Combined effects of fermentation starters and environmental factors on the microbial community assembly and flavor formation of Zhenjiang aromatic vinegar

Starting with screening strains to construct synthetic microbial communities (SynComs) for traditional food fermentation

With the elucidation of community structures and assembly mechanisms in various fermented foods, core communities that significantly influence or guide fermentation have been pinpointed and used for exogenous restructuring into synthetic microbial communities (SynComs). These SynComs simulate ecological systems or function as adjuncts or substitutes in starters, and their efficacy has been widely verified. However, screening and assembly are still the main limiting factors for implementing theoretic SynComs, as desired strains cannot be effectively obtained and integrated. To expand strain screening methods suitable for SynComs in food fermentation, this review summarizes the recent research trends in using SynComs to study community evolution or interaction and improve the quality of food fermentation, as well as the specific process of constructing synthetic communities. The potential for novel screening modalities based on genes, enzymes and metabolites in food microbial screening is discussed, along with the emphasis on strategies to optimize assembly for facilitating the development of synthetic communities.

The complex world of kefir: Structural insights and symbiotic relationships

Kefir milk, known for its high nutritional value and health benefits, is traditionally produced by fermenting milk with kefir grains. These grains are a complex symbiotic community of lactic acid bacteria, acetic acid bacteria, yeasts, and other microorganisms. However, the intricate coexistence mechanisms within these microbial colonies remain a mystery, posing challenges in predicting their biological and functional traits. This uncertainty often leads to variability in kefir milk's quality and safety. This review delves into the unique structural characteristics of kefir grains, particularly their distinctive hollow structure. We propose hypotheses on their formation, which appears to be influenced by the aggregation behaviors of the community members and their alliances. In kefir milk, a systematic colonization process is driven by metabolite release, orchestrating the spatiotemporal rearrangement of ecological niches. We place special emphasis on the dynamic spatiotemporal changes within the kefir microbial community. Spatially, we observe variations in species morphology and distribution across different locations within the grain structure. Temporally, the review highlights the succession patterns of the microbial community, shedding light on their evolving interactions.Furthermore, we explore the ecological mechanisms underpinning the formation of a stable community composition. The interplay of cooperative and competitive species within these microorganisms ensures a dynamic balance, contributing to the community's richness and stability. In kefir community, competitive species foster diversity and stability, whereas cooperative species bolster mutualistic symbiosis. By deepening our understanding of the behaviors of these complex microbial communities, we can pave the way for future advancements in the development and diversification of starter cultures for food fermentation processes.

Fermentation Performance Evaluation of Lactic Acid Bacteria Strains for Sichuan Radish Paocai Production

Fermented vegetable products play a significant role in various cuisines, and understanding the fermentation dynamics of lactic acid bacteria (LAB) strains is essential for optimizing their production and quality. Here, we sought to investigate the fermentation performance of five LAB strains isolated from Sichuan paocai as starters for paocai. Sensory evaluation revealed that the inoculation of radish paocai samples with LAB strains effectively improved the overall liking and sensory satisfaction of participants, increasing the scores to varying degrees in terms of taste, flavor, texture, and coloration. Lactiplantibacillus plantarum and Lacticaseibacillus rhamnosus exhibited a good salt resistance in radish juice and could grow in a medium containing 10% NaCl. Four indicator strains commonly found in contaminated paocai were effectively inhibited by fermented LAB broths, which improved the edibility and safe production of paocai. Compared to spontaneous fermentation (CK), radish paocai inoculated with LAB showed a significantly accelerated acid production rate, shortening the fermentation period by approximately two days. The contents of titratable total acids, organic acids, and free amino acids were higher in the inoculated samples and were enriched in the taste of radish paocai. The content of volatile organic compounds in the inoculated samples was higher than that in CK. Based on OPLS-DA analysis, 31 key indicators of paocai quality were screened and used to rank the fermentation performances of the five strains using the TOPSIS method; here, Lpb. plantarum and Lcb. rhamnosus achieved the highest scores. This study provides a reference for selecting LAB strains as efficient and secure fermentation starters to optimize paocai quality.

Metagenomics profiling of the microbial community and functional differences in solid-state fermentation vinegar starter (seed Pei) from different Chinese regions

Introduction

The starter used in solid-state fermentation (SSF) vinegar, known as seed Pei is a microbial inoculant from the previous batch that is utilized during the acetic acid fermentation stage. The seed Pei, which has a notable impact on vinegar fermentation and flavor, is under-researched with comparative studies on microorganisms.

Methods

Herein metagenomics was employed to reveal the microbes and their potential metabolic functions of four seed Pei from three regions in China.

Results

The predominant microbial taxa in all four starters were bacteria, followed by viruses, eukaryotes, and archaea, with Lactobacillus sp. or Acetobacter sp. as main functional taxa. The seed Pei used in Shanxi aged vinegar (SAV) and Sichuan bran vinegar (SBV) exhibited a higher similarity in microbial composition and distribution of functional genes, while those used in two Zhenjiang aromatic vinegar (ZAV) differed significantly. Redundancy analysis (RDA) of physicochemical factors and microbial communities indicated that moisture content, pH, and reducing sugar content are significant factors influencing microbial distribution. Moreover, seven metagenome-assembled genomes (MAGs) that could potentially represent novel species were identified.

Conclusions

There are distinctions in the microbiome and functional genes among different seed Pei. The vinegar starters were rich in genes related to carbohydrate metabolism. This research provides a new perspective on formulating vinegar fermentation starters and developing commercial fermentation agents for vinegar production.

The Complexity of Chinese Cereal Vinegar Flavor: A Compositional and Sensory Perspective

With a millennium-long history, traditional Chinese cereal vinegar (CCV) is a significant part of China's cultural heritage. The unique flavor of CCV is derived from the use of cereal and its bran as raw materials and solid-state fermentation as a brewing technique. This paper systemically summarized recent research progress on the aroma compounds in CCV, the biochemical generation of aroma compounds during the brewing process, and the association between sensory perception and the primary aroma compounds. Furthermore, a complete CCV lexicon and sensory wheel prototype were constructed. This study aims to lay a foundation for future CCV aroma research, quality improvement, and industrialization.

Spatial-temporal distribution of deoxynivalenol, aflatoxin B1, and zearalenone in the solid-state fermentation basin of traditional vinegar and their potential correlation with microorganisms

This study revealed the spatial-temporal distribution of deoxynivalenol (DON), aflatoxin B1 (AFB1), and zearalenone (ZEN) during the acetic acid fermentation (AAF) of aromatic vinegar and the corresponding correlation with the microbial community. A total of 324 samples were collected during the AAF process to analyze the mycotoxin content. The average DON content fluctuated during the first 7 d, while the average AFB1 and ZEN levels increased at 5-7 d and 7-11 d, respectively, remaining stable until the end of fermentation. In addition, the significant AFB1 and ZEN content variation was limited to the cross-sectional sampling planes in the fermentation basin, while DON was heterogeneously distributed on the cross-sectional, horizontal, and vertical sampling planes. Furthermore, the redundancy analysis and Spearman correlation coefficients revealed close relationships between three mycotoxins and certain bacterial and fungal species. This study provides new information regarding the mycotoxins during solid-state fermentation of traditional vinegar.

Microbial characterization of Sichuan Baoning vinegar: lactic acid bacteria, acetic acid bacteria and yeasts

Sichuan Baoning vinegar, a typical representative of Sichuan bran vinegar, is a famous traditional fermented food made from cereals in China. At present, there are few studies on microbial characterization of culturable microorganisms in solid-state fermentation of Sichuan bran vinegar. To comprehensively understand the diversity of lactic acid bacteria, acetic acid bacteria and yeasts, which play an important role in the fermentation of Sichuan bran vinegar, traditional culture-dependent methods combined with morphological, biochemical, and molecular identification techniques were employed to screen and identify these isolates. A total of 34 lactic acid bacteria isolates, 39 acetic acid bacteria isolates, and 48 yeast isolates were obtained. Lactic acid bacteria were dominated by Enterococcus durans, Leuconostoc citreum, Lactococcus lactis, and Lactiplantibacillus plantarum, respectively. Latilactobacillus sakei was the first discovery in cereal vinegar. Acetic acid bacteria were mainly Acetobacter pomorum and A. pasteurianus. The dominant yeast isolates were Saccharomyces cerevisiae, in addition to four non-Saccharomyces yeasts. DNA fingerprinting revealed that isolates belonging to the same species exhibited intraspecific diversity, and there were differences between phenotypic and genotypic classification results. This study further enriches studies on cereal vinegar and lays a foundation for the development of vinegar starters.

Synthesis of an autochthonous microbial community by analyzing the core microorganisms responsible for the critical flavor of bran vinegar

Traditional bran vinegar brewing unfolds through natural fermentation, a process driven by spontaneous microbial activity. The unique metabolic activities of various microorganisms lead to distinct flavors and qualities in each batch of vinegar, making it challenging to consistently achieve the desired characteristic flavor compounds. Therefore, identifying the critical microbial species responsible for flavor production and designing starter cultures with improved fermentation efficiency and characteristic flavors are effective methods to address this discrepancy. In this study, 11 core functional microbial species affecting the fermentation flavor of Sichuan shai vinegar (Cupei were placed outside solarization and night-dew for more than one year, and vinegar was the liquid leached from Cupei) (SSV), were revealed by combining PacBio full-length diversity sequencing based on previous metagenomics. The effects of environmental factors and microbial interactions on the growth of 11 microorganisms during fermentation were verified using fermentation experiments. Ultimately, the microbial community was strategically synthesized using a 'top-down' approach, successfully replicating the distinctive flavor profile of Sichuan shai vinegar (SSV). The results showed that the interaction between microorganisms and environmental factors affected microorganism growth. Compared with traditional fermentation, the synthetic microbial community's vinegar-fermented grains (Cupei) can reproduce the key flavor of SSV and is conducive to the production of amino acids. In this study, the key flavor of SSV was reproduced through rational design of the synthetic microbial community. This achievement holds profound significance for the broader application of microbiome assembly strategies in the realm of fermented foods.

Analysis on driving factors of microbial community succession in Jiuyao of Shaoxing Huangjiu (Chinese yellow rice wine)

The microbial ecosystem of fermented food is greatly disturbed by human activities.Jiuyao is important saccharification starter for brewing huangjiu. The interaction between environmental factors and microorganisms significantly affected the microbial community structure at different stages of Jiuyao manufacturing. This study combined environmental factor analysis and high-throughput sequencing technology to comprehensively analyze the specific changes of microbial community and environmental factors in each fermentation stage of Jiuyao production and their correlation. The results showed that the activities of liquefaction enzyme, glycosylation enzyme and acid protease reached the highest value on the 8 th day (192 h) after the beginning of fermentation, and the cellulase activity reached the highest value at the end of fermentation. Pediococcus（37.5 %-58.2 %）, Weissella（9.2 %-27.0 %） and Pelomonas（0.1 %-12.1 %） were the main microbial genera in the genus bacteria, and Saccharomycopsis（37.1 %-52.0 %）, Rhizopus（12.5 %-31.0 %） and Saccharomyces（4.0 %-20.5 %） were the main microbial genera in the genus fungi. The results of correlation analysis showed that the microbial communities in Jiuyao were closely related to environmental factors. Most microbial communities were positively correlated with temperature, but negatively correlated with ambient humidity, CO2 concentration, acidity and water content of Jiuyao. In addition, the transcription levels of enzymes related to microbial glucose metabolism in Jiuyao were higher in the late stage of Jiuyao fermentation. Interestingly, these enzymes had high transcription levels in fungi such as Saccharomycopsis, Rhizopus and Saccharomyces, as well as in bacteria such as Pediococcus and Lactobacillus. This study provides a reference for revealing the succession rule of microbial community structure caused by environmental factors during the preparation of Jiuyao in Shaoxing Huangjiu.

Comparison of fungal communities and flavour substances in surface and inner layers of fermented grains during stacking fermentation of sauce-flavour baijiu

The stacking fermentation process plays a vital role in the production of sauce-flavour baijiu. The aim of this paper is to elucidate the effects of environmental variables on the fungal communities of different layers of fermented grains (zaopei) during the sixth round of stacking and the changes in volatile flavour substances during this process. The composition of the fungal communities in different layers during the stacking fermentation process was analysed. Principal coordinate analysis (pCoA) showed that the dominant fungal communities in different layers differed significantly with the stacking fermentation process. The dominant fungal genera were Thermoascus, Thermomyces and Issatchenkia. The total content of flavouring substances in the surface layer of zaopei were higher, but the types of flavouring substances were less than in the inner layer. The relationship between temperature, moisture content, acidity, starch content and reducing sugar content and microbial community was analysed by Redundancy analysis. The results showed that the correlation between microbial communities and physicochemical indexes in different layers of zaopei varied. The core fungal genera in the surface layer were mainly influenced by acidity, and the microorganisms in the inner layer were more strongly correlated with temperature. Spearman correlation coefficient revealed the correlation between fungal community and volatile flavour substances, and the results showed that microorganisms in different layers of zaopei have different correlations with flavour substances. This study contributes to the understanding of the evolution of different layers fungal communities during the stacking of sauce-flavour baijiu and their relationship with volatile aroma substances.

Deciphering the brewing process of Cantonese-style rice vinegar: Main flavors, key physicochemical factors, and important microorganisms

Cantonese-style rice vinegar is one of the most important Chinese rice vinegars and is quite popular all over the southeast coast of China, especially in Guangdong. This study identified 31 volatile compounds, including 11 esters, 6 alcohols, 3 aldehydes, 3 acids, 2 ketones, 1 phenol, and 5 alkanes, using headspace solid-phase microextraction-gas chromatography-mass spectrometry. Six organic acids were detected by high performance liquid chromatography. The ethanol content was detected by gas chromatography. During acetic acid fermentation, physicochemical analysis showed that the initial concentrations of reducing sugar and ethanol were 0.0079 g/L and 23.81 g/L, respectively, and the final value of total acid was 46.5 g/L, and the pH value was stable at 3.89. High-throughput sequencing was used to identify the microorganisms, and Acetobacter, Komagataeibacter, and Ralstonia were the top three bacterial genera. Quantitative real-time polymerase chain reaction revealed patterns that were different from those of high-throughput sequencing. The co-occurrence network of microorganisms and the correlation analysis between microorganisms and flavor substances indicate that Acetobacter and Ameyamaea played crucial roles as the main functional AAB, and the failure of Cantonese-style rice vinegar fermentation can be attributed to the abnormal increase in Komagataeibacter. Microbial co-occurrence network analysis indicated that Oscillibacter, Parasutterella, and Alistipes were the top three microorganisms. Redundancy analysis disclosed that total acid and ethanol were the key environmental factors influencing the microbial community. Fifteen microorganisms closely related to the metabolites were identified using the bidirectional orthogonal partial least squares model. Correlation analysis showed that these microorganisms were strongly associated with flavor metabolites and environmental factors. The findings of this study deepen our understanding of the fermentation of traditional Cantonese-style rice vinegar.

The dynamics of physicochemical properties, microbial community, and flavor metabolites during the fermentation of semi-dry Hakka rice wine and traditional sweet rice wine

The dynamics of physicochemical properties, microbial community and flavor metabolites during fermentation of two typical Hakka rice wine were investigated. Results showed that total sugar content was 136.83 g/L in sweet rice wine, which almost 8 times higher than that in semi-dry rice wine. Its amino acid contents especially bitterness amino acids were also higher than those in semi-dry rice wine. Most organic acids in Hakka rice wine had the tendency of increase in initial stage of fermentation, following a decrease and finally being almost stable. A total of 131 volatiles including esters, alcohols, aldehydes, acids, ketones were detected. Pediococcus, Bacillus, Acinetobacter, Pantoea, Enterobacter and Lactobacillus were the dominant bacterial genera and Monascus, Saccharomyces, Rhizopus were the dominant fungal genera, which are strongly associated with the significant changes in flavor metabolites during Hakka rice wine fermentation. The obtained findings provided reference data for the optimization of Hakka rice wine fermentation.

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.

Exploring the correlation of metabolites changes and microbial succession in solid-state fermentation of Sichuan Sun-dried vinegar

BACKGROUND

The traditional Sichuan Sun-dried vinegar (SSV) with unique flavor and taste is believed to be generated by the solid-state fermentation craft. However, how microorganisms and their metabolites change along with fermentation has not yet been explored.

RESULTS

In this study, our results demonstrated that the middle and late stages of SSV fermentation were the periods showing the largest accumulation of organic acids and amino acids. Furthermore, in the bacterial community, the highest average relative abundance was Lactobacillus (ranging from 37.55 to 92.50%) in all fermentation stages, while Acetobacters ranked second position (ranging from 20.15 to 0.55%). The number of culturable lactic acid bacteria is also increased during fermentation process (ranging from 3.93 to 8.31 CFU/g). In fungal community, Alternaria (29.42%), Issatchenkia (37.56%) and Zygosaccharomyces (69.24%) were most abundant in different fermentation stages, respectively. Interestingly, Zygosaccharomyces, Schwanniomyces and Issatchenkia were first noticed as the dominant yeast genera in vinegar fermentation process. Additionally, spearman correlation coefficients exhibited that Lactobacillus, Zygosaccharomyces and Schwanniomyces were significant correlation with most metabolites during the fermentation, implying that these microorganisms might make a significant contribution to the flavor formation of SSV.

CONCLUSION

The unique flavor of SSV is mainly produced by the core microorganisms (Lactobacillus, Zygosaccharomyces and Schwanniomyces) during fermentation. This study will provide detailed information related to the structure of microorganism and correlation between changes in metabolites and microbial succession in SSV. And it will be very helpful for proposing a potential approach to monitor the traditional fermentation process.

Metabolomic analysis of the effects of a mixed culture of Saccharomyces cerevisiae and Lactiplantibacillus plantarum on the physicochemical and quality characteristics of apple cider vinegar

Introduction

This study compared differences in physicochemical characteristics of the vinegar made by a mixed culture (MC) of Saccharomyces cerevisiae and Lactiplantibacillus plantarum and a pure culture (PC) of Saccharomyces cerevisiae.

Methods

The fermentation process was monitored, and metabolomics analysis by Liquid Chromagraphy-Mass Spectrometry (LC-MS) was applied to the compositional differences between PC and MC vinegars, combined with quantification of organic acids, amino acids and B vitamins.

Results

A total of 71 differential metabolites including amino acids, organic acids and carbohydrates, and six possible key metabolic pathways were identified. MC enhanced the malic acid utilization and pyruvate acid metabolism during fermentation, increasing substrate-level phosphorylation, and supplying more energy for cellular metabolism. Higher acidity at the beginning of acetic acid fermentation, resulting from lactic acid production by Lactiplantibacillus plantarum in MC, suppressed the cellular metabolism and growth of Acetobacter pasteurianus, but enhanced its alcohol metabolism and acetic acid production in MC. MC vinegar contained more vitamin B, total flavonoids, total organic acids, amino acids and had a higher antioxidant capacity. MC enhanced the volatile substances, particularly ethyl lactate, ethyl caprate and ethyl caproate, which contributed to a stronger fruity aroma.

Discussion

These results indicated the mixed culture in alcoholic fermentation can effectively enhance the flavor and quality of apple cider vinegar.

Inoculation strategies affect the physicochemical properties and flavor of Zhenjiang aromatic vinegar

Inoculation strategy is a significant determinant of the flavor quality of Zhenjiang aromatic vinegar. Herein, the comparative analyses of the effects of various inoculation strategies on the physicochemical properties, microbial community structure, and flavoring characteristics of Zhenjiang aromatic vinegar were performed. The results showed that the contents of total acid (6.91 g/100 g), organic acid (2099.63 ± 4.13 mg/100 g) and amino acid (3666.18 ± 14.40 mg/100 g) in the direct inoculation strategy were higher than those in the traditional inoculation strategy (6.21 ± 0.02 g/100 g, 1939.66 ± 4.16 mg/100 g and 3301.46 ± 13.41 mg/100 g). At the same time, it can effectively promote the production of acetoin. The diversity of strains under the traditional inoculation strategy was higher than that under the direct inoculation strategy, and the relative abundance of major microbial genera in the fermentation process was lower than that under the direct inoculation strategy. In addition, for two different inoculation strategies, pH was proved to be an important environmental factor affecting the microbial community structure during acetic acid fermentation. The correlation between main microbial species, organic acids, non-volatile acids, and volatile flavor compounds is more consistent. Therefore, this study may help to develop direct injection composite microbial inoculants to replace traditional starter cultures in future research.

Non-gene-editing microbiome engineering of spontaneous food fermentation microbiota-Limitation control, design control, and integration

Non-gene-editing microbiome engineering (NgeME) is the rational design and control of natural microbial consortia to perform desired functions. Traditional NgeME approaches use selected environmental variables to force natural microbial consortia to perform the desired functions. Spontaneous food fermentation, the oldest kind of traditional NgeME, transforms foods into various fermented products using natural microbial networks. In traditional NgeME, spontaneous food fermentation microbiotas (SFFMs) are typically formed and controlled manually by the establishment of limiting factors in small batches with little mechanization. However, limitation control generally leads to trade-offs between efficiency and the quality of fermentation. Modern NgeME approaches based on synthetic microbial ecology have been developed using designed microbial communities to explore assembly mechanisms and target functional enhancement of SFFMs. This has greatly improved our understanding of microbiota control, but such approaches still have shortcomings compared to traditional NgeME. Here, we comprehensively describe research on mechanisms and control strategies for SFFMs based on traditional and modern NgeME. We discuss the ecological and engineering principles of the two approaches to enhance the understanding of how best to control SFFM. We also review recent applied and theoretical research on modern NgeME and propose an integrated in vitro synthetic microbiota model to bridge gaps between limitation control and design control for SFFM.

Investigating the mechanism of the flavor formation in Sichuan sun vinegar based on flavor-orientation and metagenomics

Fermentation and aging are the key stages of flavor formation in Sichuan sun vinegar (SSV), but the generation mechanisms of the flavor produced by these processes are unknown. However, complex microbial metabolism is critical to the flavor development of SSV. In this study, we analyzed the key flavor compounds present in SSV. Combined with odor activity value (OAV), the main aroma components of SSV were screened, and the relationship between microorganisms and key flavor formation was predicted using metagenomic sequencing technology. The results revealed 38 key flavor compounds in SSV. Lactobacillus, Weissella, Acetobacter, Lichtheimia, Pediococcus, Oenococcus, Brettanomyces, Kazachstania, Pichia, Xanthomonas, Lenconostoc are widely involved in the production of key flavor compounds such as 2,3-butanediol, 2-Furanmethanol, phenylethanol, 3-(Methylthio)-1-propanol, acetic acid, lactic acid, butyric acid, isovaleric acid and other organic acids. Among them, Lichtheimia and Lactobacillus are important genera for the degradation of starch, arabinoxylan and cellulose. The acetaldehyde,4-ethyl-2-methoxy-phenol and 2-methoxy-4-methyl-phenol production pathway may be related to Lactobacillus, Acetobacter and Brettanomyces. This study provides a new understanding of the key flavor-formation stage and flavor compound generation mechanism of SSV and provides a reference for the screening and isolation of functional strains and the reconstruction of microbial communities.

Development of Candida autochthonous starter for cigar fermentation via dissecting the microbiome

Introduction

The main goal of tobacco fermentation technology is to minimize the alkaloid content while improving flavor substance content.

Methods

This study revealed the microbial community structure and their metabolic functions during cigar leaf fermentation by high-throughput sequencing and correlation analysis, and evaluated the fermentation performance of functional microbes based on in vitro isolation and bioaugmentation fermentation.

Results

The relative abundance of Staphylococcus and Aspergillus increased first but then decreased during the fermentation, and would occupy the dominant position of bacterial and fungal communities, respectively, on the 21st day. Correlation analysis predicted that Aspergillus, Staphylococcus and Filobasidium could contribute to the formation of saccharide compounds, Bacillus might have degradation effects on nitrogenous substances. In particular, Candida, as a co-occurring taxa and biomarker in the later stage of fermentation, could not only degrade nitrogenous substrates and synthesize flavor substances, but also contribute to maintaining the stability of microbial community. Moreover, based on in vitro isolation and bioaugmentation inoculation, it was found that Candida parapsilosis and Candida metapsilosis could significantly reduce the alkaloids content and increase the content of flavor components in tobacco leaves.

Discussion

This study found and validated the critical role of Candida in the fermentation of cigar tobacco leaves through high-throughput sequencing and bioaugmentation inoculation, which would help guide the development of microbial starters and directional regulation of cigar tobacco quality.

A method for efficient conversion of dehydrated cabbage waste liquid into high ester vinegar

The utilization of wastewater in food processing factory has become one of the foremost essential and challengeable problems. In this study, cabbage wastewater was used for a mixed fermentation to obtain a high ester vinegar. The effect of fermentation conditions on the total acid content and total ester content of vinegar was investigated through single-factor experiments and response surface methodology analysis. Under the optimal fermentation conditions of 10.61% inoculation amount, 4.9% initial alcohol content, 29.62 °C fermentation temperature, 75.21 h fermentation time, and the exogenous esterification addition amount of 0.6%. The blending vinegar has a total acid content of 3.80 g 100 mL^-1 and a total ester content of 30.52 mg mL^-1. The significant flavor components in the blending vinegar of the ethyl lactate with a pleasant aroma accounted for 22.15% and the ethyl acetate with a strong fruit aroma accounted for 11.37%.

Exploring the role of Sichuan Baoning vinegar microbiota and the association with volatile flavor compounds at different fermentation depths

Cereal vinegar is usually produced through solid-state fermentation, and the microbial community plays an important role in fermentation. In this study, the composition and function of Sichuan Baoning vinegar microbiota at different fermentation depths were evaluated by high-throughput sequencing combined with PICRUSt and FUNGuild analysis, and variations in volatile flavor compounds were also determined. The results revealed that no significant differences (p > 0.05) were found in both total acid content and pH of vinegar Pei collected on the same day with different depths. There were significant differences between the bacterial community of samples from the same day with different depths at both phylum and genus levels (p < 0.05), however, no obvious difference (p > 0.05) was observed in the fungal community. PICRUSt analysis indicated that fermentation depth affected the function of microbiota, meanwhile, FUNGuild analysis showed that there were variations in the abundance of trophic mode. Additionally, differences in volatile flavor compounds were observed in samples from the same day with different depths, and significant correlations between microbial community and volatile flavor compounds were observed. The present study provides insights into the composition and function of microbiota at different depths in cereal vinegar fermentation and quality control of vinegar products.

Seasonal dynamics of microbiota and physicochemical indices in the industrial-scale fermentation of Sichuan Baoning vinegar

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Differences between the microbiomes in every-two seasons were observed.

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The increase in total acidity of vinegar Pei was lowest in the summer (3.40 g/100 g).

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Lactic acid and acetic acid contents in raw vinegar from each season were different.

We investigated the impact of seasons of the year on microbiota and physicochemical indices in industrial-scale fermentation of Sichuan Baoning vinegar. Illumina HiSeq sequencing results showed significant differences (P < 0.05) between the microbiomes of vinegar Pei in every-two seasons, except for bacterial communities between summer and autumn. Total acid, reducing sugar, starch, and alcohol contents of vinegar Pei from the same sampling day of each season were measurably different. Although total acid content in vinegar Pei was similar at the end of fermentation (P > 0.05), the increase in total acidity was highest in the autumn. Acetic acid content in raw vinegar was highest in the autumn (3472.42 mg/100 mL), and lowest in the summer (2304.01 mg/100 mL). This study provides a theoretical basis for the production of Sichuan bran vinegar with consistent quality and provides insights into the quality control of traditional fermented foods.

Dynamics of Microbial Communities, Flavor, and Physicochemical Properties during Ziziphus jujube Vinegar Fermentation: Correlation between Microorganisms and Metabolites

Jujube pulp separated from Ziziphus jujube is often discarded after processing, resulting in a serious waste of resources and environmental pollution. Herein, Ziziphus jujube pulp was used as a raw material for vinegar fermentation. To investigate the dynamic distribution of microorganisms and flavor substances in ZJV, correlations between environmental variables (e.g., total acid, reducing sugar, temperature) and flavor substances (organic acids, amino acids, volatile substances) and microorganisms were analyzed. Physicochemical indicators (temperature, total acid, alcohol) were the main factors affecting ZJV fermentation. The middle and later stages of ZJV fermentation were the periods showing the largest accumulation of flavor substances. Organic acids (acetic acid, malic acid, citric acid, lactic acid), amino acids (Asp, Glu, Arg) and volatile substances (ethyl phenylacetate, phenethyl alcohol) were important odor-presenting substances in ZJV. In the bacterial community, the Operational Taxonomic Units (OTUs) with an average relative abundance of more than 10% in at least one fermentation stage were mainly Acetobacter, Lactobacillus and Saccharopolyspora, while it was Thermomyces in the fungal community. Pearson correlation coefficients showed that Penicillium, Lactobacillus and Acetobacter were the core microorganisms, implying that these microorganisms contributed to the flavor formation greatly in ZJV fermentation. This study reveals the correlation between physicochemical indexes and flavor substances and microorganisms in ZJV fermentation. The results of the study can provide a theoretical basis for the development of the ZJV industry.

The dynamics of microbial community and flavor metabolites during the acetic acid fermentation of Hongqu aromatic vinegar

In this study, we investigated the dynamics of microbial community and flavor metabolites during the traditional fermentation of Hongqu aromatic vinegar (HAV) and subsequently explored the potential relationship between microbiota and flavor metabolites. The microbiome analysis based on high-throughput sequencing (HTS) of amplicons demonstrated that Lactobacillus, Acetobacter and Clostridium were the dominant bacterial genera, while Alternaria, Candida, Aspergillus and Issatchenkia were the dominant fungal genera during the acetic acid fermentation (AAF) of HAV. A total of 101 volatile flavor compounds were identified through gas chromatography-mass spectrometry (GC-MS) during HAV fermentation, including esters (35), alcohols (17), aldehydes (11), acids (11), ketones (7), phenols (10), and others (10). Redundancy analysis (RDA) was used to reveal the correlation between microbiota and volatile flavor compounds. Lactobacillus and Acetobacter were the two bacterial genera that have the great influence on the production of volatile flavor components in HAV. Among them, Lactobacillus was positively correlated with a variety of ethyl esters, while Acetobacter positively contributed to the formation of several organic acids. Furthermore, the non-volatile metabolites were detected by ultra-high-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS). A total of 41 dipeptides were identified during HAV fermentation, and most of them may have sensory characteristics and biological activities. RDA showed that Aspergillus, Epicoccum, Issatchenkia, Candida and Malassezia were the most influential fungal genera on non-volatile metabolites. In particular, Epicoccum was first reported in Hongqu vinegar and showed a positive correlation with the production of various organic acids. In conclusion, this study provides a scientific basis for understanding the flavor generation mechanism of HAV, and may be valuable for developing effective techniques to select suitable strains to improve the flavor quality of HAV.

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Microbial community in Hongqu aromatic vinegar was investigated by high-throughput sequencing.

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The key flavor metabolites during the acetic acid fermentation of HAV were selected through PLS-DA.

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Lactobacillus, Acetobacter and Clostridium were the predominant bacterial genera in HAV fermentation.

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Alternaria, Candida, Aspergillus and Issatchenkia were the predominant fungal genera in HAV fermentation.

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Redundancy analysis (RDA) revealed the correlation between microbiota and flavor metabolites.

Interaction of acetic acid bacteria and lactic acid bacteria in multispecies solid-state fermentation of traditional Chinese cereal vinegar

The microbial community plays an important role on the solid-state fermentation (SSF) of Chinese cereal vinegar, where acetic acid bacteria (AAB) and lactic acid bacteria (LAB) are the dominant bacteria. In this study, the top-down (in situ) and bottom-up (in vitro) approaches were employed to reveal the interaction of AAB and LAB in SSF of Shanxi aged vinegar (SAV). The results of high-throughput sequencing indicates that Acetobacter pasteurianus and Lactobacillus helveticus are the predominant species of AAB and LAB, respectively, and they showed negative interrelationship during the fermentation. A. pasteurianus CGMCC 3089 and L. helveticus CGMCC 12062, both of which were isolated from fermentation of SAV, showed no nutritional competition when they were co-cultured in vitro. However, the growth and metabolism of L. helveticus CGMCC 12062 were inhibited during SSF due to the presence of A. pasteurianus CGMCC 3089, indicating an amensalism phenomenon between these two species. The transcriptomic results shows that there are 831 differentially expressed genes (|log2 (Fold Change)| > 1 and, p ≤ 0.05) in L. helveticus CGMCC 12062 under co-culture condition comparing to its mono-culture, which are mainly classified into Gene Ontology classification of molecular function, biological process, and cell composition. Of those 831 differentially expressed genes, 202 genes are up-regulated and 629 genes are down-regulated. The down-regulated genes were enriched in KEGG pathways of sugar, amino acid, purine, and pyrimidine metabolism. The transcriptomic results for A. pasteurianus CGMCC 3089 under co-culture condition reveals 529 differentially expressed genes with 393 up-regulated and 136 down-regulated, and the genes within KEGG pathways of sugar, amino acid, purine, and pyrimidine metabolism are up-regulated. Results indicate an amensalism relationship in co-culture of A. pasteurianus and L. helveticus. Therefore, this work gives a whole insight on the interaction between the predominant species in SSF of cereal vinegar from nutrient utilization, endogenous factors inhibition and the regulation of gene transcription.

Relationship between flavor compounds and changes of microbial community in the solid fermented vinegar

The relationship between volatile compounds of vinegar and microorganisms is not clear, especially pyrazine, a trace component. In order to reveal their potential relationship, high throughput sequencing, solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and Spearman's correlation analysis were used. Results showed that Acetobacter and Lactobacillus with opposite abundance trends were the predominant bacteria, and the total abundance of them exceeds 98%, while the predominant fungal genera were Aspergillus and Malassezia, their highest abundances are 75.4% and 81.5% respectively. In the whole process of microbial community succession, six pyrazines were detected including trimethylpyrazine and tetramethylpyrazine, etc, and Spearman's correlation analysis showed that they were positively correlated with the presence of Vibrionimonas, Paraburkholderia, Paucibacter, Komagataeibacter, Acinetobacter and Slinibacter. In general, this study further revealed more species related to pyrazines, it will be helpful to understand the formation of pyrazines and promote the improvement of vinegar quality.