Metagenomics insights into food fermentations

The microbial terroir of Agiorgitiko cv. in the Nemea PDO zone

Agiorgitiko is a major Greek red winegrape variety of high economic importance cultivated almost exclusively in the Nemea PDO zone in Peloponnese, Greece. Here, we describe the microbiota and mycobiota of grape and soil samples collected over three consecutive harvest periods (September 2019, 2020 and 2021). The results revealed a common microbiome composition across the Nemea PDO zone vineyards, despite significant variations in the community structure regarding dominant bacterial and fungal taxa per sampling year, which were associated with weather factors. Grape samples of 2019 were enriched in several plant growth promoting bacteria, including Bradyrhizobium, Streptomyces, Massilia and Sphingomonas, selected by the particular weather conditions. On the other hand, the predominance of Botrytis in the same samples was observed, indicating again the impact of weather conditions on the microbial structure. Understanding these dynamics could improve management practices aimed at vine cultivation and wine quality.

Microbial Fermentation in Food and Beverage Industries: Innovations, Challenges, and Opportunities

Microbial fermentation is a primary method by which a variety of foods and beverages are produced. The term refers to the use of microbes such as bacteria, yeasts, and molds to transform carbohydrates into different substances. Fermentation is important for preserving, enhancing flavor, and improving the nutritional quality of various perishable foods. Historical records clearly show that fermented foods and drinks, such as wine, beer, and bread, have been consumed for more than 7000 years. The main microorganisms employed were Saccharomyces cerevisiae, which are predominantly used in alcohol fermentation, and Lactobacillus in dairy and vegetable fermentation. Typical fermented foods and drinks made from yogurt, cheese, beer, wine, cider, and pickles from vegetables are examples. Although there are risks of contamination and spoilage by pathogenic and undesirable microorganisms, advanced technologies and proper control procedures can mitigate these risks. This review addresses microbial fermentation and clarifies its past importance and contribution to food preservation, flavoring, and nutrition. It systematically separates yeasts, molds, and bacteria and explains how they are used in food products such as bread, yogurt, beer, and pickles. Larger producers employ primary production methods such as the artisanal approach, which are explored along with future trends such as solid-state fermentation, the potential of biotechnology in developing new products, and sustainability in new product development. Future research and development strategies can lead to innovations in methods that improve efficiency, product range, and sustainability.

Metagenomic and metabolomic profiling analyses to unravel the formation mechanism of n-propanol during the first and second round of Jiangxiangxing Baijiu fermentation

N-propanol is one of the higher alcohols, a moderate amount of n-propanol is beneficial for the harmony of the liquor body, whereas excessive or repeated intake will lead to discomfort and pose significant harm to human health. In actual production process of Jiangxiangxing Baijiu, the n-propanol content of the base baijiu in first round (FR) is far higher than that of second round (SR). Nevertheless, the formation mechanism and the key n-propanol producing microbials remain unclear and this limits the quality control of baijiu fermentation. Here, we combined metagenomics and metabolomics to verify the biosynthesis pathway of n-propanol and to identify characteristic microorganisms in FR and SR. The results showed that the preliminary period of pit fermentation was critical for the accumulation of n-propanol. FR was enriched in Lactobacillus plantarum, Lactobacillus ponits, Lactobacillus brevis and Lactobacillus panis, while it was harbored greater abundances of Pichia kudriazevii, Saccharomyces cerevisiae and Lactobacillus acetotolerans in SR. Function analysis combined with KEGG providing comprehensive evidence for the main synthetic pathways of n-propanol in Jiangxiangxing baijiu, and L. panis was key microbial. In addition, the experiments of inoculating L. panis and L. acetotolerans in situ indicated L. panis was mainly responsible for n-propanol production while L. acetotolerans not conducive to the production of n-propanol. Besides, the bioturbation effect on microbiota and flavor compounds were also analyzed. These results are useful for elucidating the mechanism of flavor formation in baijiu fermentation and promoting the further application of bioturbation technology in the traditional fermentation industry.

Metagenomics-based insights into the microbial community dynamics and flavor development potentiality of artificial and natural pit mud

Strong-flavor Baijiu (SFB) production has relied on pit mud (PM) as a starter culture. The maturation time of natural PM (NPM) is about 30 years, so artificial PM (APM) with a shorter maturation time has attracted widespread attention. This study reveals the microbial and functional dissimilarities of APM and NPM, and helps to elucidate the different metabolic roles of microbes during substrate degradation and flavor formation. Significant differences in the microbial community were observed between APM and NPM, manifesting as variations in the abundance of core microorganisms. Total of 187 high-quality metagenome-assembled genomes (MAGs) were obtained based on the metagenomic binning technology, mainly including Firmicutes (n = 106), Bacteroidota (n = 15) and Chloroflexota (n = 14). Furthermore, the relative concentration of flavor compounds in 4-year APM was similar to those in 30-year NPM, but different from those in 100-year NPMs. Methanosarcina, Methanobacterium, Methanoculleus, Anaerolineae bacterium and Aminobacterium were the key bacteria responsible for the flavor differences. From a functional perspective, amino acid and carbohydrate metabolism were key functions of PM microbial, and showed differences between APM and NPM. Finally, substrate degradation and flavor generation pathways were found to exist in multiple microorganisms. Combine the relative abundance of microorganisms with the absolute abundance of enzymes, Clostridium, Lactobacillus, Petrimonas, Methanoculleus, Prevotella, Methanobacterium, Methanosarcina, Methanothrix, Proteiniphilum, Bellilinea, Anaerolinea, Anaeromassilibacillus, Syntrophomonas and Brevefilum were identified as the key microorganisms in APM and NPM.

Contribution of data acquired from spectroscopic, genomic and microbiological analyses to enhance mussels' quality assessment

In this study, a large amount of heterogeneous data (i.e., microbiological, spectral and Next Generation Sequencing data) were obtained analyzing mussels of different species and origin, to acquire a comprehensive view about the quality and safety of these products. More specifically, spectral data were collected through Fourier transform Infrared (FTIR) spectroscopy, while the overall profile of microorganisms present in these samples, affecting quality and safety of mussels throughout storage, was determined through Next Generation Sequencing (NGS) using 16S rRNA metabarcoding analysis. In parallel, conventional microbiological analysis for the estimation of culturable spoilage microorganisms (total aerobes, Pseudomonas spp., B. thermosphacta, Shewanella spp. and Enterobacteriaceae) was applied. Different machine learning algorithms, namely Partial Least Square (PLS), Support Vector Machines (SVM), k-Nearest Neighbors (kNN), Random Forest (RF) Neural Networks (NN)) were applied accordingly, to assess the potential of FTIR and NGS data to provide useful information about mussels' microbiological quality. Microbial counts ranged from 3.5 to 9.0 log CFU/g, while NGS revealed several bacterial genera such as Pseudoalteromonas, Psychrobacter, Acinetobacter, Pseudomonas, B. thermosphacta, Psychrobacter, Kistimonas, Psychrilyobacter to affect the quality of mussels, depending on the mussel species, batch and storage conditions. According to the performance metrics, the SVM algorithm in tandem with FTIR achieved the highest prediction accuracy for microbial counts in M. chilensis samples (Rsquared; 0.89, RMSE; 0,74), while in the case of predicting the abundance of microbial genera using spectroscopic data, the best performing algorithm varied by bacterial genus. Indicatively, in M. chilensis, RF, kNN and NN performed better in predicting Enterococcus, Enhydrobacterium and Pseudoalteromonas, respectively (Rsquared = 0.92, 0.93, 0.99). Associations between genomics data and specific spectral regions were further investigated, revealing certain spectral regions that are associated with mussels' quality and safety. The application of "multi-omics" in seafood supply chain can provide insightful information about mussels' quality and safety compared to the methodologies followed in current quality and safety management systems.

Microbial Evolution in Artisanal Pecorino-like Cheeses Produced from Two Farms Managing Two Different Breeds of Sheep (Comisana and Lacaune)

"Pecorino" is a typical semi-hard cheese obtained with raw or heat-treated sheep milk using procedures to valorize the raw material's chemical and microbiological properties. In the present study, using a high-throughput method of 16S rRNA gene sequencing, we assessed the evolution of the microbiome composition from milk to Pecorino-like cheese in artisanal processes using milk from Comisana and Lacaune sheep breeds. The comparative analysis of the bacterial community composition revealed significant differences in the presence and abundance of specific taxa in the milk microbiomes of the Comisana and Lacaune breeds. Next-Generation Sequencing (NGS) analysis also revealed differences in the curd microbiomes related to dairy farming practices, which have a relevant effect on the final structure of the Pecorino cheese microbiome.

A Comprehensive View of Food Microbiota: Introducing FoodMicrobionet v5

Amplicon-targeted metagenomics is now the standard approach for the study of the composition and dynamics of food microbial communities. Hundreds of papers on this subject have been published in scientific journals and the information is dispersed in a variety of sources, while raw sequences and their metadata are available in public repositories for some, but not all, of the published studies. A limited number of web resources and databases allow scientists to access this wealth of information but their level of annotation on studies and samples varies. Here, we report on the release of FoodMicrobionet v5, a comprehensive database of metataxonomic studies on bacterial and fungal communities of foods. The current version of the database includes 251 published studies (11 focusing on fungal microbiota, 230 on bacterial microbiota, and 10 providing data for both bacterial and fungal microbiota) and 14,035 samples with data on bacteria and 1114 samples with data on fungi. The new structure of the database is compatible with interactive apps and scripts developed for previous versions and allows scientists, R&D personnel in industries and regulators to access a wealth of information on food microbial communities.

Metaproteomics revealing microbial diversity and activity in the spontaneous fermentation of maize dough

Maize was spontaneously fermented and metaproteomic analysis was performed on the maize dough to investigate the profile of microbial communities. pH decreased (5.36, 4.44, and 4.42 after 24, 72, and 12 h), while lactic acid increased (0.03, 0.2, and 0.31 after 24, 72, and 120 h).The number of lactic acid bacteria (179 × 106 CFU/g) and mesophilic bacteria (213 × 106 CFU/g) was high. Based on metaproteomic analysis, Actinobacteria, Proteobacteria, and Firmicutes phyla dominated the fermentation medium, and the Actinobacteria was associated with the matrix of maize during starch degradation. Fermentation parameters (pH, lactic acid and titratable sugar) were considered to be regulated during the first 24 h of the fermentation process for ensure the microbiological safety of maize dough. Assuming that metaproteomics as culture-free methods can be an excellent tool for find mechanisms for faster optimization of a new product, is indeed a good tool for investigating fermentative microbiota.

Bioinformatic approaches for studying the microbiome of fermented food

High-throughput DNA sequencing-based approaches continue to revolutionise our understanding of microbial ecosystems, including those associated with fermented foods. Metagenomic and metatranscriptomic approaches are state-of-the-art biological profiling methods and are employed to investigate a wide variety of characteristics of microbial communities, such as taxonomic membership, gene content and the range and level at which these genes are expressed. Individual groups and consortia of researchers are utilising these approaches to produce increasingly large and complex datasets, representing vast populations of microorganisms. There is a corresponding requirement for the development and application of appropriate bioinformatic tools and pipelines to interpret this data. This review critically analyses the tools and pipelines that have been used or that could be applied to the analysis of metagenomic and metatranscriptomic data from fermented foods. In addition, we critically analyse a number of studies of fermented foods in which these tools have previously been applied, to highlight the insights that these approaches can provide.

Microbiota-derived short chain fatty acids in fermented Kidachi Aloe promote antimicrobial, anticancer, and immunomodulatory activities

BACKGROUND

Fermented Aloe leaf juice is a commonly used food supplement in Japan. In a previous study, fermentation of A. arborescence juice was performed and the presence of short-chain fatty acids (SCFAs) was confirmed and quantified. Samples were collected before and after the fermentation process to be subjected, in the present study, to DNA extraction, 16S rRNA gene (V3-V4 regions) amplification, and sequencing by the next-generation Illumina MiSeq sequencer. Our work aims to analyze the sequences to assess the bacterial diversity in the juice before and after fermentation, identify the beneficial microbes responsible for the production of SCFAs, and evaluate some of the biological activities of the fermented juice.

RESULTS

Data revealed the richness and diversity of the bacterial community in the fermented juice compared to the unfermented control. Relative abundance of bacterial phyla showed that the majority of the microbial community in the test samples corresponded to Pseudomonadota (unfermented; 10.4%, fermented; 76.36%), followed by Bacillota (unfermented; 4.71%, fermented; 17.13%) and then Bacteroidota (unfermented; 0.57%, fermented; 1.64%). For the fermented sample, 84% of Bacillota were lactobacilli. A hierarchically clustered heatmap revealed that Lactobacillus was the most abundant genus in both samples suggesting its involvement in the production of SCFAs. To assess potential health benefits, the anticancer efficacy of the fermented product of A. arborescens was investigated against colorectal cancer (IC50 = 3.5 µg/ml) and liver cancer (IC50 = 6.367 µg/ml) compared to the normal peripheral blood mononuclear cells (PBMCs). Flow cytometric analysis of the cell cycle pattern revealed remarkable population arrest in G0 and G1, however, the highest percentages were mainly in the G1 phase for Hep-G2 (40.1%) and HCT-116 (53.2%) cell lines. This effect was accompanied by early apoptotic profiles of HCT-116 (36.9%) and late apoptosis for Hep-G2 (17.3%). Furthermore, immunomodulatory properties demonstrated a significantly (p < 0.001) reduced percentage of induced TNF-α while enhancing IFN-γ dramatically. For antimicrobial activities, marked broad-spectrum activities were recorded against some bacterial and fungal pathogens (17-37 mm inhibition zone diameter range).

CONCLUSION

Therefore, this study affords the basis of bacterial community composition in fermented A. arborescens juice as well as its potential biological benefits.

Taxonomy, Sequence Variance and Functional Profiling of the Microbial Community of Long-Ripened Cheddar Cheese Using Shotgun Metagenomics

Shotgun metagenomic sequencing was used to investigate the diversity of the microbial community of Cheddar cheese ripened over 32 months. The changes in taxa abundance were compared from assembly-based, non-assembly-based, and mOTUs2 sequencing pipelines to delineate the community profile for each age group. Metagenomic assembled genomes (MAGs) passing the quality threshold were obtained for 11 species from 58 samples. Although Lactococcus cremoris and Lacticaseibacillus paracasei were dominant across the shotgun samples, other species were identified using MG-RAST. NMDS analysis of the beta diversity of the microbial community revealed the similarity of the cheeses in older age groups (7 months to 32 months). As expected, the abundance of Lactococcus cremoris consistently decreased over ripening, while the proportion of permeable cells increased. Over the ripening period, the relative abundance of viable Lacticaseibacillus paracasei progressively increased, but at a variable rate among trials. Reads attributed to Siphoviridae and Ascomycota remained below 1% relative abundance. The functional profiles of PMA-treated cheeses differed from those of non-PMA-treated cheeses. Starter rotation was reflected in the single nucleotide variant profiles of Lactococcus cremoris (SNVs of this species using mOTUs2), while the incoming milk was the leading factor in discriminating Lacticaseibacillus paracasei/casei SNV profiles. The relative abundance estimates from Kraken2, non-assembly-based (MG-RAST) and marker gene clusters (mOTUs2) were consistent across age groups for the two dominant taxa. Metagenomics enabled sequence variant analysis below the bacterial species level and functional profiling that may affect the metabolic interactions between subpopulations in cheese during ripening, which could help explain the overall flavour development of cheese. Future work will integrate microbial variants with volatile profiles to associate the development of compounds related to cheese flavour at each ripening stage.

Analysing the dynamics of the bacterial community in pozol, a Mexican fermented corn dough

Pozol is a traditional prehispanic Mexican beverage made from fermented nixtamal dough; it is still part of everyday life in many communities due to its nutritional properties. It is the product of spontaneous fermentation and has a complex microbiota composed primarily of lactic acid bacteria (LAB). Although this is a beverage that has been used for centuries, the microbial processes that participate in this fermented beverage are not well understood. We fermented corn dough to produce pozol and sampled it at four key times to follow the community and metabolic changes (0, 9 24 and 48 h) by shotgun metagenomic sequencing to determine structural changes in the bacterial community, as well as metabolic genes used for substrate fermentation, nutritional properties and product safety. We found a core of 25 abundant genera throughout the 4 key fermentation times, with the genus Streptococcus being the most prevalent throughout fermentation. We also performed an analysis focused on metagenomic assembled genomes (MAGs) to identify species from the most abundant genera. Genes involving starch, plant cell wall (PCW), fructan and sucrose degradation were found throughout fermentation and in MAGs, indicating the metabolic potential of the pozol microbiota to degrade these carbohydrates. Complete metabolic modules responsible for amino acid and vitamin biosynthesis increased considerably during fermentation, and were also found to be abundant in MAG, highlighting the bacterial contribution to the well-known nutritional properties attributed to pozol. Further, clusters of genes containing CAZymes (CGCs) and essential amino acids and vitamins were found in the reconstructed MAGs for abundant species in pozol. The results of this study contribute to our understanding of the metabolic role of micro-organisms in the transformation of corn to produce this traditional beverage and their contribution to the nutritional impact that pozol has had for centuries in the traditional cuisine of southeast Mexico.

Foodborne Microbial Communities as Potential Reservoirs of Antimicrobial Resistance Genes for Pathogens: A Critical Review of the Recent Literature

Antimicrobial resistance (AMR) is a global and increasing threat to human health. Several genetic determinants of AMR are found in environmental reservoirs, including bacteria naturally associated with widely consumed fermented foods. Through the food chain, these bacteria can reach the gut, where horizontal gene transfer (HGT) can occur within the complex and populated microbial environment. Numerous studies on this topic have been published over the past decades, but a conclusive picture of the potential impact of the non-pathogenic foodborne microbial reservoir on the spread of AMR to human pathogens has not yet emerged. This review critically evaluates a comprehensive list of recent experimental studies reporting the isolation of AMR bacteria associated with fermented foods, focusing on those reporting HGT events, which represent the main driver of AMR spread within and between different bacterial communities. Overall, our analysis points to the methodological heterogeneity as a major weakness impairing determination or a causal relation between the presence of AMR determinants within the foodborne microbial reservoir and their transmission to human pathogens. The aim is therefore to highlight the main gaps and needs to better standardize future studies addressing the potential role of non-pathogenic bacteria in the spread of AMR.

Metagenomics: An Effective Approach for Exploring Microbial Diversity and Functions

Various fields have been identified in the "omics" era, such as genomics, proteomics, transcriptomics, metabolomics, phenomics, and metagenomics. Among these, metagenomics has enabled a significant increase in discoveries related to the microbial world. Newly discovered microbiomes in different ecologies provide meaningful information on the diversity and functions of microorganisms on the Earth. Therefore, the results of metagenomic studies have enabled new microbe-based applications in human health, agriculture, and the food industry, among others. This review summarizes the fundamental procedures on recent advances in bioinformatic tools. It also explores up-to-date applications of metagenomics in human health, food study, plant research, environmental sciences, and other fields. Finally, metagenomics is a powerful tool for studying the microbial world, and it still has numerous applications that are currently hidden and awaiting discovery. Therefore, this review also discusses the future perspectives of metagenomics.

Characteristics of key microorganisms and metabolites in irradiated marbled beef

Insights into changes in microorganisms and metabolites in irradiated marbled beef may help elucidate the beneficial effects of irradiation on prolonging the shelf life of meat. In this study, 16S rRNA gene sequencing, ultra-high-performance liquid chromatography-tandem mass spectrometry, and Pearson's correlation analyses were conducted to detect key microorganisms, core metabolites, and potential correlation between the microbiome and metabolome in marbling beef. Microbiome analysis showed that irradiation effectively eradicated the spoilage bacterium Leuconostoc and reduced the proportions of Carnobacterium and Lactobacillus in marbled beef. Additionally, results of metabolomic analysis involving irradiated marbled beef revealed that metabolites with significant differences were mainly organic acids and their derivatives, lipids, and lipid-like molecules, including six core metabolites. Furthermore, a significant correlation between key bacteria and metabolites was observed. Carnobacterium, Lactobacillus, and Leuconostoc affected the accumulation of core metabolites in irradiated marbled beef by influencing amino acid and lipid metabolism. Characterization of the microbiota and metabolites, as well as clarification of their correlation, can contribute to a better understanding of the mechanisms whereby irradiation helps maintain meat quality.

Integrated molecular approaches for fermented food microbiome research

Molecular technologies, including high-throughput sequencing, have expanded our perception of the microbial world. Unprecedented insights into the composition and function of microbial communities have generated large interest, with numerous landmark studies published in recent years relating the important roles of microbiomes and the environment-especially diet and nutrition-in human, animal, and global health. As such, food microbiomes represent an important cross-over between the environment and host. This is especially true of fermented food microbiomes, which actively introduce microbial metabolites and, to a lesser extent, live microbes into the human gut. Here, we discuss the history of fermented foods, and examine how molecular approaches have advanced research of these fermented foods over the past decade. We highlight how various molecular approaches have helped us to understand the ways in which microbes shape the qualities of these products, and we summarize the impacts of consuming fermented foods on the gut. Finally, we explore how advances in bioinformatics could be leveraged to enhance our understanding of fermented foods. This review highlights how integrated molecular approaches are changing our understanding of the microbial communities associated with food fermentation, the creation of unique food products, and their influences on the human microbiome and health.

Distinct dynamic phases observed in bacterial microcosms

Predicting biodiversity and dynamics of complex communities is a fundamental challenge in ecology. Leveraging bacterial microcosms with well-controlled laboratory conditions, Hu et al. recently performed a direct test of theory predicting that two community-level parameters (i.e., species pool size and inter-species interaction strength) dictate transitions between three dynamical phases: stable full coexistence, stable partial coexistence, and persistent fluctuations. Generally, communities experience species extinctions before they lose stability as either of the two parameters increases.

Molecular advances in mycoremediation of polycyclic aromatic hydrocarbons: Exploring fungal bacterial interactions

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous high global concern environmental pollutants and tend to bioaccumulate due to hydrophobic properties. These xenobiotics, having variable concentrations along different matrices, gradually undergo various physical, chemical, and biological transformation processes. Myco-remediation aids accelerated degradation by effectively transforming complex ring structures to oxidized/hydroxylated intermediates, which can further funnel to bacterial degradation pathways. Exploitation of such complementing fungal-bacterial enzymatic activity can overcome certain limitations of incomplete bioremediation process. Furthermore, high-throughput molecular methods can be employed to unveil community structure, taxon abundance, coexisting community interactions, and metabolic pathways under stressed conditions. The present review critically discusses the role of different fungal phyla in PAHs biotransformation and application of fungal-bacterial cocultures for enhanced mineralization. Moreover, recent advances in bioassays for PAH residue detection, monitoring, developing xenobiotics stress-tolerant strains, and application of fungal catabolic enzymes are highlighted. Application of next-generation sequencing methods to reveal complex ecological networks based on microbial community interactions and data analysis bias in performing such studies is further discussed in detail. Conclusively, the review underscores the application of mixed-culture approach by critically highlighting in situ fungal-bacterial community nexus and its role in complete mineralization of PAHs for the management of contaminated sites.

The rotation of primary starter culture mixtures results in batch-to-batch variations during Gouda cheese production

Industrial production of Gouda cheeses mostly relies on a rotated use of different mixed-strain lactic acid bacteria starter cultures to avoid phage infections. However, it is unknown how the application of these different starter culture mixtures affect the organoleptic properties of the final cheeses. Therefore, the present study assessed the impact of three different starter culture mixtures on the batch-to-batch variations among Gouda cheeses from 23 different batch productions in the same dairy company. Both the cores and rinds of all these cheeses were investigated after 36, 45, 75, and 100 weeks of ripening by metagenetics based on high-throughput full-length 16S rRNA gene sequencing accompanied with an amplicon sequence variant (ASV) approach as well as metabolite target analysis of non-volatile and volatile organic compounds. Up to 75 weeks of ripening, the acidifying Lactococcus cremoris and Lactococcus lactis were the most abundant bacterial species in the cheese cores. The relative abundance of Leuconostoc pseudomesenteroides was significantly different for each starter culture mixture. This impacted the concentrations of some key metabolites, such as acetoin produced from citrate, and the relative abundance of non-starter lactic acid bacteria (NSLAB). Cheeses with the least Leuc. pseudomesenteroides contained more NSLAB, such as Lacticaseibacillus paracasei that was taken over by Tetragenococcus halophilus and Loigolactobacillus rennini upon ripening time. Taken together, the results indicated a minor role of leuconostocs in aroma formation but a major impact on the growth of NSLAB. The relative abundance of T. halophilus (high) and Loil. rennini (low) increased with ripening time from rind to core. Two main ASV clusters of T. halophilus could be distinguished, which were differently correlated with some metabolites, both beneficial (regarding aroma formation) and undesirable ones (biogenic amines). A well-chosen T. halophilus strain could be a candidate adjunct culture for Gouda cheese production.

Bacteriobiota and Chemical Changes during the Ripening of Traditional Fermented "Pirot 'Ironed' Sausage"

"Pirot 'ironed' sausage" (Pis) is a traditional, fermented sausage, made from different types of meat (beef and chevon), without additives or starter cultures. The physical-chemical properties (pH, water activity, fats, moisture, and protein contents) were examined in the initial meat batter stuffing and during ripening. Total bacterial diversity was examined at different time points using both culturable (traditional) and non-culturable (NGS sequencing) approaches. During the ripening, a decrease in pH value, a_w, and moisture content was observed, as well as an increase in protein and fat content. At least a two-fold significant decrease was noted for colorimetric values during the ripening period. The dominance of Proteobacteria and Firmicutes was observed in the non-culturable approach in all studied samples. During the ripening process, an increase in Firmicutes (from 33.5% to 63.5%) with a decrease in Proteobacteria (from 65.4% to 22.3%) was observed. The bacterial genera that were dominant throughout the ripening process were Lactobacillus, Photobacterium, Leuconostoc, Weissella, and Lactococcus, while Carnobacterium, Brochothrix, and Acinetobacter were found also, but in negligible abundance. Among the culturable bacteria, Latilactobacillus sakei (Lactobacillus sakei) and Leuconostoc mesenteoides were present in all stages of ripening.

Yeasts originating from fermented foods, their potential as probiotics and therapeutic implication for human health and disease

Yeasts derived from fermented foods have historically been known for their organoleptic properties, enriching nutritional values, and producing bioactive metabolites with therapeutic potential. In this review, we discuss the yeast flora in fermented foods, their functional aspects in fermentation, as well as their probiotic and biotherapeutic properties. These yeasts have numerous physical and biochemical characteristics, such as larger cells as compared to bacteria, a rigid cell wall composed primarily of glucans and mannans, natural resistance to antibiotics, and the secretion of secondary metabolites that are both pleasing to the consumer and beneficial to the host's health and well-being. The review also focused on therapeutic applications of probiotic yeasts derived from fermented foods on infections associated with Candida species. These potential probiotic yeasts present an additional avenue to treat dysbiosis of the gut microbiota and prevent health complications that arise from opportunistic fungal colonization, especially drug-resistant superbugs, which are highlighted in this review.

Microbiota profile of filleted gilthead seabream (Sparus aurata) during storage at various conditions by 16S rRNA metabarcoding analysis

The aim of the present work was to study the microbiota profile of gilthead seabream (Sparus aurata) fillets stored either aerobically or under Modified Atmosphere Packaging (MAP) conditions at 0, 4, 8 and 12 °C, via 16S rRNA metabarcoding sequencing. Throughout storage, sensory assessment was also applied to estimate fillets' end of shelf-life. Results indicated that storage conditions strongly influenced the shelf-life of the fillets, since the sensorial attributes of air-stored samples deteriorated earlier than that of MAP-stored fillets, while higher temperatures also contributed to a more rapid products' end of shelf-life. Metataxonomic analysis indicated that Pseudomonas was by far the dominant genus at the end of fillet's shelf-life, in the vast majority of treatments, even though a sporadic but noteworthy presence of other genera (e.g, Shewanella, Carnobacterium, Brochothrix etc.) at the middle stages of MAP-stored fillets is also worth mentioning. On the other hand, a completely different profile as well as a more abundant bacterial diversity was observed at the end of shelf-life of MAP-stored fillets at 12 °C, in which Serratia was the most dominant bacterium, followed by Kluyvera, Hafnia, Rahnella and Raoultella, while Pseudomonas was detected in traces. The findings of the present work are very important, providing useful information about the spoilage status of gilthead seabream fillets during several storage conditions, triggering in parallel the need for further studies to enrich the current knowledge and help stakeholders develop innovative strategies that delay the growth of key spoiler players and consequently, retard spoilage course.

Fermented table olives from Cyprus: Microbiota profile of three varieties from different regions through metabarcoding sequencing

The knowledge about the microbial diversity of different olives varieties from diverse regions in the Mediterranean basin is limited. This work aimed to determine the microbial diversity of three different fermented olive varieties, collected from different regions in Cyprus, via Next Generation Sequencing (NGS) analysis. Olives were spontaneously fermented for 120 days, microbial DNA was extracted from the final products, and subjected to 16S rRNA gene and ITS1 loci metabarcoding analysis for the determination of bacterial and fungal communities, respectively. Results revealed that the bacterial profile of the studied varieties was similar, while no noteworthy differences were observed in olives from different regions. The bacterial profile was dominated by the co-existence of Lactobacillus and Streptococcus, while the genera Lactococcus and Salinivibrio and the family Leuconostocaceae were also present in increased relative abundances. Regarding fungal communities, the analysis indicated discrimination among the different varieties, especially in Kalamata ones. The most abundant fungi were mainly the genera Aspergillus, Botryosphaeria, Meyerozyma, and Zygosaccharomyces for Cypriot olives, the genera Botryosphaeria, Saccharomyces, Geosmithia, and Wickeromyces for Kalamata variety, while the dominant fungi in the Picual variety were mainly members of the genera Candida, Penicillium, Saccharomyces, Hanseniospora and Botryosphaeria. Potential microbial biomarkers that distinguish the three varieties are also proposed. Moreover, interaction networks analysis identified interactions among the key taxa of the communities. Overall, the present work provides useful information and sheds light on an understudied field, such as the comparison of microbiota profiles of different varieties from several regions in Cyprus. The study enriches our knowledge and highlights the similarities and the main differences between those aspects, booming in parallel the need for further works on this frontier, in the attempt to determine potentially olives' microbial terroir in Cyprus. Our work should be used as a benchmark for future works in this direction.

High pressure processing at the early stages of ripening enhances the safety and quality of dry fermented sausages elaborated with or without starter culture

To study the quality of chorizo de León dry fermented sausages (DFS), high pressure processing (HPP) applied at the early stages of ripening and the use of a functional starter culture were evaluated as additional safety measures. Furthermore, the ability to control the populations of artificially inoculated Listeria monocytogenes and Salmonella Typhimurium was investigated and the evolution of microbial communities was assessed by amplicon 16S rRNA metataxonomics. The use of HPP and the starter culture, independently or combined, induced a reduction of Listeria monocytogenes of 1.5, 4.3 and > 4.8 log CFU/g respectively, as compared to control. Salmonella Typhimurium counts were under the detection limit (<1 log) in all treated end-product samples. Both additional measures reduced the activity of undesirable microbiota, such as Serratia and Brochothrix, during the production of DFS. Moreover, the starter culture highly influencedthe taxonomic profile of samples.No adverse sensory effects were observed, and panelists showed preference for HPP treated DFS. In conclusion, this new approach of applying HPP at the early stages of ripening of DFS in combination with the use of a defined starter culture improved the safety and quality of the meat product.

The Impact of Different Inoculation Schemes on the Microbiota, Physicochemical and Sensory Characteristics of Greek Kopanisti Cheese throughout Production and Ripening

Kopanisti is a Greek PDO cheese, which is traditionally produced by the addition of an amount of over-mature Kopanisti, called Mana Kopanisti, to initiate cheese ripening. The aim of this study was the production of four types of Kopanisti cheese (A-D) using pasteurized cow milk, and a combination of the following starters/adjuncts in order to test their ability to be used in Kopanisti cheese production: A: Lactococcus lactis subsp. lactis and Lacticaseibacillus paracasei, B: L. lactis and Lc. paracasei/Mana Kopanisti, C: L. lactis and Lc. paracasei/Ligilactobacillus acidipiscis and Loigolactobacillus rennini, D: Lig. acidipiscis and Loig. rennini. Throughout production and ripening, classical microbiological, metataxonomics and physicochemical analyses were employed, while the final products (Day 35) were subjected to sensory analysis as well. Most interestingly, beta-diversity analysis of the metataxonomics data revealed the clusters constructed among the Kopanisti types based on the different inoculation schemes. On day 35, Kopanisti A-C types clustered together due to their similar 16S microbiota, while Kopanisti D was highly differentiated. On the contrary, ITS data clustered Kopanisti B and C together, while Kopanisti A and D were grouped seperately. Finally, based on the sensory evaluation, Kopanisti C appeared to have the most suitable bacteria cocktail for the Kopanisti cheese production. Therefore, not only were the conventional starters used, but also the Lig. acidipiscis and Loig. rennini strains could be used in a standardized Kopanisti cheese production that could lead to final products of high quality and safety.

Effects of post-fermentation on the flavor compounds formation in red sour soup

Red Sour Soup (RSS) is a traditional fermented food in China. After two rounds of fermentation, sour soup has a mellow flavor. However, the microbial composition and flavor formation processes in post-fermentation in RSS are unclear. This study investigates the bacteria composition of RSS during the post-fermentation stage (0–180 days) using high-throughput sequencing. The results show that lactic acid bacteria (LAB) are dominant during the post-fermentation process, and their abundance gradually increases with fermentation time. Additionally, gas chromatography-mass spectrometry was used to detect volatile flavor compounds in the post-fermentation process. Seventy-seven volatile flavor compounds were identified, including 24 esters, 14 terpenes, 9 aromatic hydrocarbons, 9 alkanes, 6 heterocyclic compounds, 3 alcohols, 3 acids, 3 ketones, 2 phenols, 2 aldehydes, 1 amine, and 1 other. Esters and aromatic hydrocarbons are the main volatile compounds in RSS during the post-fermentation process. Orthogonal partial least squares screening and correlation analysis derived several significant correlations, including 48 pairs of positive correlations and 19 pairs of negative correlations. Among them, Acetobacter spp., Clostridium spp. and Sporolactobacillus spp. have 15, 14, 20 significant correlation pairs, respectively, and are considered the most important bacterial genera post-fermentation. Volatile substances become abundant with increasing fermentation time. LAB are excessive after more than 120 days but cause a drastic reduction in volatile ester levels. Thus, the post-fermentation time should be restricted to 120 days, which retains the highest concentrations of volatile esters in RSS. Overall, these findings provide a theoretical basis to determine an optimal post-fermentation time duration, and identify essential bacteria for manufacturing high-quality starter material to shorten the RSS post-fermentation processing time.

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

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

The importance and mitigation of mycotoxins and plant toxins in Southeast Asian fermented foods

Fermented foods (ffs) and beverages are widely consumed in Southeast Asia (SEA) for their nutritional balance, flavor, and food security. They serve as vehicles for beneficial microorganisms performing a significant role in human health. However, there are still major challenges concerning the safety of ffs and beverages due to the presence of natural toxins. In this review, the common toxins found in traditional ffs in SEA are discussed with special reference to mycotoxins and plant toxins. Also, mitigation measures for preventing risks associated with their consumption are outlined. Ochratoxin, citrinin, aflatoxins were reported to be major mycotoxins present in SEA ffs. In addition, soybean-based ff food products were more vulnerable to mycotoxin contaminations. Common plant toxins recorded in ffs include cyanogenic glycosides, oxalates, phytates and saponins. Combined management strategies such as pre-harvest, harvest and post-harvest control and decontamination, through the integration of different control methods such as the use of clean seeds, biological control methods, fermentation, appropriate packaging systems, and controlled processing conditions are needed for the safe consumption of indigenous ffs in SEA.

Microbiome Associated with Slovak Raw Goat Milk, Trace Minerals, and Vitamin E Content

In Slovakia, goat milk production for direct consumption and cheese processing has attracted growing interest. However, there is a lack of information regarding the microbial consortium in Slovak raw goat milk analyzed by next-generation sequencing and trace elements and vitamin E as well. A randomly selected samples (G24-G50) of raw goat milk from different animals at farms in Slovakia were analyzed. The phylum Actinobacteria dominated (62.8%), followed by the phyla Firmicutes (20.5%), Proteobacteria (7.4%), and Bacteroidetes (6.4%). The family Microbacteriaceae was detected in the highest percentage (60.2%) followed by Staphylococcaceae, Bacteroidaceae, Streptococcaceae, Lactobacillaceae, Enterobacteriaceae, and others. Regarding the genera, the most prevalent was genus Curtobacterium (47.4%) followed by the genera such as Staphylococcus (8.3%) and Bifidobacterium (4%). The genera Streptococcus, Lactococcus, Enterococcus, Lactobacillus, and Lacticaseibacillus were evaluated in abundance percentage in range 1%-3.2%. The genus Veillonella reached abundance 3.2%. The genera Enterobacter, Pseudomonas (1.3% and 0.5%), and Bacteroides (6.4%) were evaluated in small percentage abundance too. Zinc was detected with the highest mean value (2.561 ± 0.6823 mg/L) in raw goat milk, followed by iron (1.383 ± 0.5087 mg/L). The mean value of copper and manganese was 0.1746 ± 0.0463 mg/L and 0.051 ± 0.0238 mg/L. The vitamin E reached the mean value 0.3783 ± 0.1976 mg/L. This study is an original contribution showing microbial consortium in raw goat milk from Slovak farms. It also contributes to trace elements and vitamin E status in raw goat milk showing it as a nutritionally healthy food.

Extensive diversity and rapid turnover of phage defense repertoires in cheese-associated bacterial communities

BACKGROUND

Phages are key drivers of genomic diversity in bacterial populations as they impose strong selective pressure on the evolution of bacterial defense mechanisms across closely related strains. The pan-immunity model suggests that such diversity is maintained because the effective immune system of a bacterial species is the one distributed across all strains present in the community. However, only few studies have analyzed the distribution of bacterial defense systems at the community-level, mostly focusing on CRISPR and comparing samples from complex environments. Here, we studied 2778 bacterial genomes and 188 metagenomes from cheese-associated communities, which are dominated by a few bacterial taxa and occur in relatively stable environments.

RESULTS

We corroborate previous laboratory findings that in cheese-associated communities nearly identical strains contain diverse and highly variable arsenals of innate and adaptive (i.e., CRISPR-Cas) immunity systems suggesting rapid turnover. CRISPR spacer abundance correlated with the abundance of matching target sequences across the metagenomes providing evidence that the identified defense repertoires are functional and under selection. While these characteristics align with the pan-immunity model, the detected CRISPR spacers only covered a subset of the phages previously identified in cheese, providing evidence that CRISPR does not enable complete immunity against all phages, and that the innate immune mechanisms may have complementary roles.

CONCLUSIONS

Our findings show that the evolution of bacterial defense mechanisms is a highly dynamic process and highlight that experimentally tractable, low complexity communities such as those found in cheese, can help to understand ecological and molecular processes underlying phage-defense system relationships. These findings can have implications for the design of robust synthetic communities used in biotechnology and the food industry. Video Abstract.

Dynamics of Starter and Non-Starter Lactic Acid Bacteria Populations in Long-Ripened Cheddar Cheese Using Propidium Monoazide (PMA) Treatment

The microbial community of industrially produced Canadian Cheddar cheese was examined from curd to ripened cheese at 30-32 months using a combination of viable plate counts of SLAB (GM17) and NSLAB (MRSv), qPCR and 16S rRNA gene amplicon sequencing. Cell treatment with propidium monoazide excluded DNA of permeable cells from amplification. The proportion of permeable cells of both Lactococcus spp. and Lacticaseibacillus spp. was highest at 3-6 months. While most remaining Lacticaseibacillus spp. cells were intact during later ripening stages, a consistent population of permeable Lactococcus spp. cells was maintained over the 32-month period. While Lactococcus sequence variants were significant biomarkers for viable cheese curd communities at 0-1 m, Lacticaseibacillus was identified as a distinctive biomarker for cheeses from 7 to 20 months. From 24 to 32 months, Lacticaseibacillus was replaced in significance by four genera (Pediococcus and Latilactobacillus at 24 m and at 30-32 m, Secundilactobacillus and Paucilactobacillus). These results underscore the importance of monitoring potential defects in cheeses aged over 24 months, which could be diagnosed early through microbial DNA profiling to minimize potential waste of product. Future perspectives include correlating volatile flavor compounds with microbial community composition as well as the investigation of intra-species diversity.

Comparison of the Microbiome of Artisanal Homemade and Industrial Feta Cheese through Amplicon Sequencing and Shotgun Metagenomics

Feta is the most renowned protected designation of origin (PDO) white brined cheese produced in Greece. The fine organoleptic characteristics and the quality of Feta rely on, among other factors, its overall microbial ecosystem. In this study, we employed 16S rDNA and internal transcribed spacer (ITS) amplicon sequencing, as well as shotgun metagenomics, to investigate the microbiome of artisanal homemade and industrial Feta cheese samples from different regions of Greece, which has very rarely been investigated. 16S rDNA data suggested the prevalence of the Lactococcus genus in the homemade samples, while Streptococcus and Lactobacillus genera prevailed in the industrial control samples. Species identification deriving from shotgun metagenomics corroborated these findings, as Lactococcus lactis dominated two homemade samples while Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus were found to be dominating one industrial sample. ITS data revealed a complex diversity of the yeast population among the samples analyzed. Debaryomyces, Kluyveromyces, Cutaneotrichosporon, Pichia, Candida, and Rhodotorula were the major genera identified, which were distributed in a rather arbitrary manner among the different samples. Furthermore, a number of potential metagenome-assembled genomes (MAGs) could be detected among assembled shotgun bins. The overall analysis of the shotgun metagenomics supported the presence of different foodborne pathogens in homemade samples (e.g., Staphylococcus aureus, Listeria monocytogenes, Enterobacter cloacae, and Streptococcus suis), but with low to very low abundances. Concluding, the combination of both amplicon sequencing and shotgun metagenomics allowed us to obtain an in-depth profile of the artisanal homemade Feta cheese microbiome.

Metagenetic and Volatilomic Approaches to Elucidate the Effect of Lactiplantibacillus plantarum Starter Cultures on Sicilian Table Olives

The present study aimed to evaluate the effect of selected Lactiplantibacillus plantarum strains on both microbiota composition and volatile organic compound profile of Sicilian table olives. Two mixed cultures, named O1 and O2, were set up for pilot-plan scale fermentations at 5% of NaCl. Uninoculated table olives at 5 and 8% (C5 and C8) of salt were used as control. The fermentation process was monitored until 80 days through a dual approach, which included both classical microbiological and 16S amplicon-based sequencing and volatilomics analyses. Compared with control samples (C5 and C8), experimental samples, inoculated with starter cultures (O1 and O2), exhibited a faster acidification with a more pronounced drop in pH. Metagenetics data revealed significant differences of microbiota composition among samples, highlighting the dominance of lactobacilli in both experimental samples; a high occurrence of Enterobacter genus only in control samples with 5% of NaCl; and the presence of Bacteroides, Faecalibacterium, Klebsiella, and Raoultella genera only in control samples with 8% of NaCl. Furthermore, microbiota composition dynamics, through the fermentation process, significantly affected the volatile organic compounds of the final products, whereas no compounds involved in off-odors metabolites were detected in all samples investigated. In conclusion, the addition of the proposed starter cultures and the use of low concentrations of sodium chloride positively affected the microbiota and volatile organic compounds, ensuring the microbiological safety and the pleasant flavors of the final product.

A review on the application of bioinformatics tools in food microbiome studies

There is currently a transformed interest toward understanding the impact of fermentation on functional food development due to growing consumer interest on modified health benefits of sustainable foods. In this review, we attempt to summarize recent findings regarding the impact of Next-generation sequencing and other bioinformatics methods in the food microbiome and use prediction software to understand the critical role of microbes in producing fermented foods. Traditionally, fermentation methods and starter culture development were considered conventional methods needing optimization to eliminate errors in technique and were influenced by technical knowledge of fermentation. Recent advances in high-output omics innovations permit the implementation of additional logical tactics for developing fermentation methods. Further, the review describes the multiple functions of the predictions based on docking studies and the correlation of genomic and metabolomic analysis to develop trends to understand the potential food microbiome interactions and associated products to become a part of a healthy diet.

Constructing Micro-Landscapes: Management and Selection Practices on Microbial Communities in a Traditional Fermented Beverage

Colonche is a traditional beverage produced in Mexico by the fermentation of fruits of several cacti species. In the Meridional Central Plateau region of Mexico, where this study was conducted, it is mainly produced with fruits of Opuntia streptacantha; there, the producers perform spontaneous fermentation and/or fermentations through inoculums. Several factors can change the microbial community structure and dynamics through the fermentation process, but little attention has been directed to evaluate what type and extent of change the human practices have over the microbial communities. This study aims to assess the microbiota under spontaneous and inoculated fermentation techniques, the microorganisms present in the inoculums and containers, and the changes of microbiota during the process of producing colonche with different techniques. We used next-generation sequencing of the V3-V4 regions of the 16S rRNA gene and the ITS2, to characterize bacterial and fungal diversity associated with the different fermentation techniques. We identified 701 bacterial and 203 fungal amplicon sequence variants (ASVs) belonging to 173 bacterial and 187 fungal genera. The alpha and beta diversity analysis confirmed that both types of fermentation practices displayed differences in richness, diversity, and community structure. Richness of bacteria in spontaneous fermentation (0D = 136 ± 0.433) was higher than in the inoculated samples (0D = 128 ± 0.929), while fungal richness in the inoculated samples (0D = 32 ± 0.539) was higher than in spontaneous samples (0D = 19 ± 0.917). We identified bacterial groups like Lactobacillus, Leuconostoc, Pediococcus and the Saccharomyces yeast shared in ferments managed with different practices; these organisms are commonly related to the quality of the fermentation process. We identified that clay pots, where spontaneous fermentation is carried out, have an outstanding diversity of fungal and bacterial richness involved in fermentation, being valuable reservoirs of microorganisms for future fermentations. The inoculums displayed the lowest richness and diversity of bacterial and fungal communities suggesting unconscious selection on specific microbial consortia. The beta diversity analysis identified an overlap in microbial communities for both types of fermentation practices, which might reflect a shared composition of microorganisms occurring in the Opuntia streptacantha substrate. The variation in the spontaneous bacterial community is consistent with alpha diversity data, while fungal communities showed less differences among treatments, probably due to the high abundance and dominance of Saccharomyces. This information illustrates how traditional management guides selection and may drive changes in the microbial consortia to produce unique fermented beverages through specific fermentation practices. Although further studies are needed to analyze more specifically the advantages of each fermentation type over the quality of the product, our current analysis supports the role of traditional knowledge driving it and the relevance of plans for its conservation.

Current Status, Recent Advances, and Main Challenges on Table Olive Fermentation: The Present Meets the Future

Table olives are among the most well-known fermented foods, being a vital part of the Mediterranean pyramid diet. They constitute a noteworthy economic factor for the producing countries since both their production and consumption are exponentially increasing year by year, worldwide. Despite its significance, olive’s processing is still craft based, not changed since antiquity, leading to the production of an unstable final product with potential risk concerns, especially related to deterioration. However, based on industrial needs and market demands for reproducible, safe, and healthy products, the modernization of olive fermentation processing is the most important challenge of the current decade. In this sense, the reduction of sodium content and more importantly the use of suitable starter cultures, exhibiting both technological and potential probiotic features, to drive the process may extremely contribute to this need. Prior, to achieve in this effort, the full understanding of table olive microbial ecology during fermentation, including an in-depth determination of microbiota presence and/or dominance and its functionality (genes responsible for metabolite production) that shape the sensorial characteristics of the final product, is a pre-requisite. The advent of meta-omics technology could provide a thorough study of this complex ecosystem, opening in parallel new insights in the field, such as the concept of microbial terroir. Herein, we provide an updated overview in the field of olive fermentation, pointing out some important challenges/perspectives that could be the key to the olive sector’s advancement and modernization.

Metagenomic Study on Chinese Homemade Paocai: The Effects of Raw Materials and Fermentation Periods on the Microbial Ecology and Volatile Components

“Chinese paocai” is typically made by fermenting red radish or cabbage with aged brine (6–8 w/w). This study aimed to reveal the effects of paocai raw materials on fermentation microorganisms by metagenomics sequencing technology, and on volatile organic compounds (VOCs) by gas chromatography–mass spectroscopy, using red radish or cabbage fermented for six rounds with aged brine. The results showed that in the same fermentation period, the microbial diversity in cabbage was higher than that in red radish. Secundilactobacillus paracollinoides and Furfurilactobacillus siliginis were the characteristic bacteria in red radish paocai, whereas 15 species of characteristic microbes were found in cabbage. Thirteen kinds of VOCs were different between the two raw materials and the correlation between the microorganisms and VOCs showed that cabbage paocai had stronger correlations than radish paocai for the most significant relationship between 4-isopropylbenzyl alcohol, α-cadinol, terpinolene and isobutyl phenylacetate. The results of this study provide a theoretical basis for understanding the microbiota and their relation to the characteristic flavors of the fermented paocai.

Microbial Communities in Retail Draft Beers and the Biofilms They Produce

In the beer brewing industry, microbial spoilage presents a consistent threat that must be monitored and controlled to ensure the palatability of a finished product. Many of the predominant beer spoilage microbes have been identified and characterized, but the mechanisms of contamination and persistence remain an open area of study. Postproduction, many beers are distributed as kegs that are attached to draft delivery systems in retail settings where ample opportunities for microbial spoilage are present. As such, restaurants and bars can experience substantial costs and downtime for cleaning when beer draft lines become heavily contaminated. Spoilage monitoring on the retail side of the beer industry is often overlooked, yet this arena may represent one of the largest threats to the profitability of a beer if its flavor profile becomes substantially distorted by contaminating microbes. In this study, we sampled and cultured microbial communities found in beers dispensed from a retail draft system to identify the contaminating bacteria and yeasts. We also evaluated their capability to establish new biofilms in a controlled setting. Among four tested beer types, we identified over a hundred different contaminant bacteria and nearly 20 wild yeasts. The culturing experiments demonstrated that most of these microbes were viable and capable of joining new biofilm communities. These data provide an important reference for monitoring specific beer spoilage microbes in draft systems and we provide suggestions for cleaning protocol improvements.

IMPORTANCE Beer production, packaging, and service are each vulnerable to contamination by microbes that metabolize beer chemicals and impart undesirable flavors, which can result in the disposal of entire batches. Therefore, great effort is taken by brewmasters to reduce and monitor contamination during production and packaging. A commonly overlooked quality control stage of a beer supply chain is at the retail service end, where beer kegs supply draft lines in bars and restaurants under nonsterile conditions. We found that retail draft line contamination is rampant and that routine line cleaning methods are insufficient to efficiently suppress beer spoilage. Thus, many customers unknowingly consume spoiled versions of the beers they consume. This study identified the bacteria and yeast that were resident in retail draft beer samples and also investigated their abilities to colonize tubing material as members of biofilm communities.