Recent advances in Baijiu analysis by chromatography based technology–A review

Effects of fermented tea by Aspergillus cristatus on the characteristic aroma and non-volatile components of Jiang-flavor baijiu

BACKGROUND

Fu Brick tea (FBT) extract has been demonstrated to lower blood lipids, protect liver, and prevent obesity. Despite these benefits, there are no products on the market that combine FBT with other foods or beverages.

RESULT

In this study, we developed a novel product by combining FBT with high-alcohol Jiang-flavor baijiu, resulting in FBT-baijiu. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis revealed that FBT-baijiu contains health-promoting alkaloids, including eurocristatine (13.60 ± 0.13 mg/L), (-)-neoechinulin A (10.26 ± 0.09 mg/L), neoechinulin D (7.89 ± 0.05 mg/L), variecolorin G (6.94 ± 0.05 mg/L), and echinulin (25.46 ± 0.27 mg/L), which are known to be present in FBT. The aroma compounds of the FBT-baijiu and the base baijiu were analyzed using comprehensive gas chromatography-olfactometry-mass spectrometry (GC-O-MS) technology. The major volatile compounds of two baijiu samples were identified using relative odor activity values (r-OAVs) analysis. The FBT-baijiu showed a significant reduction in ester content, but a remarkable enhancement in aromatic properties. The findings show that combining FBT with baijiu not only offers functional components but also enhances the flavor profile.

CONCLUSION

This study highlights the potential of utilizing FBT as a functional food ingredient or additive, paving the way for the development of new health-promoting products. © 2024 Society of Chemical Industry.

Applications of Microextraction Technology for the Analysis of Alcoholic Beverages Quality: Current Perspectives and Future Directions

Alcoholic beverages are loved by the majority of consumers because of their diverse characteristics and rich nutritional value; thus, ensuring their quality is necessary for maintaining the rapid development of the alcoholic beverage industry. Due to trace levels of various quality factors and the complexity of the beverage body matrix, pretreatment is usually required before analysis. Among the many pretreatment methods available, microextraction has attracted increasing attention because it aligns with the development direction of green chemistry. This review surveys advancements in microextraction techniques pertaining to three quality aspects in the most frequently consumed alcoholic beverages: baijiu and huangjiu (spirits) and wine and beer (fermented alcoholic drinks). Furthermore, new directions in their development are discussed.

Extraction of short-chain fatty acid ethyl Ester in Baijiu using covalent organic framework-based magnetic nanoparticles: Theoretical screening and experimental validation

Short-chain fatty acid ethyl esters (SFAEEs) are critical aroma compounds in Baijiu, and their wider concentration range can lead to differences in the quality grade of Baijiu. Efficiently designing an SFAEEs adsorbent before instrument analysis remains challenging. In this work, nine functionalized covalent organic frameworks (COFs) with different postmodification groups were designed for targeting SFAEEs. Based on interaction energy as the evaluation criterion, COFs modified with 5-Mercapto-1-methyltetrazole (MMTZ) had been identified through density functional theory screening. Using imine COFs and MMTZ, novel magnetic nanoparticles (Fe3O4@COFs@MMTZ) were prepared and used to develop the magnetic solid-phase extraction of SFAEEs from Baijiu. The adsorption mechanism of Fe3O4@COFs@MMTZ was analyzed using wave function analysis, revealing that adsorption occurred via vdW interaction, CH···π interaction, and hydrogen bonding. This study provides a new concept for the rapid detection of SFAEEs and theoretical support for the scientific construction of quality control during Baijiu production.

Risk of serum circulating environmental chemical residues to esophageal squamous cell carcinoma: a nested case-control metabolome-wide association study

Esophageal squamous cell carcinoma (ESCC) is the primary histological subtype of esophageal carcinoma, yet research on environmental exposure risks and associated metabolic alterations preceding ESCC is limited. In a nested case-control cohort of 396 adults (199 diagnosed with ESCC and 197 healthy controls (HC)), we combined exposomics and metabolomics to assess circulating chemical residues and early serum metabolic changes linked to ESCC risk. A cell experiment further evaluated the proliferative impact of 1H,1H,2H,2H-perfluorooctanesulfonic acid (6:2 FTS), identifying it as a risk factor for ESCC, primarily through lipid metabolism-related chronic inflammation. Significant metabolic disruptions were observed in ESCC cases, characterized by increased carnitines, phosphatidylcholines (PCs), and triglycerides (TGs) alongside reduced lysophosphatidylcholines (LPCs) and ether lysophosphatidylcholines (LPC-Os). An early-warning biomarker panel, including glutamic acid, methionine, choline, LPC-O 18:0, TG (14:0_18:2_20:5), and PC (18:0_20:4)/LPC 18:0, showed improved predictive capacity when combined with 6:2 FTS. Metabolome-exposome-wide association studies largely confirmed 6:2 FTS as a potential ESCC risk factor through lipid mediation. This study offers novel insights for ESCC prevention and early diagnosis through a combined biomarker panel integrating metabolic and environmental risk indicators.

Maillard reaction products of soybean protein hydrolysates and reducing sugar: Structure and flavor insights

Maillard reaction products (MRPs) were prepared at high temperatures using soybean protein hydrolysates (SPH) and reducing pentose (xylose and arabinose), hexose (galactose and glucose), and disaccharide (maltose), and their potential as flavoring in plant protein foods was evaluated. The results indicated that, after sugar was involved in the reaction, the unfolding of proteins enabled aromatic amino acid residues to enter a more hydrophobic environment, contributing to the reduction of bitterness in MRPs and formation of caramelization. This effect was partially attributed to the interaction forces, hydrogen bonds and van der Waals forces, that existed between the sugars and SPH involved in Maillard reaction. More basic amino acid residues interacted with pentose during the reaction, which exhibited faster reaction rate and promoted the formation of pyrazines and oxygen containing compounds, thereby contributing to meaty, roasted and caramelized flavors. Trimethyl pyrazine, 3-ethyl-2,5-dimethylpyrazine, 2-methylpyrazine, and 2-heptanone were the most abundant in pentose MRPs, and these volatile compounds were positively correlated with umami and richness. Overall, MRPs prepared with arabinose may serve as a potential meaty flavoring with notable umami, and hexose contributed to the enrichment of nutty flavor profiles, while the MRPs formed by disaccharide exhibited the characteristics of superior fruity aromas. MRPs from different reducing sugar may be used to develop different food ingredients.

Generation of a synthetic autochthonous microbiota responsible for the essential flavors and brewing properties of Daqu

Based on the 26 strains of medium-high-temperature Daqu, seed microbial inocula and mature microbial inoculants were prepared and inoculated into crushed wheat to prepare cleaner medium-high-temperature Daqu (XQ). The physicochemical properties, flavor, and microbial profile of XQ were studied using traditional medium-high-temperature Daqu (CQ) or industry standards as controls. The results showed that the liquefaction ability, saccharification activity, esterification activity, and moisture content of XQ were better than those of Daqu industry standards. The results of GC-MS and E-nose analyses showed that the main flavor compounds in the two types of Daqu were esters, alcohols, acids, and aldehydes, which had similar flavor profiles. Microbial sequencing revealed that the most abundant fungi in XQ were Aspergillus subflavus, Wickerhamomyces anomalus, Rhizopus oryzae, and Candida tropicalis, whereas the most abundant bacteria were Lactobacillus curvatus, Weissella cibaria, and Bacillus subtilis. Both types of Daqu contained a high abundance of W. anomalus. In addition, the COG (Clusters of Orthologous Groups of Proteins) analyses displayed that the two types of Daqu had their dominant functions and generally had the pathways and functional characteristics of organism growth and metabolism. This study laid some experimental research bases for the preparation of cleaner Daqu and could provide insights for producing safer microbial fermented foods.

Effect of Mixed Strains on Microbial Community and Flavor Metabolites in Fermentation Process of Chi-Flavor Baijiu

The distinct flavor of chi-flavor baijiu (CFB) has garnered significant attention in China. After the optimization of fermentation conditions, Pichia anomala and Lactobacillus plantarum were introduced into the fermentation process to enhance the flavor. Samples inoculated with these mixed strains (SY) exhibited higher levels of alcohol (from 33.04 to 178.55 mg/L) and esters (from 49.51 to 130.20 mg/L) compared to the control group (KB). In SY, P. anomala and L. plantarum were the predominant microorganisms, while Pediococcus and Saccharomyces were more prevalent in KB. Moreover, 68 volatile flavor compounds were detected in SY, as opposed to 64 in KB. Notably, Pichia showed a positive correlation with key flavor compounds. The synergistic fermentation with exogenous strains led to a 52.38% increase in phenethyl alcohol and a 4.91% increase in ethyl lactate. Additionally, the levels of other flavor compounds, like ethyl acetate, γ-nonanolactone, and (E)-2-octenal, also increased. The results demonstrated that the addition of P. anomala and L. plantarum to the fermentation process of CFB significantly increased the contents of flavor compounds. This research reveals valuable insights into flavor enhancement and the microbial community dynamics in CFB production.

Comparison of Flavor Differences between the Juices and Wines of Four Strawberry Cultivars Using Two-Dimensional Gas Chromatography-Time-of-Flight Mass Spectrometry and Sensory Evaluation

Fruit wine production is a practical approach for extending the shelf life and enhancing the value of strawberries (Fragaria × ananassa). Fruit cultivars and juices are important sources of volatile organic compounds (VOCs) that determine fruit wine sensory quality. In this study, VOCs in the juices and wines of four strawberry cultivars were identified using two-dimensional gas chromatography-time-of-flight mass spectrometry, and a sensory analysis of the wines was performed. A total of 1028 VOCs were detected. PCA and OPLS-DA distinguished the four cultivars from which the juices and wines were made. Six VOCs with variable importance in projection values greater than one were the main aroma and flavor components of strawberry wines. ZJ wine had the highest sensory scores for coordination (9.0) and overall evaluation (8.9) among the 18 descriptors of strawberry wine evaluated. Overall, the ZJ wine had the highest alcohol content (13.25 ± 0.59%, v/v) and sensory evaluation score, indicating that the ZJ cultivar is more suitable for fermentation. This study reflects the differences between wines made from four strawberry cultivars and provides a reference for brewing fruit wines.

A two-step framework integrating lasso and Relaxed Lasso for resolving multidimensional collinearity in Chinese baijiu aging research

The aging process is crucial for Chinese Baijiu production, significantly enhancing the spirit's flavor, aroma and quality. However, aging involves a complex interplay of numerous compounds, and the extensive duration required for aging leads to a scarcity of samples available for scientific research. These limitations pose a challenge in analyzing high-dimensional data with collinearity, complicating the understanding of the intricate chemical processes at play. In this article, a two-step framework was proposed that integrated Relaxed Lasso regression models with Lasso-selected predictors to address this issue. Baijiu samples subjected to various aging conditions were analyzed using direct GC-MS and HS-GC-MS, and the obtained data was processed by this approach. The results demonstrate significantly superior performance compared to other methods, including PLSR and Gradient Boosting. Analyses were also performed on a previously documented dataset, yielding enhanced results and underscoring the method's advantage in processing high dimensional data with multicollinearity. Moreover, this method proved effective in screening of potential indicative compounds, highlighting its utility in Baijiu aging research.

Analysis of Metabolite Differences in Different Tea Liquors Based on Broadly Targeted Metabolomics

To expand the development of characteristic extension products of Yunnan tea and improve the utilization rate of Yunnan tea resources, in this study, we compared the metabolite composition among raw Pu-erh tea, ripe Pu-erh tea prepared with glutinous rice (according to tea to glutinous rice ratio of 1:3), and ripe Pu-erh tea prepared with a mixture of sorghum, rice, glutinous rice, wheat, and corn as raw materials (according to a tea to glutinous rice ratio of 1:3). Rice flavor liquor prepared with 100% glutinous rice served as a control. The raw Pu-erh tea liquor (RAWJ), ripe Pu-erh tea liquor (RIPEJ), ripe Pu-erh tea mixed grain liquor (HHLSJ), and rice-flavor liquor (MJ) were all brewed by semi-solid fermentation. The non-volatile components of the liquor samples were analyzed by ultra-high-performance liquid chromatography-tandem mass spectrometry as a broadly targeted metabolomics technique. A total of 691 metabolites were identified from the four samples. Among them, 674, 671, 633, and 667 species were detected in RAWJ, RIPEJ, HHLSJ, and MJ samples, respectively. Venn diagram analysis demonstrated 19, 21, and 14 unique metabolites in RAWJ, RIPEJ, and HHLSJ, respectively, compared with the metabolite composition of MJ. Flavonoids are the most important differential metabolite between tea liquor and rice-flavor liquor. This study provides a theoretical basis for the development of tea liquor products and offers insight into the difference in non-volatile components between tea liquor and rice-flavor liquor.

Revealing the comprehensive effect of mechanization on sauce-flavor Daqu through high-throughput sequencing and multi-dimensional metabolite profiling

Mechanization has emerged as a focal point in the modernization of traditional enterprises, offering standardized production and labor reduction benefits. However, little is known about how mechanization affects the microbiota and metabolite profiles of Daqu. To address this gap, we conducted a comprehensive comparison between traditional and mechanical sauce-flavor Daqu using a multi-omics approach. Results showed that mechanical Daqu exhibited higher acidity, amino acid nitrogen and enzyme activity, alongside lower fat and moisture levels. Following mechanization, lactic acid bacteria (LAB), Staphylococcus, Aspergillus and Saccharomycopsis were enriched and identified as biomarkers, whereas Oceanobacillus, Monascus and Scopulariopsis were notably decreased. Furthermore, significant disparities in metabolic profiles were observed between the two types of Daqu based on GC-MS, GC-IMS, and LC-MS/MS analyses. The content of volatile compounds was significantly higher in mechanical Daqu (332.82 ± 22.69 mg/kg), while that of non-volatile compounds was higher in traditional Daqu (753.44 ± 41.82 mg/kg). Moreover, OPLS-DA models identified 44 volatile and 31 non-volatile compounds as differential metabolites. Multivariate statistical analysis indicated that bacteria and fungi primarily contributed to protease and saccharification activities, respectively. Additionally, the co-occurrence network revealed that Oceanobacillus and Scopulariopsis were closely associated with non-volatile compound formation, while LAB and Rhizopus significantly influenced volatile compound production. These findings elucidate the multi-dimensional relationship between mechanization and Daqu quality, offering insights to advance the modernization of traditional industries.

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.

The mechanism of Laceyella sacchari FBKL4.010 produced tetramethylpyrazine in the liquid fermentation by comparative transcriptomic techniques

Tetramethylpyrazine (TTMP) is considered a crucial flavor component in Moutai-flavored liquor. Laceyeella sacchari FBKL4.010 (L. sacchari) is the dominant species found in Moutai-flavor Daqu, and this study aims to determine the mechanism by which L. sacchari produces TTMP during liquid fermentation of Moutai-flavor Daqu. The results of the liquid fermentation performance demonstrated a gradual increase in biomass over time, while there was a gradual decline in residual glucose content and pH value. Furthermore, analysis of volatile components revealed that liquid fermentation significantly enhanced the production of TTMP in Moutai-flavor Daqu, with the relative content of TTMP reaching 14.24 mg/L after 96 h of liquid fermentation. Additionally, to explore the synthesis mechanism of TTMP, we compared differentially expressed genes (DEGs) of L. sacchari between 24 and 96 h using comparative transcriptomic techniques. The results indicated that DEGs involved in isoleucine, valine, and leucine biosynthesis pathway were upregulated, while those associated with isoleucine, valine, and leucine degradation pathway were downregulated, suggesting that the valine, leucine, and isoleucine biosynthesis pathway primarily contributes ammonia for TTMP synthesis. The findings of this study present an opportunity for further elucidating the production process of TTMP in Moutai-flavor Daqu during liquid fermentation.

Influence on the volatilization of ethyl esters: Nonnegligible role of long-chain fatty acids on Baijiu flavor via intermolecular interaction

Long-chain fatty acids (LCFAs) are commonly presented in Baijiu, but their influence on flavor is ambiguous. The interaction between LCFAs and volatiles was systematically investigated in terms of chemometrics, sensory, and chemical-physical perceptions. The static-headspace-gas-chromatography-mass-spectrometry results demonstrated LCFAs suppressed the volatilizations of most volatiles. According to Phase-ratio-variation analysis, partition coefficients of ethyl acetate (EA) and ethyl hexanoate (EH) decreased 4%-31% and 27%-74%, while those of ethyl butyrate (EB) increased. Calculated by molecular dynamic simulation, the attractive intermolecular forces related to EA/EH increased with oleic acid (OA) addition, while those related to EB decreased. Sensory evaluation confirmed the olfactory threshold of EA and EH increased by 2.4 and 2.7 times respectively, but the threshold of EB decreased from 0.36 to 0.05 mg/L in the presence of OA. Overall, LCFAs altered the intermolecular interaction forces related to esters and ethanol, subsequently affecting the volatile profile and modifying Baijiu flavor's sensory perception.

Multidimensional analysis of wheat original crucial endogenous enzymes driving microbial communities metabolism during high-temperature Daqu fermentation

Knowledge of the metabolism of functional enzymes is the key to accelerate the transformation and utilization of raw materials during high temperature Daqu (HTD) manufacturing. However, the metabolic contribution of raw materials-wheat is always neglected. In this research, the relationship between the metabolism of wheat and microorganisms was investigated using physicochemical and sequencing analysis method. Results showed that the process of Daqu generation was divided into three stages based on temperature. In the early stage, a positive correlation was found between Monascus, Rhizopus and glucoamylase metabolism (r > 0.8, p < 0.05). Meanwhile, the glucoamylase metabolism in wheat occupied 63.8 % of the total matrix at the day 4. In the middle to later stages, the wheat metabolism of proteases, α-amylases and lipases in gradually reached their peak. Additionally, Lactobacillus and α-amylases presented a positive correlation (r > 0.7, p < 0.05), and the α-amylases metabolism in wheat occupied 22.18 % of the total matrix during the same time period. More importantly, the changes of enzyme activity metabolic pathway in wheat and microorganism were reflected by respiratory entropy (RQ). Overall, these results guide the choice of substrate during Daqu production.

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.

Current situation, trend, and prospects of research on functional components from by-products of baijiu production: A review

In the present scenario marked by energy source shortages and escalating concerns regarding carbon dioxide emissions, there is a growing emphasis on the optimal utilization of biomass resources. Baijiu, as the Chinese national spirit, boasts remarkably high sales volumes annually. However, the production of baijiu yields various by-products, including solid residues (Jiuzao), liquid wastewater (Huangshui and waste alcohol), and gaseous waste. Recent years have witnessed dedicated research aimed at exploring the composition and potential applications of these by-products, seeking sustainable development and comprehensive resource utilization. This review systematically summarizes recent research, shedding light on both the baijiu brewing process and the bioactive compounds present baijiu production by-products (BPBPs). The primary focus lies in elucidating the potential extraction methods and applications of BPBPs, offering a practical approach to comprehensive utilization of by-products in functional food, medicine, cosmetic, and packaging fields. These applications not only contribute to enhancing production efficiency and mitigating environmental pollution, but also introduce innovative concepts for the sustainable advancement of associated industries. Future research avenues may include more in-depth compositional analysis, the development of utilization technologies, and the promotion of potential industrialization.

Gold nanobipyramid colorimetric sensing array for the differentiation of strong aroma-type baijiu with different geographical origins

It is of great significance to quickly and effectively distinguish strong aroma-type baijiu (SAB) with the largest baijiu market share and the most extensive production regions. Colorimetric sensor arrays based on gold nanobipyramids (AuNBPs) with extraordinary plasmonic properties were constructed for the differentiation of SAB from different geographical origins. The sensing strategy was based on silver deposition on different morphologies of AuNBPs under different reducing conditions containing amino or hydroxyl groups. The deposition process can be effective for distinguishing differences in baijiu due to the chemical interaction between the trace ingredients in baijiu and reductants. The colorimetric sensor arrays were implemented for the response of the main ingredients and further used for the differentiation of SAB from different regions by linear discriminant analysis. The results showed that the sensing strategy had excellent performance in distinguishing SAB from different origins, and provides a promising application strategy for baijiu quality control.

Comparative Analysis of Key Odorants and Aroma Characteristics in Hot-Pressed Yellow Horn (Xanthoceras sorbifolia bunge) Seed Oil Via Gas Chromatography-Ion Mobility Spectrometry and Gas Chromatography-Olfactory-Mass Spectrometry

Volatile compounds (VOCs) present in the oil extracted from yellow horn seeds were first analyzed using GC-IMS and GC-O-MS at varying roasting temperatures. A total of 97 VOCs were detected using GC-IMS, while 77 were tentatively identified using GC-O-MS. Moreover, both methods allowed the identification of 24 VOCs, of which the type of aldehydes is the most abundant. Combining the results of GC-IMS, GC-O-MS, OAVs, and VIP, it was concluded that hexanal, 2,5-dimethylpyrazine, heptanal, 2-pentylfuran, 1-hexanol, and 1-octen-3-ol were the key aroma compounds. The PLS-DA and OPLS-DA models have demonstrated the ability to discriminate between different oil roasting temperatures with high accuracy. The roasting temperature of 160 °C was found to yield the highest content of main aroma substances, indicating its optimality for yellow horn seed oil production. These findings will prove beneficial for optimizing industrial production and enhancing oil aroma control.

Comparative Analysis of Volatile Flavor Compounds in Strongly Flavored Baijiu under Two Different Pit Cap Sealing Processes

The solid-state fermentation process of strongly flavored Baijiu is complicated by the co-fermentation of many different microorganisms in the fermentation pools. The traditional fermentation pools of strong flavor Baijiu are sealed with mud, and this sealed-pit mud is not easy to maintain; therefore, the pit cap is prone to cracks and to caving in. The destruction of the sealed-pit mud may lead to instability in the composition and an abundance of microorganisms in the fermentation process that results in fluctuations of product quality. Thus, the production method of replacing the mud cap with a new steel cap is gradually attracting the attention of scientific and technical workers in the industry. However, so far, there have been relatively few reports on the use of steel lids for sealing pits for fermentation and brewing. In this study, the volatile flavor components of 270 Baijiu samples from mud-sealing and steel-sealing pits of a Chinese Baijiu distillery were studied qualitatively and quantitatively using Gas Chromatography-Mass Spectrometry (Abbreviated as GC-MS). Our statistical methods included Hierarchical Cluster Analysis (Abbreviated as HCA), Principal Component Analysis (Abbreviated as PCA), and Discriminant Analysis (Abbreviated as DA). A statistical analysis was carried out on the yield of strongly flavored Baijiu, and we made a comprehensive evaluation of the Baijiu produced under the two pit-sealing modes with regard to flavor and economic efficiency. The yield of strong flavored Baijiu was 6.7% higher with steel-sealing pits compared with mud-sealing pits. Cluster analysis categorized the strongly flavored Baijiu samples into two categories initially: (1) samples produced using mud-sealing pits and (2) samples using steel-sealing pits. Our analysis also indicated that the 28 compounds used for quantification were selected correctly. Surprising to the experimental staff, the overall score for the steel-sealing pits was greater than that of the mud-sealing pits based on PCA. Using DA, the prediction results were 100% accurate. In summary, through a comparative analysis of the flavor and yield, which are the two main factors that affect the quality of Baijiu in a distillery, and systematic combination at both experimental and theoretical levels, the differences between the Baijiu production by steel-sealing and the traditional mud-sealing were clear. Regardless of the impact of age, the detectable flavor components of Baijiu from the mud-steeling pits were very consistent with those of the steel-sealing pits in terms of richness or concentration. However, steel-sealing pits were significantly superior to mud-sealing pits with respect to output, consistency in quality, and cost (human and economic) savings.

Roles of sulfur-containing compounds in fermented beverages with 2-furfurylthiol as a case example

Aroma is a critical component of the flavor and quality of beverages. Among the volatile chemicals responsible for fragrance perception, sulfur compounds are unique odorants due to their extremely low odor threshold. Although trace amounts of sulfur compounds can enhance the flavor profile of beverages, they can lead to off-odors. Sulfur compounds can be formed via Maillard reaction and microbial metabolism, imparting coffee aroma and altering the flavor of beverages. In order to increase the understanding of sulfur compounds in the field of food flavor, 2-furfurylthiol (FFT) was chosen as a representative to discuss the current status of their generation, sensory impact, enrichment, analytical methods, formation mechanisms, aroma deterioration, and aroma regulation. FFT is comprehensively reviewed, and the main beverages of interest are typically baijiu, beer, wine, and coffee. Challenges and recommendations for FFT are also discussed, including analytical methods and mechanisms of formation, interactions between FFT and other compounds, and the development of specific materials to extend the duration of aroma after release.

Characterization of the differences in aroma-active compounds in strong-flavor Baijiu induced by bioaugmented Daqu using metabolomics and sensomics approaches

Bioaugmenting Daqu is an effective strategy to improve the quality of Baijiu, but its effect on overall flavor profiles and aroma-active compounds is unknown. Here, 168 volatiles were determined from fresh strong-flavor Baijiu (SFB) and bioaugmented Daqu increased their diversity and altered the flavor characteristics. Among 49 odorants identified by aroma extraction dilution analysis, 29 aroma-active compounds had odor activity values ≥1, of which 18, 8, and 3 components exhibited the highest content in the SFB fermented by fortified-, space- and conventional-Daqu, respectively. The contribution of increasing ethyl hexanoate and decreasing ethyl lactate of fresh SFB by bioaugmented Daqu was confirmed, and their content changed from 4650 and 1890 mg/L (conventional-SFB) to 6680 and 1760 mg/L (fortified-SFB) and 6130 and 1710 mg/L (space-SFB). Meanwhile, the discriminators among different samples were determined by multivariate statistical analysis. These findings are beneficial for the optimization and improvement of Baijiu aroma.

Machine-learning-assisted SERS nanosensor platform toward chemical fingerprinting of Baijiu flavors

A novel fingerprinting platform for multiplex detection of flavor molecules in Baijiu was developed by using a surface-enhanced Raman scattering (SERS) nanosensor array in combination with machine learning. The SERS sensors were constructed by core-shell Fe₃O₄@Ag nanoparticles modified with molecules carrying end-groups of hydroxyl, pyridyl, methyl, and amino, respectively, which interacted with flavors and led to changes in the sensors' spectra. All the Raman spectra acquired from the nanosensor array contacting with the sample were concatenated into a single SERS super-spectrum, representing the flavor fingerprint which was recognized through machine learning. Principal component analysis, support vector machine, and partial least squares were utilized to build classification and quantitation models for predictive analyses. The SERS nanosensor array was successfully used for fingerprinting ten typical flavors in Baijiu including four esters, three alcohols, and three acids, with an accuracy of 100%, linear detection ranges over two orders of magnitude, and limits of detection ranging from 3.45 × 10^-3 mg/L of phenylethyl acetate to 1.21 × 10^-2 mg/L of ethyl hexanoate. It was also demonstrated that satisfactory accuracies (recoveries) ranging from 96.2 to 104% and relative standard deviations ranging from 0.65 to 2.78% were obtained for the simultaneous quantification of 3-methylbutyl acetate and phenylethyl acetate in eighteen Baijiu samples of three flavor types including sauce flavor, strong flavor, and light flavor. Compared with the existing detection techniques, this chemical fingerprinting platform is easy to use, highly sensitive, and can perform multiplex detection, which has great potential for practical applications.

Organic acid-induced triple fluorescent emission carbon quantum dots identification of distilled liquor

An acid-sensitive carbon dot fluorescence sensing array was investigated for the differentiated recognition of distilled spirits. Due to the electrostatic interactions between CDs and organic acids, organic acids affect the protonation and fluorescence properties of CDs, which in turn modify the CDs triple fluorescence emission. The regular linear variation of the fluorescence sensor was found under acidic conditions (3.0 < pH < 6.2). A comprehensive study of acids with selectivity, different concentrations (0.1 mM, 1 mM, 10 mM, 40 mM), different types (8 species) and mixed acids (formic acid and acetic acid), and good quantification capability for acetic acid (0.01-1 mM). Demonstrating good recognition ability of the sensor array for complex analyte. On this basis, the fluorescence sensor array was applied to the classification and recognition of liquors. LDA has realized the identification of 16 kinds of Baijiu and 21 kinds of distilled liquors with an accuracy of 100%.

Effects of Four Strains of Actinomycetes on the Content of Terpenoids in Baijiu

Terpenoids not only are an important health factor in baijiu but also contribute to the elegance and finesse of baijiu, and actinomycetes act as an important source of terpenoids in baijiu. Four strains of actinomycetes—Streptomyces violascens (SPQ1), S. sampsonii (SPS1), S. thermophilus (SPG1), and S. griseus (SPH1)—obtained from the Daqu, pit mud, fermented grains and air, respectively, in the production of baijiu were used in solid-state and liquid fermentation with five brewing raw materials as the substrates. The terpenoids in the metabolites were analyzed and compared using gas chromatography-mass spectrometry (GC-MS). We found that the four strains of actinomycetes produced 31 terpenoids from the hydrolysates of five fermentation substrates during liquid fermentation, and the total terpenoid content was 989.94 μg/kg in the fermentation products. After 28 days of solid-state fermentation, the four actinomycete strains produced 64 terpenoids using the five fermentation substrates, and the total terpenoid content was 23,651.52 μg/kg in the fermentation products. The different fermentation substrates and fermentation methods have a great influence on the terpenoids produced by actinomycetes.

Characterization of aroma compounds and effects of amino acids on the release of esters in Laimao baijiu

BACKGROUND

Laimao baijiu is a typical soy-sauce aroma-type baijiu in China. Amino acids are non-volatile compounds in baijiu and are beneficial to human health. Aroma is one of the important indicators that are used to evaluate the quality of baijiu. The interaction between aroma-active compounds and non-volatile compounds can also affect the release of aroma compounds. In this study, we identified the active-aroma compounds and amino acids in Laimao baijiu by stir bar sorptive extraction (SBSE), gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC-MS), and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). The interaction between amino acids and key esters was investigated by sensory analysis and partition coefficients.

RESULTS

A total of 63 aroma compounds and 21 amino acids were identified. Twenty-one esters were identified from them as major aroma-active ester compounds with odor activity values ≥ 1. Finally, sensory analysis revealed that l-alanine had a significant effect on the strength of the aromas of esters, suggesting that low concentrations of amino acids were more likely to promote the release of esters and high concentrations were more likely to inhibit this. The partition coefficient can be a good explanation for this phenomenon.

CONCLUSION

l-Alanine can significantly affect the aroma intensity of key ester aroma compounds in Laimao baijiu, and the effects of different concentrations of amino acids are different. This work shows that amino acids, as non-volatile compounds, have a regulatory effect on the release of aroma compounds in alcoholic beverages, which may provide new technical support for the aroma modulation of alcoholic beverages. © 2022 Society of Chemical Industry.

The microbial diversity and flavour metabolism of Chinese strong flavour Baijiu: a review

Strong flavour Baijiu is widely consumed in China and is produced by the fermentation of grains using microbial starters. However, a comprehensive understanding of the diversity and metabolic characteristics of microbial communities involved in the solid-state fermentation of Baijiu is important for determining the relationship between microbial composition, flavour metabolism and understanding Baijiu fermentation conditions. Although studies have examined the metabolic pathways and impact of major processes on flavour compounds in strong flavour Baijiu, aspects of the fermentation process remain unexplored. In this review, methods are discussed for the optimisation of microbial diversity in strong flavour Baijiu and associated effects on the flavour of Baijiu. Recent studies are reviewed on starters (Daqu), fermented grains (Jiupei), and pit mud together with the effects of microbial composition on the quality of strong flavour Baijiu. The challenges of Baijiu research and production are discussed, including the role of the microbial diversity of Daqu and Jiupei in the flavour composition of strong flavour Baijiu. This review contributes to the current understanding of processing strong flavour Baijiu and serves as a reference for screening flavour related microorganisms, which is valuable for improving the quality of strong flavour Baijiu.

Comparison of the Aroma-Active Compounds and Sensory Characteristics of Different Grades of Light-Flavor Baijiu

This study comprehensively characterized and compared the aroma differences between four different grades of Fenjiu (FJ, the most representative light-flavor Baijiu). Aroma-active compounds were analyzed by liquid-liquid extraction (LLE) coupled with gas chromatography-olfactometry-mass spectrometry (GC-O-MS). A total of 88 aroma-active compounds were identified, and 70 of them were quantified. The results showed that a majority of aroma compounds in high-grade FJ had higher aroma intensities and concentrations. Among these compounds, there were 28 compounds with odor activity values (OAVs) greater than one in all four wines, which indicated that they might contribute to the characteristic aroma of FJ. Temporal dominance of sensation (TDS) and quantitative descriptive analysis (QDA) were used to characterize the sensory differences. The results suggested that high-grade FJ had a rich, pleasant and lasting retronasal aroma perception and exhibited pleasant orthonasal aroma of floral, fruity, sweet and grassy. Partial least squares regression (PLSR) analysis effectively distinguished four kinds of FJ and revealed associations between the orthonasal aroma attributes and the aroma compounds with OAVs >1. There were 15 compounds with variable importance in projection (VIP) values >1, and they were considered potential aroma markers for quality prediction.

Investigation on fresh bamboo replacing rice husks for brewing light-aroma Baijiu

Husks are the main source of bran and furfural flavor in traditional Chinese light-aroma Baijiu, but they negatively affect its smell and taste. Here, bran husks were replaced with fresh bamboo to brew light-aroma Baijiu. Flavor components in Jiupei and Baijiu were detected through headspace solid-phase microextraction with gas chromatography-mass spectrometry, and physicochemical properties were assessed; flavor results were obtained from correlation, principal component, and cluster analyses. Starch and reducing sugar content in Jiupei negatively correlated with moisture, alcohol content, and acidity. Fresh bamboo reduced furfural from bran husks in Jiupei by 88.5% and increased alcohol distillation by 51%; it also improved starch efficiency (5%). Surprisingly, isovanillin was found to be present in Baijiu. Total Baijiu yield (57% ± 2.01%) was attained when crushed bamboo size was 1.5 cm × 0.3 cm × 0.3 cm. This study supports the use of fresh bamboo (an eco-friendly alternative for husks) in brewing light-aroma Baijiu. PRACTICAL APPLICATION: The use of fresh bamboo as a replacement for rice husks in brewing light-aroma Baijiu was investigated. It attenuated the chaff taste in light-aroma Baijiu and increased the liquor yield. Surprisingly, isovanillin was also present in the base Baijiu, and it added to the fragrance. This study not only supports the use of bamboo as an auxiliary material for brewing light-aroma Baijiu but also provides a reference for brewing light-aroma Baijiu with alternative auxiliary materials.

Machine learning based age-authentication assisted by chemo-kinetics: Case study of strong-flavor Chinese Baijiu

The aged Chinese liquor, Baijiu, is highly valued for its superior organoleptic qualities. However, since age-authentication method and aging-mechanism elucidation of Baijiu is still in the exploratory stage, high-quality aged Baijiu is often replaced by lower-quality, less-aged product with fraudulent mislabeling. Authentic high-quality strong-flavor Baijiu was analyzed by gas chromatography-mass spectrometry. Total esters decreased with aging, while acids, alcohols, aldehydes, ketones, terpenes, pyrazines increased. Although concentrations of partial compounds showed non-monotonic profiling during aging, a close positive linear correlation (R² = 0.7012) of Baijiu Evenness index (0.55-0.59) with aging time was observed, indicating a more balanced composition in aged Baijiu. The reaction quotient (Qc) of each esterification, calculated by the corresponding reactant and product concentration, approached to the corresponding thermodynamic equilibrium constant Kc. This result demonstrated that the spontaneous transformation driven by thermodynamics explained part of the aging compositional profiling. Furthermore, an aging-related feature selection and an age-authentication method were established based on three models combined with five ranking algorithms. Forty-one key features, including thirty-six compound concentrations, four esterification Qc values and the Evenness index were selected out. The age-authentication based on neural network using forty-one input features accurately predicted the age group of Baijiu samples (F1 = 100 %). These findings have deepened understanding of the Baijiu aging mechanism and provided a novel, effective approach for age-authentication of Baijiu and other liquors.

Comprehensive identification of key compounds in different quality grades of soy sauce-aroma type baijiu by HS-SPME-GC-MS coupled with electronic nose

In the production of soy sauce-aroma type baijiu (SSAB), the quality of base liquor significantly affects the finished liquor's quality. Moreover, low-quality liquor may cause health problems. The different quality grades of base liquor were analyzed to investigate the relationship between the quality and the key compounds in SSAB. In this study, samples were evaluated by the sensory and further analyzed by headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) coupled with electronic nose (E-nose). First, by sensory evaluation, the sauce, floral and fruity, fermented aromas and taste indicators (softness, fullness, harmony, purity and persistence) were positively correlated with the quality grade of the base liquor. The E-nose could distinguish the different quality grades of base liquor well. Second, differential compounds were identified via untargeted metabolome based on the HS-SPME-GC-MS. 16 common differential compounds were shared in the base liquor from different fermentation rounds, including 11 esters, 1 alcohol, 2 aldehydes and 2 ketones. It was found that the higher the quality grade of the base liquor, the richer the content of aromatics, alcohols, aldehydes and ketones. The principal component analysis (PCA) biplots of the differential compounds in the different quality grades of base liquor indicated that the superior-grade base liquor has a strong fruity aroma. By correlation analysis of the differential compounds and sensors responses of E-nose, furfuryl ethyl ether, butanoic acid ethyl ester, isopentyl hexanoate, nonanoic acid ethyl ester and 3-methyl-1-butanol had a significant effect on the response intensity of E-nose sensors. In the present study, the key differential compounds between the different quality grades of base liquor were identified, and the sensory differences between the base liquor were digitized.

Investigations on color and flavor formed by roasting sesame polysaccharide-protein mixtures

Roasting is an important operation to produce attractive colors and distinctive flavors during the production of sesame oil. To investigate the contributions of macromolecules to the color and flavor during roasting sesame seeds, water-soluble polysaccharides (WSP) and chelator-soluble polysaccharides (CSP) sequentially extracted from sesame hull were mixed with sesame protein isolate (SPI) at different ratios (1:1, 1:2, and 2:1, w/w), then the mixtures were roasted at 180 °C for 35 min. Results showed that WSP, CSP, and SPI degraded approximately at 150 °C and SPI had the highest thermal stability. According to monosaccharide/amino acid analysis, glucose and galacturonic acid showed the highest reduction rates, as well as lysine and arginine. CSP + SPI mixtures showed greater reactivity than WSP + SPI mixtures, resulting in a darker color and many more Maillard reaction products. The predominant volatiles of roasted WSP/CSP + SPI mixtures were aldehydes and heterocyclic compounds identified by headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME/GC-MS). This work provides some new information about flavor and color development during roasting sesame seeds.

Synergy of physicochemical reactions occurred during aging for harmonizing and improving flavor

Numerous counterfeit vintage Baijiu are widely distributed in the market driven by economic interest which disturb the market economic rules and damage the reputation of particular Baijiu brand. Found on the situation, the Baijiu system variation during aging period, aging mechanisms and discrimination strategies for vintage Baijiu are systematically illuminated. The aging mechanisms of Baijiu cover volatilization, oxidation, association, esterification, hydrolysis, formation of colloid molecules and catalysis by metal elements or other raw materials dissolved from storage vessels. The discrimination of aged Baijiu has been performed by electrochemical method, colorimetric sensor array or component characterization coupled with multivariate analysis. Nevertheless, the characterization of non-volatile compounds in aged Baijiu is deficient. Further research on the aging principles, more easy-operation and low-cost discrimination strategies for aged Baijiu are imperative. The above information is favorable to better understand the aging process and mechanisms of Baijiu, and promote the development of artificial aging techniques.

Applications and prospects of the automation of compound flavor baijiu production by solid-state fermentation

Baijiu, the national liquor of China, is produced using traditional solid-state fermentation (SSF). SSF automation during compound flavor baijiu (CFB) production can considerably reduce labor intensity and required manpower, improve the working environment, decrease costs, and increase efficiency. The approaches for SSF automation in CFB production can provide a reference for the automation of SSF in other industries. Therefore, this review compares the traditional and automated processes for jiuqu starter production, SSF, and solid-state distillation during baijiu brewing. Furthermore, specific applications of automation technology and equipment are summarized for each process. The problems and challenges associated with the automation of the process are then detailed and future development directions are proposed. Thus, this review provides an overall introduction to and insight into the developments and challenges in the automation of the CFB brewing process, helping to promote automation in the brewing of other baijiu flavor classes and SSF products.

Colorimetric sensor arrays for the differentiation of baijiu based on amino-acid-modified gold nanoparticles

It is of great significance for quality control to realize the discrimination for baijiu from different brands and origins. Strong-aroma-type baijiu (SAB), one of the most important Chinese aroma-type baijiu, exhibits the largest variety and market share. In this study, we proposed colorimetric sensor arrays based on gold nanoparticles (AuNPs) modified with different amino acids (AAs) to recognize the organic acids, and further distinguish different SABs. Three representative AAs, namely methionine (Met), tryptophan (Trp), and histidine (His), were selected to modify the AuNPs surface. The investigation of the effect of the main ingredients of SAB on AA@AuNPs aggregation confirmed that this aggregation mainly resulted from organic acids. Moreover, this aggregation was successfully used for differentiating 11 organic acids. Different pH conditions can not only cause changes of the content of organic acids in baijiu, but also disrupt the balance among flavor substances of baijiu to some extent. Consequently, the AA@AuNPs arrays under two pH conditions have been successfully applied to distinguish 14 kinds of SABs from different brands and origins. The proposed colorimetric sensor method is simple, rapid, and visualized and provides a potential application prospect for the quality control of baijiu and other alcoholic beverages.

In-depth profiling of carboxyl compounds in Chinese Baijiu based on chemical derivatization and ultrahigh-performance liquid chromatography coupled to high-resolution mass spectrometry

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A systematic strategy for detection and annotation of carboxyl compound was developed.

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197 carboxyl compounds were detected in Chinese Baijiu for the first time.

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Annotation was based on MS1, t_R, in-silico MS/MS, and characteristic fragments.

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Three of carboxyl compounds were newly identified in Chinese Baijiu.

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Distribution of carboxyl compounds in Baijiu with different flavors was revealed.

Carboxyl compounds have a significant influence on the flavor of Chinese Baijiu. However, because of the structural diversity and low concentration, the deep profiling of carboxyl compounds in Chinese Baijiu is still challenging. In this work, a systematic method for comprehensive analysis of carboxyl compounds in Chinese Baijiu was established. After derivatized under optimized conditions, 197 p-dimethylaminophenacyl bromide-derived carboxylic compounds were annotated by multidimensional information including accurate mass, predicted t_R, in-silico MS/MS, and diagnostic ions for the first time. In addition, 48 of the 197 carboxyl compounds were positively identified, and three of them were newly identified in Chinese Baijiu. Moreover, we found the number and the concentration of carboxyl compounds in sauce-flavor Baijiu were more abundant than in strong-flavor Baijiu. This work provides a novel method for the analysis of carboxyl compounds in Baijiu and other complex samples.

Determination of 2-Pentanol Enantiomers via Chiral GC-MS and Its Sensory Evaluation in Baijiu

The enantiomeric contents of 2-pentanol of Baijiu were analyzed by liquid-liquid extraction (LLE) coupled with gas chromatography-mass spectrometry (GC-MS) using β-cyclodextrin as a chiral stationary phase. In this study, the average enantiomeric ratios R:S were 72:28, 64:36, and 94:6 in soy sauce aroma-type Baijiu (SSB), strong aroma-type Baijiu (STB), and light aroma-type Baijiu (LTB), respectively, and only (R)- configuration was found in rice aroma-type Baijiu (RTB). The highest enantiomeric concentration of 2-pentanol was found in STB. (R)-2-pentanol dominated in 48 Baijiu studied, and the concentration of (R)-2-pentanol was higher than that of the (S)-configuration. The results showed that the enantiomers of 2-pentanol were discrepant in different aroma types of Baijiu, and it may be the result of differences in raw materials, environment, and production processes. The 2-pentanol enantiomers had different odor characteristics, with different olfactory thresholds in pure water and 46% ethanol solutions by sensory analysis. (R)-2-pentanol was described as paint, rubber, grease, while the (S)-form had mint, plastic, and pungent notes. The olfactory thresholds of (R)- and (S)-form were 163.30 mg/L and 78.58 mg/L in 46% ethanol and 12.62 mg/L and 3.03 mg/L in pure water, respectively. The different enantiomeric distribution and aroma characteristics of the 2-pentanol enantiomers in Baijiu could be a potential marker for determining adulteration.

Open tubular capillary ion chromatography with online dilution for small ions determination in drinks

This work aims to develop a more robust, easy-to-use, low-pressure, and cost-effective nonsuppressed open tubular capillary ion chromatography (NS-OTIC) approach with online dialysis for small ions determination in drinks. The fabricated device was applied for two selected columns, including poly(butadiene-maleic acid) on a 50-μm bore and AS18 Latex on 25-µm bore fused silica capillaries, for the separation of mixed cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) and mixed anions (Cl^-, Br^-, NO₂^-, NO₃^-), respectively. High concentrations of ions (up to 100 mM) level can be directly introduced into the NS-OTIC system without an off-line (manual) dilution step. The linear relationship of the peak area and concentration of model ions can be obtained with a resolution > 1.1. The repeatability of the peak area for both OTIC columns was < 6% RSD. Juice and tea samples were successfully analyzed with % recoveries of 77-112 and 90-119 for cation and anion determinations, respectively.

Analysis of Bacterial Diversity in Different Types of Daqu and Fermented Grains From Danquan Distillery

Bacterial communities in high-temperature Daqu and fermented grains are important for brewing Jiang-flavor Baijiu such as Danquan Baijiu. Daqu is a saccharifying and fermenting agent, which has a significant impact on the flavor of Baijiu. However, bacterial communities in three different types of samples from the Danquan distillery (dqjq_ck, dqjqcp, and dqjp3) were still unclear, which limited further development of Danquan Baijiu. “dqjq_ck” and “dqjqcp” indicate high-temperature Daqu at days 45 and 135, respectively. “dqjp3” indicates fermented grains. In this study, the bacterial communities of three samples were analyzed by Illumina Miseq high-throughput sequencing. The bacterial communities of three samples primarily composed of thermophilic bacteria and bacteria with stress resistance. The most abundant species in dqjq_ck, dqjqcp, and dqjp3 were Comamonas, Bacillus, and unclassified Lactobacillales, respectively. The main bacteria included Bacillus, Comamonas, Myroides, Paenibacillus, Acetobacter, Kroppenstedtia, Staphylococcus, Saccharopolyspora, Planifilum, Lactobacillus, Acinetobacter, Oceanobacillus, Enterococcus, Thermoactinomyces, Lactococcus, Streptomyces, Saccharomonospora, Tepidimicrobium, Anaerosalibacter, unclassified_Lactobacillales, unclassified_Thermoactinomycetaceae_1, unclassified_Bacillaceae_2, unclassified_Bacillales, unclassified_Microbacteriaceae, unclassified_Rhodobacteraceae, unclassified_Actinopolysporineae, and unclassified_Flavobacteriaceae in three samples (percentage was more than 1% in one of three samples). In our study, the succession of microbiota in three samples representing three important stages of Danquan Baijiu brewing was revealed. This article lays a good foundation for understanding the fermentation mechanism and screening some excellent indigenous bacteria to improve the quality of Danquan Baijiu in future.

Chinese Baijiu: The Perfect Works of Microorganisms

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

Differentiation of ethanol-water clusters in Fenjiu by two-dimensional correlation fluorescence and Raman spectra

The taste of different flavor liquor is multifarious, but the same brand liquor with different quality is truth. The essence of supramolecular ethanol-water clusters and their intrinsic structural differences in three kinds of Fenjiu are studied by two-dimensional correlation spectra (2D-COS) of fluorescence and Raman. The 2D-COS of fluorescence reveals the prominent emission peaks of three Fenjiu are apparently different. The central fluorescence peak of Fenjiu (a) is located at 330 nm, corresponding to the cluster of (H₂O)_m(EtOH)_n. In Fenjiu (b), the emission peak appears near 310 nm, while those of Fenjiu (c) appear mainly near 310 and 373 nm, corresponding to the clusters of (H₂O)(EtOH)_n and (H₂O)_m(EtOH), respectively. Based on 2D-COS of Raman, the peak of Fenjiu (b) at 3440 cm^-1 changes initially, indicating its disorder degree is getting higher with continuous dilution with water. However, along with the dilution of Fenjiu (a) and Fenjiu (c), the peak located near 3200 cm^-1 changes in priority, indicating that the degree of association between ethanol and water is high, and the clusters formed there are stable. Therefore, this work provides the combined methods to distinguish different supramolecular sets in Fenjiu, applying liquor differentiation in the future.

Proton-coupled electron transfer of catechin in tea wine: the enhanced mechanism of anti-oxidative capacity

Tea wine is a Chinese traditional alcoholic drink made by cereal and tea leaves. It is rich in tea polyphenols, caffeine, amino acids, and protons and possesses various healthcare functions. In this work, electrochemical methods, as well as density functional theory (DFT) calculations, were adopted to reveal the proton-coupled electron-transfer process of catechin in tea wine. The electrochemical results showed that the catechin preferred hydrogen-bonding with ethanol and formed molecular clusters. Thus, the direct electron-transfer process of catechin changed to proton-coupled electron transfer. This procedure reduced the energy barrier of the redox reaction and enhanced the anti-oxidative capacity. Subsequently, DFT calculations were employed to explore the bond length, bond energy, and HOMO-LUMO energy gap of catechin, which confirmed the above-mentioned mechanism. Our work offers some positive value for the scientific promotion of traditional food and a greater understanding of the health mechanisms in terms of chemistry.