Microbial diversity and their roles in the vinegar fermentation process

Changes of microbial communities and metabolites in the fermentation of persimmon vinegar by bioaugmentation fermentation

To evaluate the effects of bioaugmentation fermentation inoculated with one ester-producing strain (Wickerhamomyces anomalus ZX-1) and two strains of lactic acid bacteria (Lactobacillus plantarum CGMCC 24035 and Lactobacillus acidophilus R2) for improving the flavor of persimmon vinegar, microbial community, flavor compounds and metabolites were analyzed. The results of microbial diversity analysis showed that bioaugmentation fermentation significantly increased the abundance of Lactobacillus, Saccharomyces, Pichia and Wickerhamomyces, while the abundance of Acetobacter, Apiotrichum, Delftia, Komagataeibacter, Kregervanrija and Aspergillus significantly decreased. After bioaugmentation fermentation, the taste was softer, and the sensory irritancy of acetic acid was significantly reduced. The analysis of HS-SPME-GC-MS and untargeted metabolomics based on LC-MS/MS showed that the contents of citric acid, lactic acid, malic acid, ethyl lactate, methyl acetate, isocitrate, acetoin and 2,3-butanediol were significantly increased. By multivariate analysis, 33 differential metabolites were screened out to construct the correlation between the differential metabolites and microorganisms. Pearson correlation analysis showed that methyl acetate, ethyl lactate, betaine, aconitic acid, acetoin, 2,3-butanediol and isocitrate positively associated with Wickerhamomyces and Lactobacillus. The results confirmed that the quality of persimmon vinegar was improved by bioaugmentation fermentation.

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.

Date Vinegar: First Isolation of Acetobacter and Formulation of a Starter Culture

There is a lack of scientific analysis and control over the production of date vinegar in Oman, despite its growing demand in the worldwide market. Traditional production of date vinegar may lead to elevated amounts of ethanol (≥0.5%) and reduced content of acetic acid (<4%) compared to the standard acceptable levels. This study aimed to isolate non-Gluconobacter species from date vinegar produced by spontaneous fermentation and formulate starter cultures for quick and efficient production of date vinegar. In spontaneous fermentation date vinegar samples, the highest concentration of acetic acid was 10.42% on day 50. Acetobacter malorum (5 isolates), A. persici (3 isolates), and A. tropicalis (3 isolates) were identified based on 16S rRNA gene sequences for the first time in date vinegar. For date vinegar prepared with a starter culture of Acetobacter and yeast, the highest concentration of acetic acid was 4.67%. In conclusion, spontaneous fermentation resulted in the production of date vinegar with a high concentration of acetic acid, acceptable concentrations of ethanol and methanol, and the first isolation of three Acetobacter species. The formulated starter culture produced acceptable amounts of acetic acid and the time of fermentation was reduced 10 times (from 40 days to 4 days). This can provide the basis for producing a personalized or commercial product that ensures the production of good-quality date vinegar in an easier, faster, safer, and more efficient way from low-quality and surplus dates.

The functionalities and applications of whey/whey protein in fermented foods: a review

Whey, a major by-product of cheese production, is primarily composed of whey protein (WP). To mitigate environmental pollution, it is crucial to identify effective approaches for fully utilizing the functional components of whey or WP to produce high-value-added products. This review aims to illustrate the active substances with immunomodulatory, metabolic syndrome-regulating, antioxidant, antibacterial, and anti-inflammatory activities produced by whey or WP through fermentation processes, and summarizes the application and the effects of whey or WP on nutritional properties and health promotion in fermented foods. All these findings indicate that whey or WP can serve as a preservative, a source of high-protein dietary, and a source of physiologically active substance in the production of fermented foods. Therefore, expanding the use of whey or WP in fermented foods is of great importance for converting whey into value-added products, as well as reducing whey waste and potential contamination.

Exploring diversity and functional traits of lactic acid bacteria in traditional vinegar fermentation: A review

Vinegar has been used for centuries as a food preservative, flavor enhancer, and medicinal agent. While commonly known for its sour taste and acidic properties due to acetic acid bacteria metabolism, vinegar is also home to a diverse community of lactic acid bacteria (LAB). The main genera found during natural fermentation include Lactobacillus, Lacticaseibacillus, Lentilactobacillus, Limosilactbacillus, Leuconostoc, and Pedicoccus. Many of the reported LAB species fulfill the probiotic criteria set by the World Health Organization (WHO). However, it is crucial to acknowledge that LAB viability undergoes a significant reduction during vinegar fermentation. While containing LAB, none of the analyzed vinegar met the minimum viable amount required for probiotic labeling. To fully unlock the potential of vinegar as a probiotic, investigations should be focused on enhancing LAB viability during vinegar fermentation, identifying strains with probiotic properties, and establishing appropriate dosage and consumption guidelines to ensure functional benefits. Currently, vinegar exhibits substantial potential as a postbiotic product, attributed to the high incidence and growth of LAB in the initial stages of the fermentation process. This review aims to identify critical gaps and address the essential requirements for establishing vinegar as a viable probiotic product. It comprehensively examines various relevant aspects, including vinegar processing, total and LAB diversity, LAB metabolism, the potential health benefits linked to vinegar consumption, and the identification of potential probiotic species.

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.

Latest Trends in Industrial Vinegar Production and the Role of Acetic Acid Bacteria: Classification, Metabolism, and Applications-A Comprehensive Review

Vinegar is one of the most appreciated fermented foods in European and Asian countries. In industry, its elaboration depends on numerous factors, including the nature of starter culture and raw material, as well as the production system and operational conditions. Furthermore, vinegar is obtained by the action of acetic acid bacteria (AAB) on an alcoholic medium in which ethanol is transformed into acetic acid. Besides the highlighted oxidative metabolism of AAB, their versatility and metabolic adaptability make them a taxonomic group with several biotechnological uses. Due to new and rapid advances in this field, this review attempts to approach the current state of knowledge by firstly discussing fundamental aspects related to industrial vinegar production and then exploring aspects related to AAB: classification, metabolism, and applications. Emphasis has been placed on an exhaustive taxonomic review considering the progressive increase in the number of new AAB species and genera, especially those with recognized biotechnological potential.

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.

Vinegar: A potential source of healthy and functional food with special reference to sugarcane vinegar

Vinegar is one of the most widely used acidic condiments. Recently, rapid advances have been made in the area of vinegar research. Different types of traditional vinegar are available around the globe and have many applications. Vinegar can be made either naturally, through alcoholic and then acetic acid fermentation, or artificially, in laboratories. Vinegar is the product of acetic acid fermentation of dilute alcoholic solutions, manufactured by a two-step process. The first step is the production of ethanol from a carbohydrate source such as glucose, which is carried out by yeasts. The second step is the oxidation of ethanol to acetic acid, which is carried out by acetic acid bacteria. Acetic acid bacteria are not only producers of certain foods and drinks, such as vinegar, but they can also spoil other products such as wine, beer, soft drinks, and fruits. Various renewable substrates are used for the efficient biological production of acetic acid, including agro and food, dairy, and kitchen wastes. Numerous reports on the health advantages associated with vinegar ingredients have been presented. Fresh sugarcane juice was fermented with wine yeast and LB acetate bacteria to develop a high-quality original sugarcane vinegar beverage. To facilitate the current study, the bibliometric analysis method was adopted to visualize the knowledge map of vinegar research based on literature data. The present review article will help scientists discern the dynamic era of vinegar research and highlight areas for future research.

Effect of the type of acetic fermentation process on the chemical composition of prickly pear vinegar (Opuntia ficus-indica)

BACKGROUND

In several countries, the cactus plant (Opuntia ficus-indica (L). Mill.) has received renewed attention because of its ecological, socio-economic and environmental role. In this study, prickly pear vinegar was produced employing two types of acetification processes: surface and submerged culture. Both acetification processes were performed at different temperatures (30, 37, 40 °C) by using two different species of thermotolerant acetic acid bacteria (Acetobacter malorum and Gluconobacter oxydans). Polyphenols and volatile compounds analyzed by ultra-performance liquid chromatography with diode array detection and stir bar sorptive extraction-gas chromatography-mass spectrometry, respectively, were considered as the main variables to determine the effect of the acetification process on the quality of the vinegar.

RESULTS

As a result, 15 polyphenols and 70 volatile compounds were identified and quantified in the vinegar samples produced by both acetification processes. The results showed that the surface acetification method led to an increase in the concentration of phenolic components, which was higher than that in the submerged process. However, a significant increase in volatile compounds predominated by esters and acids was observed when submerged culture acetification was employed, whereas alcohols were predominant in surface culture vinegars. Moreover, multivariate statistical analysis showed that the components that mostly contributed to the differentiation between all vinegar samples were the volatile compounds.

CONCLUSION

It has been proved that prickly pear vinegar could be successfully produced at higher temperatures than usual, by employing thermotolerant bacteria, and that the type of acetification method significantly affects the final quality of the vinegar produced. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Combining omics tools for the characterization of the microbiota of diverse vinegars obtained by submerged culture: 16S rRNA amplicon sequencing and MALDI-TOF MS

Vinegars elaborated in southern Spain are highly valued all over the world because of their exceptional organoleptic properties and high quality. Among the factors which influence the characteristics of the final industrial products, the composition of the microbiota responsible for the process and the raw material used as acetification substrate have a crucial role. The current state of knowledge shows that few microbial groups are usually present throughout acetification, mainly acetic acid bacteria (AAB), although other microorganisms, present in smaller proportions, may also affect the overall activity and behavior of the microbial community. In the present work, the composition of a starter microbiota propagated on and subsequently developing three acetification profiles on different raw materials, an alcohol wine medium and two other natural substrates (a craft beer and fine wine), was characterized and compared. For this purpose, two different "omics" tools were combined for the first time to study submerged vinegar production: 16S rRNA amplicon sequencing, a culture-independent technique, and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), a culture-dependent method. Analysis of the metagenome revealed numerous taxa from 30 different phyla and highlighted the importance of the AAB genus Komagataeibacter, which was much more frequent than the other taxa, and Acetobacter; interestingly, also archaea from the Nitrososphaeraceae family were detected by 16S rRNA amplicon sequencing. MALDI-TOF MS confirmed the presence of Komagataeibacter by the identification of K. intermedius. These tools allowed for identifying some taxonomic groups such as the bacteria genera Cetobacterium and Rhodobacter, the bacteria species Lysinibacillus fusiformis, and even archaea, never to date found in this medium. Definitely, the effect of the combination of these techniques has allowed first, to confirm the composition of the predominant microbiota obtained in our previous metaproteomics approaches; second, to identify the microbial community and discriminate specific species that can be cultivated under laboratory conditions; and third, to obtain new insights on the characterization of the acetification raw materials used. These first findings may contribute to improving the understanding of the microbial communities' role in the vinegar-making industry.

Comparison of the Chemical Properties of Vinegar Obtained via One-Step Fermentation and Sequential Fermentation from Dragon Fruit and Pineapple

Dragon fruit has many potential health benefits. It is inexpensive and widely cultivated in Thailand. The addition of dragon fruit to pineapple vinegar may help enhance the total phenolic compounds and antioxidant activity. This study aimed to study and compare the chemical characteristics of vinegar produced via one-step fermentation of a mixture of pineapple and dragon fruit juice from Krok Phra District of Thailand using Saccharomyces cerevisiae var. burgundy with that obtained using sequential fermentation using Saccharomyces cerevisiae var. burgundy and Acetobacter aceti. When the two fermentation methods were compared on day 20, the maximum acetic acid concentration obtained from sequential fermentation was 5.79 ± 0.25%, which was higher than that obtained in one-step fermentation (1.93%). The total phenolic compound content in the mixed fruit vinegar obtained from sequential fermentation and one-step fermentation was 228.01 and 242.2 mg/L gallic acid equivalents, respectively. The antioxidant content of the products obtained in sequential and one-step fermentations was 187.91 mg/L GAE and 209.33 µg/g of Trolox equivalents, respectively, which was consistent with the total phenolic compound content. This indicated that the acetic acid content in the mixed pineapple and dragon fruit juice vinegar obtained using sequential fermentation was higher than that obtained using one-step fermentation although its total phenolic content and the antioxidant activities were slightly lower. These observations will be useful for improving vinegar fermentation in the area.

Valorization of pineapple processing residues through acetification to produce specialty vinegars enriched with red-Jambo extract of Syzygium malaccense leaf

The present study proposes the production of vinegars from pineapple processing residues as an eco-friendly strategy for adding value and economic strengthening of the production chain. Pineapple pulp and peel wines were produced and acetificated to vinegar by wild strains of acetic bacteria using Orlean's method (traditional system) followed by enrichment with leaf extract of Red-Jambo, Syzygium malaccense. Appreciable phenolic contents and antioxidant potential were found in pulp and peel vinegars with the added leaf extract. Catechin, epicatechin and caffeic, p-coumaric, ferulic, and gallic acids were the main phenolic compounds found in peel vinegar. The enrichment of the vinegar with the extract promoted an increase in the content of polyphenols (443.6-337.3 mg GAE/L) and antioxidant activity. Peel wines presented higher luminosity (L^*) and higher saturation index (C^*), and their color tended more toward yellow than pulp wines. Acetification reduced the saturation index (C^*) and led to the intensification of the hue angle in the peels vinegar. Each type of pineapple vinegar produced showed biocidal activity against different bacteria and yeast, and the addition of leaf extract potentiated the antimicrobial activity of peel vinegar, especially against Staphalococcus aureus. The vinegars developed could find an attractive market niche in the food sector.

Microbiome Analysis of Traditional Grain Vinegar Produced under Different Fermentation Conditions in Various Regions in Korea

The fermentation of traditional vinegar is a spontaneous and complex process that involves interactions among various microorganisms. Here, we used a microbiome approach to determine the effects of networks, such as fermentation temperature, location, physicochemical and sensory characteristics, and bacterial profile, within traditional grain vinegar samples collected from various regions of Korea. Acetic acid and lactic acid were identified as the major metabolites of grain vinegar, and sourness and umami were determined as taste fingerprints that could distinguish between vinegar samples. Acetobacter ghanensis and Lactobacillus acetotolerans were the predominant bacterial species, and the functional composition of the microbiota revealed that the nucleotide biosynthesis pathway was the most enriched. These results reveal that vinegar samples fermented outdoors are more similar to each other than vinegar samples fermented at 30 °C, when comparing the distance matrix for comprehending bacterial networks among samples. This study may help obtain high-quality vinegar through optimized fermentation conditions by suggesting differences in sensory characteristics according to the fermentation environment.

Characteristics and Microbiome Profiling of Korean Gochang Bokbunja Vinegar by the Fermentation Process

As NGS (next-generation sequencing) technology develops, metagenomics-based microbial ecology, that is, microbiome research, has recently led to the science of fermented food. Based on the above technology, a study was conducted to understand the characteristics of vinegar made from bokbunja, a local crop in Gochang-gun, Korea. Physicochemical characteristics of vinegar, organic acid analysis, microbial community analysis, and electronic tongue analysis were explored while fermenting the vinegar for 70 days under eight fermentation conditions according to the concentration of bokbunja liquid (100% or 50%), type of fermenter (porcelain jar or stainless container), and fermentation environment (natural outdoor conditions or temperature/oxygen controlled). As a result, distinct microbial community patterns were found in the stage of acetic acid fermentation and, accordingly, this fermentation of Gochang vinegar is classified into three categories. Vinegar prepared by the traditional method of outdoor fermentation using jars showed characteristics of “Acetobacter (42.1%)/Lactobacillus (56.9%) fusion fermentation”. Under conditions where oxygen and temperature were controlled indoors using jars, characteristics of “Komagataeibacter (90.2%) fermentation” were found. “Lactobacillus (92.2%) fermentation” characteristics were discovered under natural outdoor conditions using stainless steel containers. These fermentation pattern differences were related to taxonomic phylogenetic diversity, which was also considered involved in determining organic acid production and taste. These results will be helpful as a scientific basis for understanding the fermentation characteristics of Gochang vinegar and developing high-value-added traditional vinegar products.

Microbes of traditional fermentation processes as synthetic biology chassis to tackle future food challenges

Microbial diversity is magnificent and essential to almost all life on Earth. Microbes are an essential part of every human, allowing us to utilize otherwise inaccessible resources. It is no surprise that humans started, initially unconsciously, domesticating microbes for food production: one may call this microbial domestication 1.0. Sourdough bread is just one of the miracles performed by microbial fermentation, allowing extraction of more nutrients from flour and at the same time creating a fluffy and delicious loaf. There are a broad range of products the production of which requires fermentation such as chocolate, cheese, coffee and vinegar. Eventually, with the rise of microscopy, humans became aware of microbial life. Today our knowledge and technological advances allow us to genetically engineer microbes - one may call this microbial domestication 2.0. Synthetic biology and microbial chassis adaptation allow us to tackle current and future food challenges. One of the most apparent challenges is the limited space on Earth available for agriculture and its major tolls on the environment through use of pesticides and the replacement of ecosystems with monocultures. Further challenges include transport and packaging, exacerbated by the 24/7 on-demand mentality of many customers. Synthetic biology already tackles multiple food challenges and will be able to tackle many future food challenges. In this perspective article, we highlight recent microbial synthetic biology research to address future food challenges. We further give a perspective on how synthetic biology tools may teach old microbes new tricks, and what standardized microbial domestication could look like.

Vinegar Volatile Organic Compounds: Analytical Methods, Constituents, and Formation Processes

Vinegar is an acid condiment shared all over the world. According to the raw materials, vinegar can be mainly divided into fruit and cereal ones, both of which possess unique aroma and flavor characteristics and corresponding volatile organic compounds (VOCs). Many studies about vinegar VOCs' (VVOCs) sorts, analytical methods, and forming mechanisms have been done. In this review, the main categories of vinegar and their distribution in the world are briefly introduced, then VVOCs' analytical and identified methods, types, and forming processes are summarized. Additionally, the VVOCs' research directions are discussed and prospected. According to the searched literatures, this study is the first to systematically review the analytical methods, sorts, and formation mechanisms of VVOCs, which will make the readers better understand the vinegar's aromas and flavors and their producing mechanisms.

Unraveling the Role of Acetic Acid Bacteria Comparing Two Acetification Profiles From Natural Raw Materials: A Quantitative Approach in Komagataeibacter europaeus

The industrial production of vinegar is carried out by the activity of a complex microbiota of acetic acid bacteria (AAB) working, mainly, within bioreactors providing a quite specific and hard environment. The “omics” sciences can facilitate the identification and characterization analyses of these microbial communities, most of which are difficult to cultivate by traditional methods, outside their natural medium. In this work, two acetification profiles coming from the same AAB starter culture but using two natural raw materials of different alcoholic origins (fine wine and craft beer), were characterized and compared and the emphasis of this study is the effect of these raw materials. For this purpose, the composition and natural behavior of the microbiota present throughout these profiles were analyzed by metaproteomics focusing, mainly, on the quantitative protein profile of Komagataeibacter europaeus. This species provided a protein fraction significantly higher (73.5%) than the others. A submerged culture system and semi-continuous operating mode were employed for the acetification profiles and liquid chromatography with tandem mass spectrometry (LC-MS/MS) for the protein analyses. The results showed that neither of two raw materials barely modified the microbiota composition of the profiles, however, they had an effect on the protein expression changes in different biological process. A molecular strategy in which K. europaeus would prevail over other species by taking advantage of the different features offered by each raw material has been suggested. First, by assimilating the excess of inner acetic acid through the TCA cycle and supplying biosynthetic precursors to replenish the cellular material losses; second, by a previous assimilation of the excess of available glucose, mainly in the beer medium, through the glycolysis and the pentose phosphate pathway (PPP); and third, by triggering membrane mechanisms dependent on proton motive force to detoxify the cell at the final moments of acetification. This study could complement the current knowledge of these bacteria as well as to expand the use of diverse raw materials and optimize operating conditions to obtain quality vinegars.

Novel Coconut Vinegar Attenuates Hepatic and Vascular Oxidative Stress in Rats Fed a High-Cholesterol Diet

Background

Hypercholesterolemia is an independent modifiable risk factor that accelerates the development of both non-alcoholic fatty liver and atherosclerosis. Coconut water contains a variety of phytochemicals that make it appealing for producing vinegar. Coconut vinegar is rapidly gaining popularity for health benefits in Southeast Asia. The purpose of this study is to evaluate the effect of daily supplementation of coconut vinegar on hepatic and vascular oxidative stress in rats fed a high-cholesterol diet (HCD).

Methods

Mature coconut water was fermented with coconut sap sugar using Saccharomyces cerevisiae and Acetobacter aceti vat Europeans, respectively. Bioactive compounds and antioxidant capacity of coconut vinegar were examined in vitro. Adult male Sprague-Dawley rats were randomly divided into four groups; the control group fed a standard diet (S), a group that received HCD (SC), a group that received HCD supplemented with coconut vinegar at a dose of 1 mL/kg/day (SCV), and a group that received HCD with atorvastatin at a dose of 30 mg/kg/day (SCA). After 8 weeks, serum metabolic profiles, fatty liver, hepatic, and vascular oxidative stress were determined.

Results

In in vitro studies, coconut vinegar was rich in phenolic compounds and organic acids. The antioxidant capacity of 30 μL of coconut vinegar was 181.55 ± 8.15 μM Trolox equivalent antioxidant capacity (TEAC). In the HCD fed rats, daily supplementation of coconut vinegar reduced weight gain, serum triglycerides, and fasting blood sugar levels without renal or liver toxicity. In the liver, coconut vinegar reduced the accumulation of both hepatic cholesterol and hepatic triglyceride, and it also reduced hepatic 4-hydroxynonenal (4-HNE) lipid peroxidation. In the aortic tissues, coconut vinegar increased nitric oxide bioavailability and reduced aortic 4-HNE lipid peroxidation.

Conclusion

Novel coconut vinegar is the source of antioxidants, and daily supplementation of coconut vinegar was found to attenuate dyslipidemia-induced hepatic and vascular oxidative stress by protective against cellular lipid peroxidation.

Visual detection of microbial community during three bacteria mixed fermentation through hyperspectral imaging technology

Hyperspectral imaging technology with chemometrics was used for identifying and counting each species in microbial community during mixed fermentation. Hyperspectral images of microbial community of <i>Enterobacter</i> sp, <i>Acetobacter pasteurianus</i>, and <i>Lactobacillus paracasei</i> colonies were obtained and the spectra of strain colonies were extracted. Identification models were developed using linear discriminant analysis (LDA) and least-squares support vector machine (LS-SVM) by using 23 variables selected by genetic algorithm. The optimal LS-SVM model with identification rate of 96.67 % was used to identify colonies and prepare colony distribution maps in color for strains counting. The counting results by hyperspectral imaging technology agree with that of the manual counting method with average relative error of 3.70 %. The developed counting method has been successfully used to identify and count the specific strain from the mixed strains simultaneously. The hyperspectral imaging technology has a great potential to monitor changes in the microbial community structure.

Analysis of Selected Minerals in Homemade Grape Vinegars Obtained by Spontaneous Fermentation

Fruit vinegars are widely used as a spice and food preservative. They are considered as functional food, containing many bioactive compounds with pro-health benefits. Grape vinegars can be also a source of mineral compounds. Their quantity and diversity can be determined by environmental factors and growing conditions, such as temperature, mineral composition of the soil, heavy metal contamination, sunlight availability as well as grape variety and fruit ripeness stage. The aim of the study was to determine the content of minerals in homemade grape vinegars, obtained by spontaneous fermentation. Five different grape (Vitis vinifera L.) varieties were used in the study (Cabernet Cortis, Johanniter, Solaris, Souvignier gris and Prior). Moreover, the effect of sugar addition in the fermentation process on the mineral content was examined. The mineral content was determined using the ICP-OES method. Among the analysed samples, potassium was the most abundant element (936.07-1472.3 mg/L of vinegar). Comparative analysis showed that the content of Ca, Fe and Cr was significantly higher in vinegars prepared from red varieties than in white-coloured ones. In turn, vinegars prepared from white grape varieties contained statistically significantly higher content of potassium. Vinegar colour did not have a significant influence on the content of the remaining elements included in the analysis. Furthermore, statistical analysis did not reveal any significant differences in the content of the analysed minerals in any of the grape varieties used between the samples with and without sugar addition.

Bacterial Diversity, Organic Acid, and Flavor Analysis of Dacha and Ercha Fermented Grains of Fen Flavor Baijiu

Fen flavor Baijiu needs two rounds of fermentation, which will obtain Dacha after initial fermentation and Ercha after secondary fermentation. The quality of Baijiu is closely related to the microbes within fermented grains. However, the bacterial diversity in Dacha and Ercha fermented grains of Fen flavor Baijiu has not been reported. In the present study, the structure and diversity of bacteria communities within fermented grains of Fen flavor Baijiu were analyzed and evaluated using MiSeq platform's HTS with a sequencing target of the V3-V4 region of the 16S rRNA gene. Through the analysis of physical and chemical indexes and electronic senses, the relationship between bacterial flora, organic acid, taste, and aroma in fermented grains was clarified. The results indicated that Lactobacillus was the main bacteria in Dacha, and the mean relative content was 97.53%. The bacteria within Ercha samples were Pseudomonas and Bacillus, mean relative content was 37.16 and 28.02%, respectively. The diversity of bacterial communities in Ercha samples was significantly greater than that in Dacha samples. The correlation between Lactobacillus and organic acids, especially lactic acid, led to the difference between Dacha and Ercha organic acids, which also made the pH value of Dacha lower and the sour taste significantly higher than Ercha. Lactobacillus was significantly positively correlated with a variety of aromas, which made Dacha the response value of aromas higher. In addition, Bacillus had a significant positive correlation with bitterness and aromatic compounds, which led to a higher response value of bitterness in Ercha and made it present an aromatic aroma. This study provides an in-depth analysis of the difference between different stages of Fen flavor Baijiu, and theoretical support for the standard production and improvement in quality of Fen flavor Baijiu in the future.

Sugar profile regulates the microbial metabolic diversity in Chinese Baijiu fermentation

Cereals are widely used as raw material for food fermentation, and they can provide a variety of sugars in the fermentation via saccharification. However, the effect of sugar profile on microbial metabolism in spontaneous food fermentation is still unclear. Here, this work studied the regulation of sugar profile on the diversity of microbiota and their metabolism in Chinese Baijiu fermentation using sorghum as raw material. Six sugars were detected during Baijiu fermentation with 6 different cultivars of sorghum. The diversity of microbiota (ANOSIM: bacteria: P = 0.001, R = 0.77; fungi: P = 0.009, R = 0.33) and metabolites (ANOSIM: P = 0.001, R = 0.50) had different profiles during Baijiu fermentation. Among these sugars, glucose, fructose, and arabinose were identified as key sugars driving both the microbial and the metabolic diversity during Chinese Baijiu fermentation, and the metabolic diversity was positively correlated with the microbial diversity (P < 0.05). Hence, response surface methodology was used to establish a predictive model for regulating the metabolic diversity with the combination of three key sugars. The metabolic diversity significantly increased to 0.42 with the optimized levels of glucose (31.82 g/L), fructose (4.81 g/L), and arabinose (0.20 g/L), compared with unoptimized low-level average metabolic diversity (0.29). This work would provide a strategy to control microbial metabolism in spontaneous food fermentation, hence to improve the quality of fermented foods.

Constructing a Defined Starter for Multispecies Vinegar Fermentation via Evaluating the Vitality and Dominance of Functional Microbes in Autochthonous Starter

Mature vinegar culture has usually been used as a type of autochthonous starter for rapidly initiate initiating the next batch of acetic acid fermentation (AAF) and maintaining the batch-to-batch uniformity of AAF in the production of traditional cereal vinegar. However, the vitality and dominance of functional microbes in autochthonous starters remain unclear, which hinders further improvement of fermentation yield and production. Here, based on metagenomic (MG), metatranscriptomic (MT), and 16S rRNA gene sequencings, 11 bacterial operational taxonomic units (OTUs) with significant metabolic activity (MT/MG ratio >1) and dominance (relative abundance >1%) were targeted in the autochthonous vinegar starter, all of which were assigned to 4 species (Acetobacter pasteurianus, Lactobacillus acetotolerans, L. helveticus, Acetilactobacillus jinshanensis). Then, we evaluated the successions and interactions of these 11 bacterial OTUs at different AAF stages. Last, a defined starter was constructed with 4 core species isolated from the autochthonous starter (A. pasteurianus, L. acetotolerans, L. helveticus, Ac. jinshanensis). The defined starter culture could rapidly initiate the AAF in a sterile or unsterilized environment and similar dynamics of metabolites (ethanol, titratable acidity, acetic acid, lactic acid, and volatile compounds) and environmental indexes (temperature, pH) of fermentation were observed as compared with that of autochthonous starter (P > 0.05). This work provides a method to construct a defined microbiota from a complex system while preserving its metabolic function. IMPORTANCE Complex microorganisms are beneficial to the flavor formation in natural food fermentation, but they also pose challenges to the mass production of standardized products. It is attractive to construct a defined starter to rapidly initiate fermentation process and significantly improve fermentation yield. This study provides a comprehensive understanding of vital and dominant species in the autochthonous vinegar starter via multi-omics, and designs a defined microbial community for the efficient fermentation of cereal vinegar.

Analysis of Antioxidant Capacity and Antimicrobial Properties of Selected Polish Grape Vinegars Obtained by Spontaneous Fermentation

Nowadays, products of natural origin with health-promoting properties are increasingly more common. Research shows that fruit vinegars can be a source of compounds with antioxidant activity. Research on the total antioxidant capacity, total phenolic content, and antimicrobial properties against Staphylococcus aureus, Escherichia coli, and Candida albicans of grape vinegars were conducted. Moreover, gas chromatography was used to measure acetic acid content in the vinegars. The research material consisted of vinegars produced from five different grape varieties. For each variety, two variants were prepared: with and without the addition of sugar in the fermentation process. The highest antimicrobial activity against all micro-organisms was observed in vinegar produced from Solaris grapes with added sugar. The highest polyphenol content was observed in vinegar produced from the Prior grape variety with added sugar and the highest total antioxidant capacity is the Johanniter grape variety with added sugar. The vinegars examined in this study differed, depending on grape variety, in terms of antimicrobial properties, antioxidant capacity, total phenolic content, as well as acetic acid content. Sugar addition caused significant differences in the antioxidant capacity of vinegar samples.

Unraveling the metabolic network of organic acids in solid-state fermentation of Chinese cereal vinegar

Shanxi aged vinegar (SAV) is fermented by multispecies microorganism with solid-state fermentation (SSF) technology, which contains a variety of organic acids. However, the metabolic network of them in SSF is still unclear. In this study, metagenomics technology was used to reveal the microbial community and functional genes in SAV fermentation. The metabolic network of key organic acids with taste active value higher than 1 was reconstructed for the first time, including acetate, lactate, malate, citrate, succinate, and tartrate. The results show pyruvate is the core compound in the metabolic network of organic acids. Metabolic pathway of acetate plays a pivotal role in this network, and acetate has regulatory function on metabolism of other organic acids. Acetobacter and Lactobacillus are the predominant genera for organic acid metabolism in SSF of SAV. This is also the first report on metabolic network of organic acids in cereal vinegar, adding new knowledge on the flavor substance metabolism during multispecies fermentation of traditional fermented food.

Comparative Metabolite Profiling of Traditional and Commercial Vinegars in Korea

Vinegar, composed of various organic acids, amino acids, and volatile compounds, has been newly recognized as a functional food with health benefits. Vinegar is produced through alcoholic fermentation of various raw materials followed by acetic acid fermentation, and detailed processes greatly vary between different vinegar products. This study performed metabolite profiling of various vinegar products using gas chromatography-mass spectrometry to identify metabolites that are specific to vinegar production processes. In particular, seven traditional vinegars that underwent spontaneous and slow alcoholic and acetic acid fermentations were compared to four commercial vinegars that were produced through fast acetic acid fermentation using distilled ethanol. A total of 102 volatile and 78 nonvolatile compounds were detected, and the principal component analysis of metabolites clearly distinguished between the traditional and commercial vinegars. Ten metabolites were identified as specific or significantly different compounds depending on vinegar production processes, most of which had originated from complex microbial metabolism during traditional vinegar fermentation. These process-specific compounds of vinegars may serve as potential biomarkers for fermentation process controls as well as authenticity and quality evaluation.

The Athlete and Gut Microbiome: Short-chain Fatty Acids as Potential Ergogenic Aids for Exercise and Training

Short-chain fatty acids (SCFAs) are metabolites produced in the gut via microbial fermentation of dietary fibers referred to as microbiota-accessible carbohydrates (MACs). Acetate, propionate, and butyrate have been observed to regulate host dietary nutrient metabolism, energy balance, and local and systemic immune functions. In vitro and in vivo experiments have shown links between the presence of bacteria-derived SCFAs and host health through the blunting of inflammatory processes, as well as purported protection from the development of illness associated with respiratory infections. This bank of evidence suggests that SCFAs could be beneficial to enhance the athlete's immunity, as well as act to improve exercise recovery via anti-inflammatory activity and to provide additional energy substrates for exercise performance. However, the mechanistic basis and applied evidence for these relationships in humans have yet to be fully established. In this narrative review, we explore the existing knowledge of SCFA synthesis and the functional importance of the gut microbiome composition to induce SCFA production. Further, changes in gut microbiota associated with exercise and various dietary MACs are described. Finally, we provide suggestions for future research and practical applications, including how these metabolites could be manipulated through dietary fiber intake to optimize immunity and energy metabolism.

Biotechnological Processes in Fruit Vinegar Production

The production of fruit vinegars as a way of making use of fruit by-products is an option widely used by the food industry, since surplus or second quality fruit can be used without compromising the quality of the final product. The acetic nature of vinegars and its subsequent impact on the organoleptic properties of the final product allows almost any type of fruit to be used for its elaboration. A growing number of scientific research studies are being carried out on this matrix, and they are revealing the importance of controlling the processes involved in vinegar elaboration. Thus, in this review, we will deal with the incidence of technological and biotechnological processes on the elaboration of fruit vinegars other than grapes. The preparation and production of the juice for the elaboration of the vinegar by means of different procedures is an essential step for the final quality of the product, among which crushing or pressing are the most employed. The different conditions and processing methods of both alcoholic and acetic fermentation also affect significantly the final characteristics of the vinegar produced. For the alcoholic fermentation, the choice between spontaneous or inoculated procedure, together with the microorganisms present in the process, have special relevance. For the acetic fermentation, the type of acetification system employed (surface or submerged) is one of the most influential factors for the final physicochemical properties of fruit vinegars. Some promising research lines regarding fruit vinegar production are the use of commercial initiators to start the acetic fermentation, the use of thermotolerant bacteria that would allow acetic fermentation to be carried out at higher temperatures, or the use of innovative technologies such as high hydrostatic pressure, ultrasound, microwaves, pulsed electric fields, and so on, to obtain high-quality fruit vinegars.

Functional metaproteomic analysis of alcohol vinegar microbiota during an acetification process: A quantitative proteomic approach

Vinegar is elaborated using a semi-continuous submerged culture of a complex microbiota of acetic acid bacteria. The genus Komagataeibacter provides much of the proteins of the metaproteome, being K. europaeus the main species working in this environment. In this work, the protein profile of the vinegar microbiota, obtained by means of liquid chromatography-tandem mass spectrometry (LC-MS/MS) in samples from different cycle times of an acetification process using an alcohol medium, has been used to describe the functional metaproteome throughout the process. The analysis was focused on Komagataeibacter species which supplied about 90% of the metaproteome and particularly K. europaeus which accounts for more than 70%. According to these results, the natural behaviour of a microbial community in vinegar has been predicted at a quantitative proteomic level. The results revealed that most of the identified proteins involved in the metabolism of amino acids, biosynthesis of proteins, and energy production related-metabolic pathways increased their expression throughout the cycle loading phase and afterwards experimented a decrease coming into play other proteins acting against acetic acid stress. These findings may facilitate a better understanding of the microbiota's role and contributing to obtain a quality product.

Production of glycerol by Lactobacillus plantarum NRRL B-4496 and formation of hexamine during fermentation of pea protein enriched flour

Suspensions of pea protein enriched flour (PP) inoculated with Lactobacillus plantarum NRRL B-4496 and uninoculated PP suspensions were incubated in vials covered with airtight caps. Organic compound compositions of fermented and unfermented PP suspensions (F-PP and U-PP, respectively) were analyzed using solid phase microextraction (SPME) coupled with gas chromatography - mass-spectrometry (GCMS). Acetic acid was detected in all samples; pH dropped from pH 6.5 to pH 4.1 in L. plantarum F-PP and to pH 5.3 in uninoculated F-PP. Abundance of acetic acid and minuscule presence of lactic acid in L. plantarum F-PP suggested that fermentation proceeded preferentially via the pyruvate formate lyase (PFL) pathway. Nonetheless, glycerol appeared to be the most abundant compound in L. plantarum F-PP samples; colorimetric analysis indicated that its average concentration in these samples was 1.05 g/L. A metabolic switch from the PFL pathway to glycerol production might occur due to acidity tolerance limitations of L. plantarum, glycerol production being associated with the release of phosphate, which can act as a buffer. Fermentation of PP by L. plantarum also led to formation of hexamine, which is a known food preservation agent. Presence of naturally formed hexamine and glycerol in food products may render using chemical additives needless.

Importance of Dietary Changes During the Coronavirus Pandemic: How to Upgrade Your Immune Response

The new coronavirus pandemic continues to spread causing further public health, social, and economic issues. The disparities in the rates of death between countries poses questions about the importance of lifestyle habits and the immune status of populations. An exploration of dietary habits and COVID-19-related death might unravel associations between these two variables. Indeed, while both nutritional excess and deficiency are associated with immunodeficiency, adequate nutrition leading to an optimally functioning immune system may be associated with better outcomes with regards to preventing infection and complications of COVID-19, as well as developing a better immune response to other pathogenic viruses and microorganisms. This article outlines the key functions of the immune system and how macronutrients, micronutrients, and metabolites from the gut microbiome can be essential in the development of an efficient immune system. In addition, the effects of intermittent fasting on the inflammatory state as well as metabolic parameters will be discussed.

Metabolite Profile and Immunomodulatory Properties of Bellflower Root Vinegar Produced Using Acetobacter pasteurianus A11-2

Fermented vinegar is prepared from grains and medicinal plants. Here, we produced vinegar from peeled and unpeeled roots of bellflowers (Platycodon grandiflorum) using Acetobacter pasteurianus A11-2 and analyzed bellflower vinegar (BV) samples using gas chromatography–mass spectrometry and quadrupole time-of-flight mass spectrometry over 15 days of fermentation to assess the quality. We also evaluated their antibacterial and immunoenhancing effects using RAW 264.7 macrophage cells. The major metabolites in BV are organic acids, with the main volatile compounds being ethyl acetate, isoamyl acetate, 1-pentanol, hydroxypropanoic acid, and malonic acid. When we fermented BV from unpeeled roots for 10 days with a starter culture, we observed significant antibacterial and immunoenhancing effects in macrophages. Therefore, we could determine the metabolite and functional differences in vinegar obtained from bellflower roots and proposed that bellflower roots with peel are an effective substrate for developing vinegar and healthy food products.

Metaproteomics of microbiota involved in submerged culture production of alcohol wine vinegar: A first approach

Acetic acid bacteria form a complex microbiota that plays a fundamental role in the industrial production of vinegar through the incomplete oxidation reaction from ethanol to acetic acid. The organoleptic properties and the quality of vinegar are influenced by many factors, especially by the raw material used as acetification substrate, the microbial diversity and the technical methods employed in its production. The metaproteomics has been considered, among the new methods employed for the investigation of microbial communities, since it may provide information about the microbial biodiversity and behaviour by means of a protein content analysis. In this work, alcohol wine vinegar was produced through a submerged culture of acetic acid bacteria using a pilot acetator, operated in a semi-continuous mode, where the main system variables were monitored and the cycle profile throughout the acetification was obtained. Through a first approach, at qualitative level, of a metaproteomic analysis performed at relevant moments of the acetification cycle (end of fast and discontinuous loading phases and just prior to unloading phase), it is aimed to investigate the microbiota existent in alcohol wine vinegar as well as its changes during the cycle; to our knowledge, this is the first metaproteomics report carried out in this way on this system. A total of 1723 proteins from 30 different genera were identified; 1615 out of 1723 proteins (93.73%) belonged to the four most frequent (%) genera: Acetobacter, Gluconacetobacter, Gluconobacter and Komagataeibacter. Around 80% of identified proteins belonged to the species Komagataeibacter europaeus. In addition, GO Term enrichment analysis highlighted the important role of catalytic activity, organic cyclic compound binding, metabolic and biosynthesis processes throughout acetic acid fermentation. These findings provide the first step to obtain an AAB profile at omics level related to the environmental changes produced during the typical semi-continuous cycles used in this process and it would contribute to the optimization of operating conditions and improving the industrial production of vinegar.

Dietary short-chain fatty acid intake improves the hepatic metabolic condition via FFAR3

Fermented foods represent a significant portion of human diets with several beneficial effects. Foods produced by bacterial fermentation are enriched in short-chain fatty acids (SCFAs), which are functional products of dietary fibers via gut microbial fermentation. In addition to energy sources, SCFAs also act as signaling molecules via G-protein coupled receptors such as FFAR2 and FFAR3. Hence, dietary SCFAs in fermented foods may have a direct influence on metabolic functions. However, the detailed mechanism by dietary SCFAs remains unclear. Here, we show that dietary SCFAs protected against high-fat diet-induced obesity in mice in parallel with increased plasma SCFAs without changing cecal SCFA or gut microbial composition. Dietary SCFAs suppressed hepatic weight and lipid synthesis. These effects were abolished in FFAR3-deficient mice but not FFAR2-deficient. Thus, SCFAs supplementation improved hepatic metabolic functions via FFAR3 without influencing intestinal environment. These findings could help to promote the development of functional foods using SCFAs.

Application of indigenous Saccharomyces cerevisiae to improve the black raspberry (Rubus coreanus Miquel) vinegar fermentation process and its microbiological and physicochemical analysis

In order to improve the slow ethanol fermentation during acetic acid fermentation process of black raspberry vinegar (BRV), the microbiological and physicochemical aspects of the effects of indigenous Saccharomyces cerevisiae JBCC-21A were examined. The selected S. cerevisiae JBCC-21A showed better growth and ethanol production rates than the commercial yeast strains. The ethanol production rate was 3-times faster than the traditional method. Acetic acid fermentation by S. cerevisiae JBCC-21A began 10 days earlier than the traditional method and reached up to 60 g/L acetic acid. Bacterial counts revealed Acetobacter pasteurianus was the only dominant species throughout the inoculated acetic acid fermentation. The physicochemical and functional properties of the fermented vinegar using indigenous S. cerevisiae JBCC-21A maintained a high quality similar to the traditional method, while being the faster fermentation process. Thus, it is suggested that inoculation of the indigenous S. cerevisiae strain in order to shorten the fermentation time without affecting the quality of traditional BRV.

Ester-Producing Mechanism of Ethanol O-acyltransferase EHT1 Gene in Pichia pastoris from Shanxi Aged Vinegar

The ethanol O-acyltransferase EHT1 is an important element of key signaling pathways and is widely expressed in yeast strains. In this study, we investigated the expression of EHT1 in the overexpression lines or knockout system of Pichia pastoris using qRT-PCR and western blotting. The amount of total protein was determined using the Bradford method; the esterase activity was determined using p-nitrophenyl acetate as a substrate, and the production of volatile fatty acids in wild-type, knockout, and over-expression systems was detected using SPME GC-MS. The esterase activity of EHT1-knockout P. pastoris was significantly lower than that in wild type (P<0.01), and the activities of esterase in three EHT1-overexpressing strains—OE-1, OE-2, and OE-3—were significantly higher than those in wild type (P<0.01). In the EHT1-knockout strain products, the contents of nine volatile fatty acids were significantly lower than those in wild type (P<0.01), and the relative percentages of three fatty acids, methyl nonanoate, methyl decanoate, and ethyl caprate, were significantly lower than those in the other six species in the wild-type and knockout groups (P<0.05). The nine volatile fatty acids in the fermentation products of the overexpressed EHT1 gene were significantly higher than those in the wild-type group (P<0.01). The relative percentages of the three fatty acid esters, methyl nonanoate, methyl caprate, and ethyl caprate, were significantly higher than those in the other six species (P<0.05). EHT1 plays an important regulatory role in esterase activity and the production of medium-chain volatile fatty acids.

Succession sequence of lactic acid bacteria driven by environmental factors and substrates throughout the brewing process of Shanxi aged vinegar

Lactic acid bacteria (LAB) are essential microbiota for the fermentation and flavor formation of Shanxi aged vinegar, a famous Chinese traditional cereal vinegar that is manufactured using open solid-state fermentation (SSF) technology. However, the dynamics of LAB in this SSF process and the underlying mechanism remain poorly understood. Here, the diversity of LAB and the potential driving factors of the entire process were analyzed by combining culture-independent and culture-dependent methods. Canonical correlation analysis indicated that ethanol, acetic acid, and temperature that result from the metabolism of microorganisms serve as potential driving factors for LAB succession. LAB strains were periodically isolated, and the characteristics of 57 isolates on environmental factor tolerance and substrate utilization were analyzed to understand the succession sequence. The environmental tolerance of LAB from different stages was in accordance with their fermentation conditions. Remarkable correlations were identified between LAB growth and environmental factors with 0.866 of ethanol (70 g/L), 0.756 of acetic acid (10 g/L), and 0.803 of temperature (47 °C). More gentle or harsh environments (less or more than 60 or 80 g/L of ethanol, 5 or 20 g/L of acetic acid, and 30 or 55 °C temperature) did not affect the LAB succession. The utilization capability evaluation of the 57 isolates for 95 compounds proved that strains from different fermentation stages exhibited different predilections on substrates to contribute to the fermentation at different stages. Results demonstrated that LAB succession in the SSF process was driven by the capabilities of environmental tolerance and substrate utilization.