Evaluation of the Perceptual Interaction among Ester Odorants and Nonvolatile Organic Acids in Baijiu by GC-MS, GC-O, Odor Threshold, and Sensory Analysis

Effects of lactic acid on the perception of volatile pyrazine aroma substances in Laimao Baijiu and its molecular interaction mechanisms

Lactic acid (LA) is commonly presented in Baijiu, but its influence on flavor is ambiguous. The volatile pyrazines and LA content in Laimao Baijiu were investigated by comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC-qMS) and ultra-performance liquid chromatography-tandem hybrid quadrupole-Orbitrap mass spectrometry (UPLC-Q-Exactive Orbitrap MS). The results demonstrated that 5 kinds of pyrazine with odor activity values ≥1 were identified as important odorants, and the content of LA was 857.72-1807.79 mg/L. Through sensory experiments, the perceptual interaction of LA with five types of pyrazines in a Baijiu matrix was evaluated. The results showed that after adding LA, the olfactory thresholds of tetramethylpyrazine (TMP) and 2,3,5-trimethylpyrazine (TP) significantly decreased, while the olfactory thresholds of 2,6-dimethylpyrazine (DP), 2-ethyl-3,5-dimethylpyrazine (EDP), and 2-ethyl-6-methylpyrazine (EM) increased. Ultraviolet spectrum analysis and molecular dynamics simulation results indicated that with the addition of LA, the intermolecular attraction related to TMP/TP decreases, while the intermolecular attraction related to DP/EDP/EM increases. LA and pyrazines were mainly affected by van der Waals interaction, electrostatic interaction and hydrophobic interaction. Theoretical calculation results further confirmed that the absolute binding energy of LA-DP, LA-EDP, and LA-EM was greater than that of LA-TMP, and LA-TP. The binding trend of DP, EDP, and EM with LA was more obvious. Overall, LA alters the intermolecular forces between pyrazine molecules, thereby changing the sensory perception of Baijiu flavor. It will provide theoretical guidance for enhancing the aroma quality of soy sauce aroma type Baijiu and promote a more in-depth study of Baijiu.

Novel Room-Temperature-Prepared Covalent Organic Framework as Adsorbent for Rapid Extraction of Aromatic Esters in Baijiu

Developing a rapid, efficient, and environmentally friendly analytical methodology for the determination of aromatic esters (AREs) in Baijiu presents a significant challenge. In this study, we developed a room-temperature method to synthesize core-shell Fe3O4@TPB-Dha in 1 h using pre-prepared Fe3O4 nanoparticles, enabling rapid and sensitive detection of AREs. The Fe3O4@TPB-Dha demonstrated exceptional adsorption capabilities (52.63-58.82 mg/g) with a brief adsorption duration (4 min) for four AREs as magnetic solid phase extraction (MSPE) adsorbent. Moreover, density functional theory (DFT) calculations revealed the key adsorption mechanisms to be hydrogen bonds, van der Waals forces, and π-π interactions. Ultimately, the method enabled the rapid and accurate quantification of the four AREs in real Baijiu samples, with concentrations spanning from 0.17 ± 6 × 10-4 to 2.40 ± 0.03 mg/L, and exhibited relative standard deviations below 6.57% (n = 3). These findings suggest that Fe3O4@TPB-Dha holds promise as an effective adsorbent for efficient extraction and precise quantification of aromatic esters in Baijiu.

Characterization of key aroma in Huangjincha black tea processed from four different cultivars

Huangjincha (HJC) is a cultivar rich in amino acids making it ideal for producing high-quality black tea. In this study, the aroma composition of HJC black tea from four different cultivars (HJC1, HJC2, HJC18, and HJC168) was analyzed by aroma sensory evaluation combined with volatile compound analysis. Among 271 identified volatiles, with 39 compounds as key odorants contributing to the diverse aromas of HJC black teas. The OAV and GC-O results indicated that geraniol and benzeneacetaldehyde (HJC1), 3-methylbutanal and 1-penten-3-ol (HJC2), (E, E)-2,4-hexadienal and damascenone (HJC18), as well as methyl salicylate and citral (HJC168) were the most significant aroma compounds. Furthermore, PLS analysis revealed four odorants contributed to floral characteristic, three were related to fruity attribute, four were associated with green attribute, three were connected to fresh attribute, three were linked to nutty profile, and three were tied to the sweet profile.

Chemical Isotope Labeling Liquid Chromatograph-Mass Spectrometer: A Powerful Tool for Analyzing Non-Volatile Organic Acids in Baijiu

Non-volatile organic acids (NVOAs) are essential to the flavor profile of Baijiu. However, the low levels and diversity of NVOAs in Baijiu make their isolation, annotation, and quantification challenging. In this study, a well-established pipeline combining chemical derivatization, isotope labeling, and high-resolution mass spectrometry with a three-tier annotation process was used to quantify NVOAs in three typical flavor types of Baijiu with high coverage and confidence. The results revealed the annotation of 56, 145, and 1277 NVOAs in Baijiu at tier 1, tier 2, and tier 3 levels, respectively. Among them, a total of 166 high-confidence NVOAs were first reported in Baijiu. Furthermore, multivariate statistical analyses indicated that abundant NVOAs could potentially be used as biomarkers to distinguish between different flavor types of Baijiu. This study provides a powerful tool for the qualification and quantification of NVOAs in Baijiu. The results will greatly expand the understanding of NVOAs in Baijiu.

A novel colorimetric and fluorometric dual-signal identification of crude baijiu based on La-CDs

The correct classification of strong-flavored crude baijiu affects its quality and overall standard and is crucial for the intelligent development of the baijiu industry. In this work, we developed a novel optical sensing array using lanthanum-doped carbon dots (La-CDs). Using La-CDs with three metal complex dyes-chromium black T, alizarin red, and dimethylphenol orange-we were able to detect organic acids and tannic acid (TA) in crude baijiu in a way that was both colorimetric and fluorescent for the first time. Based on the indicator displacement (IDA) principle, organic acids competitively replace the dyes' binding sites on La3+, causing the dye colors to change to varying degrees. TA quenches the fluorescence of quantum dots through an internal filtering effect. We analyzed the data using pattern recognition algorithms such as HCA, PCA, and LDA, successfully classifying and identifying 16 types of strong-flavored crude baijiu, which included 10 types of carboxylic acids and various grades. In blind tests of 32 crude baijiu samples, the colorimetric method achieved a 94 % accuracy rate, while the fluorescence method achieved 100 %. The sensor demonstrates significant advantages in response speed.

ATR-FTIR spectroscopy combined with metabolomics to analyze the taste components of boletus bainiugan at different drying temperatures

Boletus bainiugan has a unique flavor profile, its quality is correlated with metabolites. Herein, ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) is utilized to characterize the free amino acid and organic acid of Boletus bainiugan at different drying temperatures. Attenuated total internal reflectance Fourier transform infrared (ATR-FTIR) spectroscopy is employed to identify Boletus bainiugan with various treatment and to predicted compounds. The metabolome includes 72 amino acids and 64 organic acids, wherein, 11 important taste components are analyzed the changes with drying temperatures. The residual convolutional neural network (ResNet) model achieves 100 % accuracy for Boletus bainiugan with distinct treatment. The partial least squares regression (PLSR) model accurately predicted the contents of 11 compounds with an optimal R2 P of 0.975 and a best residual predictive deviation (RPD) of 4.404. The ATR-FTIR spectroscopy coupled with metabolomics can be used as a good tool to estimate the taste enhancers of Boletus bainiugan.

Exploring key aroma differences of three Fenghuang Dancong oolong teas and their perception interactions with caffeine via sensomics approach

Fenghuang Dancong tea (FHDC) is a renowned oolong tea in China due to its complex aroma characteristics. However, the aroma differences between FHDC teas with typical aroma profiles are still unknown. This study employed the sensomics approach to characterize the key odorants in three distinct FHDC samples with aroma types of Yashi, Huangzhi, and Milan, respectively. The aroma profile analysis showed the three samples evoked coconut milk-like, flowery/sweety, and fruity/sweety smelling, respectively. The quantitative analysis, odor activity values, and chemometrics showed that jasmine lactone, (Z)-jasmone, linalool, γ-hexalactone were key aroma markers to identify the three samples. Besides, the odor thresholds determination of the four aroma markers present that the addition of caffeine in water obviously lowered their respective odor thresholds, revealing the role of caffeine in strengthening the intensities of sweety, flowery and fruity notes tea infusion. This research not only offered a valuable insight into the identification of FHDC's aromatic complexity but also supported the precise aroma classification and optimization.

Olfactory perception complexity induced by key odorants perceptual interactions of alcoholic beverages: Wine as a focus case example

The odorants in alcoholic beverages are frequently experienced as complex mixtures, and there is a complex array of influence factors and interactions involved during consumption that deeply increase its olfactory perception complexity, especially the complexity induced by perceptual interactions between different odorants. In this review, the effect of olfactory perceptual interactions and other factors related to the complexity of olfactory perception of alcoholic beverages are discussed. The classification, influencing factors, and mechanisms of olfactory perceptual interactions are outlined. Recent research progress as well as the methodologies applied in these studies on perceptual interactions between odorants observed in representative alcoholic beverages, especially wine, are briefly summarized. In the future, unified theory or systematic research methodology need to be established, since up to now, the rules of perceptual interaction between multiple odorants, which is critical to the alcoholic beverage industry to improve the flavor of their products, are still not revealed.

Application of electroencephalogram (EEG) in the study of the influence of different contents of alcohol and Baijiu on brain perception

Alcoholic beverages flavour is complex and unique with different alcohol content, and the application of flavour perception could improve the objectivity of flavour evaluation. This study utilized electroencephalogram (EEG) to assess brain reactions to alcohol percentages (5 %-53 %) and Baijiu's complex flavours. The findings demonstrate the brain's proficiency in discerning between alcohol concentrations, evidenced by increasing physiological signal strength in tandem with alcohol content. When contrasted with alcohol solutions of equivalent concentrations, Baijiu prompts a more significant activation of brain signals, underscoring EEG's capability to detect subtleties due to flavour complexity. Additionally, the study reveals notable correlations, with δ and α wave intensities escalating in response to alcohol stimulation, coupled with substantial activation in the frontal, parietal, and right temporal regions. These insights verify the efficacy of EEG in charting the brain's engagement with alcoholic flavours, setting the stage for more detailed exploration into the neural encoding of these sensory experiences.

Changes in flavor profile of sauce-flavor baijiu: Perceptual interactions between 1-propanol and aroma compounds

1-Propanol is an important aroma compound in sauce-flavor Baijiu. However, the mechanism by which it affects the aroma of sauce-flavor Baijiu has not been fully investigated. In this study, an instrumental and perceptual analysis was employed to assess the impact of 1-propanol on the flavor and volatile compounds in sauce-flavor Baijiu. The combination of sensory evaluation and electronic tongue analysis revealed that 1-propanol diminished the floral and fruity flavor and increased the bitterness and astringency. According to SHS/GC-MS analysis, 1-propanol mainly inhibited the volatility of ethyl acetate, ethyl butyrate, ethyl valerate, and ethyl hexanoate. Further, the Feller additive model and odor activity value method confirmed the four binary mixtures formed by 1-propanol and four esters had masking effects. Finally, the partition coefficients were calculated to clarify the relationship between volatility and interaction of compounds.

Biochemical and chemosensory characterization of doubanjiang fermented via two-stage controlled temperature

This study aimed to elaborate the biochemical and chemosensory characteristics of doubanjiang fermentation via a two-stage controlled temperature. HL group with variable temperature (40 °C → 30 °C) and NTF group fermented following traditional technique were prepared and their volatile and non-volatile metabolites were compared through multivariate statistical analysis. HL group favored the accumulation of amino acid nitrogen, free amino acids and organic acids in the early stage and maintained adequate total acids and biogenic amines in the mid-late stage. HL group also had preferred jiang and fruity flavor through sensory evaluation. A total of 116 volatile metabolites were identified in HL or NTF groups and 22 marker volatile metabolites were screened through the combinational use of OPLS-DA and Random Forest analysis. Stronger anti-oxidant ability was observed in HL group while adequate number of acidic compounds and biogenic amines were ensured. This indicated that the two-stage controlled temperature fermentation was beneficial for doubanjiang fermentation.

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.

Study on the differentiation of sensory quality of mainstream Jiang-flavor baijiu in the Chinese market based on Pivot Profile

Jiang-flavor baijiu (JFB) is a prominent type of Chinese baijiu, known for its unique flavor attributes, sensory experience, and high tasting value. Previous research has mainly focused on the detection and identification of its flavor substances, but in-depth studies on the precise sensory description and differentiation of its flavor qualities are still lacking. In this study, a rapid sensory analysis method, Pivot Profile (PP), was applied to 30 mainstream JFBs in the Chinese market, generating 91 sensory attributes with independent definitions, from which 29 main sensory attributes were established that were easy to perceive and descriptive, as well as convenient for transmitting their sensory qualities and distinguishing differences in price and production region, including color (one descriptor), aroma (21 descriptors), taste, and mouthfeel (seven descriptors). The nine key sensory attributes that distinguish JFB quality are as follows: Jiang, Grain, Chen, Qu, Rancid, Acid, Sweet, Fullness, and Harmony. It was found that price was positively correlated with sensory quality, with greater variation in the quality of samples within the medium price range (RMB 500-1000). All samples from MTCQ1 (the core production area of Maotai Town) performed better in sensory quality. In addition, salted vegetable showed a high degree of regional characteristics, concentrated in most of the production regions of Guizhou Province. Aroma attributes were more suitable than taste and mouthfeel as sensory indicators for distinguishing production regions. This study has opened the direction of systematic construction of sensory description of JFB and provided a successful case for the evaluation of Chinese baijiu using novel sensory analysis techniques.

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.

Decoding Long-Chain Fatty Acid Ethyl Esters during the Distillation of Strong Aroma-Type Baijiu and Exploring the Adsorption Mechanism with Magnetic Nanoparticles

Simultaneous detection of the dynamic distribution of long-chain fatty acid ethyl esters (LCFAEEs) during Baijiu distillation is crucial for optimizing its flavor and health attributes. In this study, we synthesized a simple, cost-effective Fe3O4@NH2 adsorbent to simultaneously extract eight LCFAEEs from Baijiu. Through density functional theory and adsorption experiments, we elucidated 1,6-hexanediamine as a surface modifier, with the -NH2 groups providing adsorption sites for the LCFAEEs via hydrogen-bonding interactions and van der Waals forces. Additionally, we established the magnetic solid-phase extraction-GC-MS extraction technique combined with stable isotope dilution analysis to analyze LCFAEEs. This method revealed the dynamic distribution patterns of LCFAEEs during strong aroma-type Baijiu (SAB) distillation. We observed that the concentrations of the eight LCFAEEs gradually decreased with prolonged distillation and were significantly correlated with ethanol concentration. To ensure optimal flavor and clarity in SAB, it is recommended to select the heart-stage base Baijiu with an alcohol content of 58%-63%.

Nanotechnology-based optical sensors for Baijiu quality and safety control

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

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

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

Organic-Acid-Sensitive Visual Sensor Array Based on Fenton Reagent-Phenol/Aniline for the Rapid Species and Adulteration Assessment of Baijiu

Baijiu is an ancient, distilled spirit with a complicated brewing process, unique taste, and rich trace components. These trace components play a decisive role in the aroma, taste, and especially the quality of baijiu. In this paper, the redox reaction between the Fenton reagent and four reducing agents, including o-phenylenediamine (OPD), p-phenylenediamine (PPD), 4-aminophenol (PAP), and 2-aminophenol (OAP), was adopted to construct a four-channel visual sensor array for the rapid detection of nine kinds of common organic acids in baijiu and the identification of baijiu and its adulteration. By exploiting the color-changing fingerprint response brought by organic acids, each organic acid could be analyzed accurately when combined with an optimized variable-weighted least-squares support vector machine based on a particle swarm optimization (PSO-VWLS-SVM) model. What is more, this novel sensor also could achieve accurate semi-quantitative analysis of the mixed organic acid samples via partial least squares discriminant analysis (PLSDA). Most importantly, the sensor array could be further used for the identification of baijiu with different species through the PLSDA model and the adulteration assessment with the one-class partial least squares (OCPLS) model simultaneously.

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.

Evaluation of perceptual interactions between key aldehydes in Kung Pao Chicken

Aldehydes are the strongest and most abundant aromatic compounds in Kung Pao Chicken. However, the perceptual interactions between these aldehydes are not fully understood. Therefore, the flavor contribution of nine key aldehydes was estimated by determining thresholds. Except for benzaldehyde, the thresholds of all aldehydes measured in tasteless chicken matrices (TM) were significantly larger than their comparable values in water. Based on these results, the perceptual interactions of nine aldehydes were evaluated using S-curves and σ-τ plots. The interactions indicated that 31 of their 36 binary mixtures exhibited additive effects, three had masking effects, while two had synergistic effects. Recombination experiments showed that the addition of aldehydes lowered the odor threshold of aldehyde reconstitution (AR), thereby enhancing the aroma intensity of AR. These findings contribute to a better understanding of Kung Pao Chicken's aroma and can be used to improve its aroma quality.

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.

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

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

Fungal Community Succession and Volatile Compound Changes during Fermentation of Laobaigan Baijiu from Chinese Hengshui Region

To investigate the core fungal community succession and its effects of volatile compound production during different stages (D-1, D-2, D-3, E-4, E-5, and E-6) of Hengshui Laobaigan Baijiu, high-throughput sequencing (HTS) was carried out, accompanied by the identification and quantification of the volatile flavor compounds using headspace solid-phase coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). HTS results demonstrated that the fungal community of stage D-1 was similar to that of E-4 after adding Daqu, while the richness and diversity of the fungal community were most prominent at stage E-6. Moreover, the addition of Daqu at the beginning of Ercha fermentation resulted in a significant increase in the relative abundances of the fungal community at the genus level, setting the stage for the production of volatile compounds. GC-MS analysis revealed the presence of a total of 45 volatile compounds. Combining the GC-MS result with the heat map and principal component analysis (PCA), the concentrations of volatile compounds were highest in stage E-5. Meanwhile, concentrations of esters, especially ethyl acetate, ethyl lactate, isoamyl acetate and ethyl hexanoate, were high in both stages E-5 and E-6. This indicated that stage E-5 was crucial to the fermentation process of Laobaigan Baijiu. Three fungal genera (Saccharomyces, Candida, and Pichia) were indicated as the core microbiota for the production of the main volatile flavor compounds of Laobaigan Baijiu through partial least square (PLS) analysis. The information provided in this study offered valuable insights into the fermentation mechanism of Laobaigan Baijiu, thereby serving as a theoretical framework for enhancing the quality of Baijiu and realizing cost-effective production.

Comparative characterization and contribution of key aroma compounds in the typical base liquor of Jiang-flavor Baijiu from different distributions in the Chinese Chishui River basin

The characteristic of typical base liquor is crucial in controlling ultimate quality of Jiang-flavor Baijiu. This study investigates the flavor compounds of three typical base liquors (Jiangxiang, Chuntian, and Jiaodixiang) by LLE/LLME/HS-SPME, gas chromatography-mass spectrometry (GC-MS), gas chromatography-flame ionization detection (GC-FID), sensory analysis, and odor activity value (OAV). Of the 201 main volatile compounds identified, 37 significant compounds distinguished the three typical base liquors. Acid (441.72 ± 0.17 mg/L), alcohol (5388.88 ± 0.55 mg/L), and ester compounds (8181.64 ± 0.15 mg/L) were respectively marked in Jiangxiang, Chuntian, and Jiaodixiang typical base liquors. Orthogonal partial least squares discriminant analysis (OPLS-DA), correlation analysis, and aroma recombination showed that butyric acid (OAV: 102.23), butyl 2-methylbutyrate (OAV: 6045.59), and ethyl caproate (OAV: 418.37) were significantly correlated with sweet, fruity, pit mud, jiang, and ethanol aromas. It identifies the primary constituents that affect flavor variations in the three typical base liquors and provides guidance for investigations on the flavor formation of Jiang-flavor Baijiu.

Chinese Baijiu and Whisky: Research Reservoirs for Flavor and Functional Food

Baijiu is a traditional spirit with high reputation in the Chinese community, and whisky, on the other hand, is a renowned spirit in Western culture, with both contributing a major proportion to the consumption and revenue in the global spirit market. Interestingly, starting with similar raw materials, such as grains, diverse production methods lead to different organoleptic profiles. In addition, such enormous attention they attract renders them as a crucial part in food and the related industry. Therefore, great efforts are made in improving product quality and optimizing production processes, such as flavor enhancement, facility development, and deep utilization of byproducts. Given the huge impacts and great involvements of these spirits in the general food industry, research focusing on either spirit is of referential significance for other relevant fields. With the aim of facilitating such collaboration, this review discusses the current research status, in a comparative manner, of both spirits in respect to key production processes-oriented sensory and flavor analysis, deep utilization of byproducts, and spirit-derived functional food investigations. Finally, the internal correlations based on the abovementioned criteria are identified, with research prospects proposed.

Extracellular proteolytic enzyme-mediated amino exposure and β-oxidation drive the raspberry aroma and creamy flavor formation

The fermentation-driving ability of Daqu has been widely reported, while the potential influence of substances in Daqu on Baijiu flavor formation has attracted increasing interest. Pseudo-targeted metabolomics integrated proteomics combined with sensory evaluation strategy was applied to investigate the correlation between flavor characteristics and metabolic profiling of Daqu, and the mechanism of flavor formation was also elucidated. The 4-hydroxy-2,5-dimethylfuran-3-one (3.5 mg kg^-1) and 2,3-dihydro-1 h-inden-5-ol (894.3 μg kg^-1) were identified as the unique substances in qingcha qu, which were vital for raspberry flavor formation and associated with the up-regulation of amino acid metabolism. The dec-9-enoic acid (37.4 mg kg^-1) was screened out as the substance related to the formation of cream flavor in hongxin qu produced through the shortening of fatty acid carbon chains and unsaturated modification of long chain fatty and acceleration of carbon metabolism in hongxin qu mediated by filamentous Aspergillus spp. was related to the smoky aroma enhancement.

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.

Cross-modal interactions caused by nonvolatile compounds derived from fermentation, distillation and aging to harmonize flavor

Chinese liquor (Baijiu), unique liquor produced in China and among the six world-renowned distilled liquors, is never a follower of others. Flavor is the essential characteristics of Baijiu which largely affect consumers' acceptance and selection. Though the flavor of Baijiu has been widely explored, the majority of research and review mainly focused on the volatile compounds in Baijiu. The research status on detection, source and flavor contribution of nonvolatile compounds in Baijiu is clarified in the article based on available literatures and knowledge. The nonvolatile composition of Baijiu is the result of contributions of different degrees from each step involved in the production process. Gas chromatography-mass spectrometry combined with derivatization and ultra-high performance liquid chromatography coupled to mass spectrometry is the generally adopted methods for the characterization of nonvolatile compounds in Baijiu. Certain nonvolatile compounds are taste-active compounds. Cross-modal interactions caused by nonvolatile composition could affect the aroma intensity of flavor compounds in Baijiu. The work provides numerous incompletely explored but useful points for the flavor chemistry of Baijiu and lays a theoretical foundation for the better understanding of Baijiu flavor and rapid development of Baijiu industry.

Can nonvolatile tastants be smelled during food oral processing?

While accumulating evidence implied the involvement of retro-nasal sensation in the consumption of nonvolatile taste compounds, it is still unclear whether it was caused by the taste compounds themselves, and if so, how can they migrate from the oral to nasal cavity. At first, we proposed aerosol particles as an alternative oral-nasal mass transfer mechanism. The high-speed camera approved that aerosol particles could be generated by the typical oral and pharynx actions during food oral processing; while the narrow-band imaging of nasal cleft and mass spectrometry of nostril-exhaled air approved the migration of aerosol within the oral-nasal route. Then, the "smelling" of taste compounds within the aerosol particles was testified. The four-alternative forced choices (4AFC) approved that the potential volatile residues or contaminants within the headspace air of pure taste solution cannot arouse significant smell, while the taste compounds embedded in the in vitro prepared aerosol particles can be "smelled" via the ortho route. The "smell" of sucrose is very different from its taste and the "smell" of quinine, implying its actual olfaction. The sweetness intensity of sucrose solution was also reduced when the volunteers' noses were clipped, indicating the involvement of retro-nasal sensation during its drinking. At last, the efficiency of aerosol as a mechanism of oral-nasal mass transfer was demonstrated to be comparable with the volatile molecules under the experimental condition, giving it the potential to be a substantial and unique source of retro-nasal sensation during food oral processing.