Flavor mystery of Chinese traditional fermented baijiu: The great contribution of ester compounds

Characterisation of aroma compounds, sensory characteristics, and bioactive components of a new type of huangjiu fermented with Chinese wild rice (Zizania latifolia)

Chinese wild rice (CWR) is a nutritious and healthy whole grain, worth developing. To develop and use its value, a new type of huangjiu was brewed with CWR, and the flavour characteristics, sensory quality, functional and bioactive components were evaluated. CWR (67 flavour substances) and glutinous rice (GR)-CWR huangjiu (62 flavour substances) had a better flavour than GR huangjiu (54 flavour substances), and the overall style of GR-CWR huangjiu was more skewed towards GR. The fruity, honey, caramel-like, herb and smoky aroma attributes of CWR huangjiu were higher than those of GR huangjiu (P < 0.05), while only the alcoholic was weaker (P < 0.05) due to the lower alcohol content. The huangjiu brewed using CWR had a better taste than that brewed using only GR. Furthermore, CWR huangjiu had the highest content of total dietary fiber (732.0 ± 15.2 mg/100 g), followed by GR-CWR (307.0 ± 8.5 mg/100 g), and GR (127.0 ± 2.3 mg/100 g). CWR huangjiu also had the highest total phenolic compounds (3.32 ± 0.05 mg/100 g/%vol) and total saponins (2.46 ± 0.03 mg/100 g/%vol) contents, followed by GR-CWR and GR. This study provides guidance for exploring further possibilities for CWR in the future.

Integrative metagenomics, volatilomics and chemometrics for deciphering the microbial structure and core metabolic network during Chinese rice wine (Huangjiu) fermentation in different regions

Huangjiu is a spontaneously fermented alcoholic beverage, that undergoes intricate microbial compositional changes. This study aimed to unravel the flavor and quality formation mechanisms based on the microbial metabolism of Huangjiu. Here, metagenome techniques, chemometrics analysis, and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) metabolomics combined with microbial metabolic network were employed to investigate the distinctions and relationship between the microbial profiles and the quality characteristics, flavor metabolites, functional metabolic patterns of Huangjiu across three regions. Significant variations (P < 0.05) were observed in metabolic rate of physicochemical parameters and biogenic amine concentration among three regions. 8 aroma compounds (phenethyl acetate, phenylethyl alcohol, isobutyl alcohol, ethyl octanoate, ethyl acetate, ethyl hexanoate, isoamyl alcohol, and diethyl succinate) out of 448 volatile compounds were identified as the regional chemical markers. 25 dominant microbial genera were observed through metagenomic analysis, and 13 species were confirmed as microbial markers in three regions. A metabolic network analysis revealed that Saccharomycetales (Saccharomyces), Lactobacillales (Lactobacillus, Weissella, and Leuconostoc), and Eurotiales (Aspergillus) were the predominant populations responsible for substrate, flavor (mainly esters and phenylethyl alcohol) metabolism, Lactobacillales and Enterobacterales were closely linked with biogenic amine. These findings provide scientific evidence for regional microbial contributions to geographical characteristics of Huangjiu, and perspectives for optimizing microbial function to promote Huangjiu quality.

Organic acids drove the microbiota succession and consequently altered the flavor quality of Laotan Suancai across fermentation rounds: Insights from the microbiome and metabolome

Laotan Suancai, a popular traditional Chinese fermented vegetable, is manufactured in the industry via four fermentation rounds. However, the differences in flavor quality of Laotan Suancai from the four fermentation rounds and the causes of this variation remain unclear. Metabolome analysis indicated that the different content of five taste compounds and 31 aroma compounds caused the differences in flavor quality among the variated fermentation rounds of Laotan Suancai. Amplicon sequencing indicated that the microbial succession exhibited a certain pattern during four fermentation rounds and further analysis unveiled that organic acids drove the microbiota shift to more acid-resistant populations. Spearman correlation analysis highlighted that seven core microbes may be involved in the formation of differential flavor and the corresponding metabolic pathways were reconstructed by function prediction. Our findings offer a novel perspective on comprehending the deterioration of flavor quality across the fermentation rounds of Laotan Suancai.

Evolution of fermented grain yeast communities in strong-flavored baijiu and functional validation of yeasts that produce superior-flavored substances

BACKGROUND

Baijiu is a well-known alcoholic beverage in China and the quality is determined by various microorganisms during the fermentation process. Yeast is one of the most important microorganisms in the fermentation of baijiu. It has a strong esterification capacity and also affects the aroma.

RESULTS

High-throughput sequencing results showed that the fermented grains (jiupei) during baijiu production were mainly composed of eight highly abundant yeast species. The species and abundance of yeasts changed significantly with the fermentation process. The flavor of 30 yeast strains in the jiupei was determined by a sniffing test and gas chromatography-mass spectrometry (GC-MS). The strain with the highest flavor substance content (2.34 mg L-1), named YX3205, was identified as Clavispora lusitaniae. Tolerance results showed that C. lusitaniae YX3205 can tolerate up to 15% (v v-1) ethanol. In a solid-state simulated fermentation experiment, the content of 24 flavor substances was significantly increased in the fortified group, and the total ester content reached 4240.73 μg kg-1, which was 2.8 times higher than that of the control group.

CONCLUSION

The present study demonstrated the potential of C. lusitaniae YX3205 to enhance the flavor of baijiu, thereby serving as a valuable strain for the improvement of the flavor quality of baijiu. © 2024 Society of Chemical Industry.

Research on the brewing technology of Dangshen Huangjiu with low biogenic amines and high functional factors

BACKGROUND

Biogenic amines (BA) are hazardous components in Huangjiu (HJ). To ensure the quality of Dangshen Huangjiu (DSHJ), an orthogonal experiment L9 (33) was proposed to optimize the process by the main brewing factors (pre-fermentation temperature, pre- and post-fermentation time) that may affect BA and functional factors in DSHJ. DSHJ was produced with low BA content and high functional factors. Gas chromatography-ion mobility spectrometry combined with a multivariate statistical method (GC-IMS-MSM) was used to analyze the volatile components in the brewing process of DSHJ.

RESULTS

The optimum brewing process parameters of DSHJ were as follows: pre-fermentation temperature, 28 °C; pre-fermentation time, 9 days; post-fermentation time, 18 days. The average content of BA in DSHJ was 33.12 mg L-1, and the sensory score, total phenol content and DPPH free radical scavenging rate of DSHJ were significantly higher than those of HJ. A total of 14 esters, 7 acids, 7 alcohols, 1 ketone, 5 aldehydes and 1 pyrazine in DSHJ and HJ were identified by GC-IMS. There were no significant differences (P > 0.05) in DSHJ and HJ in the soaking rice and saccharification stage. 11 components, such as ethyl acetate, and 12 components, such as acetic acid, were the different components of HJ and DSHJ in pre-fermentation and post-fermentation stages, respectively. In the post-fermentation stage, the contents of 8 components in DSHJ such as ethyl acetate were higher than in HJ.

CONCLUSION

The preparation process parameters of DSHJ optimized by orthogonal experiments can ensure that DSHJ has the advantages of low BA content, high total phenol content and good antioxidant activity. Sensory score and GC-IMS-MSM analysis found that DSHJ prepared using the optimal process had the characteristics of good taste and rich aroma. © 2024 Society of Chemical Industry.

Nanotechnology-based optical sensors for Baijiu quality and safety control

Baijiu quality and safety have received considerable attention owing to the gradual increase in its consumption. However, owing to the unique and complex process of Baijiu production, issues leading to quality and safety concerns may occur during the manufacturing process. Therefore, establishing appropriate analytical methods is necessary for Baijiu quality assurance and process control. Nanomaterial (NM)-based optical sensing techniques have garnered widespread interest because of their unique advantages. However, comprehensive studies on nano-optical sensing technology for quality and safety control of Baijiu are lacking. In this review, we systematically summarize NM-based optical sensor applications for the accurate detection and quantification of analytes closely related to Baijiu quality and safety. Furthermore, we evaluate the sensing mechanisms for each application. Finally, we discuss the challenges nanotechnology poses for Baijiu analysis and future trends. Overall, nanotechnological approaches provide a potentially useful alternative for simplifying Baijiu analysis and improving final product quality and safety.

A novel organic acids-targeted colorimetric sensor array for the rapid discrimination of origins of Baijiu with three main aroma types

Given the severe problem of Baijiu authenticity, it is essential to discriminate Baijiu from different origins quickly and effectively. As organic acids (OAs) are the most dominant taste-imparting substances in Baijiu, we proposed a simple, fast, and effective OAs-targeted colorimetric sensor array based on the colorimetric reaction of 4-aminophenol (AP)/4-amino-3-chlorophenol (ACP) under oxidation of Cu(NO3)2 for the rapid discrimination of origins of Baijiu with three main aroma types. Hydrogen ions ionized from OAs induced the protonation of the amino group, which blocked the colorimetric reaction, and the different levels of OAs in Baijiu enabled the array to discriminate different origins of Baijiu. The array was implemented to analyze 10 simple OAs and 16 mixed OAs and further for the discrimination of 42 Baijius with an accuracy of 98%. This method provided an efficient research strategy for a basis for rapid quality analysis of Baijiu.

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.

A Novel Data Fusion Strategy of GC-MS and 1H NMR Spectra for the Identification of Different Vintages of Maotai-flavor Baijiu

Counterfeit Baijiu has been emerging because of the price variances of real-aged Chinese Baijiu. Accurate identification of different vintages is of great interest. In this study, the combination of gas chromatography-mass spectrometry (GC-MS) and proton nuclear magnetic resonance (1H NMR) spectroscopy was applied for the comprehensive analysis of chemical constituents for Maotai-flavor Baijiu. Furthermore, a novel data fusion strategy combined with machine learning algorithms has been established. The results showed that the midlevel data fusion combined with the random forest algorithm were the best and successfully applied for classification of different Baijiu vintages. A total of 14 differential compounds (belonging to fatty acid ethyl esters, alcohols, organic acids, and aldehydes) were identified, and used for evaluation of commercial Maotai-flavor Baijiu. Our results indicated that both volatiles and nonvolatiles contributed to the vintage differences. This study demonstrated that GC-MS and 1H NMR spectra combined with a data fusion strategy are practical for the classification of different vintages of Maotai-flavor Baijiu.

Oxygen influences spatial heterogeneity and microbial succession dynamics during Baijiu stacking process

The spontaneous solid-state stacking process (SSSP) of Baijiu is an environmentally friendly and cost-effective process for enriching and assembling environmental microorganisms to guarantee the subsequent fermentation efficiency. In this study, how SSSP create spatial heterogeneity of stacking piles were found through spatiotemporal sampling. The degree of difficulty in oxygen exchange categorizes the stacking pile into depleted (≤4%), transitional (4 %-17 %), and enriched (≥17 %) oxygen-defined layers. This results in variation in succession rates (Vdepleted > Vtransitional > Venriched), which accelerates spatial heterogeneity during SSSP. As a dominant species (65 %-99 %) in depleted and transitional layers, Acetilactobacillus jinshanensis can rapidly reduce oxygen disturbance by upregulating poxL and catE, that sustains spatial heterogeneity. The findings demonstrated the value of oxygen control in shaping spatial heterogeneity during SSSP processes, which can create specific functional microbiome. Adding spatial heterogeneity management will help achieve more precise control of such solid-state fermentation systems.

Removal of Cu (II) by ion exchange resin and its re-utilization of the residual solution from the distilled Lycium barbarum wine

In order to re-utilize the residual from the distillation of the Chinese wolfberry wine and reduce the environmental pollution, the residual is firstly filtered by the ceramic membrane of 50 nm, then the Cu (II) has transferred from the distillation is removed using the ion exchange resin, and the treated solution is recombined with the distilled liquor to make the Chinese wolfberry brandy and the comparison has conducted on the physicochemical properties, antioxidant activity and flavor compounds between the recombined brandy and the finished brandy. The results indicate that the Cu (II) was effectively removed by ceramic membrane combined with the D401 resin. Compared with finished brandy, the recombined brandy contains high contents of polysaccharides, phenols and flavonoids, thus contributing to the improvement of antioxidant capacity. The gas chromatography-ion mobility spectrometry (GC-IMS) reveals that 25 volatile compounds like esters and alcohols have identified in the brandy samples, and the differences are significant between the recombined and the finished brandy. In summary, the distilled residual from the Chinese wolfberry wine might be re-used after the appropriate treatment so as to reduce the discharge and environmental pollution.

Bioturbation analysis of microbial communities and flavor metabolism in a high-yielding cellulase Bacillus subtilis biofortified Daqu

In this study, a fortified Daqu (FF Daqu) was prepared using high cellulase-producing Bacillus subtilis, and the effects of in situ fortification on the physicochemical properties, flavor, active microbial community and metabolism of Daqu were analyzed. The saccharification power, liquefaction power, and cellulase activity of the FF Daqu were significantly increased compared with that of the traditional Daqu (CT Daqu). The overall differences in flavor components and their contents were not significant, but the higher alcohols were lower in FF Daqu. The relative abundance of dominant active species in FF Daqu was 85.08% of the total active microbiota higher than 63.42% in CT Daqu, and the biomarkers were Paecilomyces variotii and Aspergillus cristatus, respectively. The enzymes related to starch and sucrose metabolic pathways were up-regulated and expressed in FF Daqu. In the laboratory level simulation of baijiu brewing, the yield of baijiu was increased by 3.36% using FF Daqu.

The mechanism of microbial structure and flavor characteristics in Qing-Jiang-flavor Jiupei regulated by different fermentation seasons

The physicochemical characteristics of Jiupei are crucial in regulating the metabolism of microbial communities and the flavor profile of Baijiu during the fermentation process. This study systematically monitored the physicochemical characteristics of Qing-Jiang-flavor Baijiu Jiupei (QJFJ) and analyzed its microbial community structure and flavor compounds. Results indicated that dominant bacteria were significantly enriched in Summer- and Autumn-Jiupei (Spring: Summer: Autumn: Winter = 1.00: 1.40: 1.29: 1.21), while dominant fungi were significantly enriched in Spring- and Autumn-Jiupei (Spring: Summer: Autumn: Winter = 1.45: 1.00: 1.35: 1.31). Sequentially, reducing sugars (day 0), temperature (day 5 - day 10), moisture (day 15), and acidity (day 20 - day 25) in Jiupei affected the succession pattern of the microbial community, regulating the abundance of Saccharomyces, Staphylococcus, Cyberlindnera, and Lactobacillus, individually. Alcohol and acid compounds are considered seasonal differential compounds in QJFJ. This study will provide a theoretical basis for Baijiu production across different seasons.

Workshop environment heterogeneity shaped the microbiome and metabolome profiles during Xiasha round of Jiangxiangxing Baijiu

Workshop with different fermentation years plays an essential role in the yield and quality of Baijiu. In actual production, the quality of base Baijiu in newly built workshop is inferior to the older one. In this study, the microbiota of workshop environment and fermentation process from two workshops namely N (ferment 2 years) and O (ferment 20 years) and flavor compounds were studied during Xiasha round. Results showed workshop O accumulated more environmental microorganisms and fungi including P. kudriavzevii, Wickerhamomyces anomalus and Saccharomyces sp mainly came from ground. Yeasts including Pichia, Cyberlindnera, Wickerhamomyces and Candida were responsible for flavor substances formation in O while Saccharopolyspora was in N. This study for the first time explored the reasons for the brewing differences among N and O workshop from perspectives of workshop environment, microbial community and flavor substances, providing new ideas for guiding production as well as improvement of Baijiu quality.

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.

Effects of Various Flavors of Baijiu on the Microbial Communities, Metabolic Pathways, and Flavor Structures of Dongbei Suancai

This study aimed to assess the effects of Chinese Baijiu with different flavors as supplementary material on microbial communities and flavor formation during inoculated fermentation of Chinese Dongbei Suancai. The results showed that the addition of Fen flavor Baijiu significantly increased the relative abundance of Candida, Luzhou flavor Baijiu increased the relative abundance of Pedobacter and Hannaella, while Maotai flavor Baijiu increased the Chryseobacterium and Kazachstania. A total of 226 volatile metabolites were detected in Suancai fermented when adding different flavors of Baijiu. Furthermore, the significantly upregulated metabolites (p < 0.01) of Suancai after adding Baijiu increased by 328.57%, whereas the significantly downregulated metabolites decreased by 74.60%. Simultaneously, the addition of Baijiu promoted the synthesis and decomposition of amino acids and short-chain fatty acids in the early and middle stages of fermentation. Further, Maotai flavor Baijiu improved the diversification of metabolic pathways in the late stage of Suancai fermentation. The E-nose response showed that sulfur-organic, broad-alcohol, sulfur-chlor was the principal differential flavor in Suancai caused by adding Baijiu with different flavors. Simultaneously, Fen flavor Baijiu and Luzhou flavor Baijiu accelerated the formation of the Suancai flavor. These results indicated that Baijiu with different flavors had significant effects on the flavor formation of inoculated fermented Suancai.

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.

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.

Optimization of fermentation conditions for the production of γ-aminobutyric acid by Lactobacillus hilgardii GZ2 from traditional Chinese fermented beverage system

γ-Aminobutyric acid (GABA) is a crucial neurotransmitter with wide application prospects. In this study, we focused on a GABA-producing strain from a traditional Chinese fermented beverage system. Among the six isolates, Lactobacillus hilgardii GZ2 exhibited the greatest ability to produce GABA in the traditional Chinese fermented beverage system. To increase GABA production, we optimized carbon sources, nitrogen sources, temperature, pH, and monosodium glutamate and glucose concentrations and conducted fed-batch fermentation. The best carbon and nitrogen sources for GABA production and cell growth were glucose, yeast extract and tryptone. Gradual increases in GABA were observed as the glucose and monosodium glutamate concentrations increased from 10 g/L to 50 g/L. During fed-batch fermentation, lactic acid was used to maintain the pH at 5.56, and after feeding with 0.03 g/mL glucose and 0.4 g/mL sodium glutamate for 72 h, the GABA yield reached 239 g/L. This novel high-GABA-producing strain holds great potential for the industrial production of GABA, as well as the development of health-promoting functional foods and medical fields.

Discovery and mechanism explanation of a novel green biocatalyst esterase Bur01 from Burkholderia ambifaria for ester synthesis under aqueous phase

Biocatalyst catalyzing the synthesis of esters under aqueous phase is an alternative with green and sustainable characteristics. Here, a biocatalyst esterase Bur01 was identified through genome sequencing and gene library construction from a Burkholderia ambifaria BJQ0010 with efficient ester synthesis property under aqueous phase for the first time. Bur01 was soluble expressed and the purified enzyme showed the highest activity at pH 4.0 and 40 °C. It had a broad substrate spectrum, especially for ethyl esters. The structure of Bur01 was categorized as a member of α/β fold hydrolase superfamily. The easier opening of lid under aqueous phase and the hydrophobicity of substrate channel contribute to easier access to the active center for substrate. Molecular docking and site-directed mutation demonstrated that the oxyanion hole Ala22, Met112 and π-bond stacking between His24 and Phe217 played essential roles in catalytic function. The mutants V149A, V149I, L159I and F137I enhanced enzyme activity to 1.42, 1.14, 1.32 and 2.19 folds due to reduced spatial resistance and increased hydrophobicity of channel and ethyl octanoate with the highest conversion ratio of 68.28 % was obtained for F137I. These results provided new ideas for developing green catalysts and catalytic basis of mechanistic studies for ester synthetase under aqueous phase.

Unraveling the chemosensory characteristics dependence of sauce-flavor baijiu on regionality using descriptive sensory analysis and quantitative targeted flavoromics

Descriptive sensory analysis, headspace solid-phase microextraction-gas chromatography-mass spectrometry, gas chromatography-flame ionization detector and multivariate statistical analysis were used to elucidate the regional dependence of sauce-flavor baijiu (SFB). Although SFB samples from different regions couldn't be clearly classified by sensory profiles, they could be clearly divided into 5 groups in principal component analysis plot based on quantitative targeted flavoromics analysis. And then, the relationship between sensory attributes and volatile compounds were investigated by network analysis. Twenty regional aroma markers were identified by multivariate statistical analysis to distinguish SFB samples from different regions. Furthermore, the influence of manufacturing operation on SFB in Guizhou region was further analyzed. Thirty-eight potential compounds were significant different in Guizhou SFB samples with different manufacturing operations. This study not only provides a better understanding of regional dependence on SFB flavor, but also further clarifies the inheritance importance of manufacturing operation in traditional SFB production.

Characterizing the Contribution of Functional Microbiota Cultures in Pit Mud to the Metabolite Profiles of Fermented Grains

Elevating the flavor profile of strong flavors Baijiu has always been a focal point in the industry, and pit mud (PM) serves as a crucial flavor contributor in the fermentation process of the fermented grains (FG). This study investigated the influence of wheat flour and bran (MC and FC) as PM culture enrichment media on the microbiota and metabolites of FG, aiming to inform strategies for improving strong-flavor Baijiu flavor. Results showed that adding PM cultures to FG significantly altered its properties: FC enhanced starch degradation to 51.46% and elevated reducing sugar content to 1.60%, while MC increased acidity to 2.11 mmol/10 g. PM cultures also elevated FG's ester content, with increases of 0.36 times for MC-FG60d and 1.48 times for FC-FG60d compared to controls, and ethyl hexanoate rising by 0.91 times and 1.39 times, respectively. Microbial analysis revealed that Lactobacillus constituted over 95% of the Abundant bacteria community, with Kroppenstedtia or Bacillus being predominant among Rare bacteria. Abundant fungi included Rasamsonia, Pichia, and Thermomyces, while Rare fungi consisted of Rhizopus and Malassezia. Metagenomic analysis revealed bacterial dominance, primarily consisting of Lactobacillus and Acetilactobacillus (98.80-99.40%), with metabolic function predictions highlighting genes related to metabolism, especially in MC-FG60d. Predictions from PICRUSt2 suggested control over starch, cellulose degradation, and the TCA cycle by fungal subgroups, while Abundant fungi and bacteria regulated ethanol and lactic acid production. This study highlights the importance of PM cultures in the fermentation process of FG, which is significant for brewing high-quality, strong-flavor Baijiu.

N-Doping CQDs as an Efficient Fluorescence Probe Based on Dynamic Quenching for Determination of Copper Ions and Alcohol Sensing in Baijiu

To address an accurate detection of heavy metal ions in Baijiu production, a nitrogen-doping carbon quantum dots (N-CQDs) was prepared by hydrothermal method from citric acid and urea. The as-prepared N-CQDs had an average particle size of 2.74 nm, and a large number of functional groups (amino, carbonyl group, etc.) attached on its surface, which obtained a 9.6% of quantum yield (QY) with relatively high and stable fluorescence performance. As a fluorescent sensor, the fluorescence of N-CQDs at 380 nm excitation wavelength could be quenched quantitatively by adding Cu2+, due to the dynamic quenching of electron transfer caused by the binding of amine groups and Cu2+, which showed excellent sensitivity and selectivity to Cu2+ in the range of 0.5-5 μM with a detection limit (LOD) of 0.032 μM. In addition, the N-CQDs as well as could be applied to quantitative determine alcohol content in the range of 10-80 V/V% depending on the fluorescence enhancement. Upon the experiment, the fluorescent mechanism was studied by Molecular dynamics (MD) simulations, which demonstrated that solvent effect played an influential role on sensing alcohol content in Baijiu. Overall, the work provided a theoretically guide for the design of fluorescence sensors to monitor heavy metal ion in liquid drinks and sense alcohol content.

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.

Analysis of Fungal Diversity, Physicochemical Properties and Volatile Organic Compounds of Strong-Flavor Daqu from Seven Different Areas

Strong-flavor Daqu, as a fermentation agent, plays a significant role in shaping the quality of strong-flavor baijius, and fungal species in Daqu are important factors affecting the quality of Daqu. Therefore, we selected strong-flavor Daqu from seven different origins to study the fungal composition and the effects of the fungal composition on the physicochemical properties and volatile organic compounds (VOCs). It was found that the fungal composition influences the physicochemical properties of Daqu. Specifically, there was a positive link between Rhizomucor, Rhizopus, Thermomyces, and liquefying activity and a positive correlation between Aspergillus and fermenting activity. Furthermore, the relationships between esterifying activity and Thermomyces, Rhizomucor, Aspergillus, Pichia, and Saccharomycopsis were found to be positive. The VOCs in Daqu were affected by Aspergillus, Issatchenkia, Pichia, and Thermoascus. Issatchenkia was significantly positively correlated with benzeneethanol as well as Aspergillus and pentadecanoic acid ethyl ester, ethyl myristate. Pichia and Thermoascus were significantly negatively correlated with benzaldehyde and 2-furaldehyde. This study deepens our understanding of the relationship between VOCs, the physicochemical properties with microbial communities, and reference significance for the production of better-quality strong-flavor Daqu.

Using in situ untargeted flavoromics analysis to unravel the empty cup aroma of Jiangxiang-type Baijiu: A novel strategy for geographical origin traceability

"Empty cup aroma" is an important characteristic and quality evaluation standard of Jiangxiang-type Baijiu (JXB). In this study, an in situ detection method for the empty cup aroma of JXB was established, and the authenticity and origin information of JXB were identified with an untargeted flavoromics strategy. The complex composition of JXB leads to slow ethanol volatilization, which is a potential method for identifying artificial JXB. The results of the sensory analysis showed that acidic, sauce, burnt and qu in the empty cup of JXB were the strongest at the 45 min stage. A total of 155 compounds were detected in the empty cups of 15 JXB from different regions during 45 min of standing, and 34 compounds were identified as key aroma compounds in the empty cups of JXB. Eleven potential markers were screened (VIP > 1), which can be used to distinguish JXB produced in Guizhou/Sichuan and other regions.

Characterization of Flavor Profiles of Cigar Tobacco Leaves Grown in China via Headspace-Gas Chromatography-Ion Mobility Spectrometry Coupled with Multivariate Analysis and Sensory Evaluation

Although cigar tobacco leaves (CTLs) have a high economic value, research regarding the flavor characteristics of CTLs is currently limited. A comprehensive study of the flavor characteristics of CTLs from different regions of China was conducted by identifying their volatile-flavor-containing compounds (VFCs) and flavors. The samples were analyzed via gas chromatography-ion mobility spectrometry (GC-IMS) and sensory evaluation. Results revealed considerable differences in the VFC contents of CTLs from different regions of China, suggesting that the VFLs of CTLs could be influenced by geographical origin. Mainly, phenols, pyrazines, and aldehydes were present in the CTLs from Sichuan. High contents of esters and pyrazines were present in the CTLs from Hubei, while esters were the major components of the CTLs from Hainan. Multivariate analysis results showed the effective differentiation of samples from different geographical origins based on the GC-IMS results. Sensory evaluation revealed that the flavors of CTLs from different geographical origins were different. 1,8-Pinene, 3-methyl-3-butene-1-ol, 2,3-dimethyl-5-ethylpyrazine, 4-methyl-3-penten-2-one, and (E)-2-pentenal might serve as geographical marker compounds, indicating the geographical origin of CTLs based on the results of GC-IMS and sensory evaluation. This study may be beneficial for the trade of CTLs and the development of cigar products.

Co-culture fermentation by Saccharomycopsis fibuligera and lactic acid bacteria improves bioactivity and aroma profile of wheat bran and the bran-containing Chinese steamed bread

Co-culture fermentation with yeast and lactic acid bacteria (LAB) exhibits advantages in improving the bioactivity and flavor of wheat bran compared to single-culture fermentation, showing application potentials in bran-containing Chinese steamed bread (CSB). To explore the effects of combination of yeast and different LAB on the bioactivity and flavor of fermented wheat bran, this study analyzed the physicochemical properties, phytate degradation capacity, antioxidant activities, and aroma profile of wheat bran treated with co-culture fermentation by Saccharomycopsis fibuligera and eight different species of LAB. Further, the phenolic acid composition, antioxidant activities, texture properties, aroma profile, and sensory quality of CSB containing fermented wheat bran were evaluated. The results revealed that co-culture fermentation brought about three types of volatile characteristics for wheat bran, including ester-feature, alcohol and acid-feature, and phenol-feature, and the representative strain combinations for these characteristics were S. fibuligera with Limosilactobacillus fermentum, Pediococcus pentosaceus, and Latilactobacillus curvatus, respectively. Co-culture fermentation by S. fibuligera and L. fermentum for 36 h promoted acidification with a phytate degradation rate reaching 51.70 %, and improved the production of volatile ethyl esters with a relative content of 58.47 % in wheat bran. Wheat bran treated with co-culture fermentation by S. fibuligera and L. curvatus for 36 h had high relative content of 4-ethylguaiacol at 52.81 %, and exhibited strong antioxidant activities, with ABTS•+ and DPPH• scavenging rates at 65.87 % and 69.41 %, respectively, and ferric reducing antioxidant power (FRAP) at 37.91 μmol/g. In addition, CSB containing wheat bran treated with co-culture fermentation by S. fibuligera and L. fermentum showed a large specific volume, soft texture, and pleasant aroma, and received high sensory scores. CSB containing wheat bran treated with co-culture fermentation by S. fibuligera and L. curvatus, with high contents of 4-ethylguaiacol, 4-vinylguaiacol, ferulic acid, vanillin, syringaldehyde, and protocatechualdehyde, demonstrated strong antioxidant activities. This study is beneficial to the comprehensive utilization of wheat bran resources and provides novel insights into the enhancement of functions and quality for CSB.

Production of cost-competitive bioethanol and value-added co-products from distillers' grains: Techno-economic evaluation and environmental impact analysis

Here, Baijiu distillers' grains (BDGs) were employed in biorefinery development to generate value-added co-products and bioethanol. Through ethyl acetate extraction at a 1:6 solid-liquid ratio for 10 h, significant results were achieved, including 100 % lactic acid and 92 % phenolics recovery. The remaining BDGs also achieved 99 % glucan recovery and 81 % glucan-to-glucose conversion. Simultaneous saccharification and fermentation of remaining BDGs at 30 % loading resulted in 78.5 g bioethanol/L with a yield of 94 %. The minimum selling price of bioethanol varies from $0.149-$0.836/kg, contingent on the co-product market prices. The biorefinery processing of one ton of BDGs caused a 60 % reduction in greenhouse gas emissions compared to that of the traditional production of 88 kg corn-lactic acid, 70 kg antioxidant phenolics, 234 kg soybean protein, and 225 kg corn-bioethanol, along with emissions from BDG landfilling. The biorefinery demonstrated a synergistic model of cost-effective bioethanol production and low-carbon emission BDGs treatment.

Quality properties of fish ball with abalone and its relationship with sensory properties

In this work, whiteness, water-holding capacity, gel strength, textural profile analysis were performed to examine the quality of fish balls with abalone (FBA). In addition, a correlation between quality and sensory properties was established. The addition of abalone significantly increased the water holding capacity, gel strength and textural properties of FBA, and decreased their whiteness, the best overall quality was achieved at 9 % w/w abalone addition. The E-nose and E-tongue results revealed that the addition of abalone changed the flavour of FBA. HS-SPME-GC-MS identified 65 volatile organic compounds (VOCs) and proved to be effective in reducing fishy flavour. E-nose can distinguish between the VOCs in FBA. Moreover, Umami and 1-octen-3-ol can serve as important indicators to observe changes in the quality of FBA, as they were positively connected with WHC, gumminess, chewiness, resilience, a*, hexanal, etc. The results provided a theoretical basis for the development of abalone and surimi products.

Association between Baijiu chemistry and taste change: Constituents, sensory properties, and analytical approaches

Typical flavors, such as sourness, sweetness, and bitterness, possess numerous functions and physiological significance, and are closely related to Baijiu production management, quality control, and product development. However, current research on Baijiu flavor primarily focuses on the volatile constituents and distinctive aroma compounds. Furthermore, studies on taste substance recognition, identification, and formation are remain in the preliminary phase. Herein, we take an integrated account of the signal transduction, recognition, composition, and sensory properties of the three main basic tastes of Baijiu, including sourness, sweetness, and bitterness. Moreover, to elucidate the factors that might influence the taste perception of Baijiu, we also discussed the biotic and abiotic factors within the fermentation system. Finally, further elucidating the contribution underlying the three main tastes in Baijiu using a combination of the "Sensomics" and "Flavoromics", will allow for Baijiu taste characteristics to be manipulated.

Exploring the regulated effects of solid-state fortified Jiuqu and liquid-state fortified agent on Chinese Baijiu brewing

Zaopei is the direct source of Chinese liquor (Baijiu). Adding functional strains to Zaopei is a potential strategy to regulate Baijiu brewing, mainly including the two ways of solid-state fortified Jiuqu (SFJ) and liquid-state fortified agent (LFA). Here, to explore their regulated details, the response patterns of Zaopei microecosystem and the changes in the product features were comprehensively investigated. The results showed that SFJ more positively changed the physicochemical properties of Zaopei and improved its ester content, from 978.57 mg/kg to 1078.63 mg/kg over the fermentation of 30 days, while LFA decreased the content of esters, alcohols, and acids. Microbial analysis revealed that SFJ significantly increased Saccharomycopsis and Aspergillus from the start of fermentation and induced a positive interaction cluster driven by the added functional Paenibacillus, while LFA exhibited a community structure near that of the original microecosystem and led to a simpler network with the reduced microbial nodes and correlations. Metabolism analysis found that both SFJ and LFA weakened the flavor-producing metabolism by suppressing some key enzyme pathways, such as EC 3.2.1.51, EC 4.2.1.47, EC 1.1.1.27, EC 1.1.1.22, EC 1.5.1.10, EC 1.14.11.12. As a result, SFJ improved the raw liquor yield by 28.5 % and endowed the final product with a more fragrant aroma, mainly through ethyl (E)-cinnamate, ethyl isovalerate, ethyl phenacetate with the higher odor activity values, while LFA promoted the yield by 13.2 % and resulted in a purer and less intense aroma through the aroma-active β-damascenone, ethyl heptoate, ethyl phenacetate. These results facilitated the regulated mechanism of SFJ and LFA on Baijiu brewing and indicated that the used functional strains in this study could be applicated in SFJ way for the further industrial-scale application.

Insight investigation into the response pattern of microbial assembly succession and volatile profiles during the brewing of sauce-flavor baijiu based on bioaugmentation

To improve the flavor profile and sensory quality of baijiu, the utilization of bioaugmented fermentation inoculated with functional microbiota normally serves as an effective method for directional regulation during the baijiu fermentation process. In this study, a systematic analysis of the succession patterns and volatile flavor compound profiles of microbial communities was carried out by high-throughput sequencing and solid-phase microextraction gas chromatography-mass spectrometry, respectively. The results demonstrated that the Saccharomyces cerevisiae YS222-related bioaugmentation clearly altered the microbial composition, particularly the assembly of bacteria, and promoted the quantity of the most volatile flavoring compounds, including alcohols, esters, and pyrazines. In addition, the correlation analysis showed that Saccharomyces and Lactobacillus in the augmented group were the main biomarkers associated with the dynamics of microbial community and greatly contributed to the brewing of sauce-flavor baijiu, which congruent with the outcomes of the enrichment analysis of integrated metabolic pathway. Thus, this work is beneficial for promoting the quality of baijiu and will serve as a useful reference for clarifying the possible mechanism of augmented fermentation on flavor development.

Analysis of the differences in physicochemical properties, volatile compounds, and microbial community structure of pit mud in different time spaces

Pit mud (PM) is among the key factors determining the quality of Nongxiangxing baijiu, a Chinese liquor. Microorganisms present inside PM are crucial for the unique taste and flavor of this liquor. In this study, headspace solid-phase microextraction was used in combination with gas chromatography and high-throughput sequencing to determine the volatile compounds and microbial community structure of 10- and 40-year PM samples from different spaces. The basic physicochemical properties of the PM were also determined. LEfSe and RDA were used to systematically study the PM in different time spaces. The physicochemical properties and ester content of the 40-year PM were higher than those of the 10-year PM, but the spatial distribution of the two years PM samples exhibited no consistency, except in terms of pH, available phosphorus content, and ester content. In all samples, 29 phyla, 276 families, and 540 genera of bacteria, including four dominant phyla and 20 dominant genera, as well as eight phyla, 24 families, and 34 genera of archaea, including four dominant phyla and seven dominant genera, were identified. The LEfSe analysis yielded 18 differential bacteria and five differential archaea. According to the RDA, the physicochemical properties and ethyl caproate, ethyl octanoate, hexanoic acid, and octanoic acid positively correlated with the differential microorganisms of the 40-year PM, whereas negatively correlated with the differential microorganisms of the 10-year PM. Thus, we inferred that Caproiciproducens, norank_f__Caloramatoraceae, and Methanobrevibacter play a dominant and indispensable role in the PM. This study systematically unveils the differences that affect the quality of PM in different time spaces and offers a theoretical basis for improving the declining PM, promoting PM aging, maintaining cellars, and cultivating an artificial PM at a later stage.

High-Resolution Mass Spectrometry-Based Chemical Fingerprinting of Baijiu, a Traditional Chinese Liquor

Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, coupled with electrospray ionization (ESI) or atmospheric-pressure photoionization (APPI), was employed for chemical fingerprinting of baijiu, a traditional Chinese liquor. Baijiu is the most consumed distilled alcoholic beverage globally, with over 10 billion liters sold annually. It is a white (transparent) spirit that exhibits similarities to dark spirits such as whisky or rum in terms of aroma and mouthfeel. In this study, direct-infusion FT-ICR mass spectrometry was used to analyze 10 commercially available baijiu liquors, enabling the examination of both volatile and nonvolatile constituents without the need for tedious sample extractions or compound derivatizations. The chemical fingerprints obtained by FT-ICR MS revealed substantial compositional diversity among different baijiu liquors, reflecting variations in the raw materials and production methods. The main compounds identified included a variety of acids, esters, aldehydes, lactones, terpenes, and phenolic compounds. The use of ESI and APPI provided complementary compositional information; while ESI demonstrated greater selectivity toward polar, aliphatic sample constituents, APPI also ionized semipolar and nonpolar (aromatic) ones.

Comparison of Aroma Compounds and Sensory Characteristics between Two Different Types of Rice-Based Baijiu

Rice-based Baijiu has gained popularity in the Chinese market. Qingya-flavored Baijiu, a variant of Xiaoqu-fermented Baijiu, employs rice as its primary raw material, with an improved production process compared to traditional rice-flavored Baijiu. We comprehensively characterized and compared the aroma profiles of these two rice-based Baijiu types using static sensory experiments (QDA, quantitative descriptive analysis) and dynamic sensory experiments (TDS, temporal dominance of sensations). Qingya-flavored Baijiu exhibited pronounced plant, oily, and roasted aromas, while traditional rice-flavored Baijiu displayed more prominent fruity, floral, and sour notes. Utilizing GC-O-MS (gas chromatography-olfactometry-mass spectrometry) and multi-method quantification, we qualitatively and quantitatively analyzed 61 key aroma compounds, identifying 22 compounds with significant aroma contributions based on odor activity values (OAVs). Statistical analyses, combining sensory and chemical results, were conducted to predict important aroma compounds responsible for the aroma differences between the two Baijiu types. Aroma Recombination and Omission experiments showed that seven compounds play key roles in the aroma of Qingya-flavored Baijiu, including (2E,4E)-Deca-2,4-dienal, linalool, apricolin, ethyl acetate, ethyl isobutyrate, ethyl caprylate, and ethyl isovalerate.

Contribution of microorganisms from pit mud to volatile flavor compound synthesis in fermented grains for nongxiangxing baijiu brewing

BACKGROUND

Nongxiangxing baijiu (NB) is known for its distinct flavor profile, which is attributed to key aroma compounds. The exposed fermentation technique, utilizing daqu and solid-state fermentation in pit muds, plays a crucial role in flavor development. Though previous studies have investigated the impact of microorganisms from pit ?ud and fermented grains on flavor compound production, a comprehensive understanding of microbial functions in the entire pit fermentation system is lacking. Herein, we aimed to explore the role of pit-mud-derived microorganisms in shaping the microbial community and flavor compound synthesis in NB.

RESULTS

There are 76 volatile flavor compounds that have been identified in fermented grains during NB fermentation. The main flavor compounds in NB clustered within the same network module, and 27.27% of microorganisms in the core modules of the fermented grain co-occurrence network originated from pit mud. The relationship between pit mud microorganisms and flavor compounds revealed a significant positive correlation (92%). Notably, Prevotella and Sarocladium were identified as the main contributors to this effect on flavor.

CONCLUSION

Microorganisms originating from pit mud influenced the composition and activity of microorganisms in fermented grains and facilitated the production of flavor compounds in NB. © 2023 Society of Chemical Industry.

Airborne microbes in five important regions of Chinese traditional distilled liquor (Baijiu) brewing: regional and seasonal variations

Baijiu is one of the six primary distilled spirits in the world. It is produced through the solid-state fermentation of grains in the open environment, so high-quality Baijiu brewing largely depends on terrior. Environmental microbes are one of the most important factors affecting the quality, quantity, and flavors of Baijiu. As atmosphere is a pool and transport pathway for microbes from the ambient environment to Baijiu brewing ecosystems, we explored the functional microbes of Baijiu brewing in five important regions. The regions fell into two topographical types, namely, plain and river-valley. In total, 41 functional microbes were identified rich (relative abundance >0.1%) in at least one of the regions, such as the fungi of Aspergillus, Candida, Cladosporium, Debaryomyces, Penicillium, Pichia, Rhizopus, Saccharomyces, and Wickerhamomyces and the bacteria of Acetobacter, Bacillus, Clostridium, Enterobacter, Lactobacillus, Methanosarcina, Methanobacterium, Methanobrevibacter, and Pseudomonas. However, some functional bacteria (e.g., Clostridia, Gluconacetobacter, and Weissella) and fungi (e.g., Dekkera, Eurotium, Issatchenkia, Mucor, and Phoma) were not rich or were not detected in the atmosphere. Airborne microbiomes and the Phylogenetic Diversity (PD) index were significantly different between the main brewing season (winter) and the summer break in each region, except for the fungi in one region. In winter, airborne microbiomes were significantly different among almost all the regions. The relative abundance of bacterial fermentation function in each region increased from summer to winter. The relative abundances of fungal yeast function were higher in winter for the plain regions but were higher in summer for the river-valley regions. In sum, our results suggested that: (1) atmosphere was one but not the sole important source of functional microbes for Baijiu brewing and (2) microbiomes in different regions might be quite different but they could share some major functions related to Baijiu brewing.

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

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

The improvement of Hovenia acerba-sorghum co-fermentation in terms of microbial diversity, functional ingredients, and volatile flavor components during Baijiu fermentation

The quality of Baijiu was largely affected by raw materials, which determine the flavor and taste. In the present study, organic acids, polyphenols, volatile flavor components and microbial community in Hovenia acerba-sorghum co-fermented Baijiu (JP1) and pure sorghum-fermented Baijiu (JP2) were comprehensively analyzed. Organic acids, polyphenols and volatile flavor components in JP1 were more abundant than JP2. The abundance and diversity of bacteria and fungi in JP1 was higher than that in JP2 in the early stage of fermentation, but presented opposite trend in the middle and late stages. Leuconostoc, Lentilactobacillus and Issatchenkia were dominant genera in JP1. Whereas, Cronobacter, Pediococcus and Saccharomyces occupied the main position in JP2. Lentilactobacillus and Issatchenkia were positively related to most of organic acids and polyphenols. Pseudomonas, Rhodococcus, Cronobacter, Pediococcus, Brucella, Lentilactobacillus, Lactobacillus, Saccharomycopsis, Wickerhamomyces, Aspergillus, Thermomyces and unclassified_f-Dipodascaccae were associated with the main volatile flavor components. The main metabolic pathways in two JPs exhibited the variation trend of first decreasing and then increasing, and the metabolism activity in JP1 were higher than that in JP2. The results demonstrated the introduction of Hovenia acerba improved the functional ingredients and volatile flavor components, which is helpful for the quality promotion of Baijiu. This study identified the key microorganisms and discussed their effect on organic acids, polyphenols and volatile flavor components during the fermentation of Baijiu with different raw materials, providing a scientific basis for the development and production of high-quality Baijiu.

Complete genome sequence of Acinetobacter indicus and identification of the hydrolases provides direct insights into phthalate ester degradation

A strain designated Acinetobacter indicus WMB-7 with the ability to hydrolyze phthalate esters (PAEs) was isolated from the fermented grains of Baijiu. The genome of the strain was sequenced with a length of 3,256,420 bp and annotated with 3183 genes, of which 36 hydrolases encoding genes were identified. The hydrolases were analyzed by protein structure modeling and molecular docking, and 14 enzymes were docked to the ligand di-butyl phthalate with the catalytic active regions, and showed binding affinity. The 14 enzymes were expressed in E. coli and 5 of them showed the ability for PAEs hydrolysis. Enzyme GK020_RS15665 showed high efficiency for PAEs hydrolysis and could efficiently hydrolyze di-butyl phthalate under an initial concentration of 1000 mg/L with a half-life of 4.24 h. This work combined a series of methods for identifying PAEs hydrolases and offered a molecular basis for PAEs degradation of A. indicus strains from Baijiu.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01334-w.

Exploring the heterogeneity of community and function and correspondence of "species-enzymes" among three types of Daqu with different fermentation peak-temperature via high-throughput sequencing and metagenomics

The enzyme activity of Daqu is an important prerequisite for defining it as a Baijiu starter. However, little is known about the functional species related to enzymes in different types of Daqu at the metagenomic level. Therefore, we analyzed the differences in enzymatic properties, microbial composition and metabolic function of three types of Daqu, namely high-, medium- and low-temperature Daqus (HTD, MTD and LTD), by combining chemical feature and multi-dimensional sequencing. The results showed that both liquefaction, saccharification, fermentation and esterification powers were remarkably weaker in HTD compared to MTD and LTD. Totally, 30 bacterial and 5 fungal phyla were identified and significant differences in community structures were also observed among samples, with Brevibacterium/Microascus, Pseudomonas, and Lactobacillus/Saccharomycopsis identified as biomarkers for HTD, MTD and LTD, respectively. Additionally, the importance of deterministic assembly in bacterial communities was proportional to the fermentation peak-temperature, while stochastic assembly dominated in fungal ones. Metagenomics analysis indicated eukaryota (>80 %, mainly Ascomycota) predominated in HTD and MTD while bacteria (54.3 %, mainly Actinobacteriota) were more abundant in LTD. However, the functional profiles and pathways of MTD and LTD were more similar, and the synthesis and metabolism of carbohydrates and amino acids were the crucial biological functions of all samples. Finally, the relationship between species and enzymes in different samples was constructed and the functional species in LTD and MTD were more diverse than HTD, which elucidated the functional species associated with enzyme activity in each type of Daqu. These results will greatly enrich our understanding of the core functional species in three typical Daqu, which provide available information for rational regulation of Daqu quality and the Baijiu fermentation.

Effects of gallic acid on the release of aroma compounds in Moutai Baijiu

Due to the trace concentrations of gallic acid (GA), the interaction mechanism between GA and flavor compounds is limited, and the effects on the aroma compounds of Moutai Baijiu are even more unclear. In this study, the aroma compounds and phenolic compounds in Moutai Baijiu were investigated by stir bar sorptive extraction (SBSE), gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). A total of 63 volatiles and 10 phenolic compounds were identified, and 16 esters and 4 alcohols were identified as the important aroma substances (odor activity values ≥1). The effect of GA on the release of aroma compounds was investigated by sensory analysis and partition coefficient. The results showed that GA mainly inhibited the volatilization of alcohols, low concentrations of GA promoted the release of esters, and high concentrations slowed down or even inhibited the release effect affected by the hydrophobicity of aroma compounds. UV spectroscopy and thermodynamic analysis further revealed that the interaction of GA with 1-propanol was attributed mainly to hydrogen bonding and van der Waals forces, and the interaction with other compounds was mainly influenced by hydrophobic effects. These results show that gallic acid can effectively control the release of the aromas of Moutai Baijiu, highlight the important role of GA on the volatiles of baijiu, and provide theoretical support for further healthy improvement of the sensory quality of baijiu.

Characterization of key aroma compounds in gray sufu fermented using Leuconostoc mesenteroides subsp. Mesenteroides F24 as a starter culture

Gray sufu is a traditional fermented bean product with strong flavor in China, but traditional fermentation methods often lead to its off-flavor. This study was performed to investigate the flavor quality characteristics of gray sufu fermented using L. mesenteroides F24. Results showed 220 volatile compounds in gray sufu, among which alcohols and esters were the main volatiles. Inoculation with L. mesenteroides F24 considerably affected the contents of flavor substances in gray sufu and substantially increased the main flavor compounds. In addition, 29 kinds of key volatile compounds were identified by analyzing the ROAVs. Four unique key flavor substances were found in gray sufu inoculated with L. mesenteroides F24. This study is the first report on the feasibility of L. mesenteroides F24 as a promising starter culture to improve the flavor quality of gray sufu. The results provide a theoretical basis for improving the processing and quality control of gray sufu.

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.

Analysis of Volatile Components in Rosa roxburghii Tratt. and Rosa sterilis Using Headspace-Solid-Phase Microextraction-Gas Chromatography-Mass Spectrometry

Volatile organic compounds (VOCs) and flavor characteristics of Rosa roxburghii Tratt. (RR) and Rosa sterilis (RS) were analyzed using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The flavor network was constructed by combining relative odor activity values (ROAVs), and the signature differential flavor components were screened using orthogonal partial least squares discriminant analysis (OPLS-DA) and random forest (RF). The results showed that 61 VOCs were detected in both RR and RS: 48 in RR, and 26 in RS. There were six key flavor components (ROAVs ≥ 1) in RR, namely nonanal, ethyl butanoate, ethyl hexanoate, (3Z)-3-hexen-1-yl acetate, ethyl caprylate, and styrene, among which ethyl butanoate had the highest contribution, whereas there were eight key flavor components (ROAVs ≥ 1) in RS, namely 2-nonanol, (E)-2-hexenal, nonanal, methyl salicylate, β-ocimene, caryophyllene, α-ionone, and styrene, among which nonanal contributed the most to RS. The flavor of RR is primarily fruity, sweet, green banana, and waxy, while the flavor of RS is primarily sweet and floral. In addition, OPLS-DA and RF suggested that (E)-2-hexenal, ethyl caprylate, β-ocimene, and ethyl butanoate could be the signature differential flavor components for distinguishing between RR and RS. In this study, the differences in VOCs between RR and RS were analyzed to provide a basis for further development and utilization.

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

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

Exploring the controllability of the Baijiu fermentation process with microbiota orientation

Product quality and stability improvement is important for development of the Baijiu industry. Generally, Baijiu brewing is carried out in a spontaneous fermentation system mediated by microbiota. Thus, complexity and instability are major features. Due to the insufficient understanding of the mechanism for producing Baijiu, the precise control of the fermentation progress has still not been realized, ultimately affecting product quality and stability. The flavor of Baijiu is the most important factor in determining its quality and is formed by microbiota under the driving force of various physicochemical parameters, such as moisture, acidity, and temperature. Therefore, exploring the association among microbiota (core), physicochemical factors (reference) and flavor compounds (target) has become a key point to clarify the formation mechanism for the flavor quality of Baijiu. Daqu fermentation and liquor fermentation are the two major stages of Baijiu brewing. Daqu, distillers' grains, and pit mud, as the most important fermentation substrates of the microbiota respectively, provide a large number of functional microorganisms related to the flavor components. To this end, we reviewed the relevant research progress of microbiota diversity in different fermentation substrates and the interaction mechanisms among microbiota, physicochemical parameters, and flavor components in this paper. Moreover, a research hypothesis of precise control of the Baijiu fermentation process by building fermentation models based on this is proposed. The key point for this idea is the identification of core microbiota closely associated with the formation of key flavor components by multi-omics technology and the acquisition of culturable strains. With this foundation, fermentation models suitable for different brewing environments will be established by constructing synthetic microbiota, designing mathematical models, and determining key fermentation model parameters. The ultimate goal will be to effectively improve the quality and stability of Baijiu products through model regulation.

Genome Analysis and Optimization of Caproic Acid Production of Clostridium butyricum GD1-1 Isolated from the Pit Mud of Nongxiangxing Baijiu

Caproic acid is a precursor substance for the synthesis of ethyl caproate, the main flavor substance of nongxiangxing baijiu liquor. In this study, Clostridium butyricum GD1-1, a strain with high caproic acid concentration (3.86 g/l), was isolated from the storage pit mud of nongxiangxing baijiu for sequencing and analysis. The strain's genome was 3,840,048 bp in length with 4,050 open reading frames. In addition, virulence factor annotation analysis showed C. butyricum GD1-1 to be safe at the genetic level. However, the annotation results using the Kyoto Encyclopedia of Genes and Genomes Automatic Annotation Server predicted a deficiency in the strain's synthesis of alanine, methionine, and biotin. These results were confirmed by essential nutrient factor validation experiments. Furthermore, the optimized medium conditions for caproic acid concentration by strain GD1-1 were (g/l): glucose 30, NaCl 5, yeast extract 10, peptone 10, beef paste 10, sodium acetate 11, L-cysteine 0.6, biotin 0.004, starch 2, and 2.0% ethanol. The optimized fermentation conditions for caproic acid production by C. butyricum GD1-1 on a single-factor basis were: 5% inoculum volume, 35°C, pH 7, and 90% loading volume. Under optimal conditions, the caproic acid concentration of strain GD1-1 reached 5.42 g/l, which was 1.40 times higher than the initial concentration. C. butyricum GD1-1 could be further used in caproic acid production, NXXB pit mud strengthening and maintenance, and artificial pit mud preparation.

Insights into the influence of physicochemical parameters on the microbial community and volatile compounds during the ultra-long fermentation of compound-flavor Baijiu

Introduction

While the variation in physicochemical parameters, microbial communities, metabolism, composition, and the proportion of volatile components in fermented grains (FG) affect final Baijiu quality, their complex interactions during the ultra-long fermentation of compound-flavor Baijiu (CFB) are still poorly understood.

Methods

In this study, amplicon sequencing was used to analyze the microbial community, and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to analyze the volatile components in FG during ultra-long fermentation of CFB. The relationships between the dominant microbial communities, physicochemical parameters, and volatile components were analyzed using redundancy analysis and network analysis.

Results

During ultra-long fermentation, bacterial diversity was initially higher than during the mid and late stages. Fungal diversity in the mid stages was higher than that initially and later in the process. A total of 88 volatile components, including six alcohols, 43 esters, eight aldehydes and ketones, 13 acids, and 18 other compounds were detected in FG. Starch and reducing sugars in FG strongly affected the composition and function of bacterial and fungal communities. However, acidity had little effect on the composition and function of the bacterial flora. Lactobacillus, Bacillus, Weissella, and Pichia were the core microbial genera involved in metabolizing the volatile components of FG.

Discussion

We provide insights into the relationships and influences among the dominant microbial communities, physicochemical parameters, and volatile components during ultra-long fermentation of CFB. These insights help clarify the fermentation mechanisms of solid-state fermentation Baijiu (SFB) and control and improve the aroma quality of CFB.