Determination of the microbial origin of geosmin in Chinese liquor

Moldy odors in food - a review

Food products are susceptible to mold contamination, releasing moldy odors. These moldy odors not only affect the flavor of food, but also pose a risk to human health. Moldy odors are a mixture of volatile organic compounds (VOCs) released by the fungi themselves, which are the main source of moldy odors in moldy foods. These VOCs are secondary metabolites of fungi and are synthesized through various biosynthetic pathways. Both the fungi themselves and environmental factors affect the release of moldy odors. This review summarized the main components of musty odors in moldy foods and their producing fungi. In addition, this review focused on the functions of moldy volatile organic compounds (MVOCs) and the biosynthetic pathways of the major MVOCs, and summarized the factors affecting the release of MVOCs as well as the detection methods. It expected to provide a basis for ensuring food safety.

Unraveling the core microorganisms and metabolic pathways related to off-flavor compounds formation during Jiang-flavor Baijiu fermentation

Off-flavor is one of the most frequent and serious causes for the aroma deterioration in Jiang-flavor Baijiu. However, the key compounds and their formation mechanism responsible for off-flavor are still unclear. This study identified 271 volatile compounds from 1 normal and 5 types of off-flavor fermented grains (putrid, rancidity, mud, musty, and burnt) by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry. Using VIP and OAV analysis, 47 key flavor compounds including indole, phenol, isoamyl alcohol, diacetyl, acetic acid, isobutyric acid, and isovaleric acid were found to distinguish normal and off-flavor fermented grains. Furthermore, 40 microbial genera (mainly Monascus, Enterococcus, Dyadobacter, Ottowia, Pseudoxanthomonas, Stenotrophomonas, Pseudomonas, and Xanthomonas) were significantly (p < 0.05, Pearson correlation) related to these 47 compounds. Finally, metabolic pathways for off-flavor compounds formation were constructed. This study provides comprehensive information on the off-flavor compounds and their potential formation mechanism during Jiang-flavor Baijiu fermentation.

Volatile sensation: The chemical ecology of the earthy odorant geosmin

Geosmin may be the most familiar volatile compound, as it lends the earthy smell to soil. The compound is a member of the largest family of natural products, the terpenoids. The broad distribution of geosmin among bacteria in both terrestrial and aquatic environments suggests that this compound has an important ecological function, for example, as a signal (attractant or repellent) or as a protective specialized metabolite against biotic and abiotic stresses. While geosmin is part of our everyday life, scientists still do not understand the exact biological function of this omnipresent natural product. This minireview summarizes the current general observations regarding geosmin in prokaryotes and introduces new insights into its biosynthesis and regulation, as well as its biological roles in terrestrial and aquatic environments.

Synergistic Fermentation with Functional Microorganisms Improves Safety and Quality of Traditional Chinese Fermented Foods

Traditional fermented foods are favored by people around the world for their positive health and taste advantages. Many of the fermented foods, including Chinese traditional fermented foods, are produced through mixed-culture fermentation. Apart from reducing the formation of harmful compounds such as ethyl carbamate (EC) and biogenic amines (BAs) during food fermentation, it is also difficult to precisely control and regulate the fermentation process based on the control of environmental conditions alone, due to the complex microbiota and an unclarified fermentation mechanism. In this review, key microorganisms involved in Chinese fermented foods such as baijiu, soy sauce, and vinegar production are elaborated, and relations between microbial composition and the aroma or quality of food are discussed. This review focuses on the interpretation of functions and roles of beneficial (functional) microorganisms that participate in food fermentation and the discussion of the possibilities of the synergistic use of functional microorganisms to improve the safety and quality of Chinese fermented foods. Conducting work toward the isolation of beneficial microorganisms is a challenge for modern food fermentation technology. Thus, methods for the isolation and mutagenesis of functional microbial strains for synergistic food fermentation are summarized. Finally, the limitations and future prospects of the use of functional microorganisms in traditional Chinese fermented foods are reviewed. This review provides an overview of the applications of synergistic fermentation with functional microorganisms in the improvement of the safety or sensory qualities of fermented foods.

What Are the Main Factors That Affect the Flavor of Sauce-Aroma Baijiu

Sauce-aroma Baijiu is a distilled Baijiu well-known in China, and features a unique sauce-aroma style formed by a complex producing process in a specific geographical environment. However, there are few comprehensive reviews of the factors influencing the formation of its flavor. To this end, reviews are hereby carried out over factors including different components in brewing raw materials, geographical environment of Baijiu production, brewing technology including the production of high-temperature Daqu and the brewing process, storage technology including the type of storage containers, storage time and storage temperature involved in the production of Sauce-aroma Baijiu. In addition, the effects of these factors on the flavor formation of Sauce-aroma Baijiu are also revealed, providing references and forging a foundation for stabilizing and improving the quality of Sauce-aroma Baijiu.

Biocontrol of Geosmin Production by Inoculation of Native Microbiota during the Daqu-Making Process

Geosmin produced by Streptomyces can cause an earthy off-flavor at trace levels, seriously deteriorating the quality of Chinese liquor. Geosmin was detected during the Daqu (Chinese liquor fermentation starter)-making process, which is a multi-species fermentation process in an open system. Here, biocontrol, using the native microbiota present in Daqu making, was used to control the geosmin contamination. Six native strains were obtained according to their inhibitory effects on Streptomyces and then were inoculated into the Daqu fermentation. After inoculation, the content of geosmin decreased by 34.40% (from 7.18 ± 0.13 μg/kg to 4.71 ± 0.30 μg/kg) in the early stage and by 55.20% (from 8.86 ± 1.54 μg/kg to 3.97 ± 0.78 μg/kg) in the late stage. High-throughput sequencing combined with an interaction network revealed that the fungal community played an important role in the early stage and the correlation between Pichia and Streptomyces changed from the original indirect promotion to direct inhibition after inoculation. This study provides an effective strategy for controlling geosmin contamination in Daqu via precisely regulating microbial communities, as well as highlights the potential of biocontrol for controlling off-flavor chemicals at trace levels in complex fermentation systems.

Geographically Associated Fungus-Bacterium Interactions Contribute to the Formation of Geography-Dependent Flavor during High-Complexity Spontaneous Fermentation

Fermented foods often have attractive flavor characteristics to meet various human demands. An ever-challenging target is the production of fermented foods with equal flavor profiles outside the product's origin. However, the formation of geography-dependent flavor in high-complexity fermentations remains poorly understood. Here, taking Chinese liquor (baijiu) fermentation as an example, we collected 403 samples from 9 different locations in China across a latitude range of 27°N to 37°N. We revealed and validated the geography-dependent flavor formation patterns by using culture-independent (metabolomics, metagenomics, and metatranscriptomics) and culture-dependent tools. We found that the baijiu microbiomes along with their metabolites were flavor related and geography dependent. The geographical characteristics were determined mainly by 20 to 40 differentiated chemical markers in metabolites and the latitude-dependent fungal structure of the microbiome. About 48 to 156 core microbiota members out of 735 bacterial genera and 290 fungal genera contributed to the chemical markers. The contributions of both fungi and bacteria were greater than those from either bacteria or fungi alone. Representatively, we revealed that dynamic interdependent interactions between yeasts and Lactobacillus facilitated the metabolism of heterocyclic flavor chemicals such as 2-acetylpyrrole, 2,3,5-trimethylpyrazine, and 2-acetylfuran. Moreover, we found that the intraspecific genomic diversity and microbial structure were two biotic factors that contributed to dynamic microbiome assembly. Based on the assembly pattern, adjusting the composition and distribution of initial species was one option to regulate the formation of diverse flavor characteristics. Our study provided a rationale for developing a microbiome design to achieve a defined flavor goal. IMPORTANCE People consume many spontaneously fermented foods and beverages with different flavors on a daily basis. One crucial and hotly discussed question is how to reproduce fermented food flavor without geographical limitations to meet diverse human demands. The constantly enriched knowledge of the microbial contribution to fermented flavor offers valuable insights into flavor biotechnological development. However, we still have a poor understanding of what factors limit the reproduction of fermented flavor outside the product's origin in high-complexity spontaneous fermentations. Here, taking baijiu fermentation as an example, we revealed that geography-dependent flavor was contributed mainly by fungus-bacterium cooperative metabolism. The distinct initial microbial composition, distribution, and intraspecific genomic diversity limited reproducible microbial interactions and metabolism in different geographical areas. The abundant microbial resources and predicted fungus-bacterium interactions found in baijiu fermentation enable us to design a synthetic microbial community to reproduce desired flavor profiles in the future.

Analysis of Bacterial Diversity in Different Types of Daqu and Fermented Grains From Danquan Distillery

Bacterial communities in high-temperature Daqu and fermented grains are important for brewing Jiang-flavor Baijiu such as Danquan Baijiu. Daqu is a saccharifying and fermenting agent, which has a significant impact on the flavor of Baijiu. However, bacterial communities in three different types of samples from the Danquan distillery (dqjq_ck, dqjqcp, and dqjp3) were still unclear, which limited further development of Danquan Baijiu. “dqjq_ck” and “dqjqcp” indicate high-temperature Daqu at days 45 and 135, respectively. “dqjp3” indicates fermented grains. In this study, the bacterial communities of three samples were analyzed by Illumina Miseq high-throughput sequencing. The bacterial communities of three samples primarily composed of thermophilic bacteria and bacteria with stress resistance. The most abundant species in dqjq_ck, dqjqcp, and dqjp3 were Comamonas, Bacillus, and unclassified Lactobacillales, respectively. The main bacteria included Bacillus, Comamonas, Myroides, Paenibacillus, Acetobacter, Kroppenstedtia, Staphylococcus, Saccharopolyspora, Planifilum, Lactobacillus, Acinetobacter, Oceanobacillus, Enterococcus, Thermoactinomyces, Lactococcus, Streptomyces, Saccharomonospora, Tepidimicrobium, Anaerosalibacter, unclassified_Lactobacillales, unclassified_Thermoactinomycetaceae_1, unclassified_Bacillaceae_2, unclassified_Bacillales, unclassified_Microbacteriaceae, unclassified_Rhodobacteraceae, unclassified_Actinopolysporineae, and unclassified_Flavobacteriaceae in three samples (percentage was more than 1% in one of three samples). In our study, the succession of microbiota in three samples representing three important stages of Danquan Baijiu brewing was revealed. This article lays a good foundation for understanding the fermentation mechanism and screening some excellent indigenous bacteria to improve the quality of Danquan Baijiu in future.

Analysis of Difference in Microbial Community and Physicochemical Indices Between Surface and Central Parts of Chinese Special-Flavor Baijiu Daqu

Special-flavor Baijiu is a unique Baijiu in Jiangxi Province, China, whose uniqueness mainly depends on the unique production process of special-flavor Baijiu Daqu. However, the microbial structure and physicochemical indices of different parts of the special-flavor Baijiu Daqu are still unknown. This greatly reduces the actual value of Daqu in the production of special-flavor Baijiu. Therefore, culture-dependent and Illumina MiSeq sequencing methods were used to analyze the microbial structure of special-flavor Baijiu Daqu. The results indicated that there was a complicated microbial diversity in Chinese special-flavor Baijiu Daqu. The predominant bacterial communities were Bacillales, Lactobacillales, and Rhodospirillales, while Saccharomycetales and Eurotiales were the predominant fungal communities. Significant differences in microbial community and distribution were shown between the surface and central parts of Daqu. Acetobacter and Pichia genera were the predominant microorganisms in the surface part of Daqu, whereas Aspergillus, Kroppenstedtia, Oceanobacillus, and Bacillus genera were the predominant microorganisms in the central part of Daqu. Meantime, the different microbial distributions between the surface and central parts of Daqu caused the significant differences in the physicochemical indices. These results can provide an important theoretical basis for improving the brewing process and the quality of special-flavor Baijiu.

Comparison of microbial community and metabolites in spontaneous fermentation of two types Daqu starter for traditional Chinese vinegar production

Daqu starter, an important saccharifying and fermenting agent for the brewing process of traditional vinegar, is manufactured by spontaneous solid-state fermentation which routinely undergoes low or medium incubation temperature. Previous studies have demonstrated that the temperature plays a pivotal role in Daqu quality. Hence, to explore the feasibility of high temperature fermentation applied in the vinegar Daqu brewing and provide guidelines of controlling environmental parameters in traditional vinegar industries, the microbial community and metabolites of vinegar Daqu during medium-temperature and high-temperature fermentation processes (namely, MTFP and HTFP) were compared. The results indicated that the glucoamylase activity, amylase activity and microbial community showed no significant difference in the end of two batches (P > 0.05). Enterobacteriales, Lactobacillales, Bacillales, Saccharomycetales and Mucorales were the dominant orders during MTFP and HTFP. Redundancy analysis revealed that incubation temperature showed positive correlation with the microbial composition from days 3-14 of the fermentation process and was positively associated with the predominant phylotypes of Bacillales, Mucorales, Xanthomonadales and Rickettsiales. The acidity and moisture showed major correlations with microbial composition on day 1 of MTFP and were positively related with the predominant phylotypes of Mucorales and Lactobacillales at the order level. Moreover, higher relative contents of all volatiles were shown in the end of HTFP (13.91 mg/100 g Daqu) compared to MTFP (10.01 mg/100 g Daqu). This work illustrates high temperature (approximately 60°C) fermentation is promising to improve the vinegar Daqu flavor and shall likely contribute to preferably make traditional Daqu by modulating steerable environmental parameters.

Compositional Differences and Similarities between Typical Chinese Baijiu and Western Liquor as Revealed by Mass Spectrometry-Based Metabolomics

Distilled liquors are important products, both culturally and economically. Chemically, as a complex mixture, distilled liquor comprises various chemical compounds in addition to ethanol. However, the chemical components of distilled liquors are still insufficiently understood and compositional differences and similarities of distilled liquors from different cultures have never been compared. For the first time, both volatile organic compounds (VOCs) and non-VOCs in distilled liquors were profiled using mass spectrometry-based metabolomic approaches. A total of 879 VOCs and 268 non-VOCs were detected in 24 distilled liquors including six typical Chinese baijiu and 18 typical Western liquors. Principal component analysis and a correlation network revealed important insights into the compositional differences and similarities of the distilled liquors that were assessed. Ethyl esters, a few benzene derivatives, and alcohols were shared by most distilled liquors assessed, suggesting their important contribution to the common flavor and mouthfeel of distilled liquors. Sugars and esters formed by fatty alcohol differ significantly between the assessed Chinese baijiu and Western liquors, and are potential marker compounds that could be used for their discrimination. Factors contributing to the differences in chemical composition are proposed. Our results improve our understanding of the chemical components of distilled liquors, which may contribute to more rigorous quality control of alcoholic beverages.

Diversity and Function of Microbial Community in Chinese Strong-Flavor Baijiu Ecosystem: A Review

Strong flavor baijiu (SFB), also called Luzhou-flavor liquor, is the most popular Chinese baijiu. It is manufactured via solid fermentation, with daqu as the starter. Microbial diversity of the SFB ecosystem and the synergistic effects of the enzymes and compounds produced by them are responsible for the special flavor and mouthfeel of SFB. The present review covers research studies focused on microbial community analysis of the SFB ecosystem, including the culturable microorganisms, their metabolic functions, microbial community diversity and their interactions. The review specifically emphasizes on the most recently conducted culture-independent analysis of SFB microbial community diversity. Furthermore, the possible application of systems biology approaches for elucidating the molecular mechanisms of SFB production were also reviewed and prospected.

Key blackening and stinking pollutants in Dongsha River of Beijing: Spatial distribution and source identification

Elimination of black-stinking water contamination has been listed as an urgent task in the Water pollution prevention action plan promulgated by State Council of China. However, the key blackening and stinking pollutants and their sources are still unclear. In this study, water quality of a black-stinking urban river in Beijing, Dongsha River, was evaluated firstly; then the distribution of the blackening and stinking pollutants was investigated, and the key pollutants and their potential sources were identified; and finally, the health risk of those pollutants was assessed. The results showed that NH₃N, total phosphorus, dissolved oxygen and chemical oxygen demand ranged from 1.3 to 5.3 mg/L, 0.7-3.0 mg/L, 1.0-3.2 mg/L and 29-104 mg/L, respectively. The value of TP-based trophic level index indicated that Dongsha River reached severe eutrophication level; the maximum value of chroma and odor level reached 32 and 4, respectively. The main dissolved organic compounds included aromatic protein II, soluble microbiological metabolites, fulvic acids and humic acids. The blackening pollutants Fe, Mn, Cu and S^2- were extensively detected, with significantly spatial differences along the river. Dimethyl sulfide, β-ionone, 2-methylisoborneol and geosmin were identified to be the stinking pollutants. Their concentrations covered wide ranges, and even the lowest concentration value was thousands of times higher than its olfactory threshold. Correlation analysis indicated that in the overlaying water S^2- was the key blackening pollutant, while β-ionone and geosmin were the key stinking pollutants. Principal components analysis combining with the site survey revealed their potential sources. S^2- was mainly associated with the decomposition of endogenous sulfur-containing organics; β-ionone might be generated by the endogenous β-carotene bio-conversion and the exogenous discharges, while geosmin might originate from the endogenous humus bio-conversion and anthropic wastes. Furthermore, multi-metals in the sediment posed health risks to children, while dimethyl sulfide had non-cancer health risk for adults and children.

Geosmin as a source of the earthy-musty smell in fruits, vegetables and water: Origins, impact on foods and water, and review of the removing techniques

The earthy-musty smell produced by Streptomyces sp. is assigned to geosmin and is responsible for the major organoleptic defects found in drinking water, fruits and vegetables such as grapes, mushrooms, carrots, and beet. Geosmin is also found in juices and musts before fermentation and its presence has been associated with partial presence of Botrytis cinerea. It has a variable detection threshold depending on the matrix and the detection level ranges from 5 to 50 ng/L. On the sensory level, very few individuals are immune to geosmin and although the intensity of the defect caused by this molecule decreases rapidly in the nose, a bad taste is very persistent in the mouth. As the origin of geosmin is fungal, conventional control techniques used for geosmin prevention are limited to ventilation, improving the integrity of plants and use of storage temperatures around 1 °C in a humidity-controlled environment. However, it has been demonstrated that only the combination of different prophylactic and preventive measures provide a relatively sufficient efficacy. Therefore, prevention of factors favoring the formation of geosmin is still topical. Some chemical treatments showed relatively good results against Botrytis cinerea. However, there is a requirement that must be met, namely that only one chemical per family per year must be used. Moreover, a multi-year alternation of chemical families is a strong agronomic recommendation. Regarding Penicillium, no active material is 100% approved and it negative effects plants such as beet and grapes. Consequently, the importance of finding effective ways to fight against geosmin formation is still relevant. From analytical point of view, measurement of geosmin is mainly based on gas chromatography.

Biocontrol of geosmin-producing Streptomyces spp. by two Bacillus strains from Chinese liquor

Streptomyces spp. producing geosmin have been regarded as the most frequent and serious microbial contamination causing earthy off-flavor in Chinese liquor. It is therefore necessary to control the Streptomyces community during liquor fermentation. Biological control, using the native microbiota present in liquor making, appears to be a better solution than chemical methods. The objective of this study was to isolate native microbiota antagonistic toward Streptomyces spp. and then to evaluate the possible action mode of the antagonists. Fourteen Bacillus strains isolated from different Daqu (the fermentation starter) showed antagonistic activity against Streptomyces sampsonii, which is one of the dominant geosmin producers. Bacillus subtilis 2-16 and Bacillus amyloliquefaciens 1-45 from Maotai Daqu significantly inhibited the growth of S. sampsonii by 57.8% and 84.3% respectively, and effectively prevented the geosmin production in the simulated fermentation experiments (inoculation ratio 1:1). To probe the biocontrol mode, the ability of strain 2-16 and 1-45 to produce antimicrobial metabolites and to reduce geosmin in the fermentation system was investigated. Antimicrobial substances were identified as lipopeptides by ultra-performance liquid chromatography tandem electrospray ionization/quadrupole-time-of-flight mass spectrometry (UPLC-ESI/Q-TOF MS) and in vitro antibiotic assay. In addition, strains 2-16 and 1-45 were able to remove 45% and 15% of the geosmin respectively in the simulated solid-state fermentation. This study highlighted the potential of biocontrol, and how the use of native Bacillus species in Daqu could provide an eco-friendly method to prevent growth of Streptomyces spp. and geosmin contamination in Chinese liquor fermentation.

Identification and quantification of the caproic acid-producing bacterium Clostridium kluyveri in the fermentation of pit mud used for Chinese strong-aroma type liquor production

Chinese strong-aroma type liquor (CSAL) is a popular distilled alcoholic beverage in China. It is produced by a complex fermentation process that is conducted in pits in the ground. Ethyl caproate is a key flavor compound in CSAL and is thought to originate from caproic acid produced by Clostridia inhabiting the fermentation pit mud. However, the particular species of Clostridium associated with this production are poorly understood and problematic to quantify by culturing. In this study, a total of 28 closest relatives including 15 Clostridia and 8 Bacilli species in pit muds from three CSAL distilleries, were detected by culture-dependent and -independent methods. Among them, Clostridium kluyveri was identified as the main producer of caproic acid. One representative strain C. kluyveri N6 could produce caproic, butyric and octanoic acids and their corresponding ethyl esters, contributing significantly to CSAL flavor. A real time quantitative PCR assay of C. kluyveri in pit muds developed showed that a concentration of 1.79×10(7) 16S rRNA gene copies/g pit mud in LZ-old pit was approximately six times higher than that in HLM and YH pits and sixty times higher than that in LZ-new pit respectively. This method can be used to improve the management of pit mud microbiology and its impact on CSAL quality.

Influence of geosmin-producing Streptomyces on the growth and volatile metabolites of yeasts during chinese liquor fermentation

Diverse Streptomyces species act as geosmin producers in the Chinese liquor-making process, causing an earthy, off-odor containment. Through microbiological and metabolite analyses, this paper investigates the influence of several geosmin-producing Streptomyces on the microbial community of a brewing system. The antifungal activity against functional liquor-brewing microbes was assayed by an agar diffusion method. Several Streptomyces, most notably Streptomyces sampsonii QC-2, inhibited the growth of the brewing functional yeasts and molds in pure culture. In a simulated coculture, Streptomyces spp. reduced the flavor compounds (alcohols and esters) contributed by yeasts. Nine components in Streptomyces sampsonii QC-2 broth were detected by ultraperformance liquid chromatography coupled with photo diode array (UPLC–PDA), with characteristic ultraviolet absorptions at 360, 380, and 400 nm. The main products of Streptomyces sampsonii QC-2 were identified by ultraperformance liquid chromatography–quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF–MS/MS), and confirmed by standard mass spectrometry. The antifungal active components were revealed as a series of heptaene macrolide antibiotics.

Effect of temperature on microbial composition of starter culture for Chinese light aroma style liquor fermentation

Light aroma style liquor is one of the basic types of Chinese liquor and is produced with a special technique of using a combination of three types of Daqu as starter culture. The succession of incubation temperature, a main operating parameter, and microbial composition in Daqu were investigated during the manufacturing process. The most significant difference in temperature occurred during the middle stage at which the highest and the lowest temperatures were detected in Houhuo (HH) and Qingcha (QC), respectively. It was shown that for the counting data, the population of fungi was identical and that of bacteria was different between three types of Daqu. According to analysis results of microbial community structure using PCR-denaturing gradient gel electrophoresis (PCR-DGGE), lactic acid bacteria were one of the dominant bacterial groups in all of Daqu and fungal diversity in QC was higher than that in HH and Hongxin (HX). The difference in incubation temperature led to the accumulation of different heat-tolerant and heat-sensitive fungi in the completed Daqu. PCA of DGGE profiles revealed that microbial community structure was distinct between three types of Daqu. It was presumed that temperature might play a decisive role in the formation of micro-organism composition in starter cultures.

SIGNIFICANCE AND IMPACT OF THE STUDY

The usage of a combination of three types of Daqu including Qingcha, Hongxin and Houhuo as starter culture is an important characteristic of production technology of Chinese light aroma style liquor. Micro-organisms from the environment naturally inoculated in Daqu are propagated to form the special microbial community under the control of several operating parameters, especially temperature, and finally play various roles in the fermentation process of liquor. An in-depth study of the relationship between incubation temperature and microbiota in Daqu during the manufacturing is fundamental to understand this complicated process and to prepare high-quality starter culture for fermentation.

Development of a colorimetric sensor array for the discrimination of Chinese liquors based on selected volatile markers determined by GC-MS

A new colorimetric sensor array was developed for the discrimination of 12 high-alcoholic Chinese base liquors from Luzhou Co., Ltd., and 15 commercial Chinese liquor of different brands as well as flavor types. Seventeen volatile compounds within four chemical groups were determined as markers in the base liquor by GC-MS analysis and factor analysis method (FAM). A specialized colorimetric sensor array composed of 20 sensitive dots was fabricated accordingly to obtain sensitive interaction with different types of volatile markers. Discrimination of the liquor samples was subsequently performed using chemometric and statistical methods, including principal component analysis (PCA) and hierarchical clustering analysis (HCA). The results suggested that facile identification of either base liquors with high-alcoholic volume or commercial liquors of the same flavor types could be achieved by analysis of the color change profiles. The response of the sensor improved significantly in comparison with those that rely on nonspecific interactions, and no misclassification was observed for both liquor samples using two chemometric methods. Besides, it was also found that the discrimination is closely related to the characteristic flavor compounds (esters, aldehydes, and acids) and alcoholic strength in liquors, and its performance was even comparable with that of GC-MS.

Aroma characterization of chinese rice wine by gas chromatography-olfactometry, chemical quantitative analysis, and aroma reconstitution

The aroma profile of Chinese rice wine was investigated in this study. The volatile compounds in a traditional Chinese rice wine were extracted using Lichrolut EN and further separated by silica gel normal phase chromatography. Seventy-three aroma-active compounds were identified by gas chromatography-olfactometry (GC-O) and gas chromatography-mass spectrometry (GC-MS). In addition to acids, esters, and alcohols, benzaldehyde, vanillin, geosmin, and γ-nonalactone were identified to be potentially important to Chinse rice wine. The concentration of these aroma-active compounds in the Chinese rice wine was further quantitated by combination of four different methods, including headsapce-gas chromatography, solid phase microextraction-gas chromatography (SPME)-GC-MS, solid-phase extraction-GC-MS, and SPME-GC-pulsed flame photometric detection (PFPD). Quantitative results showed that 34 aroma compounds were at concentrations higher than their corresponding odor thresholds. On the basis of the odor activity values (OAVs), vanillin, dimethyl trisulfide, β-phenylethyl alcohol, guaiacol, geosmin, and benzaldehyde could be responsible for the unique aroma of Chinese rice wine. An aroma reconstitution model prepared by mixing 34 aroma compounds with OAVs > 1 in an odorless Chinese rice wine matrix showed a good similarity to the aroma of the original Chinese rice wine.

Community of environmental streptomyces related to geosmin development in Chinese liquors

Diverse Streptomyces species act as geosmin producers in the Chinese liquor-making process. In this paper, the ecology of these Streptomyces species was analyzed using denaturing gradient gel electrophoresis (DGGE) of amplified Actinobacteria -specified rDNA. The result showed that Streptomyces were widely distributed during Daqu incubation, and multiple processing, geographic, and climate factors can affect their distribution and diversity. The genes associated with geosmin production were characterized in four geosmin-producing Streptomyces strains, all of which were isolated from geosmin-contaminated Daqu. On the basis of this information, a real-time PCR method was developed, enabling the detection of traces of Streptomyces in complex solid-state matrices. The primer was targeted at the gene coding for geosmin synthase (geoA). The real-time PCR method was found to be specific for geosmin-producing Streptomyces and did not show any cross-reactivity with geosmin-negative isolates, which are frequently present in the Chinese liquor-brewing process. Quantification of geoA in the Chinese liquor-making process could permit the monitoring of the level of geosmin producers prior to the occurrence of geosmin production. Comparison of the qPCR results based on the gene encoding geosmin synthase and Actinobacteria-specified rDNA showed that about 1-10% of the Actinobacteria carry the geosmin synthesis gene.

Impact of water quality on the bacterial populations and off-flavours in recirculating aquaculture systems

A variety of factors affecting water quality in recirculating aquaculture systems (RAS) are associated with the occurrence of off-flavours. In this study, we report the impact of water quality on the bacterial diversity and the occurrence of the geosmin-synthesis gene (geoA) in two RAS units operated for 252 days. Unit 2 displayed a higher level of turbidity and phosphate, which affected the fresh water quality compared with unit 1. In the biofilter, nitrification is one of the major processes by which high water quality is maintained. The bacterial population observed in the unit 1 biofilter was more stable throughout the experiment, with a higher level of nitrifying bacteria compared with the unit 2 biofilter. Geosmin appeared in fish flesh after 84 days in unit 2, whereas it appeared in unit 1 after 168 days, but at a much lower level. The geoA gene was detected in both units, 28 days prior to the detection of geosmin in fish flesh. In addition, we detected sequences associated with Sorangium and Nannocystis (Myxococcales): members of these genera are known to produce geosmin. These sequences were observed at an earlier time in unit 2 and at a higher level than in unit 1. This study confirms the advantages of new molecular methods to understand the occurrence of geosmin production in RAS.