Effects of metals released in strong-flavor baijiu on the evolution of aroma compounds during storage

Effects of storage time on flavor characteristics of bran-free fermented Baijiu by using electronic sensory, descriptive sensory analysis, GC × GC-MS, and ICP-MS

By examining and analyzing bran-free fermented Baijiu (BFB) with varying storage periods (0-20 years), it was observed that the overall concentration of volatile compounds initially increases and subsequently decreases over time. Furthermore, BFB exhibited more kinds of long chain esters, higher concentration of acetals, and reduced furfural content. The process of cellaring can enhance the aged, sweet, and fruity aroma of BFB. 16 flavor compounds, including 1,1-diethoxyethane, ethyl dodecanoate, and ethyl hexadecanoate, can be used as markers for vintage BFB, and electronic sensory technology was capable of discerning BFB in different years. The results of redundancy analysis (RDA) showed a positive correlation between metals and aldehydes, esters, and ketones, while indicating a negative correlation with acids and alcohols. Al, Fe, and Ca underwent the most significant changes during storage period, and they were positively correlated with differential substances, such as benzaldehyde, vanillin, ethyl isovalerate, and ethyl palmitate (P < 0.01).

Hydrogen bonding dominated self-assembly mechanism of amphiphilic molecules in Chinese Baijiu

Molecular mechanisms underlying the aging of Chinese Baijiu remained elusive. This study proposed the self-assembly behavior of amphiphilic molecules dominated by hydrogen bonds in Chinese Baijiu for the first time. The self-assembly degree of amphiphilic clusters gradually intensifies with the prolonged storage time of Baijiu, comprehensively characterized at both micro and macro levels. The results indicated that the blue-shift of the Raman hydrogen bond vibrational peak (about 11 cm-1 and 7 cm-1, respectively), the increase in viscosity (5.71% and 2.22%, respectively), and the rise in dielectric constant (95.63% and 94.99%, respectively) during the 17-year cellaring process of Strong-flavor Baijiu and Jiang-flavor Baijiu were consistent with the evolutionary trends observed in molecular dynamics simulations. The essential driving factors of cluster structure alteration of amphiphilic aroma substances in Chinese Baijiu during cellaring were demonstrated from molecular level. This study provided a research approach to comprehending the aging mechanism of Chinese Baijiu from the micro level.

Strengthening the microbial community and flavor structure of jiupei by simulating strong-aroma baijiu fermentation with Bacillus velezensis DQA21

BACKGROUND

Bacillus velezensis DQA21 is a functional strain used in the fermentation process of strong-aroma baijiu; however, its specific role in the process is still unclear.

RESULTS

In this study, specific roles of B. velezensis DQA21 in the fermentation process were explored. Bioaugmentation of B. velezensis DQA21 increased the diversity and abundance of the bacterial community during the first 32 days of fermentation and significantly inhibited the diversity and richness of the fungal community during days 12 to 32. According to cluster analysis, changes in the microbial community structure were observed during fermentation, and the fermentation process could be divided into two stages: stage I, days 0-12; and stage II, days 12-45. Additionally, the microbial community structures during the two fermentation stages were significantly different. Co-occurrence analysis showed that bioaugmentation with Bacillus increased the correlation between microorganisms in jiupei and had a significant impact on the overall network structure of the microbial community. In addition, Bacillus significantly increased the production of flavor substances in jiupei, causing the total esters, total alcohols, and total acids contents to increase by 19.1%, 81.1%, and 25.9% respectively.

CONCLUSION

The results suggested that bioaugmentation with B. velezensis DQA21 had a strong impact on the microbial community structure in strong-aroma baijiu, enhancing the volatile flavor components. Additionally, the work also provides a better understanding on the effect of augmentation on the microbial community in jiupei, which could help better regulation of solid-state fermentation in strong-aroma baijiu. © 2024 Society of Chemical Industry.

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.

Rapid, simple, and simultaneous electrochemical determination of cadmium, copper, and lead in Baijiu using a novel covalent organic framework based nanocomposite

It is of great significance to develop a simple and rapid electrochemical sensor for simultaneous determination of heavy metal ions (HMIs) in Baijiu by using new nanomaterials. Here, graphene (GR) was utilized to combine with covalent organic frameworks (COFs) that was synthesized via the aldehyde-amine condensation between 2, 5-dimethoxyterephthalaldehyde (DMTP) and 1, 3, 5-tris(4-aminophenyl) benzene (TAPB) to prepare a new GR/COFDPTB/GCE sensor for electrochemical sensing multiple HMIs. Compared with the glass carbon electrode (GCE), GR/GCE and COFDPTB/GCE, the developed sensor exhibited excellent electrochemical analysis ability for the simultaneous detection of Cd2+, Pb2+, and Cu2+ owing to the synergistically increased the specific surface area, the periodic porous network and plenty of effective binding sites, as well as the enhanced conductivity. Under the optimized experimental parameters, the proposed sensor showed good linearity range of 0.1-25 μM for Cd2+, and both 0.1-11 μM for Pb2+ and Cu2+ with the detection limits of Cd2+, Pb2+, and Cu2+ being 0.011 μM, 8.747 nM, and 6.373 nM, respectively. Besides, the designed sensor was successfully applied to the simultaneous detection of the three HMIs in Baijiu samples, suggesting its good practical application performance and a new method for the rapid detection of HMIs being expended.

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

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

The types of brewing water affect tea infusion flavor by changing the tea mineral dissolution

The effects of different brewing water samples, including natural drinking water (NDW), pure water (PW), mineral water (MW), distilled water (DW), and tap water (TW) on flavor and quality of green tea infusion were investigated. The results showed the dissolution rate of mineral substances varied greatly depend on the type of water used. Notably, the tea infusion brewed with MW showed the highest taste response and darker but higher brightness in color. Furthermore, the content of volatile compounds was highest in tea infusion brewed with NDW and lowest in tea infusion brewed with MW. The mineral substances content and pH were the main factors affecting volatile compounds in green tea infusion. Thereinto, Ca²⁺ and Fe³⁺ remarkably affected the content of alcohols and aldehydes in volatile compounds. These results suggested that water with a neutral pH value and lower mineral substance content is more conducive for brewing green tea.

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.

Impact of Aging Microbiome on Metabolic Profile of Natural Aging Huangjiu through Machine Learning

Aging is a time-consuming step in the manufacturing of fermented alcoholic beverages. Natural-aging huangjiu sealed in pottery jars was taken as an example to investigate the changes of physiochemical indexes during aging and to quantify intercorrelations between aging-related factors and metabolites through machine learning methods. Machine learning models provided significant predictions for 86% of metabolites. Physiochemical indexes well reflected the metabolic profile, and total acid was the most important index that needed to be controlled. For aging-related factors, several aging biomarkers of huangjiu were also well predicted. Feature attribution analysis showed aging year was the most powerful predictive factor, and several microbial species were significantly associated with aging biomarkers. Some of the correlations, mostly connected to environmental microorganisms, were newly found, showing considerable microbial influence on aging. Overall, our results reveal the potential determinants that affect the metabolic profile of aged huangjiu, paving the way for a systematical understanding of changes in metabolites of fermented alcoholic beverages.

Distilled beverage aging: A review on aroma characteristics, maturation mechanisms, and artificial aging techniques

The market value of distilled beverage relies on its quality with a major contribution of distinctive and fascinating aromas. The aroma of distilled beverage is built on the basis of chemical components and can be modified through a series of physical and chemical processes such as aging. Revealing the hidden knowledge behind the evolution of numerous chemical components during these physicochemical processes in distilled beverages is not only significant but also challenging due to its complex system. In this review, the trends in the changes of associated aroma compounds over aging are proposed on the basis of understanding the relationship between chemical components and aroma profiles of numerous typical distilled beverages. The different aging systems, both classical platforms from Eastern countries (pottery jars) to Western countries (wood barrels), and modern platforms such as artificial aging technologies are outlined and compared with their respective applications. Optimizing aging processes is a challenging but imperative step, which warrants further fundamental knowledge from targeting aging-related molecules to the exploration of multitude physicochemical reaction mechanisms that occur during this process, such as the formation of potent odorant compounds in specific containers and environments, as well as mass transfer processes between solid and liquid interfaces. Understanding these maturation mechanisms of distilled beverages expressed by chemosensory signature holds promise for major improvements in future aging technologies that can efficiently yield stable and high-quality products.

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.

Insights into the mechanism of flavor compound changes in strong flavor baijiu during storage by using the density functional theory and molecular dynamics simulation

The aging procedure/storage is essential to enhance the organoleptic quality of strong flavor baijiu (SFB). How the storage affects flavor changes in SFB, that is, the aging mechanisms remains unclear. Herein, the physical and chemical effects on the main flavor compounds of SFB during storage were investigated using the density functional theory (DFT) and molecular dynamics (MD) simulation. DFT calculation results showed that the activation energy of ester alkyl-oxygen protonation was lower than that of acid hydroxyl-oxygen protonation, which explained the reason why the concentrations of acids increased and those of esters decreased during SFB storage. MD simulation results showed that electrostatic interaction was a major contributor to SFB and that the ethanol-water system containing acids had a stronger electrostatic energy and more hydrogen bonds than the ethanol-water system containing esters. These findings revealed that acids are prone to generating and strengthening associative structures in SFB during storage.

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

Chinese traditional fermented baijiu is a famous alcoholic beverage with unique flavor. Despite its consumption for millennia, the flavor mystery behind baijiu is still unclear. Studies indicate that esters are the most important flavor substances, and bring health benefits. However, the aroma contribution and formation mechanism of esters still need to be clarified to reveal the flavor profile of baijiu. This review systematically summarizes all the 510 esters and finds 9 ethyl esters contribute greatly to the flavor of baijiu. The 508 different microbial species that have been identified affect the synthesis of esters through fatty acid and amino acid metabolism. The determination of minimum functional microbial groups and the analysis of their metabolic characteristics are crucial to reveal the mechanism of formation of baijiu flavor, and ensure the reproducible formation of flavor substances.

Untargeted Headspace-Gas Chromatography-Ion Mobility Spectrometry in Combination with Chemometrics for Detecting the Age of Chinese Liquor (Baijiu)

This paper proposes the combination of headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and chemometrics as a method to detect the age of Chinese liquor (Baijiu). Headspace conditions were optimized through single-factor optimization experiments. The optimal sample preparation involved diluting Baijiu with saturated brine to 15% alcohol by volume. The sample was equilibrated at 70 °C for 30 min, and then analyzed with 200 μL of headspace gas. A total of 39 Baijiu samples from different vintages (1998–2019) were collected directly from pottery jars and analyzed using HS-GC-IMS. Partial least squares regression (PLSR) analysis was used to establish two discriminant models based on the 212 signal peaks and the 93 identified compounds. Although both models were valid, the model based on the 93 identified compounds discriminated the ages of the samples more accurately according to the goodness of fit value (R²) and the root mean square error of prediction (RMSEP), which were 0.9986 and 0.244, respectively. Nineteen compounds with variable importance for prediction (VIP) scores > 1, including 11 esters, 4 alcohols, and 4 aldehydes, played vital roles in the model established by the 93 identified compounds. Overall, we determined that HS-GC-IMS combined with PLSR could serve as a rapid and accurate method for detecting the age of Baijiu.

Elucidating metal ion-regulated flavour formation mechanism in the aging process of Chinese distilled spirits (Baijiu) by electrochemistry, ICP-MS/OES, and UPLC-Q-Orbitrap-MS/MS

Elucidating the organometallic interactions in Baijiu will promote a deeper understanding of the flavour formation mechanism during Baijiu aging. However, the organometallic interactions during aging are difficult to explore because the concentration and status of metals in Baijiu samples are affected by other substances (such as organic acids), and the concentrations of these substances also change dynamically. Hence, the flavour formation mechanism of aged Baijiu was investigated based on a multi-method analysis (i.e. electrochemistry, ICP-MS/OES, and UPLC-Q-Orbitrap-MS/MS), which enabled us to solve the difficulty above. The key finding is that, in the aging period, the organic acids induce the transformation of the metal ion state from the complex state to the free state. As a result, the flavour compound (i.e. the esters) contents in aged Baijiu are regulated by the free metal ion-catalyzed reactions.

Unraveling the acetals as ageing markers of Chinese Highland Qingke Baijiu using comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry combined with metabolomics approach

Objectives

The ageing process has a significant impact on the aroma of Chinese Baijiu, which could strengthen the desirable flavor characteristics and reduce the undesirable ones. The aim of this study was to observe the initiation of meaningful changes in volatile fraction and locate the ageing markers during ageing storage of Chinese Highland Qingke Baijiu.

Materials and Methods

Samples of Chinese Qingke Baijiu were aged for 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11 months before analysis. The samples were isolated by liquid–liquid extraction and then analyzed by comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry. The acquired data were processed by untargeted and targeted metabolomics approach to locate the ageing markers.

Results

The untargeted metabolomics analysis (hierarchical clustering analysis, HCA) shows that the chemical composition of Qingke Baijiu presents a statistically significant deviation from the reference scenario after 5 months. Subsequently, supervised statistics analysis (orthogonal partial least squares discrimination analysis) was performed to locate the markers, which changed significantly during ageing. Fifteen markers were located, and seven of them were acetals. Notably, 1,1-diethoxy-propane, 1,1-diethoxy-butane, and 1,1-diethoxy-3-methyl-butane are important contributors to the flavor of Chinese Baijiu. The identified markers were applied for the untargeted metabolomics (HCA), and the results revealed that these markers could divide the Qingke Baijiu into two ageing stages, 0–5 months and 6–11 months.

Conclusion

The results suggest that it is a valuable tool for monitoring the changes of volatile compounds and locating the age markers in Chinese Baijiu.

Flavor Formation in Chinese Rice Wine (Huangjiu): Impacts of the Flavor-Active Microorganisms, Raw Materials, and Fermentation Technology

Huangjiu (Chinese rice wine) has been consumed for centuries in Asian countries and is known for its unique flavor and subtle taste. The flavor compounds of Huangjiu are derived from a wide range of sources, such as raw materials, microbial metabolic activities during fermentation, and chemical reactions that occur during aging. Of these sources, microorganisms have the greatest effect on the flavor quality of Huangjiu. To enrich the microbial diversity, Huangjiu is generally fermented under an open environment, as this increases the complexity of its microbial community and flavor compounds. Thus, understanding the formation of flavor compounds in Huangjiu will be beneficial for producing a superior flavored product. In this paper, a critical review of aspects that may affect the formation of Huangjiu flavor compounds is presented. The selection of appropriate raw materials and the improvement of fermentation technologies to promote the flavor quality of Huangjiu are discussed. In addition, the effects of microbial community composition, metabolic function of predominant microorganisms, and dynamics of microbial community on the flavor quality of Huangjiu are examined. This review thus provides a theoretical basis for manipulating the fermentation process by using selected microorganisms to improve the overall flavor quality of Huangjiu.