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This study utilized metabolomics and metagenomics to investigate the microbial composition and functions in low- and high-salt Chinese horse bean-chili pastes (CHCPs). The results showed that 25 key metabolites were identified to distinguish the flavor attributes between the two samples. Leuconostoc was identified as the dominant microbiota in low-salt CHCP, while Pantoea prevailed in the high-salt CHCP. Compared to traditional high-salt fermentation, low-salt and inoculated fermentation promoted the increase in the relative abundances of Companionlactobacillus, Levilactobacillus, Tetragenococcus, Zygosaccharomyces and Wickerhamiella as well as the enrichment of carbohydrate and amino acid metabolic pathways, which contributed to the enhancement of characteristic flavor compounds. Further metabolic pathway reconstruction elucidated 21 potential microbial genera associated with the formation of key metabolites, such as Leuconostoc, Levilactobacillus, Pantoea, and Pectobacterium. This study may provide insights for optimizing the fermentation process and improving the flavor quality of low-salt CHCP and similar fermentation products. KEYWORDS: Low-salt fermentation Hight-salt fermentation Chinese horse-bean chili paste Flavor formation Metabolomics Metagenomics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The unique flavors of fermented foods significantly influence consumer purchasing choices, prompting widespread scientific interest in the flavor development process. Fermented rice and wheat foods are known for their unique flavors and they occupy an important place in the global diet. Many of these are produced on an industrial scale using starter cultures, whereas others rely on spontaneous fermentation, homemade production, or traditional activities. Microorganisms are key in shaping the sensory properties of fermented products through different metabolic pathways, thus earning the title "the essence of fermentation." Therefore, this study systematically summarizes the key microbial communities and their interactions that contribute positively to iconic fermented rice and wheat foods, such as steamed bread, bread, Mifen, and rice wine. This study revealed the mechanism by which these core microbial communities affect flavor and revealed the strategies of core microorganisms and related enzymes to enhance flavor during fermentation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. We confirm that there are no financial, personal, or professional interests that could potentially bias our research findings or influence the interpretation of the results presented in the manuscript. Additionally, we have not received any financial support, grants, or other forms of compensation that could be perceived as influencing the objectivity of our research. Furthermore, we declare that there are no relationships or affiliations with any organizations, companies, or individuals that could pose a conflict of interest for the content of the manuscript. We affirm that this Declaration of Interest accurately reflects our commitment to transparency and integrity in research, and we stand by the authenticity and impartiality of the findings reported in the manuscript., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Sour bamboo shoots are a traditional fermented delicacy that has garnered appreciation both domestically and internationally. This study investigates the intricate dynamics of microbial communities and volatile flavor compounds primarily derived from salted and pickled bamboo shoots during the fermentation process of Phyllostachys purpurea (PP). The dynamics of microorganisms and volatile flavor compounds were thoroughly examined initially using conventional isolation and cultivation methods in conjunction with high-throughput sequencing (HTS), headspace solid-phase microextraction (HS-SPME), and gas chromatography-mass spectrometry (GC-MS). In addition, we analyzed the core microorganisms responsible for modulating the volatile flavor profile. Our findings revealed 60 volatile compounds, 14 of which were the predominant contributors to the aroma of fermented PP. This group primarily comprised alcohols, aldehydes, and olefins. Notably, our investigation identified Lactobacillus and Candida as the dominant microbial genera during the middle and late stages of fermentation. These two genera exert a significant influence on the formation of characteristic aromas. Furthermore, we discovered that acids, sugars, and proteins pivotally influence the succession of microorganisms. Specifically, acids and soluble sugars drove the transition of Lactococcus to Lactobacillus and Pediococcus, whereas soluble proteins facilitated fungal succession from Candida to Kazachstania and Issatchenkia. These insights shed light on the community structure and succession patterns of flavor compounds throughout the PP fermentation process. Ultimately, they provide a foundation for optimizing the fermentation process and ensuring quality control in the production of sour bamboo shoots., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background: Microbiota succession determines the flavor and quality of fermented foods. Quantitative PCR-based quantitative microbiome profiling (QMP) has been applied broadly for microbial analysis from absolute abundance perspectives, transforming microbiota ratios into counts by normalizing 16S ribosomal RNA (16S rRNA) gene sequencing data with gene copies quantified by quantitative PCR. However, the application of QMP in fermented foods is still limited., Results: QMP elucidated microbial succession of Taiwanese pickled cabbage. In the spontaneous first-round fermentation (FR), the 16S rRNA gene copies of total bacteria increased from 6.1 to 10 log copies mL -1 . The dominant lactic acid bacteria genera were successively Lactococcus, Leuconostoc and Lactiplantibacillus. Despite the decrease in the proportion of Lactococcus during the succession, the absolute abundance of Lactococcus still increased. In the backslopping second-round fermentation (SR), the total bacteria 16S rRNA gene copies increased from 7.6 to 9.9 log copies mL -1 . The addition of backslopping starter and vinegar rapidly led to a homogenous microbial community dominated by Lactiplantibacillus. The proportion of Lactiplantibacillus remained consistently around 90% during SR, whereas its absolute abundance exhibited a continuous increase. In SR without vinegar, Leuconostoc consistently dominated the fermentation., Conclusion: The present study highlights that compositional analysis would misinterpret microbial dynamics, whereas QMP reflected the real succession profiles and unveiled the essential role of vinegar in promoting Lactiplantibacillus dominance in backslopping fermentation of Taiwanese pickled cabbage. Quantitative microbiome profiling (QMP) was found to be a more promising approach for the detailed observation of microbiome succession in food fermentation compared to compositional analysis. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

Temperature is an important driving force that shapes the texture of fermented vegetables through driving the molecular distribution and microbial invasion between the liquid phase (brine) and the solid phase (vegetables) during fermentation. The objective of this study was to investigate the texture softening by investigating firmness, microstructure, physicochemical properties, molecular distribution and microbial community between brine and vegetables of Paocai as affected by fermentation temperatures of 10 °C, 20 °C and 30 °C. Results demonstrated that, compared with 10 °C and 30 °C, 20 °C attenuated softening of Paocai by restraining microbial invasion and suppressing pectinolysis. Moreover, at 20 °C, a balanced molecular distribution and microbial community were achieved between vegetables and brine, thus accomplishing acid-production fermentation. By contrast, 10 °C and 30 °C promoted nonfermentative microbial genera, retarding fermentation. This study provided an understanding of the divergent influence of temperature on quality formation of fermented vegetables during fermentation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study aimed to improve the quality of fermented fish Zaoyu by inoculating different starters (Chuzhai starter, Aroma starter and Sweetness starter), and examining the role of key microorganisms. High-throughput sequencing showed the microbial composition of Aroma starter was similar to Sweetness starter, but both were different from Chuzhai starter. Compared to traditional fermentation, inoculated fermentation with Aroma starter and Sweetness starter strengthened the color of Zaoyu by Maillard reaction and softened the muscle by degrading muscle fibers, endomysium and epicardium. Additionally, the taste and odor of Zaoyu were obviously improved, because the proportion of sweet, umami and aroma compounds increased by 2.51 %, 7.09 %, and 22.94 %, respectively. Correlation analysis combined with metabolic functions showed key microorganisms, such as Trichococcus, Rhizopus, Saccharomycopsis, Saccharomyces, etc., improved the quality mainly by promoting sugar production and conversion, and protein degradation. Overall, Aroma starter and Sweetness starter were superior in improving the quality of Zaoyu., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

White colony-forming yeast (WCFY) forms white colonies on kimchi during fermentation, causing off-flavors and quality deterioration, which are significantly damaging to kimchi industry. To study its impact, kimchi samples were inoculated with representative WCFYs (Candida sake, Debaryomyces hansenii, Kazachstania servazzii, and Pichia kudriavzevii) and monitored for 50 days at 15 °C using high-throughput DNA sequencing and gas chromatography/mass spectrometry. Dominant bacteria at the end of fermentation were Companilactobacillus and Latilactobacillus in the control and WCFY-inoculated samples, respectively. The fungal communities of control sample remained stable, whereas those for WCFY-inoculated samples showed Kazachstania or Pichia dominance. Metabolite analysis revealed significant increases in glycerol, erythritol, and myo-inositol in WCFY-inoculated samples. Correlation analysis showed that Lactococcus and Weissella were negatively correlated with Kazachstania. This study underscores ecological role of WCFYs in kimchi fermentation, particularly their impact on microbial communities and metabolites, suggesting the need for strategies that control WCFY growth to improve kimchi quality., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Suantangzi is a fermented corn food product with Manchu characteristics from Liaoning Province, China. To analyze the microbial diversity and flavor compounds in Suantangzi dough, this study utilized high-throughput sequencing of the 16S rRNA and internal transcribed spacer regions, high-performance liquid chromatography, and gas chromatography time-of-flight mass spectrometry. Spearman correlation analysis and random forest model were conducted to investigate the correlation between the dominant genera and flavor compounds. A total of 267 and 123 bacterial and fungal genera, respectively, were identified. Flavor compound analysis identified 7 and 156 organic acids and other flavor compounds, respectively, and partial least squares discriminant analysis was used to screen 22 differential flavor compounds. Additionally, Paucilactobacillus, Pediococcus, and Tausonia genera were speculated to produce different flavors in Suantangzi dough made in different regions. These findings provide a theoretical foundation for microbial community dynamics and the formation of key flavor compounds in Suantangzi dough., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The diet in early life is essential for the growth and intestinal health later in life. However, beneficial effects of a diet enriched in branched short-chain fatty acids (BSCFAs) for infants are ambiguous. This study aimed to develop a novel fermented protein food, enriched with BSCFAs and assess the effects of dry and wet ferment products on young pig development, nutrient absorption, intestinal barrier function, and gut microbiota and metabolites. A total of 18 young pigs were randomly assigned to three groups. The dry corn gluten-wheat bran mixture (DFCGW) and wet corn gluten-wheat bran mixture (WFCGW) were utilized as replacements for 10% soybean meal in the basal diet. Our results exhibited that the WFCGW diet significantly increased the growth performance of young pigs, enhanced the expression of tight junction proteins, and regulated associated cytokines expression in the colonic mucosa. Simultaneously, the WFCGW diet led to elevated levels of colonic isobutyric and isovaleric acid, as well as the activation of GPR41 and GPR109A. Furthermore, more potential probiotics including Lactobacillus , Megasphaera , and Lachnospiraceae_ND3007_group were enriched in the WFCGW group and positively associated with the beneficial metabolites such as 5-hydroxyindole-3-acetic acid. Differential metabolite KEGG pathway analysis suggested that WFCGW might exert gut health benefits by modulating tryptophan metabolism. In addition, the WFCGW diet significantly increased ghrelin concentrations in serum and hypothalamus and promoted the appetite of young pigs by activating hypothalamic NPY/AGRP neurons. This study extends the knowledge of BSCFAs and provides a reference for the fermented food application in the infant diet.

Environmental-origin microbiota significantly influences Red Heart Qu (RH_Qu) stratification, but their microbial migration and metabolic mechanisms remain unclear. Using high-throughput sequencing and metabolomics, we divided the stratification of RH_Qu into three temperature-based stages. Phase I features rising temperatures, causing microbial proliferation and a two-layer division. Phase II, characterized by peak temperatures, sees the establishment of thermotolerant species like Bacillus, Thermoactinomyces, Rhodococcus, and Thermoascus, forming four distinct layers and markedly altering metabolite profiles. The Huo Quan (HQ), developing from the Pi Zhang (PZ), is driven by the tyrosine-melanin pathway and increased MRPs (Maillard reaction products). The Hong Xin evolves from the Rang, associated with the phenylalanine-coumarin pathway and QCs (Quinone Compounds) production. Phase III involves the stabilization of the microbial and metabolic profile as temperatures decline. These findings enhance our understanding of RH_Qu stratification and offer guidance for quality control in its fermentation process., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background: Yangjiang douchi (YD) is a traditional fermented soybean product, which is popular in Chinese cuisine for its unique flavor. However, due to its high salt content and unstable flavor, its competitiveness in the international market is gradually weakening. Microorganisms have a key role in the production process of YD because it is a fermented food but the effect of microorganisms on the volatile compounds of YD is also not currently clear., Results: In this paper, aroma compounds and microbial diversity in different fermentation stages of YD were analyzed using gas chromatography-mass spectrometry/olfactometry (GC-MS/O) and IlluminaMiseq system sequencing. A total of 78 aroma-active compounds were detected throughout the fermentation process and they influenced the formation of flavor in YD. Fungi flora were relatively single in YD, and bacteria were rich and varied. A total of 418 species of bacteria were present during fermentation, with unclassified_Staphylococcus, Staphylococcus_kloosii, and Bacillus_velezensis_Bacillus predominating. There were 25 species of fungi at the species level, and Aspergillus minisclerotigenes (OTU 4) played a dominant role in the whole fermentation process., Conclusion: Staphylococcus and Bacillus in the bacterial genus were strongly correlated with most flavor compounds detected, and A. minisclerotigenes in the fungi were more relevant to flavor compounds. This research provides a theoretical basis for the enhancement of the flavor of traditional fermented douchi in China. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

Laotan Suancai, a popular traditional Chinese fermented vegetable, is manufactured in the industry via four fermentation rounds. However, the differences in flavor quality of Laotan Suancai from the four fermentation rounds and the causes of this variation remain unclear. Metabolome analysis indicated that the different content of five taste compounds and 31 aroma compounds caused the differences in flavor quality among the variated fermentation rounds of Laotan Suancai. Amplicon sequencing indicated that the microbial succession exhibited a certain pattern during four fermentation rounds and further analysis unveiled that organic acids drove the microbiota shift to more acid-resistant populations. Spearman correlation analysis highlighted that seven core microbes may be involved in the formation of differential flavor and the corresponding metabolic pathways were reconstructed by function prediction. Our findings offer a novel perspective on comprehending the deterioration of flavor quality across the fermentation rounds of Laotan Suancai., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that influenced the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

The study investigated the effect of different sodium chloride (NaCl) concentrations (10%, 15%, and 20%) on the ripening fermentation of Pixian-Douban, a traditional fermented condiment. The results showed that NaCl affected the dynamics of physicochemical parameters, volatile components, fatty acids, amino metabolites, organic acids, and microbial composition, and their dynamic modes were different. After 253 days fermentation, the 10% NaCl Pixian-Douban had significantly (p < 0.05) higher levels of total organic acids (20,308.25 mg/kg), amino metabolites (28,144.96 mg/kg), and volatiles (3.36 mg/kg) compared to 15% and 20% NaCl Pixian-Douban. Notably, the possible health risk associated with high concentration of biogenic amines in 10% NaCl Pixian-Douban is of concern. Moreover, correlation analyses indicated that the effect of NaCl on the quality of Pixian-Douban may be mainly related to bacteria. This study deepens the knowledge about the role of NaCl in ripening fermentation of Pixian-Douban and contributes to develop low-NaCl Pixian-Douban product., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Paojiao, a typical Chinese traditional fermented pepper, is favored by consumers for its unique flavor profile. Microorganisms, organic acids, amino acids, and volatile compounds are the primary constituents influencing the development of paojiao's flavor. To elucidate the key flavor compounds and core microorganisms of Qicaipaojiao (QCJ), this study conducted a comprehensive analysis of the changes in taste substances (organic acids and amino acids) and volatile flavor compounds during QCJ fermentation. Key flavor substances in QCJ were identified using threshold aroma value and odor activity value and the core microorganisms of QCJ were determined based on the correlation between dominant microorganisms and the key flavor substances. During QCJ fermentation, 16 key taste substances (12 free amino acids and 4 organic acids) and 12 key aroma substances were identified. The fermentation process involved 10 bacteria and 7 fungal genera, including Lactiplantibacillus, Leuconostoc, Klebsiella, Pichia, Wickerhamomyces, and Candida. Correlation analysis revealed that the core functional microorganisms encompassed representatives from 8 genera, including 5 bacterial genera (Lactiplantibacillus, Weissella, Leuconostoc, Klebsiella, and Kluyvera) and 3 fungal genera (Rhodotorula, Phallus, and Pichia). These core functional microorganisms exhibited significant correlations with approximately 70 % of the key flavor substances (P < 0.05). This study contributes to an enhanced understanding of flavor formation mechanisms and offers valuable insight into flavor quality control in food fermentation processes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Paocai is a traditional Chinese fermented vegetable food. As the most important ingredient, salt has crucial effects on the bacterial community and volatile compounds of paocai. To demonstrate the effects of salt on the fermentation of paocai, the bacterial composition and volatile compounds were investigated using high-throughput sequencing and gas chromatography-mass spectrometry (GC-MS)., Results: The salt had no significant effects on the bacterial community at the phylum level. Proteobacteria and Bacteroidetes gradually decreased during the fermentation, and Firmicutes gradually increased as the dominant bacteria in the late stage of fermentation. At the genus level, Lactobacillus and Lactococcus gradually increased in relative abundance during the fermentation and became the dominant bacteria in paocai. High salt levels can contribute to the growth of Lactobacillus, which became the dominant genus in paocai. The salt concentration affected the profiles of volatile compounds in paocai after fermentation. A total of 42 volatile components were detected by GC-MS, among which phenols, aldehydes, and nitriles were the main ones. A high salt concentration will increase the volatile compound content, mainly aldehydes and alcohols, and improve the flavor of paocai. At the same time, the electronic tongue analysis also showed that a high salt concentration made a major contribution to the flavor of paocai., Conclusions: These data are helpful to elucidate the effects of salt on the quality of paocai and contribute to improving the quality and reducing the use of salt. © 2021 Society of Chemical Industry., (© 2021 Society of Chemical Industry.)

Background: As a Chinese traditional flavor condiment, Pixian Douban (PXDB) is produced using a traditional open fermentation process. In this study, an experimental fermentation of PXDB was conducted at 40 °C for 90 days in a closed system, which has not been applied to PXDB production. The flavor, microbial community and correlations of the samples in the closed system were compared with those in the traditional fermentation., Results: The content of organic acids and free amino acids in the closed fermentation of constant temperature (CFCT) achieved the standards of product quality, although they were lower than those in the traditional fermentation. Of the 140 detected aroma components, 98 were shared in the two fermentation processes. Enterobacter, Bacteroides and Megamonas were the core microbial genera related to 26 flavor components in the traditional fermentation, while Pantoea was the core microbial genus related to 18 flavor components in CFCT. The CFCT has its own unique advantages over traditional fermentation in forming aromas. It produced a greater impact on the succession of fungi than those of bacteria after changing traditional fermentation to CFCT. The influence of microorganisms on the formation of flavor components was relatively more balanced in CFCT, while the changed fermentation process impacted greatly on the functions of Zygosaccharomomyces and Pichia but little on those of Sphingomonas, Megamonas and Parabacteroides., Conclusion: The study indicated that it was feasible to ferment PXDB in the closed system, and provides a basis to realize controllable PXDB production. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

Effect of capsaicinoids in hot pepper powder (HP) contains various chemical compounds, including capsaicin and dihydrocapsaicin, which are the main ingredients of the spicy taste. To evaluate the effect of HP on the microbial community in kimchi fermentation, kimchi [kimchi-HP, kimchi-HPE and kimchi-HPER made by adding HP, HP alcohol extract (HPE) and HPE residues (HPER)] was fermented at 4°C for 28 days. The pH and titratable acidity of the samples and the number of bacteria changed with fermentation time. Kimchi-HPER had significantly higher total viable and lactic acid bacteria (LAB) than other samples after 28 days of fermentation. The capsaicinoids content did not differ before and after fermentation, whereas the major free sugar content decreased, and the mannitol content increased. The principal component analysis (PCA) biplots showed similar patterns between kimchi-HP and -HPE. It was confirmed that Leuconostoc and Weissella were related to the initial fermentation, and Lactobacillus was involved in late fermentation. Kimchi-HP and kimchi-HPE increased the ratio of Lactobacillus sakei and decreased that of Leuconostoc mesenteroides compared to kimchi-HPER. Overall, these results revealed that capsaicinoids contained in HP affected Lactobacillus proliferation and mannitol increase during kimchi fermentation., (© 2021 Institute of Food Technologists®.)

Table olives are considered the most widespread fermented food in the Mediterranean area and their consumption is expanding all over the world. This fermented vegetable can be considered as a natural functional food thanks to their high nutritional value and high content of bioactive compounds that contribute to the health and well-being of consumers. The presence of bioactive compounds is strongly influenced by a complex microbial consortium, traditionally exploited through culture-dependent approaches. Recently, the rapid spread of omics technologies has represented an important challenge to better understand the function, the adaptation and the exploitation of microbial diversity in different complex ecosystems, such as table olives. This review provides an overview of the potentiality of omics technologies to in depth investigate the microbial composition and the metabolic processes that drive the table olives fermentation, affecting both sensorial profile and safety properties of the final product. Finally, the review points out the role of omics approaches to raise at higher sophisticated level the investigations on microbial, gene, protein, and metabolite, with huge potential for the integration of table olives composition with functional assessments., (Copyright © 2020. Published by Elsevier Ltd.)

Background: Serofluid dish, a traditional Chinese fermented food, possesses unique flavors and health beneficial effects. These properties are likely due to the sophisticated metabolic networks during fermentation, which are mainly driven by microbiota. However, the exact roles of metabolic pathways and the microbial community during this process remain equivocal., Results: Here, we investigated the microbial dynamics by next-generation sequencing, and outlined a differential non-targeted metabolite profiling in the process of serofluid dish fermentation using the method of hydrophilic interaction liquid chromatography column with ultra-high-performance liquid chromatography-quadruple time-of-flight mass spectrometry. Lactobacillus was the leading genus of bacteria, while Pichia and Issatchenkia were the dominant fungi. They all accumulated during fermentation. In total, 218 differential metabolites were identified, of which organic acids, amino acids, sugar and sugar alcohols, fatty acids, and esters comprised the majority. The constructed metabolic network showed that tricarboxylic acid cycle, urea cycle, sugar metabolism, amino acids metabolism, choline metabolism, and flavonoid metabolism were regulated by the fermentation. Furthermore, correlation analysis revealed that the leading fungi, Pichia and Issatchenkia, were linked to organic acids, amino acid and sugar metabolism, flavonoids, and several other flavor and functional components. Antibacterial tests indicated the antibacterial effect of serofluid soup against Salmonella and Staphylococcus., Conclusion: This work provides new insights into the complex microbial and metabolic networks during serofluid dish fermentation, and a theoretical basis for the optimization of its industrial production. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

Background: Suansun is a traditional salt-free fermented bamboo shoot product that has been widely consumed as a cooking ingredient in south China for centuries. The aim of this study was to evaluate and compare the microbial and metabolic diversity in samples of two kinds of suansun, namely Guangdong suansun (GD) and Yunnan suansun (YN), using high-throughput sequencing (HTS) and headspace solid-phase microextraction-gas chromatograph-mass spectrometry (HS-SPME/GC-MS), respectively, and then to assess the influence of environmental factors on the microbial communities., Results: The results showed that Lactobacillus and Serratia were the most abundant bacterial genera in both the GD and YN groups. For the fungi, Pichia, Candida, and Debaryomyces were the major genera in the GD group, whereas Pichia and Zygosaccharomyces were the dominant genera in the YN group. The canonical correlation analysis (CCA) results demonstrated that three environmental factors - temperature, longitude, and altitude - play a more important role in affecting the microbial community composition of suansun than physical and chemical factors. The fugal community composition was more influenced by environmental factors than the bacterial community. The volatile profile of the GD group differed from that of the YN group, and the difference was mainly reflected in the relative alcohol, aldehyde, ester, and aromatic compound content., Conclusions: This study provided insights into the microbial and metabolic profiles of suansun products. The findings might be useful for the improvement and standardization of suansun production. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

A 16S rRNA next-generation sequencing technique was applied to investigate the microbial diversity and liquid chromatography-tandem mass spectrometry was used to identify glutamyl peptide profiles of 10 Thai fermented freshwater fish (Pla-ra) samples. A total of 12 genera of bacteria were able to be detected, with Tetragenococcus spp., Staphylococcus spp., and Lactobacillus spp. dominating. Of the 18 glutamyl peptides analyzed, 17 were found, even though the amounts detected were lower than the taste threshold. Despite this, an increase in mouthfulness sensation, reflecting kokumi activity, was clearly identified in most of the samples, which might be because of a synergistic effect of different sub-threshold compounds present in the samples. In principle component analysis, the relationship between microorganisms and glutamyl peptide generation was observed, especially between Tetragenococcus spp. and Lentibacillus spp. and the generation of γ-Glu-Val-Gly. Correlations between microbial diversity and the generation of taste enhancers were identified in this study.

Fermented foods have unique microbiota and metabolomic profiles that can support dietary diversity, digestion, and gut health of consumers. Laowo ham (LWH) is an example of an indigenous fermented food from Southwestern China that has cultural, ecological, economic, and health significance to local communities. We carried out ethnobiological surveys coupled with metagenomic and metabolomic analyses using GC-TOF-MS and UPLC-QTOF-MS to elucidate the microbiota and metabolic profiles of LWH samples at different ripening stages. The results from high-throughput sequencing showed a total of 502 bacterial genera in LWH samples with 12 genera of bacteria and 6 genera of fungi identified as dominant groups. This is the first study to our knowledge to report the bacteria of Lentibacillus and Mesorhizobium along with fungi Eremascus and Xerochrysium on a fermented meat product. Findings further revealed that the metabolite profiles among LWH samples were significantly different. In total, 27 and 30 metabolites from GC-TOF-MS and UPLC-QTOF-MS analysis, respectively, were annotated as highly discriminative metabolites. Among the differential compounds, the relative contents of most amino acids showed the highest in the LWH sample ripened for two years, while some metabolites with potential therapeutic effects such as levetiracetam were the most abundant in the LWH sample ripened for three years. The correlation analysis indicated that the dominant microbes were closely related to differential metabolites, highlighting the importance of their functional characterization. Findings indicate that the consumption of LWH contributes to microbiological and chemical diversity of human diets as well as suggests efficacy of combining GC-MS and LC-MS to study the metabolites in dry-cured meat products.

As the spirit of Chinese Sichuan cuisine, Pixian Doubanjiang (DBJ) is an indispensable flavor condiment and has been widely used for centuries, which is made from red pepper (Capsicum annuum L.), meju and brine after open ripening fermentation. In this study, the physicochemical factors including pH value, titratable acidity, moisture, organic acids, free amino acids and volatile components etc., were identified; the compositions of microbial communities and representative microbiota were investigated; the correlations between physicochemical factors and representative microbial taxa were analyzed, at different ripening stages. The results indicated that the organic acids were all relatively stable starting from the 12th month; most of the free amino acids (17/20) reached the peak concentrations at the 6th month and 28 volatile components were considered as major odorant flavors in DBJ. Zygosaccharomyces rouxii could be the key microorganism associated with 10 volatile components to the maturing of DBJ flavor. The comprehensive analysis on the physicochemical changes related to the succession of microbiota is expected to help us understand the maturing of the taste and flavor in DBJ production., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The quality of fermented soybeans can be determined by diverse metabolites produced by microorganisms. Mass spectrometry-based metabolomic approach was applied to investigate the differences in volatile and non-volatile metabolite profiles of fermented soybeans by different microorganisms [e.g., molds, yeasts, lactic acid bacteria (LAB), and other bacteria]. The partial least squares-discriminant analysis (PLS-DA) for volatile metabolites profiles indicated that the fungi group (mold/yeast) was clearly discriminated from the bacteria group (bacteria/LAB). The metabolic pathways related to the formation of volatile metabolites also differed according to microorganisms. In particular, the formation of branched-chain aliphatic alcohols and esters increased in the fungi group, while that of volatiles derived from fatty acids was superior in the bacteria group. In addition, we could determine the microorganism-specific metabolites using a correlation network analysis. This study can provide the fundamental knowledge on the metabolic differences according to the type of microorganisms in fermented soybeans., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Khanom-jeen are traditional Thai fermented rice noodles with a characteristic flavour and texture. Based on their ability to hydrolyse rice proteins, five strains of proteolytic bacteria were isolated from fermented rice flour used to produce noodles in Thailand. Enterobacter ludwigii strain SK01 showed the highest degree of rice protein hydrolysis among the five strains and was selected as a starter culture for khanom-jeen production. The viable count of micro-organisms, acidity, pH, and protein and starch contents were compared throughout the fermented rice production with and without the SK01 strain. The pH of fermented rice increased on the first day of solid-state fermentation and subsequently decreased to 3·7-3·8 under both conditions. The protein content of rice significantly decreased from 80 to 18·2 ± 0·5 mg g -1 and 26 ± 0·6 mg g -1 during fermentation with and without the SK01 strain, respectively. The tensile strength, breaking length, brightness, and whiteness, which are important factors for the texture and appearance of khanom-jeen, were improved using the SK01 strain to ferment rice. The results of this laboratory-scale study indicated that the use of the proteolytic SK01 strain in fermented rice production can improve the quality of khanom-jeen noodles. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of Enterobacter ludwigii strain SK01 as a proteolytic bacterial starter culture improved the quality of khanom-jeen noodles. Compared with khanom-jeen noodles produced without E. ludwigii strain SK01, those produced using this strain showed increased tensile strength, breaking length, brightness and whiteness. These findings will be useful for the development of specific and controllable methods for producing khanom-jeen noodles with desirable texture and colour., (© 2019 The Society for Applied Microbiology.)

In Africa, fermented foods and beverages play significant roles in contributing to food security. Endotoxins are ubiquitous heat stable lipopolysaccharide (LPS) complexes situated in the outer cell membranes of Gram-negative bacteria. This study evaluated the microbiological quality of fermented foods (ogiri, ugba, iru, ogi and ogi baba) and beverages (mahewu and umqombothi) from selected Nigerian and South African markets. The bacterial diversity of the fermented foods was also investigated and the identity of the isolates confirmed by biochemical and molecular methods. Isolate grouping was established through hierarchal clustering and the samples were further investigated for endotoxin production with the chromogenic Limulus Amoebocyte Lysate assay. The total aerobic count of the samples ranged from 5.7 to 10.8 Log CFU/g. Fourteen bacteria genera were detected with most of the isolates being members of the Enterobacteriaceae family. Sphingomonas paucimobilis and Escherichia coli were the dominant Gram-negative bacterial species detected. There were considerable variations in the concentrations of endotoxins produced and the lowest endotoxin concentration was found in ogi (4.3 × 10 EU/g) and the highest in iru (5.5 × 10 4 EU/g) while, 44% of umqombothi samples had endotoxins. Ogi baba samples had better microbial quality than other samples due to its reduced bacterial load and endotoxin levels. There was a strong positive (r = 0.714, r = 0.996) and significant (p < 0.01) correlation between the endotoxin levels and bacterial loads of the samples. Some previously unreported species of bacteria found in the fermented foods included Aeromonas haemolyticus and Rhizobium radiobacter. This is the first comprehensive report on endotoxins in fermented foods and beverages in Africa. Furthermore, the occurrence of pathogenic bacteria and toxins in the foods and beverages is of serious concern that calls for immediate action., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: Chinese jiang-shui is fermented food without salt. In consideration of the few studies of the bacterial community and dynamics of jiang-shui fermentation, the aim of this study was to investigate the microbial diversity and dynamics of jiang-shui fermentation using high-throughput sequencing (HTS), denaturing gradient gel electrophoresis (DGGE) and the culture-dependent method., Results: The culture-dependent method showed that pathogenic bacteria (Staphylococcus aureus, Salmonella and Escherichia coli) and yeast mainly existed in the early stage and lactic acid bacteria dominated until the end stage. HTS and DGGE revealed that Serratia marcescens, Serratia sp., Lactobacillus curvatus, Lactococcus lactis, uncultured bacterium and Bacillus thuringiensis started the fermentation, followed by the middle stage with Lactococcus lactis, Weissella sp. and Bacillus arthracis as the predominant species. The end stage was characterized with Lactobacillus pentosus, Weissella cibaria and Weissella sp. as the major bacteria., Conclusions: The results showed that genera Serratia, Lactococcus, Weissella and Lactobacillus dominated the whole process of jiang-shui fermentation. This study provided a good analysis of the bacterial changes of jiang-shui fermentation, and future studies should consider the relationships among the sensory characteristics, microbial communities and metabolites. © 2019 Society of Chemical Industry., (© 2019 Society of Chemical Industry.)

The effect of iodine present in 1.0% table salt in combination with the use of starter cultures in sauerkraut fermentations were investigated in order to determine whether iodine interferes with lactic acid bacteria responsible for the fermentation. The effect of iodine was tested in fermentations performed using selected starter cultures or without starters (spontaneous fermentation). Lactobacillus plantarum and Leuconostoc mesenteroides used as starters at levels of ca. 1 × 10 7  cfu ml -1 led to a quick establishment of lactic acid bacteria (LAB) as predominant microorganisms, reaching 1 × 10 9  cfu ml -1 after 24 h decreasing the pH to below 4.0. In contrast, LAB counts in control fermentations without starters increased slower from 1 × 10 5  cfu ml -1 to 1 × 10 9  cfu ml -1 and a pH reduction below 4.0 was achieved only after 3 days fermentation. A metagenomic investigation showed a more diverse bacterial community in fermentations without starters, consisting of enterobacteria and pseudomonads in the first days of fermentation, and of LAB such as lactococci in the later stages. In fermentations with starters, lactobacilli predominated. Leuconostocs also occurred, but at much lower sequence abundance than lactobacilli, and thus were not able to predominate. Determination of iodine in the fermentation with starter bacteria and with iodized salt showed that the fermentation did not affect iodine concentration. The use of iodized salt did not statistically significantly influence microbial populations in the fermentation. Thus, there is no basis for the popular held belief that the use of iodized salt inhibits the growth of the bacteria important for the sauerkraut fermentation. A statistically near significant effect (p = 0.06), however, was noted for the effect of iodine on yeasts and mould populations in the fermentations performed without starter cultures. As sauerkraut is usually produced without starters, this should be further investigated., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Slow fermented sausages with reduced ingoing amounts of sodium nitrate were manufactured: control (250 ppm), 15% (212.5 ppm) and 25% (187.5 ppm) reduction. The effect of nitrate reduction on microbiology and chemical parameters, volatile compounds and aroma production was studied. Parameters like, pH, a w and colour decreased during ripening, without being affected by nitrate reduction. Lipid oxidation increased during ripening and it was higher in control sausages due to fat content. Residual nitrite was below the detection limit during the whole process and residual nitrate decreased during ripening, with higher reduction in RN25 sausages. Lactic acid bacteria, total mesophilic bacteria and yeasts and moulds increased during ripening but Gram positive cocci decreased. Microbial counts from nitrate reduced sausages at the end of the manufacturing process were not statistically different from the control sausages with nitrate. Regarding volatile compounds formation, compounds derived from amino acid degradation were increased by nitrate reduction. Aroma compounds derived from amino acid degradation and responsible for strong odours, dimethyl disulphide (toasted, garlic) and methional (cooked potato) and, to a lesser extent, compounds derived from esterase activity producing fruity odours (ethyl acetate, ethyl butanoate, ethyl‑2‑hydroxypropanoate, ethyl‑2‑methylbutanoate and ethyl‑3‑methylbutanoate) and several compounds from carbohydrate fermentation acetic acid (vinegar odour) and 2-butanone (fruity) were related to the high nitrate reduction (25%). Despite nitrate reduction up to 25% produced minor effect on microbial growth, their metabolism is regulated by nitrate content and therefore by nitrite generation affecting the production of key aroma compounds that alter the sausage aroma profile., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Fermented foods may confer several benefits to human health and play an important role in a healthy and balanced diet. Stinky tofu is an important traditional fermented soy product in Asia. In this study, a comprehensive analysis of bacterial diversity in terms of rarefaction abundance, rank abundance, alpha diversity, and principal coordinates analysis was conducted using next-generation sequencing. The results obtained were further verified by culture-dependent methods. In addition, eight biogenic amines were also quantified to determine their levels in stinky tofu during conventional production. Our study revealed that lactobacillus was the major lactic acid bacteria throughout the fermentation process. Further, some potentially harmful bacterial belonging to the genera Halomonas and Solobacterium, were also found existing in the stinky tofu. In case of biogenic amines, the concentration of putrescine, cadaverine and histamine finally increased to high levels while spermine disappeared after the fermentation was completed. After the soaking step, putrescine, tryptamine and β-phenethylamine increased sharply. This work provided an improved understanding of microbes and biogenic amines content associated with the traditionally consumed fermented food. However, there is a need to understand microbial interactions related to biogenic amines during the fermentation, and the origin and survival strategies of two important pathogens detected in our study., (Copyright © 2018 Elsevier Ltd. All rights reserved.)