Characterization of key aroma compounds in aged Qingxiangxing baijiu by Comparative Aroma Extract Dilution Analysis, Quantitative Measurements, Aroma Recombination, and Omission Studies

Molecular and sensory characterization of Chinese Baijiu aged in Jiuhai container and contribution of volatile odorous terpenes to Jiuhai-aroma

Baijiu aged in Jiuhai container will produce a special Jiuhai-aroma, which has not been fully studied. In this study, check-all-that-apply method and quantitative descriptive analysis were used to characterize Jiuhai-aroma, and it was found that the aroma characteristics of herbs, spicy, cut hay and woody were prominent in Baijiu aged in Jiuhai container. According to the results of GC-O and quantification, 71 odorants were identified in Jiuhai sample. Through recombination and omission experiments, it was found that 4-ethylphenol, 4-ethylguaiacol and 3-methyl-2,4-nonanedione played a key role in Jiuhai-aroma. In addition to this, the omission of seven sub-threshold terpenes mixture (α-pinene, camphene, β-pinene, longifolene, 4-terpineol, α-terpineol and cedar) also had a significant effect on Jiuhai-aroma. The interactions between sub-threshold terpenes which can promote aroma perception was further confirmed by Feller's additive model.

Characterization of aroma differences in Jiangxiangxing Baijiu with varying ethanol concentrations: Emphasis on olfactory threshold changes of aroma compounds

In this study, the aroma profiles of high- and low-alcohol Jiangxiangxing Baijiu were compared through sensory analysis, revealing significant differences in acidic, floral, fruity, smoky and oxidized oil notes. To further clarify the underlying causes of aroma differences, we examined the concentrations of 106 important compounds, revealing that the concentrations differences between the two were generally 1 to 2 times. Furthermore, the determination results of the olfactory thresholds (OTs) indicated that the OT40% vol of 87 aroma compounds was less than the OT50% vol, with 68 compounds exhibiting OT changes ranging from 2 to 17 times. Finally, in terms of odor activity values (OAVs), it was established that changes in OTs of aroma compounds might be the primary reason behind the differences in aroma profiles. Overall, focusing on the impact of ethanol concentration on the OTs of aroma compounds is a key point of flavor modulation in low-alcohol Jiangxiangxing Baijiu.

The hidden palette: Uncovering key substances driving color variation in sesame-flavor Baijiu

Color is a pivotal in the visual quality of sesame-flavor Baijiu (SFB), may significantly influence consumers' perception. This study investigated the sensory differences among samples with different colors and identified potential substances responsible for these color variations. Sensory evaluation revealed subtle quality differences (Adonis R2 = 0.0990), and color served as a crucial basis to judge quality prior to tasting. Among samples with different colors, volatile metabolites were not correlated with color (p > 0.05). Conversely, metal ions and non-volatile metabolites demonstrated significant correlations with color (p < 0.001), accounting for 76.74 % of the observed color variation. Notably, Fe3+ was identified as the primary driver of color variation, being the only substance with a significant effect on ΔE. Additionally, non-volatile metabolites, such as palmitic acid, oleic acid, and linoleic acid, also played roles in color variation. These findings provide a valuable direction for controlling the visual quality of Baijiu.

The influence of different geographical origins and grades on the flavor of Qingxiangxing Baijiu: An integrated analysis using descriptive sensory evaluation, GC×GC-MS, E-nose, and ICP-MS

The origin and grade are the important factors that influence the flavor and price of Qingxiangxing Baijiu (QXB). As the grade increased, sensory differences and geographical differences become more pronounced. The aromas of floral, fruity, and sweet become more noticeable, while the acidity decreased. The different substances among three grades of QXB mainly focused on esters and alcohols. Correlation analysis indicated that the increase in the concentration of ester compounds was one of the reasons for the significant differences in floral, fruity, and sweet fragrances. Because of the higher concentration of acidic compounds in northern QXB, its acidic taste was more pronounced. Meanwhile, the esters and ketones in southern QXB accounted for a higher proportion, which made its floral and fruity fragrance more prominent. PLS-DA was more suitable for the classification of QXB based on grade and region. And the metal elements in QXB could be used for regional identification.

Unraveling Shengmuxiang in Jiang-flavor base baijiu using a combination of metabolomics and sensomics strategy

Shengmuxiang (SMX), an important aroma in Jiang-flavor base baijiu, significantly influences the quality of the product. This study employed untargeted metabolomics combined with sensomics to explore the key compounds responsible for SMX. Results indicated that SMX samples had higher intensities of green and woody-like odors compare to control samples. A total of 87 aroma compounds were identified by headspace solid phase microextraction combined with gas chromatography-mass spectrometry technology. Based on the variable projection importance, PCA and OPLS-DA were employed to identify 22 potential marker compounds. Quantitative results combined with hierarchical cluster and OAV analysis revealed that 9 aroma compounds (OAV > 1) had high concentrations in SMX samples. Aroma recombination and omission experiments further indicated that acetaldehyde and acetal were the key compounds responsible for the characteristic aroma of SMX in Jiang-flavor base baijiu. These findings provide valuable insights into the distinct aroma profile of SMX and offer a basis for quality control of Jiang-flavor base baijiu.

Study on the Interaction between Polyol Glycerol and Flavor Compounds of Baijiu: A New Perspective of Influencing Factors of Baijiu Flavor

The interaction among flavor compounds is a crucial determinant of Baijiu's flavor. Yet, the interaction between glycerol, a prominent polyol in Baijiu, and volatile flavor compounds remains elusive. The effect of glycerol concentration on the volatility of 13 Baijiu flavor compounds was analyzed by GC-IMS and GC-MS. The findings reveal that glycerol's impact on the volatility of these compounds increases with its concentration. Postglycerol addition, olfactory threshold and S-curve analyses reveal a decrease in the perception threshold of dimethyl trisulfide, while the perception thresholds of 3-methylbutanal, 1-propanol, 2-methyl-1-propanol, and ethyl lactate increase. Additionally, the independent gradient model based on Hirshfeld partitioning showed that hydrogen bonding is crucial in the interactions, aligning well with GC-IMS and odor threshold results to underscore glycerol's consistent impact on Baijiu flavor compounds. This research highlights glycerol's significant role in shaping Baijiu's complex flavor profile, enhancing our understanding of flavor interactions.

Unveiling the aroma profile of anhydrous milk fat: Insights into key odorants during biocatalysis by aroma extract dilution analysis, aroma recombination, and omission experiment

Determination and verification of the key aroma compounds of anhydrous milk fat (AMF) were conducted during biocatalysis at different times using commercial immobilized Lipozyme RMC from Rhizomucor miehei and Lipozyme TL-IM from Thermomyces lanuginosus. The analysis techniques employed included headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) coupled with olfactory port, aroma extract dilution analysis (AEDA), odor activity values (OAV), aroma recombination model, and omission experiments. A total of 17 main odorants were identified and quantified in AMF, and characterized by flavor dilution factors ranging from 4 to 128. Among them, butanoic acid, methyl octanoate, hexanoic acid, methyl butanoate, and methyl decanoate revealed the highest flavor dilution. These aroma-active compounds were confirmed as important odorants based on their OAVs ≥ 1. Furthermore, the omission and recombination model sensory experiments successfully identified 12 key odorants including butanoic acid, methyl octanoate, hexanoic acid, octanoic acid, methyl hexanoate, and methyl butanoate in AMF catalyzed with Lipozyme RMC. Overall, this research provides valuable insights into the enzymatic modification of AMF and its impact on flavor modulation in dairy products.

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).

Alterations in physico-chemical properties, microstructure, sensory characteristics, and volatile compounds of red pepper (Capsicum annuum var. conoides) during various thermal drying durations

Red pepper (Capsicum annuum var. conoides) is commonly used for dried pepper production in China, and the drying process, particularly the during duration, profoundly affects its quality. The findings indicate that prolonged exposure to high temperatures during thermal drying results in significant darkening, an evident decrease in red and yellow tones, and gradual transformation of the pepper's microscopic structure from granular to compact, along with 88% reduction in moisture content and 81% decrease in thickness. The capsaicinoid content increased, resulting in a 4.3-fold increase in spiciness after drying compared to that of fresh pepper. The pepper aroma shifts from fruity, choking, and grassy to herb, dry wood, and smoky. Compounds such as 2-Acetylfuran, furfural, 2-methylfuran, 1-methylpyrrole, 2-methylpyrazine, and 2,5-dimethylpyrazine exhibited positive correlations with drying time, whereas ethyl 2-methylpropanoate, ethyl butanoate, ethyl 2-methylbutanoate, ethyl hexanoate, and 3-methylbutyl butanoate showed negative correlations, indicating their potential as markers for monitoring thermal drying processes.

Fast and non-invasive identification of Baijiu based on Tyndall effect and chemometrics

The value of Baijiu is affected by its flavor, age, and adulteration. Therefore, a simple and rapid identification method is crucial for the market. In this study, we present a rapid, non-intrusive identification technique for Baijiu utilizing the Tyndall effect combined with chemometrics analysis. Our experiment begins illuminating Baijiu with a 405 nm wavelength laser and recording the resulting bright light path due to the Tyndall effect. To further analyze the color and brightness information, Principal Component Analysis (PCA), Linear Discriminant Analysis (LDA), Hierarchical Cluster Analysis (HCA), and Multilayer Perceptron (MLP) were employed. This study establishes correlations between the brightness of the Tyndall light path and seven trace flavor compounds in Baijiu. The findings demonstrate that this method effectively identifies the flavor, age cellar, and adulteration of Baijiu and also quantitatively detects the concentrations of flavor compounds. Additionally, an analysis platform was developed to enable the rapid identification of Baijiu.

Investigating the impact of various sorghum types on the key aroma compounds of Sichuan Xiaoqu Baijiu through application of the sensomics approach

The aroma of Sichuan Xiaoqu Baijiu (SXB) greatly benefits from the use of sorghum as its primary brewing ingredient. Nevertheless, the impact of different sorghum variety on the primary aroma compounds of SXB has not been thoroughly investigated. Gas chromatography-mass spectrometry (GC-MS) in conjunction with headspace solid phase microextraction (HS-SPME) and liquid-liquid extraction (LLE) were employed in this investigation. Using 5 sorghum varieties as raw materials, five different types of SXB were analysed for their aroma compounds using GC-MS, GC-O, AEDA, aroma recombination, and aroma omission. Key aroma compounds of SXB were successfully identified as ethyl acetate, ethyl 2-methylbutyrate, isoamyl acetate, ethyl hexanoate, ethyl heptanoate, ethyl lactate, ethyl octanoate, ethyl decanoate, phenylethyl acetate, ethyl laurate, ethyl palmitate, isoamyl alcohol, phenylethanol, 1,1-diethoxyethane, 3-hydroxy-2- butanone, furfural, and glacial acetic acid. Glacial acetic acid, ethyl acetate, ethyl lactate, phenylethyl acetate, acetoin, phenylethanol, and ethyl caproate were found to be the seven major aroma compounds that had the biggest impact on the variations of the five SXB aroma properties, according to partial least squares regression (PLS-R) analysis. The collinear network analysis also revealed that the largest positive correlation weight was discovered between the protein and furfural content, tannin content and cereal-like aroma profile while the highest negative correlation weight was found between the moisture and acetoin content. This study is a valuable resource for understanding how raw materials control the directional regulation of the sensory quality of the SXB liquor body.

Strategies and Challenges of Microbiota Regulation in Baijiu Brewing

The traditional Chinese Baijiu brewing process utilizes natural inoculation and open fermentation. The microbial composition and abundance in the microecology of Baijiu brewing often exhibit unstable characteristics, which directly results in fluctuations in Baijiu quality. The microbiota plays a crucial role in determining the quality of Baijiu. Analyzing the driving effect of technology and raw materials on microorganisms. Elucidating the source of core microorganisms and interactions between microorganisms, and finally utilizing single or multiple microorganisms to regulate and intensify the Baijiu fermentation process is an important way to achieve high efficiency and stability in the production of Baijiu. This paper provides a systematic review of the composition and sources of microbiota at different brewing stages. It also analyzes the relationship between raw materials, brewing processes, and brewing microbiota, as well as the steps involved in the implementation of brewing microbiota regulation strategies. In addition, this paper considers the feasibility of using Baijiu flavor as a guide for Baijiu brewing regulation by synthesizing the microbiota, and the challenges involved. This paper is a guide for flavor regulation and quality assurance of Baijiu and also suggests new research directions for regulatory strategies for other fermented foods.

GC/MS-based untargeted metabolomics reveals the differential metabolites for discriminating vintage of Chenxiang-type baijiu

The "outstanding and unique aged aroma" of Chinese Chenxiang-type baijiu (CXB)-Daoguang 25 (DG25) mainly originates from a "extraordinary storage technology" of Mujiuhai (a wooden container), so it is mysterious and interesting. In this study, an untargeted GC/MS-based metabolomics was used to reveals the volatile differential metabolites for discriminating six different vintages of DG25 combing with chemometrics. A total of 100 volatile metabolites (including unknowns) were extracted and identified, including esters (41%), alcohols (10%) and acids (7%) so on. Finally, 33 differential metabolites were identified as aging-markers. Among them, 25 aging-markers showed a downtrend, including 17 esters such as ethyl acetate, ethyl hexanoate and ethyl palmitate so on. Moreover, it was interesting and to further study that furans showed a significant downtrend. Statistically speaking, ethyl benzoate played an important role in discriminating vintage of 1Y and 3Y, and the other 24 differential metabolites with downtrend discriminating the unstored (0Y-aged) DG25. Eight differential metabolites, such as ethyl octanoate, benzaldehyde, 3-methylbutanol and 1,1-diethoxyaccetal so on increased during aging of DG25, and they played a statistical role in discriminating the 5Y-, 10Y- and 20Y-aged DG25. This study provides a theoretical basis way for the formation mechanism of aging aroma for CXB.

Variations in Key Aroma Compounds and Aroma Profiles in Yellow and White Cultivars of Flammulina filiformis Based on Gas Chromatography-Mass Spectrometry-Olfactometry, Aroma Recombination, and Omission Experiments Coupled with Odor Threshold Concentrations

Flammulina filiformis (F. filiformis) is called the 'benefiting intelligence' mushroom. There is a notable difference between a yellow cultivar (with a robust aroma) and a white mutant cultivar (with a high yield) of F. filiformis. A thorough analysis of aroma differences is essential to improve the aroma of high-yield strains. This study employed a combination of gas chromatography-mass spectrometry-olfactometry (GC-MS-O) and aroma extract dilution analysis (AEDA) to analyze the variations in aroma compounds. Then, the contribution of the odorants was determined using flavor dilution (FD) factors and odor activity values (OAVs). Aroma omission and recombination experiments were used to identify the key odorants. A total of 16 key aroma compounds were characterized in F. filiformis, along with four eight-carbon volatiles (3-octanone, 3-octanol, octanal, and 1-octen-3-ol). Finally, the dominant aroma characteristic was "sweet" for the yellow strain, while it was "green" for the white strain. More research is required to investigate the enzymes and corresponding genes that regulate the synthesis of aroma compounds in F. filiformis for future breeding programs.

Flavor characteristics of Shanlan rice wines fermented for different time based on HS-SPME-GC-MS-O, HS-GC-IMS, and electronic sensory analyses

Flavor characteristics of Shanlan rice wines with different fermentation time were analyzed. Results suggested that 3-methyl-1-butanol, phenylethyl alcohol, ethyl acetate, and diethyl succinate were the characteristic volatiles of Shanlan rice wine by using headspace solid-phase microextraction-gas chromatography-mass spectrometry-olfactometry. The most varieties (38) of volatiles appeared at a 3-year-fermentation time, contributing a unique and harmonious aroma to the Shanlan rice wine fermented for 3 years, but only 19 types were observed at 45-days and 1-year fermentation times. A similar trend was intuitively visible in the headspace-gas chromatography-ion mobility spectrometry analysis. The Shanlan rice wine fermented for 3 years had a similar taste profile to that fermented for 45 days, but with distinguishing contents of free amino acids (1352.80 mg/L and 2261.50 mg/L, respectively) and organic acids (9.58 g/L and 49.88 g/L, respectively). The Shanlan rice wine fermented for 1 year had a strong taste with more intensity of most taste attributes.

Characterization of Key Aging Aroma Compounds in Aged Jiangxiangxing Baijiu and Their Formation Influencing Factors during the Storge Process

Long-term storage Baijiu has an appealing sensory property, yet the chemical makeup is rarely reported. This study investigated a 30-year-old Jiangxiangxing (JXX) Baijiu and recognized and measured 69 aroma compounds. 3-Methyl-2,4-nonanedione (2.76 μg/L), 2,5-dimethyl-4-hydroxy-3(2H)-furanone (HDMF, 46.2 μg/L), 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone (HEMF, 61.7 μg/L), and piperitone (3.66 μg/L) were detected for the first time in Baijiu. Compared with 3-year-old JXX Baijiu, 24 compounds were significantly higher in the 30-year-old, mainly including furans, pyrazines, and aromatics. Notably, 4,5-dimethyl-3-hydroxy-2(5H)-furanone (sotolon), HDMF, HEMF, vanillin, acetovanillone, and alkyl pyrazines in 30-year-old JXX Baijiu were 2-7 times higher than those of a 3-year-old, and they increased steadily during aging for 3, 15, and 30 years, assumed to be associated with the aging aroma. Following 24 months of storing JXX Baijiu under different conditions, the pottery significantly promoted the synthesis of sotolon, HDMF, HEMF, and alkyl pyrazines. These findings suggest that pottery is a potential catalyst for enhancing aged Baijiu.

Characterization of Key Odorants in Chinese Texiang Aroma and Flavor Type Baijiu (Chinese Liquor) by Means of a Molecular Sensory Science Approach

The popularity of texiang aroma type baijiu (liquor), known for its unique production technology and multilayered flavor, has been steadily increasing among consumers. So far, no research has determined its key aroma compounds for characterizing the unique flavor, which is the purpose of this paper. Using gas chromatography-olfactometry (GC-O) coupled with the GC-mass spectrometry (GC-MS) method, 87 aroma-active compounds were identified and screened out with intensity values ≥2.0. 1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) was first confirmed by GC-O in Chinese liquor. According to a quantitative study and odor activity values (OAVs), 42 odorants were determined as important aroma compounds. These odorants were recombined based on quantitative concentrations, successfully simulating the overall aroma profile. Omission experiments verified ethyl hexanoate, β-damascenone, and 2-furfuryl ethyl ether as the key aroma compounds and revealed that ethyl acetate, furfural, and ethyl 2-phenylacetate were important aroma compounds to the overall flavor of texiang aroma and flavor type liquor.

Development of the gas chromatography/mass spectrometry-based aroma designer capable of modifying volatile chemical compositions in complex odors

Many volatile organic compounds (VOCs) are used to produce various commercial products with aromas mimicking natural products. The VOCs responsible for aromas have been identified from many natural products. The current major strategy is to analyze chemical compositions and aroma qualities of individual VOCs using gas chromatography/mass spectrometry (GC/MS) and GC-olfactometry. However, such analyses cannot determine whether candidate VOCs contribute to the characteristic aroma in mixtures of many VOCs. In this study, we developed a GC/MS-based VOC collection/omission system that can modify the VOC compositions of samples easily and rapidly. The system is composed of GC/MS with a switching unit that can change gas flow routes between MS and a VOC collection device. We first applied this system to prepare gas samples for omission tests, and the aroma qualities of VOC mixtures with and without some VOCs were evaluated by panelists. If aroma qualities were different between the 2 samples, the omitted VOCs were likely key odorants. By collecting VOCs in a gas bag attached to the collection device and transferring some VOCs to MS, specific VOCs could be omitted easily from the VOC mixture. The system could prepare omission samples without chemical identification, preparation of each VOC, and laborious techniques for mixing VOCs, thus overcoming the limitations of previous methods of sample preparation. Finally, the system was used to prepare artificial aromas by replacing VOC compositions between different samples for screening of key odorants. In conclusion, the system developed here can improve aroma research by identifying key odorants from natural products.