Metabolic profile of main organic acids and its regulatory mechanism in solid-state fermentation of Chinese cereal vinegar

Diversity and Functional Roles of Microorganisms in Anatolian Black Pine Cone Vinegar Fermentation

The parts of some pine species are a rich source of bioactive compounds that can be used in various food products. The current work, the physicochemical, bioactive, antimicrobial, sensory, and aromatic properties of traditional vinegar produced from Anatolian Black Pine Cones from different provinces of Turkey were determined, as well as the cultivable microbial diversity and metagenomic analysis. The total phenolic content of the vinegars ranged from 163.88 to 174.79 mg GAE/L. Antioxidant activity, measured via DPPH and ABTS assays, varied among the samples. CnB vinegar, made from Burdur province cones, stood out for its bioactive compounds, including terpenes, acetic acid, ascorbic acid, and the highest α-terpineol content (3.13%). CnB also exhibited the strongest antimicrobial activity, with the largest inhibition zone (44.91 mm) against E. coli type A, while CnM showed the lowest activity. Sensory evaluations favored CnB for its balanced flavor, while CnV was criticized for excessive sharpness, and CnM was deemed too mild. The bacterial microbiome of CnB was predominantly composed of acetic acid bacteria, with an average concentration of 7.36 log CFU/mL in the enumeration of culturable microorganisms. The dominant bacterial taxa at the phyla level included Proteobacteria (72.296%), Firmicutes (22.062%), Bacteroidota (3.665%), followed by Acetobacteraceae (71.47%), Clostridia (13.187%), Bacilli (5.066%), Bacteroidetes (3.665%), and C. negativicutes (3.737%) at the phylum level. The fungal microbiome was mainly represented by Ascomycota (78.717%) and Eukaryota Incertae sedis (15.840%). The findings demonstrate that pine cone vinegar can be employed in a multitude of applications, including food preservation and health promotion.

Identification of phenols and their formation network during the brewing process of Shanxi aged vinegar

Phenols are important functional compounds present in vineagr, however, their composition and formation pathways remain uncertain. Herein, non-targeted metabolomics and macrotranscriptomics methods were applied to identify phenols and analyze their formation network during the brewing process of Shanxi aged vinegar. A total of 82 phenols were detected from the raw material and the brewing process. Results indicated that phenolic acids were the major phenols and were mainly formed during acetic acid fermentation stages. Water, reducing sugars, lactic acid, and 7 amino acids influenced the formation and transformation of phenols, as shown through Spearman analysis. Furthermore, 16 genera and 38 enzymes were involved in substrates decomposition and phenols formation according to the metabolic pathway analysis, with Xenobiotics biodegradation and metabolism identified as the main pathway for phenols formation. Lactobacillus and Acetobacter were the key genera responsible for the phenols transformation. This study provides new insights into the phenols formation mechanisms in cereal vinegars and it is helpful for isolating the functional strains to reinforce the phenols formation.

Effect of Different Fermentation Methods on the Physicochemical, Bioactive and Volatile Characteristics of Wolfberry Vinegar

Wolfberry (Lycium barbarum L.) as a functional food is rich in nutrients and bioactive substances. However, the fresh wolfberry is difficult to preserve, and its deep-processing products are required to improve. In the present study, single-strain fermentation vinegar (SFV) and mixed-strain fermentation vinegar (MFV) were prepared, and the physicochemical, bioactive compounds, antioxidant capacities and volatile characteristics were examined to obtain an optimal method. The results showed that reducing sugar was sufficiently utilized during mixed-strain fermentation, and more acid substances were produced compared with single-strain fermentation. Meanwhile, total phenols content (2.64 ± 0.04 mg GAE/mL), total flavonoids content (1.81 ± 0.01 mg GAE/mL) and antioxidant activities in MFV were significantly increased compared with those in SFV. Rutin, p-hydroxycinnamic acid, and 4-hydroxybenzoic acid presented higher contents in MFV than those in SFV. The contents of total organic acids (88.13 ± 0.13 mg/mL) and total amino acids (6.50 ± 0.17 mg/mL) in MFV were significantly improved compared with those in SFV. Proline, alanine and serine were the top three amino acids in MFV. Moreover, acids, eaters, and alcohols were the pre-dominant volatile organic compounds in MFV, which were higher 9.49%, 55.27%, 18.72% in MFV than those in SFV, respectively. The results suggest that MFV efficiently enhances potential health benefits and flavor, which increases the economic value of wolfberry.

Comprehensive analysis of the metabolism of core microorganisms in polyphenolic compound formation during the acetic acid fermentation stage of millet vinegar

BACKGROUND

Polyphenolic compounds in millet vinegar are crucial functional substances, but the mechanisms underlying their formation and metabolism remain unclear. Acetic acid fermentation (AAF) represents the most active microbial metabolism stage and is pivotal for forming polyphenolic compounds. This study comprehensively analyzed the role of the microbiome in polyphenolic compound production and metabolism during AAF.

RESULTS

Changing patterns were observed in both the microbiome and polyphenolic monomer compounds during AAF of millet vinegar. Lactobacillus harbinensis (0.624-0.454%) was identified as the dominant species in the pre-AAF stage, exhibiting a significant positive correlation with caffeic acid, kaempferic acid and kaempferolide (P < 0.05). Lactobacillus harbinensis-mediated polyphenolic compound metabolism was further confirmed through genomic analysis and pure culture fermentation techniques. Lactobacillus harbinensis encodes enzymes such as carbohydrate hydrolases, glycosidases and cellulases, which promote the release and metabolism of polyphenolic compounds from grain hulls.

CONCLUSION

This study confirmed that L. harbinensis, as a core microorganism in millet vinegar fermentation, can significantly augment the content of total phenols and specific polyphenolic compounds. These findings provide valuable insights for optimizing millet vinegar production. © 2024 Society of Chemical Industry.

Uncovering the microbial community dynamics and metabolic pathways of primary organic acids in Sichuan Baoning vinegar through metagenomics

Sichuan Baoning vinegar, a renowned traditional vinegar in China, exhibits a higher lactic acid content compared to acetic acid. The microbiota plays a crucial role in shaping the unique flavor of vinegar, but the species-level succession of key microorganisms and metabolic pathways of major organic acids in this vinegar are still unclear. This study utilized metagenomic sequencing to elucidate microbial succession during fermentation and the functional roles of the microbial community, as well as explore the metabolic network of lactic acid and acetic acid. Our findings revealed that bacteria dominated the fermentation process, with Acetilactobacillus jinshanensis, Lactobacillus amylovorus, and Limosilactobacillus sp. emerging as the top three species. Notably, Acetilactobacillus jinshanensis, Limosilactobacillus sp., Lactobacillus amylovorus, and Limosilactobacillus pontis were key players in lactic acid production, while acetic acid synthesis might be primarily driven by Lactobacillus amylovorus, Limosilactobacillus sp., Lactobacillus acetotolerans, and Acetobacter pasteurianus. This study enhances our understanding of the key microorganisms and organic acids metabolism in vinegar, shedding light on the fermentation mechanism of cereal vinegar.

The Metabolic Pathways of Yeast and Acetic Acid Bacteria During Fruit Vinegar Fermentation and Their Influence on Flavor Development

Fruit vinegar is a beverage derived from fruits or fruit processing by-products through microbial fermentation. This vinegar possesses a distinctive flavor profile and contains bioactive compounds. It is typically produced using liquid fermentation technology. As consumer demand for the flavor quality of fruit vinegar has increased, precise control over flavor compounds has become crucial for enhancing the quality of fermentation products. Vinegar contains numerous characteristic flavor compounds, including esters, aldehydes, alcohols, and organic acids. These unique flavors primarily result from the accumulation of flavor compounds generated by different raw materials and microorganisms during fermentation. Specifically, yeast and acetobacter promote the formation of distinct fruit vinegar flavors by facilitating the breakdown of carbohydrates, amino acids, and proteins in fruits, as well as the redox and esterification reactions involving alcohols. This paper reviews the metabolic pathways of yeast and acetic acid bacteria during fruit vinegar fermentation and discusses key volatile compounds that influence the flavor of fruit vinegar and their potential relationships, providing theoretical support for regulating flavor quality.

Isolation and Characterization of a Thermotolerant Acetic Acid Bacteria Strain for Improved Zhenjiang Aromatic Vinegar Production

This study aimed to isolate a thermotolerant acetic acid bacteria (AAB) strain from Zhenjiang aromatic vinegar (ZAV) and evaluate its potential as a starter culture for high-temperature solid-state vinegar fermentation. Acetobacter pasteurianus TCBRC 103 was successfully isolated and demonstrated superior thermotolerance compared to the industrial strain A. pasteurianus Huniang 1.01. A. pasteurianus TCBRC 103 exhibited robust growth and acetic acid production at 42 °C. When employed in the solid-state fermentation of ZAV, inoculation with A. pasteurianus TCBRC 103 resulted in higher fermentation temperatures, leading to enhanced accumulation of organic acids and volatile compounds. Notably, the concentrations of flavor compounds such as isoamyl acetate, acetic acid 2-phenylethyl ester, and acetoin were significantly higher in vinegar fermented by A. pasteurianus TCBRC 103 compared to those fermented by A. pasteurianus Huniang 1.01. Orthogonal partial least squares-discriminant analysis (OPLS-DA) identified 14 discriminative flavor compounds that could serve as potential markers for distinguishing between vinegars fermented by A. pasteurianus TCBRC 103 and A. pasteurianus Huniang 1.01. These findings highlight the promising application of A. pasteurianus TCBRC 103 as a starter culture for the production of high-quality ZAV under high-temperature conditions, with implications for reducing cooling costs and improving vinegar productivity in industry.

Unraveling the microbial community and succession during the maturation of Chinese cereal vinegar Daqu and their relationships with flavor formation

Daqu, the fermentation starter of Shanxi aged vinegar (a traditional Chinese cereal vinegar), is produced by natural fermentation of barley and/or peas under conditions of open environment. However, the succession of microbial communities and its effects on volatile compounds during Daqu maturation were still unclear, which are closely related to the flavor and quality of Shanxi aged vinegar. In this study, the dynamics of physicochemical properties, microbial communities, and volatile compounds and their inter-relationships during the production of Shanxi aged vinegar Daqu were investigated. High-throughput sequencing analysis showed that Lactobacillus and Rhizopus were the most abundant bacteria and fungi during Daqu maturation, respectively. Co-occurrence network analysis showed that Lactobacillus, Saccharopolyspora, Leuconostoc, and Weissella were the important taxa affecting the diversity of Daqu microbial community. Spearman correlation analysis showed that Leuconostoc, Aspergillus, Rhizopus, and Wickerhamomyces were positively correlated with starch and reducing sugars; Wickerhamomyces, Aspergillus, and Bacillus were positively correlated with esterification; Lactobacillus, Enterobacter, Bacillus, Aspergillus, and Rhizopus were positively correlated with lactic acid and acetic acid. Based on the Mean Decrease Accuracy index analysis showed that, ethyl acetate, 1-nonanal, 1-octen-3-ol, ethylbenzene, 3-furanmethanol, and methyl isovalerate were the volatile characteristic compounds during Daqu maturation, respectively. Aspergillus, Byssochlamys, Lichtheimia, Rasamsonia, Rhizopus, Syncephalastrum, Enterobacter, Lactobacillus, Leuconostoc, and Staphylococcus were strongly correlated with volatile compounds; among them, fungi had a greater impact on volatile compounds than bacteria. This study may further improve our understanding concerning the microbial system and microbial roles of Chinese cereal vinegar Daqu and may contribute to optimize the production process of Daqu.

Research advances in technologies and mechanisms to regulate vinegar flavor

New vinegar needs a long maturing time to improve its poor flavor before sale, which greatly increases its production cost. Therefore, it is urgent to explore regulation technologies to accelerate vinegar flavor maturation. Based on literature and our research, this review introduces the latest advances in flavor regulation technologies of vinegar including microbial fortification/multi starters fermentation, key production processes optimization and novel physical processing technologies. Microbial fortification or multi starters fermentation accelerates vinegar flavor maturation via enhancing total acids, esters and aroma precursors content in vinegar. Adjusting raw materials composition, fermentation temperature, and oxygen flow reasonably increase alcohols, organic acids, polyphenols and esters levels via generating more corresponding precursors in vinegar, thereby improving its flavor. Furthermore, novel processing technologies greatly promote conversion of alcohols into acids and esters in vinegar, shortening flavor maturation time for over six months. Meanwhile, the corresponding mechanisms are discussed and future research directions are addressed.

The physicochemical, mechanical, and antifungal properties of sodium alginate film containing Japanese rice vinegar and peppermint (Mentha piperita) oil as bio-composite packaging

Sodium Alginate has a high demand and is favored for food packaging; however, this film typically exhibits poor antimicrobial activity. In this study, sodium alginate film containing peppermint essential oil, Japanese rice vinegar, or a combination of both, is used to analyze antimicrobial, mechanical, structural, and optical properties. The scanning electron microscopy (SEM) technique is utilized to observe the film's surface and cross-section homogeneity. The addition of peppermint essential oil and Japanese rice vinegar to the alginate film solution improves fungal growth and spore germination prevention. Unlike the film containing vinegar, the film with peppermint essential oil shows the lowest transparency. It also has the lowest tensile strength and exhibits the highest elongation at break and water vapor permeability. Conclusively, the film containing a combination of vinegar and essential oil indicates moderate values. According to AFM topography, the film with a mix of essential oil and vinegar has a smoother, more homogeneous surface than other films. Our results prove that combining vinegar and oil with sodium alginate film is an ideal choice. This combination significantly improves the performance of food packaging.

Comparative Study on the Fermentation Characteristics of Selective Lactic Acid Bacteria in Shanxi Aged Vinegar: Pure Culture Versus Co-Culture

The diversity of the microbial community structure plays a crucial role in the flavor and nutritional value of Shanxi aged vinegar in fermentation. Illumina Miseq high-throughput sequencing identified thirteen bacterial genera, with Lactobacillales (44.89%) and Acetobacter (21.04%) being the predominant species. Meanwhile, the fermentation characteristics of selected lactic acid bacteria strains isolated from Shanxi aged vinegar were studied in different media. The results showed that the biomass, and physical and chemical indices, as well as flavor compounds of the four strains of lactic acid bacteria in the simulated vinegar fermented grains medium were superior to those in barley and pea medium and sorghum juice medium. The bacterial interaction was conducted to investigate the effects on growth, the physicochemical indices, and flavor substances in order to determine the optimal combination. Furthermore, the interaction between pure cultures and co-cultures of lactic acid bacteria in a simulated vinegar culture medium was investigated, with a focus on the impact of this interaction on strain growth, fermentation characteristics, and flavor compound production. Compared with the pure culture, when strains L7 and L729 were co-inoculated, the reducing sugar content was 0.31 ± 0.01 g/100 g, total acid content was 3.02 ± 0.06 g/100 g, acetoin content was 2.41 ± 0.07 g/100 g, and total organic acid content was 3.77 ± 0.17 g/100 g. In terms of flavor compounds, the combined culture system exhibited higher levels of esters, aldehydes, and acids compared to pure cultures or other co-culture systems. This study revealed the fermentation characteristics of selected lactic acid strains in Shanxi aged vinegar under different conditions and their interaction in simulated vinegar fermentation media, which could provide theoretical support for the safety and health evaluation of aged vinegar.

Seasonal environmental factors drive microbial community succession and flavor quality during acetic acid fermentation of Zhenjiang aromatic vinegar

This study investigated the impact of seasonal environmental factors on microorganisms and flavor compounds during acetic acid fermentation (AAF) of Zhenjiang aromatic vinegar (ZAV). Environmental factors were monitored throughout the fermentation process, which spanned multiple seasons. Methods such as headspace solid phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), high performance liquid chromatography (HPLC), and high-throughput sequencing were employed to examine how these environmental factors influenced the flavor profile and microbial community of ZAV. The findings suggested that ZAV brewed in autumn had the strongest flavor and sweetness. The key microorganisms responsible for the flavor of ZAV included Lactobacillus acetotolerans, Lactobacillus plantarum, Lactobacillus reuteri, Lactobacillus fermentum, Acetobacter pasteurianus. Moreover, correlation analysis showed that room temperature had a significant impact on the composition of the microbial community, along with other key seasonal environmental factors like total acid, pH, reducing sugar, and humidity. These results provide a theoretical foundation for regulating core microorganisms and environmental factors during fermentation, enhancing ZAV quality.

Dynamic changes of microbiota and metabolite of traditional Hainan dregs vinegar during fermentation based on metagenomics and metabolomics

Hainan dregs vinegar (HNDV) is a traditional fermented food in China that is renowned for its unique flavor. HNDV is one of the most popular vinegars in Southeast Asia. However, research on the microorganisms and characteristic metabolites specific to HNDV is lacking. This study investigated the changes in microbial succession, volatile flavor compounds and characteristic non-volatile flavor compounds during HNDV fermentation based on metagenomics and metabolomics. The predominant microbial genera were Lactococcus, Limosilactobacillus, Lactiplantibacillus, and Saccharomyces. Unlike traditional vinegar, l-lactic acid was identified as the primary organic acid in HNDV. Noteworthy flavor compounds specific to HNDV included 3-methylthiopropanol and dl-phenylalanine. Significant associations were observed between six predominant microorganisms and six characteristic volatile flavor compounds, as well as seven characteristic non-volatile flavor compounds. The present results contribute to the development of starter cultures and the enhancement of HNDV quality.

Identifying and characterization of novel broad-spectrum bacteriocins from the Shanxi aged vinegar microbiome: Machine learning, molecular simulation, and activity validation

Shanxi aged vinegar microbiome encodes a wide variety of bacteriocins. The aim of this study was to mine, screen and characterize novel broad-spectrum bacteriocins from the large-scale microbiome data of Shanxi aged vinegar through machine learning, molecular simulation and activity validation. A total of 158 potential bacteriocins were innovatively mined from 117,552 representative genes based on metatranscriptomic information from the Shanxi aged vinegar microbiome using machine learning techniques and 12 microorganisms were identified to secrete bacteriocins at the genus level. Subsequently, employing AlphaFold2 structure prediction and molecular dynamics simulations, eight bacteriocins with high stability were further screened, and all of them were confirmed to have bacteriostatic activity by the Escherichia coli BL21 expression system. Then, gene_386319 (named LAB-3) and gene_403047 (named LAB-4) with the strongest antibacterial activities were purified by two-step methods and analyzed by mass spectrometry. The two bacteriocins have broad-spectrum antimicrobial activity with minimum inhibitory concentration values of 6.79 μg/mL-15.31 μg/mL against Staphylococcus aureus and Escherichia coli. Furthermore, molecular docking analysis indicated that LAB-3 and LAB-4 could interact with dihydrofolate reductase through hydrogen bonds, salt-bridge forces and hydrophobic forces. These findings suggested that the two bacteriocins could be considered as promising broad-spectrum antimicrobial agents.

Impacts of Aspergillus oryzae 3.042 on the flavor formation pathway in Cantonese soy sauce koji

To investigate the mechanism of flavor formation during the traditional preparation Cantonese soy sauce koji (TP), the changes of microorganisms, physicochemical properties, and flavor compounds in TP were comprehensively and dynamically monitored by absolute quantitative methods. Results demonstrated that inoculating Aspergillus oryzae 3.042 in TP was crucial role in enhancing enzyme activity properties. Absolute quantification of flavor combined with multivariate statistical analysis yielded 5 organic acids, 15 amino acids, and 2 volatiles as significantly different flavors of TP. Amplicon sequencing and RT-qPCR revealed that the dominant genera were Staphylococcus, Weissella, Enterobacter, Lactic streptococci, Lactobacillus, and Aspergillus, which exhibited a increasing trend in TP. Correlation analysis exhibited that Staphylococcus and Aspergillus were the pivotal genera contributing to the enzyme activities and flavor of TP. The flavor formation network involved lipid and protein degradation, carbohydrate metabolism and other pathways. Simultaneously, TP can appropriately increase the fermentation time to improve product quality.

Investigation of bioactive compounds and their correlation with the antioxidant capacity in different functional vinegars

There are complex and diverse substances in traditional vinegars, some of which have been identified as biologically active factors, but the variety of functional compounds is currently restricted. In this study, it was aimed to determine the bioactive compounds in 10 typical functional vinegars. The findings shown that total flavonoids (0.21-7.19 mg rutin equivalent/mL), total phenolics (0.36-3.20 mg gallic acid equivalent/mL), and antioxidant activities (DPPH: 3.17-47.63 mmol trolox equivalent/L, ABTS: 6.85-178.29 mmol trolox equivalent/L) varied among different functional vinegars. In addition, the concentrations of the polysaccharides (1.17-44.87 mg glucose equivalent/mL) and total saponins (0.67-12.46 mg oleanic acid equivalent/mL) were determined, which might play key role for the function of tested vinegars. A total of 8 organic acids, 7 polyphenol compounds and 124 volatile compounds were measured and tentatively identified. The protocatechuic acid (4.81-485.72 mg/L), chlorogenic acid (2.69-7.52 mg/L), and epicatechin (1.18-97.42 mg/L) were important polyphenol compounds in the functional vinegars. Redundancy analysis indicated that tartaric acid, oxalic acid and chlorogenic acid were significantly positively correlated with antioxidant capacity. Various physiologically active ingredients including cyclo (Pro-Leu), cyclo (Phe-Pro), cyclo (Phe-Val), cyclo (Pro-Val), 1-monopalmitin and 1-eicosanol were firstly detected in functional vinegars. Principle component analysis revealed that volatiles profile of bergamot Monascus aromatic vinegar and Hengshun honey vinegar exhibited distinctive differences from other eight vinegar samples. Moreover, the partial least squares regression analysis demonstrated that 11 volatile compounds were positively correlated with the antioxidant activity of vinegars, which suggested these compounds might be important functional substances in tested vinegars. This study explored several new functionally active compounds in different functional vinegars, which could widen the knowledge of bioactive factor in vinegars and provide new ideas for further development of functional vinegar beverages.

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.

Recent advances in applying omic technologies for studying acetic acid bacteria in industrial vinegar production: A comprehensive review

Vinegar and related bioproducts containing acetic acid as the main component are among the most appreciated fermented foodstuffs in numerous European and Asian countries because of their exceptional organoleptic and bio-healthy properties. Regarding the acetification process and obtaining of final products, there is still a lack of knowledge on fundamental aspects, especially those related to the study of biodiversity and metabolism of the present microbiota. In this context, omic technologies currently allow for the massive analysis of macromolecules and metabolites for the identification and characterization of these microorganisms working in their natural media without the need for isolation. This review approaches comprehensive research on the application of omic tools for the identification of vinegar microbiota, mainly acetic acid bacteria, with subsequent emphasis on the study of the microbial diversity, behavior, and key molecular strategies used by the predominant groups throughout acetification. The current omics tools are enabling both the finding of new vinegar microbiota members and exploring underlying strategies during the elaboration process. The species Komagataeibacter europaeus may be a model organism for present and future research in this industry; moreover, the development of integrated meta-omic analysis may facilitate the achievement of numerous of the proposed milestones. This work might provide useful guidance for the vinegar industry establishing the first steps towards the improvement of the acetification conditions and the development of new products with sensory and bio-healthy profiles adapted to the agri-food market.

Hydrogels based on seafood chitin: From extraction to the development

Chitin is extensively applied in vast applications due to its excellent biological properties, such as biodegradable and non-toxic. About 50 % of waste generated during seafood processing is chitin. Conventionally, chitin is extracted via chemical method. However, it has many shortcomings. Many novel extraction methods have emerged, including enzymatic hydrolysis, microbial fermentation, ultrasonic or microwave-assisted, ionic liquids, and deep eutectic solvents. Chitin and its derivatives-based hydrogels have attracted much attention due to their excellent properties. Nevertheless, they all have many limitations. Therefore, the preparation and application of chitin and its derivatives-based hydrogels are still facing great challenges. This review focuses on the challenges and prospects for sustainable chitin extraction from seafood waste and the preparation and application of chitin and its derivatives-based hydrogels. First section summarizes the mechanism and application of several methods of extracting chitin. The different extraction methods were evaluated from the aspects of yield, degree of acetylation, and protein and mineral residuals. The shortcomings of the extraction methods are also discussed. Next section summarizes the preparation and application of chitin and its derivatives-based hydrogels. Overall, we hope this mini-review can provide a practical reference for selecting chitin extraction methods from seafood and applying chitin and its derivatives-based hydrogels.

Metabolomics and metatranscriptomics reveal the influence mechanism of endogenous microbe (Staphylococcus succinus) inoculation on the flavor of fermented chili pepper

This study integrated metabolomic and metatranscriptomic techniques to examine how the endogenous microbe, Staphylococcus succinus, influenced the essential flavor of fermented chili peppers. The mechanisms governing spontaneous fermentation and S. succinus-inoculated fermentation were also elucidated. Esters (e.g., ethyl undecanoate, isoamyl acetate, and methyl salicylate), terpenes (e.g., terpinen-4-ol), and alcohols (e.g., α-terpineol, linalool, and 4-methyl-3-heptanol) were found to be the key aroma-active compounds, aspartic acid (Asp) and glutamic acid (Glu) were identified as primary flavoring free amino acids. Notably, during the early stages of S. succinus-inoculated fermentation, the production of these essential metabolites was abundant, while their gradual increase over time was observed in the case of spontaneous fermentation. Metatranscriptomic analysis revealed that S. succinus inoculation could up-regulate genes related to glycolysis, amino acid metabolism, and aroma compound synthesis. These changes sequentially boosted the production of sweet and umami free amino acids, enhanced organic acid levels, increased unique aroma compound generation, and further improved the flavor and quality of the fermented chili peppers. Therefore, S. succinus inoculation can augment the sensory quality of fermented chili peppers, making this strain a promising candidate for Sichuan pickle fermentation starters.

Effect of inoculating Pichia spp. starters on flavor formation of fermented chili pepper: Metabolomics and genomics approaches

The influence of Pichia spp. on flavor formation and metabolic pathways during chili pepper fermentation was investigated in this study. Multiple omics approaches were employed, including metabolomics analysis to identify volatile and non-volatile flavor compounds, and genomic analysis to gain insights into the underlying molecular mechanism driving flavor formation of chili peppers inoculated with Pichia spp. The results showed that inoculation with Pichia spp. accelerated fermentation process of chili peppers compared to spontaneous fermentation. Metabolomics analysis showed P. fermentans promoted characteristic terpenes [e.g., (Z)-β-ocimene and linalool], L-glutamate, gamma-aminobutyric acid, and succinate production, while P. manshurica produced more alcohols (e.g., isoamyl alcohol and phenylethyl alcohol) and phenols (e.g., 4-ethylguaiacol and 2-methoxy-4-methylphenol). Genomics analysis revealed that a substantial portion of the genes in Pichia spp. were associated with amino acid and carbohydrate metabolism. Specifically, the pathways involved in amino acid metabolism and the release of glycoside-bound aromatic compounds were identified as the primary drivers behind the unique flavor of fermented chili peppers, facilitated by Pichia spp.

Optimization of the Process for Green Jujube Vinegar and Organic Acid and Volatile Compound Analysis during Brewing

Healthy fruit vinegar has become very popular recently in China. This study aimed to produce fruit vinegar with a good taste, high nutritional value, and strong functional properties from green jujube. This study investigated the optimization of the process for green jujube vinegar using response surface methodology. The optimum fermentation parameters for green jujube vinegar were determined as follows: initial alcoholicity 6%, acetobacter 8%, fermentation temperature 32 °C, and time 7 d. The organic acids of the optimized sample were evaluated by HPLC, and the volatile substances were identified and analyzed by HS-SPME and GC-MS during the fermentation and aging of the green jujube vinegar. The results showed that the variation trends of the different organic acids during the making of the green jujube vinegar were significantly different. Organic acids are the key flavor compounds of green jujube vinegar, and their changes were mainly attributed to microbial metabolism. In particular, the green jujube vinegar stood out in terms of volatile aroma compounds, including a total of 61 volatile compounds whose major components were acetic acid, isoamyl acetate, ethyl acetate, 3-hydroxy-2-butanone, methyl palmitate, and ethanol. The results can provide theoretical support for the production of green jujube vinegar.

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.

Isolation and characterization of a gas-producing and acid-resistant bacterium from spoiled vinegar

To understand the deterioration of vinegar that has frequently occurred in China recently and to address such a concern, the physicochemical indicators and bacterial structure of the spoiled vinegar collected from Sichuan were preliminarily investigated. Results showed that Lactobacillaceae was most likely responsible for the decrease of vinegar total sugar and furfural, through which total acid and furfuryl alcohol were generated. Then, an unreported difficult-to-cultivate gas-producing bacterium named Z-1 was isolated using a modified MRS medium. Strain Z-1 was identified as Acetilactobacillus jinshanensis subsp. aerogenes on the basis of physiological, biochemical, molecular biological and whole genome analyses. According to the investigation, such species was present throughout the fermentation process and not limited in Sichuan. The analysis of genetic diversity indicated that all the obtained A. jinshanensis isolates displayed high sequence similarity and an absence of recombination. Although it demonstrated acid resistance, Z-1 could be completely deactivated through heating (60 °C). Based on the above results, suggestions for safe production are made for vinegar enterprises.

The need for an integrated multi-OMICs approach in microbiome science in the food system

Microbiome science as an interdisciplinary research field has evolved rapidly over the past two decades, becoming a popular topic not only in the scientific community and among the general public, but also in the food industry due to the growing demand for microbiome-based technologies that provide added-value solutions. Microbiome research has expanded in the context of food systems, strongly driven by methodological advances in different -omics fields that leverage our understanding of microbial diversity and function. However, managing and integrating different complex -omics layers are still challenging. Within the Coordinated Support Action MicrobiomeSupport (https://www.microbiomesupport.eu/), a project supported by the European Commission, the workshop "Metagenomics, Metaproteomics and Metabolomics: the need for data integration in microbiome research" gathered 70 participants from different microbiome research fields relevant to food systems, to discuss challenges in microbiome research and to promote a switch from microbiome-based descriptive studies to functional studies, elucidating the biology and interactive roles of microbiomes in food systems. A combination of technologies is proposed. This will reduce the biases resulting from each individual technology and result in a more comprehensive view of the biological system as a whole. Although combinations of different datasets are still rare, advanced bioinformatics tools and artificial intelligence approaches can contribute to understanding, prediction, and management of the microbiome, thereby providing the basis for the improvement of food quality and safety.

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.

Role of bacterial community succession in flavor formation during Sichuan sun vinegar grain (Cupei) fermentation

Sichuan sun vinegar (SSV) is a traditional Chinese vinegar with a unique flavor and it is fermented with bran as the main raw material. In the present study, we explored the bacterial community succession in fermented grains (Cupei) during SSV production. High-throughput sequencing results showed that bacterial community richness and diversity peaked on day 7 of fermentation. Lactobacillus and Acetobacter were the dominant bacteria throughout the fermentation process. However, Acetobacter, Cupriavidus, Sphingomonas, Pelomonas, and Lactobacillus were the most abundant genera in the late phase of fermentation on day 17. The boundaries of trilateral co-fermentation were determined through cluster analysis. Days 1-3 were considered the early fermentation stage (starch saccharification), days 5-11 were the middle fermentation stage (alcoholic fermentation), and days 13-17 represented the late fermentation stage (acetic acid fermentation). Changes in flavor compounds during Cupei fermentation were subsequently analyzed and a total of 86 volatile compounds, 9 organic acids, and 17 amino acids were detected. Although acetic acid, lactic acid, alcohols, and esters were the main metabolites, butyrate was also detected. Correlation analysis indicated that 20, 21, and 28 microorganisms were positively correlated with the abundance of amino acids, organic acids, and volatile flavor compounds, respectively. We further explored the microbial and metabolic mechanisms associated with the dominant volatile flavor compounds during SSV fermentation. Collectively, the findings of the current study provide detailed insights regarding the fermentation mechanisms of SSV, which may prove relevant for producing high-quality fermented products.

Changes in vinegar quality and microbial dynamics during fermentation using a self-designed drum-type bioreactor

The bioreactor based on solid-state fermentation technology has been developed for vinegar production, standardization of fermentation process and stabilization of vinegar quality. The microbial community diversity, and volatile compounds of six cultivars of vinegar samples fermented in a self-designed solid-state fermentation bioreactors were investigated using Illumina MiSeq platform and gas chromatography mass spectrometry (GC-MS) technology. The correlations between the richness and diversity of microbiota and volatile profiles, organic acids, as well as physicochemical indicators were explored by R software with the coplot package. The findings indicated that Acetobacter, norank-c-Cyanobacteria, and Weissella played key roles during fermentation process. Norank-f-Actinopolyporaceae, norank-c-Cyanobacteria, Pediococcus, and Microbacterium had significant correlations with the physicochemical characteristics. The most common bacterial species were associated with a citric acid content, whereas the least number of bacterial species correlated with malic acid content. Findings could be helpful for the bioreactor optimization, and thus reaching the level of pilot scale and industrialization.

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.

Exploration of the roles of microbiota on biogenic amines formation during traditional fermentation of Scomber japonicus

The influence of microbiota composition and metabolisms on the safety and quality of fermented fish products is attracting increasing attention. In this study, the total viable count (TVC), pH, total volatile base nitrogen (TVB-N) as well as biogenic amines (BAs) of traditional fermented Scomber japonicus (zaoyu) were quantitatively determined. To comprehend microbial community variation and predict their functions during fermentation, 16S rRNA-based high-throughput sequencing (HTS) and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) were employed, respectively. The fresh samples stored without fermentation were used as controls. TVC and TVB-N values increased rapidly, and the content of BAs exceeded the permissible limit on day 2 in the controls, indicating serious spoilage of the fish. In contrast, a slower increase in TVC and TVB-N was observed and the content of BAs was within the acceptable limit throughout the fermentation of zaoyu. Significant differences in microbiota composition were observed between zaoyu and the controls. The bacterial community composition of zaoyu was relatively simple and Lactobacillus was identified as the dominant microbial group. The accumulation of histamine was inhibited in zaoyu, which was positively correlated with the relative abundance of Vibrio, Enterobacter, Macrococcus, Weissella, et al. based on Redundancy analysis (RDA), while Lactobacillus showed a positive correlation with tyramine, cadaverine, and putrescine. Functional predictions, based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis, revealed that the relative abundance of metabolic function exhibited a decreasing trend with prolonged fermentation time and the abundance of metabolism-related genes was relatively stable in the later stage of fermentation. Those metabolisms related to the formation of BAs like histidine metabolism and arginine metabolism were inhibited in zaoyu. This study has accompanied microbiota analysis and functional metabolism with the accumulation of BAs to trace their correspondences, clarifying the roles of microorganisms in the inhibition of BAs during fermentation of Scomber japonicus.

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.

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.

Insights into carbon and nitrogen metabolism and antioxidant potential during vegetative phase in quinoa (Chenopodium quinoa Willd.)

The present investigation was carried out to understand the impact of carbon and nitrogen metabolism in quinoa genotypes IC411824, IC411825, EC507747 and EC507742 during pre-anthesis stage. It was observed that activities of acid invertase, sucrose synthase (cleavage) and sucrose phosphate synthase (SPS) increased up to 75 days after sowing (DAS) and this might be responsible for providing reducing sugars for the development of vegetative parts. Enhanced activities of nitrate reductase, glutamate synthase, glutamine synthetase during vegetative growth of leaves and stem at 90 DAS assist the fixation of ammonia on glutamate molecule to synthesize amino acids at early stages. However, the glutamate dehydrogenase and nitrite reductase play a central role in the re-assimilation of amides from the amino group of asparaginase. As a result, these photosynthetic products will be responsible for providing both the energy and the C-skeletons for ammonium assimilation during amino acid biosynthesis. Leaves and stem of IC411824 and IC411825 had higher total phenol and total flavonoid content. DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity was found to be higher in leaves of IC411825 and in stem of IC411824 and IC411825 indicating their capability to act as natural antioxidants.