Interactions between moisture, acidity, and microbes may drive the succession of the microbial community, which further affects the formation of metabolites.

Inoculation of Zaopei with biofortification: Inducing variation in community structure and improving flavor compounds in Nongxiangxing baijiu

The deterioration of the quality of raw liquor caused by the low content of ethyl hexanoate in Nongxiangxing baijiu has become a pervasive problem in the baijiu industry. Therefore, this study attempted to increase the synthesis of ethyl hexanoate by microorganisms with high esterase activity to increase Zaopei fermentation. The results showed that biofortification was a feasible and important way to improve the quality of the raw liquor and increase the ethyl hexanoate content. Adding Bacillus subtilis, Staphylococcus epidermidis, and Millerozyma farinosa for biofortified fermentation disturbed the microbial community structure of Zaopei and increased the abundance of Wickerhamomyces, Saccharomyces, and Thermoascus. The contents of ethyl hexanoate, ethyl valerate, ethyl caprylate, and ethyl heptanoate also increased noticeably in baijiu. The results of E-nose and sensory analysis tested and verified that the baijiu in the fortified group had better flavor characteristics.

Analysis of differences in microorganisms and aroma profiles between normal and off-flavor pit mud in Chinese strong-flavor Baijiu

The unique cellar fermentation process of Chinese strong-flavor Baijiu is the reason for its characteristic cellar aroma flavor. The types, abundance, community structure and metabolic activity of microorganisms in the pit mud directly affect the microbial balance in the white spirit production environment, promoting the formation of typical aromas and influencing the quality of CFSB. During the production process, the production of off-flavor in the cellar may occur. The aim of this study is to elucidate the differences in microbiota and flavor between normal pit mud and abnormal pit mud (pit mud with off-flavor). A total of 46 major volatile compounds were identified, and 24 bacterial genera and 21 fungal genera were screened. The esters, acids, and alcohols in the abnormal pit mud were lower than those in the normal pit mud, while the aldehydes were higher. 3-Methyl indole, which has been proven to be responsible for the muddy and musty flavors, was detected in both types of pit mud, and for the first time, high levels of 4-methylanisole was detected in the pit mud. The microbial composition of the two types of pit mud showed significant differences in the bacterial genera of Sporosarcina, Lactobacillus, Garciella, Anaerosalibacter, Lentimicrobium, HN-HF0106, Petrimonas, Clostridium_sensu_stricto_12 and Bacillus, and the fungal genera of Millerozyma, Penicillium, Mortierella, Monascus, Saccharomyces, Issatchenkia, Pithoascus, Pseudallescheria, and Wickerhamomyces. Additionally, we speculate that Sporosarcina is the predominant bacterial genus responsible for the imbalance of microbiota in pit mud.

Identifying Variables Influencing Traditional Food Solid-State Fermentation by Statistical Modeling

Solid-state fermentation is widely used in traditional food production, but most of the complex processes involved were designed and are carried out without a scientific basis. Often, mathematical models can be established to describe mass and heat transfer with the assistance of chemical engineering tools. However, due to the complex nature of solid-state fermentation, mathematical models alone cannot explain the many dynamic changes that occur during these processes. For example, it is hard to identify the most important variables influencing product yield and quality fluctuations. Here, using solid-state fermentation of Chinese liquor as a case study, we established statistical models to correlate the final liquor yield with available industrial data, including the starting content of starch, water and acid; starting temperature; and substrate temperature profiles throughout the process. Models based on starting concentrations and temperature profiles gave unsatisfactory yield predictions. Although the most obvious factor is the starting month, ambient temperature is unlikely to be the direct driver of differences. A lactic-acid-inhibition model indicates that lactic acid from lactic acid bacteria is likely the reason for the reduction in yield between April and December. Further integrated study strategies are necessary to confirm the most crucial variables from both microbiological and engineering perspectives. Our findings can facilitate better understanding and improvement of complex solid-state fermentations.

Effects of different storage containers on the flavor characteristics of Jiangxiangxing baijiu

Storage is a key factor controlling the quality of Jiangxiangxing baijiu, and storage time and the type of storage container play crucial roles in shaping the baijiu's distinct flavor. To investigate the influence of storage containers on the flavor characteristics of Jiangxiangxing baijiu, the sensory qualities, flavor components, and metal ions of Jiangxiangxing baijiu were measured during 24 months of storage in a pottery jar or a stainless steel tank. The results showed that Jiangxiangxing baijiu preserved in a pottery jar was superior to that stored in a stainless steel tank. A total of 96 flavor substances were detected, and 17 key flavor characteristic substances were screened by combining the results of odor activity values (OAV) and orthogonal partial least squares-discriminant analysis (OPLS-DA). A correlation heat map and redundancy analysis (RDA) showed that aluminum, cadmium, iron, cobalt, magnesium, potassium, and copper ions promoted the formation of key characteristic substances including diethoxymethane, lactic acid, 2,3-dimethyl-5-ethylpyrazine, 1-hexanol, and 2-methyl-1-propanol. Overall, the results show that 24-month pottery jar storage can promote the flavor quality of Jiangxiangxing baijiu. This study established a theoretical foundation to select the appropriate storage conditions and control the flavor quality of Jiangxiangxing baijiu.

Metaproteomics profiling of the microbial communities in fermentation starters (Daqu) during multi-round production of Chinese liquor

Introduction

The special flavor and fragrance of Chinese liquor are closely related to microorganisms in the fermentation starter Daqu. The changes of microbial community can affect the stability of liquor yield and quality.

Methods

In this study, we used data-independent acquisition mass spectrometry (DIA-MS) for cohort study of the microbial communities of a total of 42 Daqu samples in six production cycles at different times of a year. The DIA MS data were searched against a protein database constructed by metagenomic sequencing.

Results

The microbial composition and its changes across production cycles were revealed. Functional analysis of the differential proteins was carried out and the metabolic pathways related to the differential proteins were explored. These metabolic pathways were related to the saccharification process in liquor fermentation and the synthesis of secondary metabolites to form the unique flavor and aroma in the Chinese liquor.

Discussion

We expect that the metaproteome profiling of Daqu from different production cycles will serve as a guide for the control of fermentation process of Chinese liquor in the future.

The Influence of Seasons on the Composition of Microbial Communities and the Content of Lactic Acid during the Fermentation of Fen-Flavor Baijiu

During the fermentation of Fen-flavor Baijiu, the number of lactic acid bacteria is high in summer, resulting in excessive lactic acid and an unpleasant astringent taste. Thus, it is necessary to identify the critical influence factors for the formation of lactic acid and the composition of the microbial community in the fermented grains during the brewing process of Fen-flavor Baijiu in cold and hot seasons using HPLC and high-throughput sequencing technology. The results suggest that Lactobacillus acetotolerans is the key microorganism causing different contents of lactic acid in fermented grains and that Lactobacillus plantarum is a favorable factor for acid production in the fermentation process during hot seasons. Twelve lactic-acid-producing strains were isolated from the fermented grains at the latter stage of fermentation, and the analysis of these strains showed that the Lactobacillus plantarum LP strain has the strongest capacity for lactic acid production and the Lacticaseibacillus rhamnosus LR strain has the strongest capacity for acid production, respectively. In addition, the Lentilactobacillus hilgardii LH strain has the characteristics of both acid and alcohol resistance. The results obtained from this study provide a reference for reducing the content of lactic acid in summer and have potential value for further improving the quality of Fen-flavor Baijiu.

Research on interaction regularities and mechanisms between lactic acid and aroma compounds of Baijiu

This study investigated the interactions between lactic acid (LA) and odorants of Baijiu using headspace solid phase microextraction with gas chromatography-mass spectrometry (HS-SPME-GC-MS), ultraviolet absorption spectroscopy (UV) and nuclear magnetic resonance (NMR). The HS-SPME-GC-MS analysis results showed that LA promoted the volatilities of most of low boiling acids, esters, alcohols, aldehydes and ketones, especially short-chain branched esters were promoted by 41-49%. In contrast, LA suppressed the volatilities of most aromatic compounds. UV spectroscopy, thermodynamic analysis, and NMR combined with theoretical calculations further revealed that the interactions between LA and 4-ethyl-2-methoxyphenol (4-EP), 2-methoxy-4-methylphenol (2-MP) and 1-butanol were dominated by van der Waals forces and supplemented by electrostatic interactions, which included hydrogen bonds formed between the carboxyl group in LA and the hydroxyl and methoxy groups in 4-EP or 2-MP and π-hydrogen bonds between the hydrogen of the carboxyl group of LA and the benzene ring of 4-EP or 2-MP.

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.

Deep sequencing reveals changes in prokaryotic taxonomy and functional diversity of pit muds in different distilleries of China

Purpose

The microbial community in the pit mud correlated closely with the quality of the final product of Chinese strong-flavored Baijiu (CSFB). However, environmental conditions and brewing processes can vary by region and distilleries. This may lead to differences in microbial composition and function in pit mud. Therefore, revealing the features of the pit mud microbial community structure and functions of different distilleries will provide key information for understanding the diversity and difference of microbes in the brewing of CSFB, which will be beneficial for the improvement of the quality of pit mud and CSFB in the future.

Methods and results

Illumina MiSeq sequencing of 16S rRNA gene amplicons was used to analyze the similarities and differences in microbial community structure and function in pit muds of different distilleries located in Shihezi (Xinjiang), Xiangyang (Hubei), and Yibin (Sichuan). At the genus level, Clostridium, Lactobacillus, Aminobacterium, Petrimonas, Syntrophomonas, Methanoculleus, Syntrophaceticus, Sedimentibacter, Caloramator, Ruminococcus, Bacillus, Methanosarcina, and Garciella were the dominated genera of pit muds. There were great differences in the composition of microorganisms in pit muds used by different distilleries. The significantly enriched prokaryotic microbiotas of pit muds collected in the distilleries of Xiangyang were mainly affiliated with Bacillus, Lactobacillus, and Croceifilum, and the relative abundance of methanogens, such as Methanomicrobia and Methanobacteria, were only significantly enriched in the pit mud collected from the distilleries of Yibin (P < 0.05). Functional analysis indicated that the difference of microbial composition in pit mud will further lead to significant differences in various metabolic functions.

Conclusion

The compositions and functions of dominant microorganisms in pit mud used for the production of CSFB by different enterprises across regions in China were greatly different, and there was a close relationship between the compositions and functions of microorganisms in pit mud. Therefore, it may be an effective method to improve CSFB fermentation processes by directionally regulating the microbial community functions of pit mud using specific strains.

Research trends in Jiang-flavor baijiu fermentation: From fermentation microecology to environmental ecology

Chinese baijiu is one of the six major distilled spirits worldwide and is widely enjoyed because of its unique flavor. Among typical baijiu, Jiang-flavor baijiu is gaining popularity. However, the fermentation mechanisms of baijiu remain unclear due to its open inoculation environment and complex brewing process. In recent years, advances in high-throughput sequencing and multi-omics technologies have yielded meaningful information regarding fermentation microbiome. Therefore, this paper reviews recent developments in the investigation of the diversity, stability, and metabolism of the Jiang-flavor baijiu microbial community. Furthermore, the importance of protecting the ecology of the production environment is proposed based on the putative contribution of environmental factors to the fermentation microbiome and baijiu characteristics. Finally, this paper discusses current research challenges that need to be addressed, including the limitations of sequencing technologies and difficulties unveiling the mechanisms of microbial interaction between the fermentation microbiome and the environmental ecology. The findings of this review will promote further understanding of the Jiang-flavor baijiu fermentation process and provide valuable information for the research and development of traditional baijiu and other naturally fermented foods. PRACTICAL APPLICATION: Baijiu, a transparent strong alcoholic drink, is the world's largest consumed and the most valuable spirit in the market. However, the fermentation mechanisms of baijiu remain unclear due to its open inoculation environment and complex brewing process. Therefore, if we can summarizes the current advances and research challenges of microbial fermentation in baijiu, it will deepen the reader's understanding of the complex fermentation process and fermentation mechanism in baijiu. Furthermore, based on the putative contribution of environmental factors to the fermentation process, the importance of protecting the ecology of the production environment is proposed in future research trends, which will provide valuable information for the research and development of other traditional naturally fermented foods. This will not only achieve breakthroughs in academic value, but also bring higher practical value to fermented foods.

A CRISPR-Cas12a-Based Assay for Efficient Quantification of Lactobacillus panis in Chinese Baijiu Brewing Microbiome

Although the quantification of key microorganisms in fermentation microbiomes is important for monitoring and regulating fermented food production, conventionally used methods are generally time-consuming, involve complicated operations, and have a high level of equipment dependence. We developed a CRISPR-Cas12a-based quantitative Chinese Baijiu brewing microorganism assay (CQAOB) for Lactobacillus panis, the most important lactic acid-producing fermentative microorganism. We initially verified the feasibility of CQAOB for detecting L. panis, and then optimized the reaction parameters to enhance Cas12a detection sensitivity. The specificity of the developed method was verified via the accurate distinction of L. panis nucleic acids from those of other lactic acid bacteria. The quantitative range and detection time for L. panis were 106–109 copies/μL and 40 min, respectively. Finally, we successfully applied CQAOB for quantifying L. panis count in fermented grains. Given its rapid detection and low level of equipment dependence, CQAOB may make an important contribution to quantifying key microorganisms in brewing processes.

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.

Metabolomics-Driven Elucidation of Interactions between Saccharomyces cerevisiae and Lactobacillus panis from Chinese Baijiu Fermentation Microbiome

Saccharomyces cerevisiae and Lactobacillus panis are ethanol and lactic acid producers in Maotai-flavor Baijiu fermentation. Understanding their interaction is important to regulate the microbiome composition during fermentation and biosynthesis of ethanol and lactic acid. This study is the first to analyze the interaction between S. cerevisiae and L. panis at different growth phases during co-cultivation. Results showed that the different growth phases of S. cerevisiae modulated L. panis growth. Metabolomics analysis showed that amino acids and nucleoside secreted by S. cerevisiae promote L. panis growth, while ethanol inhibited L. panis growth. Furthermore, S. cerevisiae modulated L. panis cell growth under varying sugar concentrations. Simulated solid-state fermentation demonstrated that regulating the sugar concentration or the ratio of S. cerevisiae to L. panis could inhibit L. panis cell growth and reduce lactic acid accumulation. This study provided an understanding on Maotai-flavor Baijiu microbiome, which might be useful for metabolite regulation.

Diversity of microbiota, microbial functions, and flavor in different types of low-temperature Daqu

Light-flavor Baijiu is made from grain materials using a combination of three types of low-temperature Daqu (Hongxin, Houhuo, and Qingcha). This study comprehensively examined the microbial structure, microbial functions, and flavor characteristics of the three types of low-temperature Daqu using high-throughput sequencing and electronic senses, and it further clarified the relationship between the microbiota and flavor in low-temperature Daqu. The results showed that Hongxin had the highest bacterial richness and diversity, while Houhuo had the lowest. Both fungal richness and diversity were significantly higher in Qingcha than in Hongxin and Houhuo. The differences in peak temperature during Daqu-making led to significant differences in the structure of microbial communities, microbial functions, and flavor quality in the three types of low-temperature Daqu, and could be leveraged for screening and enriching functional microorganisms for Baijiu-making. Co-exclusion patterns between lactic acid bacteria and Bacillus in low-temperature Daqu resulted in a negative correlation between amino acid transport metabolism and carbohydrate transport metabolism. The different types of low-temperature Daqu had distinct flavor profiles, and the differences in the taste profiles were more significant. Dominated by Thermoactinomyces and Lactobacillus, and together with Saccharopolyspora, Bacillus, Streptomyces, Saccharomycopsis, and Thermoascus, they formed the core microbiota that influencing the flavor of low-temperature Daqu. The bacteria mainly influenced the taste of low-temperature Daqu, whereas the fungi mainly influenced the aroma. Each type of low-temperature Daqu contributed to the flavor of light-flavor Baijiu: Hongxin could elevate the levels of aromatic compounds, Houhuo could regulate the bitterness and sourness, and Qingcha could inhibit the generation of sulfur organic compounds. The results of the present study enrich and refine our knowledge of low-temperature Daqu, promoting the further evolution of traditional brewing methods.

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.

Analysis of microbial diversity and functional differences in different types of high-temperature Daqu

Bacterial communities that enrich in high-temperature Daqu are important for the Chinese maotai-flavor liquor brewing process. However, the bacterial communities in three different types of high-temperature Daqu (white Daqu, black Daqu, and yellow Daqu) are still undercharacterized. In this study, the bacterial diversity of three different types of high-temperature Daqu was investigated using Illumina MiSeq high-throughput sequencing. The bacterial community of high-temperature Daqu is mainly composed of thermophilic bacteria, and seven bacterial phyla along with 262 bacterial genera were identified in all 30 high-temperature Daqu samples. Firmicutes, Actinobacteria, Proteobacteria, and Acidobacteria were the dominant bacterial phyla in high-temperature Daqu samples, while Thermoactinomyces, Staphylococcus, Lentibacillus, Bacillus, Kroppenstedtia, Saccharopolyspora, Streptomyces, and Brevibacterium were the dominant bacterial genera. The bacterial community structure of three different types of high-temperature Daqu was significantly different (p < .05). In addition, the results of microbiome phenotype prediction by BugBase and bacterial functional potential prediction using PICRUSt show that bacteria from different types of high-temperature Daqu have similar functions as well as phenotypes, and bacteria in high-temperature Daqu have vigorous metabolism in the transport and decomposition of amino acids and carbohydrates. These results offer a reference for the comprehensive understanding of bacterial diversity of high-temperature Daqu.

Analysis of Difference in Microbial Community and Physicochemical Indices Between Surface and Central Parts of Chinese Special-Flavor Baijiu Daqu

Special-flavor Baijiu is a unique Baijiu in Jiangxi Province, China, whose uniqueness mainly depends on the unique production process of special-flavor Baijiu Daqu. However, the microbial structure and physicochemical indices of different parts of the special-flavor Baijiu Daqu are still unknown. This greatly reduces the actual value of Daqu in the production of special-flavor Baijiu. Therefore, culture-dependent and Illumina MiSeq sequencing methods were used to analyze the microbial structure of special-flavor Baijiu Daqu. The results indicated that there was a complicated microbial diversity in Chinese special-flavor Baijiu Daqu. The predominant bacterial communities were Bacillales, Lactobacillales, and Rhodospirillales, while Saccharomycetales and Eurotiales were the predominant fungal communities. Significant differences in microbial community and distribution were shown between the surface and central parts of Daqu. Acetobacter and Pichia genera were the predominant microorganisms in the surface part of Daqu, whereas Aspergillus, Kroppenstedtia, Oceanobacillus, and Bacillus genera were the predominant microorganisms in the central part of Daqu. Meantime, the different microbial distributions between the surface and central parts of Daqu caused the significant differences in the physicochemical indices. These results can provide an important theoretical basis for improving the brewing process and the quality of special-flavor Baijiu.

Advances in Chemical and Biological Methods to Identify Microorganisms-From Past to Present

Fast detection and identification of microorganisms is a challenging and significant feature from industry to medicine. Standard approaches are known to be very time-consuming and labor-intensive (e.g., culture media and biochemical tests). Conversely, screening techniques demand a quick and low-cost grouping of bacterial/fungal isolates and current analysis call for broad reports of microorganisms, involving the application of molecular techniques (e.g., 16S ribosomal RNA gene sequencing based on polymerase chain reaction). The goal of this review is to present the past and the present methods of detection and identification of microorganisms, and to discuss their advantages and their limitations.