Development of a method for identification and accurate quantitation of aroma compounds in Chinese Daohuaxiang liquors based on SPME using a sol–gel fibre

High-Resolution Mass Spectrometry-Based Chemical Fingerprinting of Baijiu, a Traditional Chinese Liquor

Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, coupled with electrospray ionization (ESI) or atmospheric-pressure photoionization (APPI), was employed for chemical fingerprinting of baijiu, a traditional Chinese liquor. Baijiu is the most consumed distilled alcoholic beverage globally, with over 10 billion liters sold annually. It is a white (transparent) spirit that exhibits similarities to dark spirits such as whisky or rum in terms of aroma and mouthfeel. In this study, direct-infusion FT-ICR mass spectrometry was used to analyze 10 commercially available baijiu liquors, enabling the examination of both volatile and nonvolatile constituents without the need for tedious sample extractions or compound derivatizations. The chemical fingerprints obtained by FT-ICR MS revealed substantial compositional diversity among different baijiu liquors, reflecting variations in the raw materials and production methods. The main compounds identified included a variety of acids, esters, aldehydes, lactones, terpenes, and phenolic compounds. The use of ESI and APPI provided complementary compositional information; while ESI demonstrated greater selectivity toward polar, aliphatic sample constituents, APPI also ionized semipolar and nonpolar (aromatic) ones.

Airborne microbes in five important regions of Chinese traditional distilled liquor (Baijiu) brewing: regional and seasonal variations

Baijiu is one of the six primary distilled spirits in the world. It is produced through the solid-state fermentation of grains in the open environment, so high-quality Baijiu brewing largely depends on terrior. Environmental microbes are one of the most important factors affecting the quality, quantity, and flavors of Baijiu. As atmosphere is a pool and transport pathway for microbes from the ambient environment to Baijiu brewing ecosystems, we explored the functional microbes of Baijiu brewing in five important regions. The regions fell into two topographical types, namely, plain and river-valley. In total, 41 functional microbes were identified rich (relative abundance >0.1%) in at least one of the regions, such as the fungi of Aspergillus, Candida, Cladosporium, Debaryomyces, Penicillium, Pichia, Rhizopus, Saccharomyces, and Wickerhamomyces and the bacteria of Acetobacter, Bacillus, Clostridium, Enterobacter, Lactobacillus, Methanosarcina, Methanobacterium, Methanobrevibacter, and Pseudomonas. However, some functional bacteria (e.g., Clostridia, Gluconacetobacter, and Weissella) and fungi (e.g., Dekkera, Eurotium, Issatchenkia, Mucor, and Phoma) were not rich or were not detected in the atmosphere. Airborne microbiomes and the Phylogenetic Diversity (PD) index were significantly different between the main brewing season (winter) and the summer break in each region, except for the fungi in one region. In winter, airborne microbiomes were significantly different among almost all the regions. The relative abundance of bacterial fermentation function in each region increased from summer to winter. The relative abundances of fungal yeast function were higher in winter for the plain regions but were higher in summer for the river-valley regions. In sum, our results suggested that: (1) atmosphere was one but not the sole important source of functional microbes for Baijiu brewing and (2) microbiomes in different regions might be quite different but they could share some major functions related to Baijiu brewing.

Variations in physicochemical characteristics, antioxidant activity, phenolic and volatile profiles, and sensory attributes of tea-flavored Chardonnay wine during bottle aging

A novel Chardonnay wine flavored with either green tea or black tea was subjected to bottle aging for 9 months, and the physicochemical properties, antioxidant capacity, total phenolic content, volatile content and sensory properties were monitored. There were 272 phenolic and non-phenolic compounds characterized in the aged Chardonnay wines, including newly formed 9, 1, 3 and 8 phenolic compounds and 10, 6, 1 and 6 non-phenolic compounds after aging for 1, 3, 6 and 9 months, respectively. For all the aged wines, catechin was determined as the most abundant phenolic compound, and epigallocatechin mainly contributed toward the antioxidant power. A total of 54 volatile compounds were identified in the aged Chardonnay wines, including 17 odor-active compounds. The aging process diminished floral and fruity odors, but intensified green odor. The consumer study revealed the highest consumer liking for 1% (w/v) black tea infused wine. This study revealed the quality and bioactivity of this novel flavored wine type during aging which is critical to understand the shelf-life and functionality of the product.

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.

Style Characteristics Investigation of Quan-Xing Baijiu by Comparing Other Strong-Aroma Baijiu Brands in China

Quan-xing Baijiu, a famous brand with different style characteristics from traditional strong-aroma Baijiu, is considered superior due to its “jiao-xiang” (caramel) flavor and the “he-run” (soft, moistening, and harmonious) style. In this study, gas chromatography-olfactometry (GC-O) was used to analyze the special flavors of Quan-xing Baijiu. The flavor fingerprints of six traditional strong-aroma Baijiu were determined using fragrance, taste, and entirety style in order to establish the individual style of Quan-xing Baijiu. The results indicated that 3-methyl butanol, ethyl butyrate, ethyl hexanoate, ethyl acetate, and ethyl caprylate were the main important aroma compound, which contributed to the he-run style in Quan-xing Baijiu. A standard of Quan-xing Baijiu’s typical style was established by flavor fingerprint. Together with the concordance rate evaluation method, this standard can help determine the characteristics of Baijiu samples for quality control. A rate above 81% represents a typical product staleness and good stability, while a rate below 73% represents a nontypical Quan-xing Baijiu product.

Insights into a new alternative method with graphene oxide/polyacrylamide/Fe3O4 nanocomposite for the extraction of six odor-active esters from Strong-aroma types of Baijiu

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A novel approach of MSPE-GC/MS based on GO/PAM/Fe₃O₄ was developed for odor-active esters determination in Baijiu samples.

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GO/PAM/Fe₃O₄ earned highly selective recognition properties and larger adsorption capacities for six odor-active esters.

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The method provided lower LODs, better precision and faster separation.

Liquid-liquid extraction (LLE) is the most commonly utilized technique for the extraction of odor-active esters (OAEs) in strong-aroma types of Baijiu (SAB). However, since the contents of different OAEs in SAB vary widely, it is still a puzzle to ensure that all OAEs to be thoroughly extracted by LLE without the problem of saturated adsorption. Herein, a novel approach of magnetic solid phase extraction (MSPE), based on the magnetic graphene oxide nanocomposite modified with polyacrylamide (GO/PAM/Fe₃O₄), was employed for the efficient extraction of six OAEs from SAB. Compared with LLE, GO/PAM/Fe₃O₄ exhibited highly selective recognition properties and larger adsorption capacities for OAEs (ranging from 13.68 to 39.06 mg/g), resulting in better extraction performances for OAEs. Coupled with GC–MS, six OAEs in real SAB were successfully determined, with recoveries ranged from 70.1 ∼ 90.0% and LODs at 0.08 ∼ 1.35 µg/L. Overall, the MSPE-GC/MS is a promising alternative for accurate determination of OAEs in SAB.

Insights into the Aroma Profile of Sauce-Flavor Baijiu by GC-IMS Combined with Multivariate Statistical Analysis

Aroma is among the principal quality indicators for evaluating Baijiu. The aroma profiles of sauce-flavor Baijiu produced by 10 different manufacturers were determined by GC-IMS. The results showed that GC-IMS could effectively separate the volatile compounds in Baijiu, and a total of 80 consensus volatile compounds were rapidly detected from all samples, among which 29 volatile compounds were identified, including 5 alcohols, 14 esters, 2 acids, 2 ketones, 5 aldehydes, and 1 furan. According to the differences in aroma profile found by multivariate statistical analysis, these sauce-flavor Baijiu produced by 10 different manufacturers can be further divided into three types. The relative odor activity value of the identified volatile compounds indicated that seven volatile compounds contributed most to the aroma of sauce-flavor Baijiu in order of aroma contribution rate, and they were ethyl hexanoate, ethyl pentanoate, ethyl 2-methylbutanoate, ethyl octanoate (also known as octanoic acid ethyl ester), ethyl 3-methylbutanoate, ethyl butanoate, and ethyl isobutyrate. Correspondingly, the main aromas of these sauce-flavor Baijiu produced by 10 different manufacturers were sweet, fruity, alcoholic, etheral, cognac, rummy, and winey. On the one hand, this study proved that GC-IMS is well adapted to the detection of characteristic volatile aroma compounds and trace compounds in Baijiu, which is of positive significance for improving the aroma fingerprint and database of sauce-flavor Baijiu. On the other hand, it also enriched our knowledge of Baijiu and provided references for the evaluation and regulation of the flavor quality of sauce-flavor Baijiu.

Research trends in Jiang-flavor baijiu fermentation: From fermentation microecology to environmental ecology

Chinese baijiu is one of the six major distilled spirits worldwide and is widely enjoyed because of its unique flavor. Among typical baijiu, Jiang-flavor baijiu is gaining popularity. However, the fermentation mechanisms of baijiu remain unclear due to its open inoculation environment and complex brewing process. In recent years, advances in high-throughput sequencing and multi-omics technologies have yielded meaningful information regarding fermentation microbiome. Therefore, this paper reviews recent developments in the investigation of the diversity, stability, and metabolism of the Jiang-flavor baijiu microbial community. Furthermore, the importance of protecting the ecology of the production environment is proposed based on the putative contribution of environmental factors to the fermentation microbiome and baijiu characteristics. Finally, this paper discusses current research challenges that need to be addressed, including the limitations of sequencing technologies and difficulties unveiling the mechanisms of microbial interaction between the fermentation microbiome and the environmental ecology. The findings of this review will promote further understanding of the Jiang-flavor baijiu fermentation process and provide valuable information for the research and development of traditional baijiu and other naturally fermented foods. PRACTICAL APPLICATION: Baijiu, a transparent strong alcoholic drink, is the world's largest consumed and the most valuable spirit in the market. However, the fermentation mechanisms of baijiu remain unclear due to its open inoculation environment and complex brewing process. Therefore, if we can summarizes the current advances and research challenges of microbial fermentation in baijiu, it will deepen the reader's understanding of the complex fermentation process and fermentation mechanism in baijiu. Furthermore, based on the putative contribution of environmental factors to the fermentation process, the importance of protecting the ecology of the production environment is proposed in future research trends, which will provide valuable information for the research and development of other traditional naturally fermented foods. This will not only achieve breakthroughs in academic value, but also bring higher practical value to fermented foods.

Near-Infrared Spectral Characteristic Extraction and Qualitative Analysis Method for Complex Multi-Component Mixtures Based on TRPCA-SVM

Quality identification of multi-component mixtures is essential for production process control. Artificial sensory evaluation is a conventional quality evaluation method of multi-component mixture, which is easily affected by human subjective factors, and its results are inaccurate and unstable. This study developed a near-infrared (NIR) spectral characteristic extraction method based on a three-dimensional analysis space and establishes a high-accuracy qualitative identification model. First, the Norris derivative filtering algorithm was used in the pre-processing of the NIR spectrum to obtain a smooth main absorption peak. Then, the third-order tensor robust principal component analysis (TRPCA) algorithm was used for characteristic extraction, which effectively reduced the dimensionality of the raw NIR spectral data. Finally, on this basis, a qualitative identification model based on support vector machines (SVM) was constructed, and the classification accuracy reached 98.94%. Therefore, it is possible to develop a non-destructive, rapid qualitative detection system based on NIR spectroscopy to mine the subtle differences between classes and to use low-dimensional characteristic wavebands to detect the quality of complex multi-component mixtures. This method can be a key component of automatic quality control in the production of multi-component products.

Characterization of major volatile compounds in whey spirits produced by different distillation stages of fermented lactose-supplemented whey

This research aimed to advance the understanding of acceptable sensory qualities of potable whey-based spirit from nonsupplemented, mid-supplemented, and high-supplemented whey samples by analyzing major volatile compounds during different stages of distillation (head, heart, and tail). The results demonstrated that commercial Saccharomyces cerevisiae strain in lactase-hydrolyzed whey showed rapid and complete sugar hydrolysis and efficient ethanol production in 24, 30, and 36 h on average, producing up to 29.5, 42.1, and 56.4 g/L of ethanol, respectively. The variations in titratable acidity, specific gravity, pH value, residual protein, sugar content, and alcohol yield were investigated during the fermentation. The total amount of volatile compound concentrations significantly decreased from the head (2,087-2,549 mg/L) to the tail whey spirits (890-1,407 mg/L). In the whey spirit, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-1-propanol, 1-propanol, acetaldehyde, and ethyl acetate were the most prevalent ruling compounds, accounting for the largest proportion of total volatile compounds. The volatile compounds detected were far below the acceptable legal limit. The results suggest that high sensory qualities of potable whey-based spirits can be produced by fermentation of lactose-supplemented whey with S. cerevisiae cells.

Flavor classification and year prediction of Chinese Baijiu by time-resolved fluorescence

Baijiu is a traditional and popular Chinese liquor with enormous sale potential, which is affected by factors such as flavor and storage time. Chinese Baijiu is a complex and transparent mixture that makes analyzing difficult. The utility of time-resolved fluorescence helped to develop a new method to analyze Baijiu. Forty-two Baijiu samples among six brands with three flavors were prepared, and their fluorescence spectra were analyzed with an excitation light of 374.2 nm. Hexanoic acid and ethyl butyrate were found to have an impact on Baijiu fluorescence. The properties of lifetimes in Baijiu were investigated, and its mechanism was studied by calculations through density function theory. Using parameters of fluorescence lifetimes, Baijiu samples were classified according to their flavors. Additionally, the correlations between fluorescence lifetimes and storage time of Baijiu in Luzhou flavor were obtained, leading to a reliable and efficient method to establish the year forecast model of Chinese Baijiu with a mean error of 2.79 months. It also provides an important reference of the utility of time-resolved fluorescence for quantitative research of multi-component systems.

Dynamic changes of volatile compounds and bacterial diversity during fourth to seventh rounds of Chinese soy sauce aroma liquor

Chinese soy sauce aroma liquor (CSSL) is a famous Baijiu. Multiple rounds of fermentation, the characteristic of CSSL processing, contributes to the differences in the quality of the liquor of different rounds. In this study, the grains on cooled, stacked, and fermented stages of 4th to 7th rounds were taken, of which the environmental factors, bacterial diversity, and volatile compounds were comprehensively analyzed. Lactobacillaceae, Bacillaceae, Thermoactinomycetaceae, and Enterobacteriaceae were the top four families, of which Lactobacillaceae dominated the fermented stage of each round. Principal component analysis (PCA) and principal coordinate analysis (PCoA) supported the popular view that the liquors of 3rd to 5th rounds possess the best quality. Lactobacillaceae is an extremely critical bacterium for CSSL fermentation. This study provides comprehensive understanding regarding the dynamic changes in fermented grains during the 4th to 7th rounds, which could help to improve the processing technology of CSSL.

Liquor Flavour Is Associated With the Physicochemical Property and Microbial Diversity of Fermented Grains in Waxy and Non-waxy Sorghum (Sorghum bicolor) During Fermentation

The fermentation process of Chinese Xifeng liquor involves numerous microbes. However, the sources of microbes in fermented grain and the link between liquor flavour and physicochemical properties and microbial diversity during fermentation still remain unknown. Herein, two waxy (JiNiang 2 [JN-2] and JinNuo 3 [JN-3]) and four non-waxy (JiZa 127 [JZ-127], JinZa 34 [JZ-34], LiaoZa 19 [LZ-19], and JiaXian [JX]) sorghum varieties were selected for the comprehensive analysis of the relationship between liquor flavour and the physicochemical properties and microbial diversity of fermented grains. Results showed that ethyl acetate was the main flavour component of JZ-127, JZ-34, and JX, whereas ethyl lactate was mainly detected in JN-2, JN-3, and LZ-19. Ethyl lactate accounted for half of the ethyl acetate content, and JX exhibited a higher liquor yield than the other sorghum varieties. The fermented grains of waxy sorghum presented higher temperature and reducing sugar contents but lower moisture and starch contents than their non-waxy counterparts during fermentation. We selected JN-3 and JX sorghum varieties to further investigate the microbial changes in the fermented grains. The bacterial diversity gradually reduced, whereas the fungal diversity showed nearly no change in either JN-3 or JX. Lactobacillus was the most abundant bacterial genus, and its level rapidly increased during fermentation. The abundance of Lactobacillus accounted for the total proportion of bacteria in JX, and it was higher than that in JN-3. Saccharomyces was the most abundant fungal genus in JX, but its abundance accounted for a small proportion of fungi in JN-3. Four esters and five alcohols were significantly positively related to Proteobacteria, Bacteroidetes, and Actinobacteria; Alphaproteobacteria, Actinobacteria, and Bacteroidia; Bacillales, Bacteroidales, and Rhodospirillales; and Acetobacter, Pediococcus, and Prevotella_7. This positive relation is in contrast with that observed for Firmicutes, Bacilli, Lactobacillales, and Lactobacillus. Meanwhile, Aspergillus was the only fungal microorganism that showed a significantly negative relation with such compounds (except for butanol and isopentanol). These findings will help in understanding the fermentation mechanism and flavour formation of fermented Xifeng liquor.

Characterization of key odorants in Langyatai Baijiu with Jian flavour by sensory-directed analysis

A study was carried out to determine systematically the key aroma-active compounds of Langyatai Baijiu with Jian flavour (LBJF) using sensory omics analysis (SOA). A total of 56 odorants were screened out using gas chromatography-olfactometry-mass spectrometry (GC-O-MS)/Osme analysis. Among them, 15 aroma-active components were first identified. After quantitation, 30 odorants had odour activity values (OAVs) > 1.0 in LBJF. Recombinant and omission experiments proved that the esters, alcohols, acids, especially ethyl hexanoate, γ-nonalactone, and dimethyl trisulfide, were critical to the flavour of LBJF. The basic and commercial liquors had obvious differences in the skeleton compositions of esters and acids. This study uncovers the characteristics of Jian flavour Baijiu (JFB) and provides a scientific basis for the quality control of JFB, which is helpful for the development of Chinese Baijiu flavour styles.

Research on the application of liquid-liquid extraction-gas chromatography-mass spectrometry (LLE-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) in distinguishing the Baiyunbian aged liquors

The purpose of the study was to reveal the differences of the flavor compounds among five Baiyunbian aged liquors by liquid-liquid extraction-gas chromatography-mass spectrometry (LLE-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). In optimizing the LLE parameters, an extractant, methyl tert-butyl ether, was found which has a good extract effect and has never been used for the extraction of liquor flavor substances. Then the optimized LLE method has been applied to comprehensively analyze flavor compounds in 3-year-storage liquors (3Y), 5Y, 12Y, 15Y, and 20Y of Baiyunbian liquors combined with GC-MS. The results showed that the number and concentration of total flavor compounds also enhanced with the increase of cellaring ages. The total concentration of flavor compounds in 20Y was the highest (4543.23 mg/L), and the 3Y was the lowest (3984.96 mg/L). Among them, the significant differences among five samples were esters, alcohols, acids and nitrogen-containing compounds. Cluster analysis was used to analyze the aromas profiles by LLE-GC-MS, which revealed relationship among five samples. The results showed that the similarity of the samples was highest between 15Y and 20Y, followed by 3Y and 5Y. The characteristic flavors fingerprints of five kinds of Baiyunbian aged liquors were established by HS-GC-IMS. The results showed that the characteristic peaks in GC-IMS 3D spectra corresponding to flavor compounds can effectively characterize the sample information areas. The sectional intensities of 60 characteristic peaks in the corresponding three-dimensional spectra were selected as variables. After the principal components analysis (PCA) was used to reduce information dimensionality, it was further distinguished by HS-GC-IMS that 3Y and 5Y can be completely separated, but 15Y and 20Y were very similar and cannot be completely distinguished. The obtained results are valuable for the in-depth understanding and further study of flavors of Baiyunbian liquors.

Discrimination of Chinese Baijiu grades based on colorimetric sensor arrays

In this study, a novel colorimetric sensor array based on chemo dyes including porphyrins and pH indicators were developed to analyse the volatile organic compounds of Chinese Baijiu with different grades. Ethyl acetate, ethyl butyrate and ethyl caproate appeared by significantly different concentration in different Baijiu grades measuring by gas chromatography and mass spectrometry and they were chosen as characteristic volatile organic components. The olfactory visualization system based on colorimetric sensor arrays was used to identify different Baijiu grades. The data were processed by building the principle components analysis, linear discriminant analysis and K-nearest neighbor classification models with the results of sensory evaluation and olfactory visualization system. This work presents a new-style colorimetric sensor using sensitive chemo dyes which has significant potential in quantitative analysis of volatile organic compounds, afterwards identifying different grades of Baijiu.

Unraveling the chemosensory characteristics of strong-aroma type Baijiu from different regions using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry and descriptive sensory analysis

Comprehensive 2D gas chromatography-time-of-flight mass spectrometry was combined with descriptive sensory analysis to elucidate the specificity of strong-aroma type Baijiu (Chinese liquor) from different regions, based on regionally distinct flavor characterized by chemical and sensory profiles. Numerous potential aroma compounds (262) were identified, among which 58 aroma compounds were significantly different between the samples from Sichuan and Jianghuai regions. Relationships between these potential aroma compounds and sensory attributes were investigated by partial least squares regression and network analysis. The compounds that dominantly contributed to the important sensory attributes were identified. The high pyrazines, furanoids, and carbonyls amounts contributed to the high intensities of the cellar, toasted, and grain aroma profiles of the Sichuan region samples, while the high ester and alcohol levels contributed to the fruity and floral aroma profiles of the Jianghuai region samples. This approach may have practical application in flavor characterization of other alcoholic beverages.

Structural and metabolic performance of p-cresol producing microbiota in different carbon sources

p-Cresol (PC) is a potential off-flavor and carcinogenic compound that affects food flavor and safety. However, controlling the production of PC when making fermented food is hindered by a lack of knowledge of the microbial diversity and the growth requirements of the microbiota that produce PC. To address this, the present study used three media with selected carbon sources (glucose, ethanol and lactic acid) to explore the microbial origin of PC and to determine the preferred carbon source for the PC-producing microbiota in the pit mud of the strong-aroma type Baijiu. The results showed that the different carbon sources affected the microbial structure, especially of the PC-producing microbiota. Glucose led to the highest production of PC and lactic acid to the lowest. The production of PC was significantly correlated (p < 0.05, |ρ| > 0.6) with Dorea, Sporanaerobacter, Tepidimicrobium, Tissierella Soehngenia, Clostridium and Sedimentibacter in the glucose medium; with Proteiniborus, Ruminococcus and Sporanaerobacter in the ethanol medium; and with Lutispora and Tepidimicrobium in the lactic acid medium. Multiphasic metabolite target analysis further indicated that the PC-producing microbiota could also metabolize flavor compounds. Lactic acid could inhibit the production of PC and ensure that the microbiota produced the appropriate flavor compounds during culture. Collectively, Dorea, Sporanaerobacter, Tepidimicrobium, Tissierella_Soehngenia, Clostridium, Sedimentibacter, Proteiniborus, Ruminococcus and Lutispora were identified as potential PC producers in three media with glucose preferred as the carbon source. These findings provide a perspective on the microbiota and carbon source preference for ultimately improving the quality of distilled alcoholic beverage.

Engineering Synthetic Microbial Communities through a Selective Biofilm Cultivation Device for the Production of Fermented Beverages

Production of Cambodian rice wine involves complex microbial consortia. Indeed, previous studies focused on traditional microbial starters used for this product revealed that three microbial strains with complementary metabolic activities are required for an effective fermentation, i.e., filamentous fungi (Rhizopus oryzae), yeast (Saccharomycescerevisiae), and lactic acid bacteria (Lactobacillusplantarum). Modulating the ratio between these three key players led to significant differences, not only in terms of ethanol and organic acid production, but also on the profile of volatile compounds, in comparison with natural communities. However, we observed that using an equal ratio of spores/cells of the three microbial strains during inoculation led to flavor profile and ethanol yield close to that obtained through the use of natural communities. Compartmentalization of metabolic tasks through the use of a biofilm cultivation device allows further improvement of the whole fermentation process, notably by increasing the amount of key components of the aroma profile of the fermented beverage (i.e., mainly phenylethyl alcohol, isobutyl alcohol, isoamyl alcohol, and 2-methyl-butanol) and reducing the amount of off-flavor compounds. This study is a step forward in our understanding of interkingdom microbial interactions with strong application potential in food biotechnology.

Conformal Prediction Based on Raman Spectra for the Classification of Chinese Liquors

This work extends the conventional back-propagation neural network (BPNN) to the classification of Chinese liquors of different flavors according to their Raman spectra. Conformal prediction is applied to assign reliable confidence measures for each classification and support an effective framework to make the machine learning on classification trustable. The BPNN can be used to predict the flavors of Chinese liquors according to their Raman spectra, and a classification rate of 88.96% can be achieved. In order to evaluate each classification, a non-conformity score is defined to generate a P-value for each classification. Moreover, the validity of conformal prediction in online mode is discussed. The number of cumulative errors in the conformal prediction is much less than that without conformal prediction. The relationship between the cumulative error and confidence levels shows that a high confidence level leads to low cumulative errors, but many cumulative errors will occur under a very high confidence level. The result implies that conformal prediction is a useful framework, which can employ classification satisfying a certain level of confidence. Meanwhile, the conformal prediction can improve our classification using a BPNN, when the number of data points is limited.

Characterization of key aroma compounds in Chinese rice wine using gas chromatography-mass spectrometry and gas chromatography-olfactometry

To determine the key aroma compounds in Chinese rice wine (CRW), four types of CRW (YH, JF, SN, and XX) were analyzed by gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O), and sensory evaluation. The contributions of the key aroma compounds to the flavor characteristics were determined by partial least squares regression. Sixty-one aroma compounds were detected. Twenty-five components were identified as odor-active compounds. On the basis of their odor active values, 18 odor-active compounds were determined as key aroma compounds. Ethyl isovalerate, ethyl butyrate, ethyl acetate, ethyl hexanoate, and phenylethyl alcohol were key aroma compounds in all four types of wine. The unique key aroma compounds of JF wine were isovaleraldehyde and isoamyl acetate; those of XX wine were 1-butanol, benzaldehyde, ethyl benzoate, ethyl phenylacetate, 2-octanone, and furfural; that of YH wine was ethyl 2-methylbutyrate; and those of SN wine were 1-butanol, 1-hexanol, 2-butenoic acid ethyl ester, and 3-methyl-1-butanol.

Characterization of key aroma compounds in Meilanchun sesame flavor style baijiu by application of aroma extract dilution analysis, quantitative measurements, aroma recombination, and omission/addition experiments

The aroma components in Meilanchun sesame flavor style baijiu were identified by aroma extract dilution analysis (AEDA), quantitative analysis, aroma active compound recombination, and omission/addition experiments. 92 components in Meilanchun were identified. Among them, 47 odor active compounds were further confirmed by GC-MS/O with aroma extract dilution analysis (AEDA). Ethyl pentanoate, 3-methy-1-butanol, methional, ethyl 3-phenylpropanoate, phenethyl alcohol had the highest flavor dilution (FD) factors (FD = 2187). Among the 88 components that were determined in terms of their odor activity values (OAVs), 35 compounds showed OAVs ≥ 1. Furthermore, a reconstitution model was prepared by mixing the above mentioned 35 compounds, lactic acid, phenethyl alcohol and 2-methoxy-1,3-dioxolane, and showed a good similarity to the aroma of Meilanchun baijiu. Omission/addition experiments further confirmed that ethyl hexanoate (OAV 1945), ethyl butanoate (OAV 838), 3-methyl-1-butanol (OAV 2), 3-methylbutanal (OAV 618), methional (OAV 59), and dimethyl trisulfide (OAV 44), might be the most important compounds for the unique flavor of Meilanchun baijiu. In addition, phenols and acetoin (OAV 66) were confirmed to be the key odorants and the odorless compound lactic acid played a significant role in the roasted sesame flavor baijiu by the omission experiments.

The aroma components in Meilanchun sesame flavor style baijiu were identified by aroma extract dilution analysis (AEDA), quantitative analysis, aroma active compound recombination, and omission/addition experiments.

Quality assessment of Chinese liquor with different ages and prediction analysis based on gas chromatography and electronic nose

The economic value of Chinese liquor is closely related with its age. Results from gas chromatograph (GC) analysis indicated that 8 dominant compounds were decreased with the increase of liquor age (0 to 5 years) while ethyl lactate was found to be the most stable dominant compound as no significant change was observed in it during the aging process. Liquor groups with different ages were well-discriminated by principal component analysis (PCA) based on electronic nose signals. High-accurate identification of liquor ages was realized using linear discriminant analysis (LDA) with the accuracy of 98.3% of the total 120 samples from six age groups. Partial least squares regression (PLSR) exhibited satisfying ability for liquor age prediction (R²: 0.9732 in calibration set and 0.9101 in validation set). The feasibility of volatile compounds prediction using PLSR combined with electronic nose was also verified by this research. However, the accuracies of PLSR models can be further promoted in future researches, perhaps by using more suitable sensors or modeling approaches.

Solid-phase microextraction of methadone in urine samples by electrochemically co-deposited sol-gel/Cu nanocomposite fiber

Electrochemically co-deposited sol-gel/Cu nanocomposites have been introduced as a novel, simple and single-step technique for preparation of solid-phase microextraction (SPME) coating to extract methadone (MDN) (a synthetic opioid) in urine samples. The porous surface structure of the sol-gel/Cu nanocomposite coating was revealed by scanning electron microscopy. Direct immersion SPME followed by HPLC-UV determination was employed. The factors influencing the SPME procedure, such as the salt content, desorption solvent type, pH and equilibration time, were optimized. The best conditions were obtained with no salt content, acetonitrile as desorption solvent type, pH 9 and 10 min equilibration time. The calibration graphs for urine samples showed good linearity. The detection limit was about 0.2 ng mL^-1 . Also, the novel method for preparation of nanocomposite fiber was compared with previously reported techniques for MDN determination. The results show that the novel nanocomposite fiber has relatively high extraction efficiency.

Characterization of Chinese liquor aroma components during aging process and liquor age discrimination using gas chromatography combined with multivariable statistics

Chinese liquor aroma components were characterized during the aging process using gas chromatography (GC). Principal component and cluster analysis (PCA, CA) were used to discriminate the Chinese liquor age which has a great economic value. Of a total of 21 major aroma components identified and quantified, 13 components which included several acids, alcohols, esters, aldehydes and furans decreased significantly in the first year of aging, maintained the same levels (p > 0.05) for next three years and decreased again (p < 0.05) in the fifth year. On the contrary, a significant increase was observed in propionic acid, furfural and phenylethanol. Ethyl lactate was found to be the most stable aroma component during aging process. Results of PCA and CA demonstrated that young liquor (fresh) and aged liquors were well separated from each other, which is in consistent with the evolution of aroma components along with the aging process. These findings provide a quantitative basis for discriminating the Chinese liquor age and a scientific basis for further research on elucidating the liquor aging process, and a possible tool to guard against counterfeit and defective products.

Effect of high pressure treatment on the aging characteristics of Chinese liquor as evaluated by electronic nose and chemical analysis

Several high pressure (HP) treatments (100-400 MPa; 15 and 30 min) were applied to Chinese "Junchang" liquor, and aging characteristics of the liquor were evaluated. Results from the principal component analysis and the discriminant factor analysis of E-Nose demonstrated that HP treatment at 300 and 400 MPa resulted in significant (p < 0.05) changes in aroma components of the liquor. An increase in total ester content and a decrease in total acid content were observed for all treated samples (p < 0.05), which was verified by gas chromatography analysis. In addition, a slight decrease in alcohol content was found for HP treatment at 400 MPa for 30 min. These changes and trends were in accordance with the natural aging process of Chinese liquor. However, HP treatment caused a slight increase in solid content, which might be somewhat undesirable. Sensory evaluation results confirmed that favorable changes in color and flavor of Chinese liquor were induced by HP treatment; however, overall gaps still existed between the quality of treated and six-year aged samples. HP treatment demonstrated a potential to accelerate the natural aging process for Chinese liquor, but long term studies may be needed further to realize the full potential.