Reconstitution of the Flavor Signature of Laobaigan-Type Baijiu Based on the Natural Concentrations of Its Odor-Active Compounds and Nonvolatile Organic Acids

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.

Analysis of flavor substances in Shaoxing traditional hand-made Jiafan wine with different amounts of ZaoShao liquor

BACKGROUND

Adding ZaoShao liquor (high-concentration liquor) is one of the most important steps in the brewing process of Shaoxing Jiafan wine, a product protected by Chinese geographical indications. The focus of this study is the effect of different additive amounts of liquor on the flavor of end products.

RESULTS

In this study, four kinds of Shaoxing Jiafan wine were brewed by changing the amount of ZaoShao liquor. Headspace solid-phase microextraction and gas chromatography-mass spectrometry were used to detect the flavor substances of four kinds of Jiafan wine. The difference in flavor of four kinds of Jiafan wine was evaluated by electronic nose analysis technology and verified by sensory evaluation. Finally, the reliability of the experimental results was verified through an aroma reconstruction experiment of rice wine. In this study, the differences in flavoring substances under different amounts of ZaoShao liquor were verified from various angles. The results showed that the flavors of the four kinds of wines were significantly different.

CONCLUSION

The composition of flavor substances in Shaoxing rice wine varies with the amount of ZaoShao liquor. This study provided a scientific basis for the improvement of production technology of Shaoxing wine. © 2024 Society of Chemical Industry.

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.

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.

Integration of Chemometrics and Sensory Metabolomics to Validate Quality Factors of Aged Baijiu (Nianfen Baijiu) with Emphasis on Long-Chain Fatty Acid Ethyl Esters

The storage process of Baijiu is an integral part of its production (the quality undergoes substantial changes during the aging process of Baijiu). As the storage time extends, the flavor compounds in Baijiu tend to undergo coordinated transformation, thereby enhancing the quality of Baijiu. Among them, long-chain fatty acid ethyl esters (LCFAEEs) were widely distributed in Baijiu and have been shown to have potential contributions to the quality of Baijiu. However, the current research on LCFAEEs in Baijiu predominantly focuses on the olfactory sensation aspect, while there is a lack of systematic investigation into their influence on taste and evaluation after drinking Baijiu during the aging process. In light of this, the present study investigates the distribution of LCFAEEs in Baijiu over different years. We have combined modern flavor sensory analysis with multivariate chemometrics to comprehensively and objectively explore the influence of LCFAEEs on Baijiu quality. The results demonstrate a significant positive correlation between the concentration of LCFAEEs and the fruity aroma (p < 0.05, r = 0.755) as well as the aged aroma (p < 0.05, r = 0.833) of Baijiu within a specific range; they can effectively reduce the off-flavors and spicy sensation of Baijiu. Furthermore, additional experiments utilizing a single variable suggest that LCFAEEs were crucial factors influencing the flavor of Baijiu, with Ethyl Palmitate (EP) being the most notable LCFAEE that merits further systematic investigation.

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.

Advances in the Biosynthesis of Terpenoids and Their Ecological Functions in Plant Resistance

Secondary metabolism plays an important role in the adaptation of plants to their environments, particularly by mediating bio-interactions and protecting plants from herbivores, insects, and pathogens. Terpenoids form the largest group of plant secondary metabolites, and their biosynthesis and regulation are extremely complicated. Terpenoids are key players in the interactions and defense reactions between plants, microorganisms, and animals. Terpene compounds are of great significance both to plants themselves and the ecological environment. On the one hand, while protecting plants themselves, they can also have an impact on the environment, thereby affecting the evolution of plant communities and even ecosystems. On the other hand, their economic value is gradually becoming clear in various aspects of human life; their potential is enormous, and they have broad application prospects. Therefore, research on terpenoids is crucial for plants, especially crops. This review paper is mainly focused on the following six aspects: plant terpenes (especially terpene volatiles and plant defense); their ecological functions; their biosynthesis and transport; related synthesis genes and their regulation; terpene homologues; and research and application prospects. We will provide readers with a systematic introduction to terpenoids covering the above aspects.

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.

Elucidation of the Impact of Steaming on the Key Odorants of Jinhua Dry-Cured Ham Using the Sensomics Approach

Jinhua dry-cured ham (JDH) is a traditional fermented meat product favored by Chinese consumers. In this paper, the impact of steaming on the key odorants of JDH was investigated using the sensomics approach. Compounds with odor activity values (OAV) ≥1 were re-engineered in a triglyceride matrix to imitate the odor profiles of both raw and steamed JDHs. The aroma-active compounds were then confirmed by recombination and omission tests using triangle tests. The odor profiles of raw and steamed JDHs were obtained by quantitative descriptive analysis to compare the differences between the original and recombined models. The results showed that pentanal, hexanal, dimethyl trisulfide, (E,E)-2,4-decadienal, (E)-2-heptenal, furaneol, 3-methylbutanoic acid, 1-octen-3-one, and methional influenced the overall raw JDH odor significantly. Furaneol was first reported as a key compound that provides a caramel smell to the raw JDH. Apart from (E)-2-heptenal, dimethyl trisulfide, furaneol, 3-methylbutanoic acid, and methional, the remaining three compounds including 2-furfurylthiol, benzeneacetaldehyde, and phenylethyl alcohol showed a significant influence on the odor profile of steamed JDH. The statistical analysis of the odor profiles showed an 80.0% similarity between the recombination raw JDH and the real raw JDH, and a 76.3% similarity between the model and the real steamed JDH.

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.

Array-based sensing and discrimination of segmented Baijiu using organic molecules-regulated PEI@Ag NPs@Ln as fluorescent probes

Quickly discriminating different segmented Baijiu can directly control its grade and indirectly affect the quality of the finished Baijiu. A fluorescence sensor array was constructed based on PEI-terminated silver nanoparticles and lanthanide metal ions (PEI@Ag NPs@Ln). Ag NPs were stably dispersed in the PEI-woven network, initially accompanied by excellent fluorescence signals. Organic molecules disrupted the PEI structure and dragged the Ag NPs out. The free Ag NPs sintered or aggregated with the diffusion, resulting in fluorescence quenching. The three lanthanide ions speed up the process, allowing different organic molecules to exhibit more distinct signals. Thus, this sensor was used to map 11 organic molecules' fingerprints and to discriminate segmented Baijiu. The whole process takes only 2 min. With the assistance of pattern recognition, segmented Baijiu from three cellars were successfully discriminated. Fast, effective and simple are highlights, which opens up its practical application potential in the detection field.

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.

Elucidating the effects of Lactobacillus plantarum fermentation on the aroma profiles of pasteurized litchi juice using multi-scale molecular sensory science

Three Lactobacillus Plantarum (LP), namely LP28, LP226 and LPC2W, were employed to investigate the effect on the aroma profiles of pasteurized litchi juice using E-nose, GC-IMS, GC-MS, and sensory evaluation. The E-nose results showed that pasteurization weakened the flavor profile of litchi juice, while LP fermentation effectively promoted flavor formation. The GC-MS analysis demonstrated that pasteurization significantly reduced the content of alcohols (28.51%), especially geraniol and citronellol, which give litchi juices a fruity and floral aroma. Different LP fermentation enhances the characteristic aroma and produces some new compounds that give it a strong fruity and citrus-like aroma. Moreover, 37 aroma-active compounds (OAV>1) indicated that the linalool (OAV 7504) was the highest, followed by (Z)-rose oxide (OAV 4265), 1-octen-3-ol (OAV 1055) and geraniol (OAV 764), which jointly form the main characteristic flavor. More esters were identified by GC-IMS, indicating the advantage of the combined approach for a better understanding of the impact of pasteurization and fermentation on the litchi juice. The sensory evaluation confirmed that the aroma attributes of fruity, citrus-like, floral, sweet and litchi-like were stronger for the samples fermented by LP28 than those for the other samples. The combination strategy used in this study would facilitate the awareness of litchi juice aroma and broaden our insight into the deep processing of litchi.

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.

Whether the Research on Ethanol-Water Microstructure in Traditional Baijiu Should Be Strengthened?

Baijiu is a unique and traditional distilled liquor in China. Flavor plays a crucial rule in baijiu. Up to now, the research on the flavor of baijiu has progressed from the identification of volatile compounds to the research on key aroma compounds, but the release mechanism of these characteristic compounds is still unclear. Meanwhile, volatile compounds account for only a tiny fraction, whereas ethanol and water account for more than 98% of the content in baijiu. By summarizing the ethanol-water hydrogen bond structure in different alcoholic beverages, it was found that flavor compounds can affect the association strength of the ethanol-water hydrogen bond, and ethanol-water can also affect the interface distribution of flavor compounds. Therefore, the research on ethanol-water microstructure in baijiu is helpful to realize the simple visualization of adulteration detection, aging determination and flavor release mechanism analysis of baijiu, and further uncover the mystery of baijiu.

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

By applying the aroma extract dilution analysis, 13 esters were found to have high FD factors in the Laobaigan flavor type of Baijiu. These were then quantified using GC-MS. In addition, 35 nonvolatile organic acids were quantified by a derivatization method combined with GC-MS. The perceptual interactions of lactic acid and ethyl lactate and that of lactic acid and ethyl acetate were studied through the olfactory threshold. The S curve was used to evaluate the changes in the olfactory thresholds. After adding lactic acid (1142, 20 000, and 53 703 mg/L), the olfactory thresholds of ethyl lactate (1000, 724, and 295 mg/L) and ethyl acetate (398, 324, and 257 mg/L) decreased obviously, which revealed that lactic acid gave additive or synergistic odor effects for the two esters. Furthermore, it was discovered that as the concentrations of lactic acid increased, the extent of the interaction among these compounds was also greater in the mixture.

Effects of Short-Chain Peptides on the Flavor Profile of Baijiu by the Density Functional Theory: Peptidomics, Sensomics, Flavor Reconstitution, and Sensory Evaluation

The effect of peptides on the flavor profile of Baijiu is unclear as a result of their trace concentrations in the complex matrix, and therefore, the study involving the interaction mechanism between peptides and flavor compounds is limited. In this study, short-chain peptides (amino acid number between 2 and 4, SCPs) associated with the Feng-flavor Baijiu (FFB) were comprehensively analyzed by a dedicated workflow using ultra-high-performance liquid chromatography Q Orbitrap high-resolution mass spectrometry, flavor reconstitution experiments, sensory analysis, and density functional theory (DFT) analysis. The concentrations of 96 SCPs intimately related with six different grades of honey aroma intensity in FFB were quantified (0.12-155.01 μg L^-1) after multivariable analysis, Spearman's correlation analysis (ρ ≥ 0.7), and confirmation with synthetic standards, and 32 dominant odorants with an odor activity value of ≥1 in FFB with the highest intensity of honey aroma were quantified by gas chromatography-mass spectrometry and gas chromatography-flame ionization detection analyses. The results of flavor reconstitution experiments and sensory analysis indicated that the SCPs can obviously influence the honey aroma with amplifying the fruity, sweet, and flora flavor odor characters (p < 0.05) while significantly reducing the acidic character (p < 0.001), which could be attributed to the most stable complex structure between SCPs and odor-active compounds calculated by DFT being butanoic acid, followed by β-damascenone, 3-methylbutanal, and ethyl hexanoate, and the multiple sites as a hydrogen bond donor or acceptor in SCPs can form a stable ternary structure with water and ethanol inside the peptide chain or carboxyl terminal of SCPs, consequently improving the stability of the Baijiu system. The results highlighted the important role of SCPs on the volatiles in Baijiu and laid the foundation for further facilitating the sensory quality of Baijiu products.

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.