Comparison of northeast sauerkraut fermentation between single lactic acid bacteria strains and traditional fermentation

Decoding microbiota and metabolite transformation in inoculated fermented suansun using metagenomics, GC-MS, non-targeted metabolomics, and metatranscriptomics:Impacts of different Lactobacillus plantarum strains

Using metagenomics, GC-MS, non-targeted metabolomics, and metatranscriptomics, we investigated the microbial communities and metabolites in two different Lactobacillus plantarum fermentations. Metagenomics revealed Weissella cibaria dominantly contributed to the DACN766-fermented suansun (LPS1) and Lactiplantibacillus pentosus to the DACN760-fermented suansun (LPS2). GC-MS identified 38 and 40 flavor compounds in LPS1 and LPS2, respectively, with p-cresol, 4-hydroxybenzaldehyde, acetic acid, hexanal, and propionic acid crucial for aroma development. LPS2 exhibited higher levels of p-cresol and acetic acid, contributing to its stronger sour and pungent flavors, which was achieved by regulating many metabolisms like glycolysis and tyrosine metabolism. In contrast, Weissella cibaria plays a role in mitigating off-flavors, resulting in a milder flavor profile in LPS1. Non-targeted metabolomics indicated 70.78% of differential metabolites were upregulated in LPS1. Conversely, the elevated expression of tryptophan and tyrosine underscores the more pronounced sour and odor-producing characteristics observed in LPS2. Metatranscriptomics highlighted the regulation of genes like XFA, XFT, and XFM, which inhibit the formation of the precursors of p-cresol and indole in LPS2. This integrated multi-omics analysis provides deep insights into the fermentation dynamics, facilitating the targeted selection of Lactobacillus plantarum strains with flavor-regulating capabilities.

Dynamics of microbial communities and metabolites during the fermentation of Ningxia goji berry wine: An integrated metagenomics and metabolomics approach

Ningxia Goji Berry Wine (NGBW), a traditional Chinese fermented beverage, exhibits complex flavor quality changes during fermentation, the mechanisms of which remain insufficiently elucidated. This study aimed to elucidate the dynamic shifts in physicochemical properties, metabolites, and microbial communities throughout the controlled fermentation process of NGBW. Metabolomic analysis identified 8 key differential volatile metabolites (VOCs) and 406 differential non-volatile metabolites. The enrichment analysis of KEGG metabolic pathways revealed that, during the fermentation of NGBW, ten critical metabolic pathways-Purine metabolism, Glycine, Serine, and Threonine metabolism, Galactose metabolism, and the Citric Acid (TCA) Cycle-play essential roles. Amplicon sequencing indicated that 25 bacterial genera dominated the microbial ecosystem (relative abundance ≥ 0.1 %). Spearman correlation analysis revealed significant associations between 5 core microorganism and flavor compounds, and 25 core microbes with non-volatile metabolites, suggesting their pivotal roles in flavor formation. This study provides a theoretical basis for optimizing the fermentation process and enhancing the flavor quality of NGBW.

The dynamic changes and correlations between biochemical properties, flavor and microbial community during fermentation of asparagus by-products

Asparagus by-products are the promising resource that urgently need to be re-valorized. This study investigated the dynamic changes in physicochemical properties, organic acids, free amino acids, volatile flavor compounds, microbial succession, and their correlations during 7-day spontaneous fermentation of asparagus by-products. Dominant organic acids (lactic acid and acetic acid) and free amino acids (Ser, Glu, and Ala) increased with fermentation time, with lactic acid reaching 7.73 ± 0.05 mg/mL and Ser increasing 56-fold after 7 days. A total of 58 volatile flavor compounds were identified using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPEM/GC-MS), with esters, alcohols and acids as the main volatile flavor compounds. Fourteen volatile flavor compounds had odor activity value >1. High-throughput sequencing showed Firmicutes and Proteobacteria as the main bacterial phyla, dominated by lactic acid bacteria (Levilactobacillus, Lactiplantibacillus, Weissella). Correlation analysis revealed that five bacterial genera (Levilactobacillus, Lactiplantibacillus, Enterobacter, Pediococcus and Acetobacter) were highly correlated with organic acids, free amino acids, and volatile flavor compounds, indicating their pivotal role in forming the characteristic flavor of fermented asparagus by-products (FAPS). This study provides new insights into the flavor and microbial profile of FAPS, offering a strategy for value-added processing and industrial production.

Deciphering the flavor constituents, microbiota and physicochemical properties of Yancaigao, a traditional sour rice paste from Southwest China

Yancaigao, a distinctive fermented condiment indigenous to Southwest China, imparts unique sour flavor profile to various culinary applications. This study investigated the organic acid profile, volatile flavor constitutes, and microbial community of two fermented and six blended Yancaigao samples. Organic acid analysis revealed that lactic acid (86.51-117.28 mg/g) was the predominant organic acid in fermented Yancaigao, accounting for 97.40-98.08 % of total organic acids. It was significantly higher than those observed in blended Yancaigao (1.92-13.91 mg/kg). Headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis identified 88 volatile compounds, mainly encompassing acids (10), alcohols (23), aldehydes (19), ketones (13), esters (5), pyrazines (4), ethers (2), olefins (2), benzene (1), and sulfide (1). Lactic acid, 2,3-butanediol, dimethyl trisulfide, 1-octen-3-one, and dimethyl disulfide were determined to be key aroma compounds of the eight Yancaigao samples, based on odor activity value and Orthogonal partial least squares-discriminant analysis (OPLS-DA). Notably, trans-α,α-5-trimethyl-5-vinyltetrahydro-2-furanmethanol and 2,3-pentanedione were exclusively detected in fermented Yancaigao. Microbial community analysis revealed that Pseudomonas (43.37 %) and Methyloversatilis (14.03 %) were the dominant microorganisms, indicating potential microbial contamination. This study could provide valuable insights for quality evaluation and integrated development of traditional fermented Yancaigao.

Analysis of Microbial Diversity Dominating Nitrite Enzymatic Degradation and Acidic Degradation in the Fermentation Broth of Northeast Sauerkraut

Nitrite hazard is an important food safety issue in the production process of Chinese Northeastern sauerkraut, but this nitrite can be eliminated through microbial enzymatic degradation and acidic degradation as fermentation progresses. Therefore, analyzing the microbial diversity that dominates nitrite degradation in Chinese Northeastern sauerkraut can provide a reference for its safe production. In this study, based on the dynamic monitoring of nitrite concentration, pH, and the abundance of nitrite reductase genes (nirK and nirS) and the application of high-throughput sequencing technology and various statistical analysis methods, the microbial groups associated with nitrite enzymatic degradation and acidic degradation in Northeast sauerkraut fermentation broth were analyzed. During the nitrite peak period of Northeast sauerkraut fermentation broth, the nitrite concentration reached 32.15 mg/kg, the pH was 4.7, and the abundances of the nitrite reductase genes nirK and nirS were 3.0 × 104 and 4.9 × 104 copies/μL, respectively. At this stage, nitrite degradation was likely dominated by enzymatic activities. Microbial phyla such as Bacteroidetes (38.8%), Proteobacteria (19.2%), and the archaeal phylum Euryarchaeota (1.1%) showed strong correlations with nitrite. Among the genera within these three phyla, Chryseobacterium, Elizabethkingia, and Aeromonas exhibited significant differences in abundance compared to the late fermentation stage and were identified as the primary microbial groups likely driving the enzymatic degradation. During the nitrite degradation period, the nitrite concentration decreased to 0.04 mg/kg, the pH dropped to 3.6, and the abundances of nirK and nirS genes were reduced to 1.0 × 103 copies/μL. At this stage, the nitrite degradation was primarily driven by acid activity. The bacterial phylum Firmicutes (99%) exhibited a strong correlation with pH. Within this phylum, the genus Lactobacillus, which showed significant differences in abundance compared to the early fermentation stage, was identified as the primary microbial group indirectly contributing to acidic degradation. This study provides guidance for the isolation of food-grade prokaryotic microbial strains capable of nitrite degradation. Additionally, the findings offer a methodological reference for conducting future research on nitrite-degrading microorganisms in fermented vegetable broths.

Effects of Different Production Methods on the Quality and Microbial Diversity of Sauerkraut in Northeast China

Sauerkraut is a popular fermented food in Northeast China. However, owing to the different production methods used, the quality of commercial sauerkraut is often quite different, which is reflected mainly in the differences between starter culture (Group-L), additive addition (Group-P) and natural fermentation (Group-H) methods. The purpose of this study was to explore the differences among the three fermentation methods by measuring physical and chemical indices, microbial diversity indices, flavour indices and volatile substances. The results revealed that there was no significant difference in the physical or chemical indices among the groups. The content of esters and alcohols in Group-L was the highest, and the taste richness, aftertaste-a and aftertaste-b were the highest, which had a positive effect on flavour. The highest level of microbial diversity was found in Group-H, which contained many pathogenic bacteria, such as Janibacter, Pseudomonas, and Vagococcus, which reduced the food safety of sauerkraut. At the genus level, the dominant bacterial genera in the starter and additive groups included Lactobacillus and Pediococcus. The correlation analysis revealed that Group-L was positively correlated with the contents of Lactobacillus plantarum, Lactobacillus brevis, Pediococcus, ethyl oleate and vanillin. In summary, this study evaluated the different production methods of northeast sauerkraut, providing theoretical support for the production of high-quality northeast sauerkraut.

Characterization of key aroma-active compounds in fermented chili pepper (Capsicum frutescens L.) using instrumental and sensory techniques

The aroma profile of fermented chili pepper was analyzed using gas chromatography-mass spectrometry (GC-MS) coupled with chromatography-olfactometry (GC-O). A total of 19 aroma-active compounds were detected, exhibiting aroma intensities spanning from 1.8 to 4.2. And 12 aroma-active compounds were determined as pivotal odorants through odor activity value (OAV) calculation. Concentrations of these aroma-active compounds were quantified and subsequently employed in reconstructing the aroma profile of fermented chili pepper. Quantitative descriptive sensory analysis and electronic nose analysis proved that the aroma profile of fermented chili pepper was basically reconstituted. Omission experiments confirmed that methyl salicylate, linalool, 2-methoxy-3-isobutylpyrazine, and phenylethyl alcohol were the key aroma-active compounds of fermented chili pepper. Moreover, the perceptual interactions between the key aroma-active compounds were investigated. It was found that methyl salicylate masked the floral aroma, while phenylethyl alcohol had an additive effect on the aroma of linalool and 2-methoxy-3-isobutylpyrazine.

Analysis of flavor substances changes during fermentation of Chinese spicy cabbage based on GC-IMS and PCA

This study employed a combination of principal component analysis (PCA) and gas chromatography-ion mobility spectrometry (GC-IMS) to examine the distinctive taste mixtures produced by Chinese spicy cabbage (CSC) fermented at varying temperatures. As the fermentation progressed, the pH gradually decreased and stabilized after the 11 days of fermentation, and the total content of organic acids and short-chain fatty acids increased. A total of 49 volatile mixtures were detected during CSC fermentation and storage for 21 days. These included 7 aldehydes, 6 alcohols, 7 esters, 6 ketones, 5 pyrazines, 4 sulfides, 4 phenols, 2 ethers, 2 olefins, and 1 acid. With time, the content of most volatile flavor substances decreased. PCA of the signal intensities of the volatile chemicals in the samples showed significant differences in the flavor of CSC fermented at different temperatures; consequently, the samples fermented at different temperatures were effectively separated in relatively independent regions of CSC. Therefore, low-temperature fermentation and storage at 4 °C were more suitable for CSC. Based on the identified volatile chemicals, HS-GC-IMS and PCA could effectively construct the flavour fingerprints of CSC samples. This study provided a theoretical basis for improving the fermentation quality of CSC.

Effects of community ecological network construction on physicochemical, microbial, and quality characteristics of inoculated northeast sauerkraut: A new insight in food fermentation processes

The enhancement of the quality of northeast sauerkraut can be achieved by inoculation with lactic acid bacteria. However, a comprehensive ecological understanding of the intricate dynamic processes involved is currently lacking, which could yield valuable insights for regulating sauerkraut fermentation. This study compares spontaneously sauerkrauts with the sauerkrauts inoculated with autochthonous Lactiplantibacillus plantarum SC-MDJ and commercial L. plantarum, respectively. We examine their physicochemical properties, quality characteristics, bacterial community dynamics, and ecological network interactions. Inoculation with L. plantarum leads to reduced bacterial community richness and niche breadth, but an increase in robustness, interactions, and assembly processes. Notably, there appears to be a potential correlation between bacterial community structure and quality characteristics. Particularly, sauerkraut inoculated with L. plantarum SC-MDJ may produce a sourness more quickly, possibly attributed to the enhanced ecological role of L. plantarum SC-MDJ. This study establishes a foundation for the targeted regulation of sauerkraut fermentation.

Organic acids drove the microbiota succession and consequently altered the flavor quality of Laotan Suancai across fermentation rounds: Insights from the microbiome and metabolome

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.

Improving the bacterial community, flavor, and safety properties of northeastern sauerkraut by inoculating autochthonous Levilactobacillus brevis

The effect of Levilactobacillus brevis as a starter in northeastern sauerkraut fermentation is still unknown, and further evaluation is worthwhile. Hence, this study aimed to evaluate the effect of autochthonous L. brevis inoculation on the bacterial community succession and formation of flavor and harmful substances in sauerkrauts. Inoculation with L. brevis lowered the pH and increased the total acid content of sauerkrauts (P < 0.05). The nitrite content of the inoculated sauerkraut was significantly lower than that of control (P < 0.05). Moreover, the spoilage bacteria of the inoculated sauerkraut were decreased and nitrogen metabolism was improved. The contents of aldehydes, alcohols, esters, acids, and alkanes increased significantly (P < 0.05), and the sensory attributes such as aroma, sourness, and gloss were also improved. L. brevis was positively and negatively correlated with flavor metabolites and nitrite, respectively, which proved to be a potential starter culture to manufacture sauerkraut.

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

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

Advancing Insights into Probiotics during Vegetable Fermentation

Fermented vegetables have a long history and are enjoyed worldwide for their unique flavors and health benefits. The process of fermentation improves the nutritional value, taste, and shelf life of foods. Microorganisms play a crucial role in this process through the production of metabolites. The flavors of fermented vegetables are closely related to the evaluation and succession of microbiota. Lactic acid bacteria (LABs) are typically the dominant bacteria in fermented vegetables, and they help inhibit the growth of spoilage bacteria and maintain a healthy gut microbiota in humans. However, homemade and small-scale artisanal products rely on spontaneous fermentation using bacteria naturally present on fresh vegetables or from aged brine, which may introduce external microorganisms and lead to spoilage and substandard products. Hence, understanding the role of LABs and other probiotics in maintaining the quality and safety of fermented vegetables is essential. Additionally, selecting probiotic fermentation microbiota and isolating beneficial probiotics from fermented vegetables can facilitate the use of safe and healthy starter cultures for large-scale industrial production. This review provides insights into the traditional fermentation process of making fermented vegetables, explains the mechanisms involved, and discusses the use of modern microbiome technologies to regulate fermentation microorganisms and create probiotic fermentation microbiota for the production of highly effective, wholesome, safe, and healthy fermented vegetable foods.

The Impact of Different Cooking Methods on the Flavor Profile of Fermented Chinese Spicy Cabbage

Chinese spicy cabbage (CSC) is a common traditional fermented vegetable mainly made of Chinese cabbage. In addition to eating raw, boiling and stir-frying are the most common cooking methods for CSC. To identify the impacts of boiling or stir-frying on the quality of CSC, the physicochemical properties, flavor compounds, and sensory properties of CSC were analyzed. A total of 47 volatile flavor compounds (VFCs) were detected by gas chromatography-mass spectrometry. Sulfide was determined as the main flavor compound of CSC, mainly contributed by cabbage, garlic, and onion odors. The content of sulfide decreased significantly after cooking. Nonanal, geranyl acetate, and linalool were newly generated after boiling with odor activity value (OAV) > 1, and contributed fatty, sweet, fruity, and floral odors to BL-CSC. 1-Octen-3-one, 1-octen-3-ol, octanal, nonanal, and (E)-2-nonenal were newly generated after stir-frying with OAV > 1, and contributed mushroom, fatty, and green odors to SF-CSC. Diallyl trisulfide, nonanal, (E)-β-ionone, β-sesquiphellandrene, and (E)-2-decenal were considered as the potential key aroma compounds (KACs) to distinguish the CSCs after different heat treatment. After cooking, the total titratable acidity of CSC increased and the sensory properties changed significantly. This study provides valuable information and guidance on the sensory and flavor changes of thermal processing fermented vegetables.

Flavor Formation in Dry-Cured Fish: Regulation by Microbial Communities and Endogenous Enzymes

Dried salted fish is a traditional dry-cured fish that is sprinkled with salt before the curing process. With a unique flavor as well as diverse varieties, dry-cured fish is popular among consumers worldwide. The presence of various microbial communities during the curing process leads to numerous metabolic reactions, especially lipid oxidation and protein degradation, which influence the formation of flavor substances. However, during industrial curing, the quality of dry-cured fish is difficult to control, leading to the formation of products with diverse flavors. This review describes the curing process of dried salted fish, the key microorganisms involved in the curing process of typical dried salted fish products at home and abroad, and the correlation between biological metabolism and flavor formation and the underlying mechanism. This review also investigates the prospects of dried salted fish products, proposing methods for the analysis of improved curing processes and the mechanisms of dried salted fish. Through a comprehensive understanding of this review, modern production challenges can be addressed to achieve greater control of microbial growth in the system and improved product safety. In addition to advancing our understanding of the processes by which volatile flavor compounds are formed in conventional dry-cured fish products, we expect that this work will also offer a theoretical framework for enhancing their flavor in food processing.

Evaluation and comparison of physicochemical properties, volatile substances, and microbial communities of leaf mustard (Brassica juncea var. multiceps) under natural and inoculated fermentation

Due to the uncontrolled fermentation process and unstable quality of naturally fermented leaf mustard, inoculated fermentation is receiving more attention. Here, the physicochemical properties, volatile compounds, and microbial community in leaf mustard under natural fermentation (NF) and inoculated fermentation (IF) were analyzed and compared. The contents of total acid, crude fiber, and nitrite of leaf mustard were measured. Headspace-solid phase microextraction-gas chromatography-mass spectrometry and orthogonal projection on latent structure-discriminant analysis were used to analyze the differences of volatile compounds in NF and IF leaf mustard. Moreover, Illumina MiSeq high-throughput sequencing technology was employed to reveal the composition of microbiota. The results showed that the nitrite content in leaf mustard after IF (3.69 mg/kg) was significantly lower than that after NF (4.43 mg/kg). A total of 31 and 25 kinds of volatile components were identified in IF and NF, respectively. Among the detected compounds, 11 compounds caused the differences between IF and NF leaf mustard. The results of inter-group difference analysis showed that there were significant differences in fungal flora between IF and NF samples. Saccharomycetes, Kazachstania, and Ascomycota were the landmark microorganisms in IF leaf mustard and the landmark microorganisms in NF were Mortierellomycota, Sordariomycetes, and Eurotiomycetes. The abundance of probiotics (such as Lactobacillus) in IF leaf mustard (51.22%) was higher than that in NF (35.20%) and the abundance of harmful molds (such as Mortierella and Aspergillus) was opposite. Therefore, IF leaf mustard showed the potential to reduce the content of nitrite and harmful molds and increase the beneficial volatile compounds and probiotics. PRACTICAL APPLICATION: Leaf mustard of inoculated fermentation (IF) showed better fermented characteristics than natural fermentation in terms of lower nitrite content, greater beneficial volatile substances, and better potential for increasing probiotics and reducing harmful molds. These results provided a theoretical basis for IF leaf mustard and contributed to the industrial production of fermented leaf mustard.

Fermented Whey Ewe's Milk-Based Fruit Smoothies: Bio-Recycling and Enrichment of Phenolic Compounds and Improvement of Protein Digestibility and Antioxidant Activity

This study aimed to recycle whey milk by-products (protein source) in fruit smoothies (phenolic compounds source) through started-assisted fermentation and delivering sustainable and healthy food formulations capable of providing nutrients that are unavailable due to an unbalanced diet or incorrect eating habits. Five lactic acid bacteria strains were selected as best starters for smoothie production based on the complementarity of pro-technological (kinetics of growth and acidification) traits, exopolysaccharides and phenolics release, and antioxidant activity enhancement. Compared to raw whey milk-based fruit smoothies (Raw_WFS), fermentation led to distinct profiles of sugars (glucose, fructose, mannitol, and sucrose), organic acids (lactic acid and acetic acid), ascorbic acid, phenolic compounds (gallic acid, 3-hydroxybenzoic acid, chlorogenic acid, hydrocaffeic acid, quercetin, epicatechin, procyanidin B2, and ellagic acid) and especially anthocyanins (cyanidin, delphinidin, malvidin, peonidin, petunidin 3-glucoside). Protein and phenolics interaction enhanced the release of anthocyanins, notably under the action of Lactiplantibacillus plantarum. The same bacterial strains outperformed other species in terms of protein digestibility and quality. With variations among starters culture, bio-converted metabolites were most likely responsible for the increase antioxidant scavenging capacity (DPPH, ABTS, and lipid peroxidation) and the modifications in organoleptic properties (aroma and flavor).

Isolation and Identification of Lactic Acid Bacteria and Their Effects on the Off-odor of Burdocks

Burdocks have diverse nutritional and pharmacological functions, but their unique odor is unwelcome. Here, the effect and mechanism of lactic acid bacteria fermentation on the off-odor of burdocks were investigated. The sensory evaluation showed that burdocks had earthy, musty, grassy, and pepper odors. 2-Isobutyl-3-methoxypyrazine (IBMP) and 2-secbutyl-3-methoxypyrazine (IPMP) mainly contributed to burdock's unique off-odor and were identified by gas chromatography-mass spectrometry combined with headspace-solid phase microextraction (HS-SPME-GC-MS) and relative odor activity value (ROAV) analysis. Weissella cibaria ZJ-5 from screened strains performed with the strongest ability to remove the off-odor and generate a fragrant odor, as determined by sensory evaluation. When incubated aerobically together with IBMP during fermentation, ZJ-5 degraded IBMP directly from 149.56 ± 0.72 to 71.55 ± 1.81 ng/mL. Additionally, linoleic acid content in fermented burdocks was significantly decreased compared with unfermented burdocks. (E,Z)-2,6-Nonadienal, which mainly contributed to fermented burdock's odor, may have been generated from linoleic acid during ZJ-5 fermentation, through the acid catalysis pathway. It indicated that LAB fermentation could improve burdock odor by degrading off-odor compounds and precursors and by generating new aldehydes.

Fermented Vegetables and Legumes vs. Lifestyle Diseases: Microbiota and More

Silages may be preventive against lifestyle diseases, including obesity, diabetes mellitus, or metabolic syndrome. Fermented vegetables and legumes are characterized by pleiotropic health effects, such as probiotic or antioxidant potential. That is mainly due to the fermentation process. Despite the low viability of microorganisms in the gastrointestinal tract, their probiotic potential was confirmed. The modification of microbiota diversity caused by these food products has numerous implications. Most of them are connected to changes in the production of metabolites by bacteria, such as butyrate. Moreover, intake of fermented vegetables and legumes influences epigenetic changes, which lead to inhibition of lipogenesis and decreased appetite. Lifestyle diseases' feature is increased inflammation; thus, foods with high antioxidant potential are recommended. Silages are characterized by having a higher bioavailable antioxidants content than fresh samples. That is due to fermentative microorganisms that produce the enzyme β-glucosidase, which releases these compounds from conjugated bonds with antinutrients. However, fermented vegetables and legumes are rich in salt or salt substitutes, such as potassium chloride. However, until today, silages intake has not been connected to the prevalence of hypertension or kidney failure.

The Survival of Psychobiotics in Fermented Food and the Gastrointestinal Tract: A Review

In recent years, scientists have been particularly interested in the gut-brain axis, as well as the impact of probiotics on the nervous system. This has led to the creation of the concept of psychobiotics. The present review describes the mechanisms of action of psychobiotics, their use in food products, and their viability and survival during gastrointestinal passage. Fermented foods have a high potential of delivering probiotic strains, including psychobiotic ones. However, it is important that the micro-organisms remain viable in concentrations ranging from about 10⁶ to 10⁹ CFU/mL during processing, storage, and digestion. Reports indicate that a wide variety of dairy and plant-based products can be effective carriers for psychobiotics. Nonetheless, bacterial viability is closely related to the type of food matrix and the micro-organism strain. Studies conducted in laboratory conditions have shown promising results in terms of the therapeutic properties and viability of probiotics. Because human research in this field is still limited, it is necessary to broaden our understanding of the survival of probiotic strains in the human digestive tract, their resistance to gastric and pancreatic enzymes, and their ability to colonize the microbiota.

Bacterial Diversity Analysis of Chaozhou Sauerkraut Based on High-Throughput Sequencing of Different Production Methods

In this study, high-throughput sequencing technology was used to analyze the bacterial diversity of sauerkraut produced at home and in factories in Chaozhou. The differences in bacterial community structure among different sauerkraut samples were studied by diversity analysis and heat map analysis, and the dominant bacterial genera were analyzed. The results showed that 54 phyla and 622 genera were identified from 10 Chaozhou sauerkraut samples. The bacterial community structures of Chaozhou sauerkraut produced by five factories were similar, and the dominant bacterial genera were the same, which were Lactobacillus, Pediococcus and Weissella. The dominant genus in the sauerkraut samples produced by three families was similar to that in samples produced by the factories. However, the samples from two other families were quite different, and there may be environmental pollution. The samples may also contain possible pathogenic microorganisms such as Pseudomonas and Vibrio. Overall, there were still some differences in the bacterial community structure of Chaozhou sauerkraut factory-produced and household-handmade samples. To the best of our knowledge, this paper is the first to compare the bacterial diversity of homemade and factory-produced Chaozhou sauerkraut, laying the foundation for further research on Chaozhou sauerkraut.

Analysis of Microbial Diversity and Metabolites in Sauerkraut Products with and without Microorganism Addition

The microbial compositions and metabolites of fermented sauerkraut with and without the addition of microorganisms have been compared. The OTU clustering, nonvolatile compounds, volatile compounds and associations between bacterial taxa and metabolites were analyzed by 16S rRNA high-throughput sequencing technology, ultra performance liquid chromatography (UPLC), gas chromatography ion mobility mass spectrometry (GC-IMS) and the O2PLS model studies. The results showed that at the phylum level, the microbial species in the four sauerkraut types consisted mainly of the phyla Firmicutes and Proteobacteria, but different modes of microbial addition formed their own unique microbial communities. There were significant differences in the microbial communities among different northeast China sauerkraut samples, and different microbial communities exerted similar effects to inhibit Firmicutes production. At the genus level, sauerkraut without added microorganisms had the lowest microbial diversity. A total of 26 amino acids and 11 organic acids were identified and were more abundant in nonmicrobially fermented sauerkraut; 88 volatile organic compounds were identified in the 4 types of sauerkraut, with the microbially fermented sauerkraut being richer in alcohols, esters and acids. Different brands of sauerkraut contain their own unique flavor compounds. Cystine and tyrosine, ascorbic acid and acetic acid, and alcohols and esters are closely related to a wide range of microorganisms in sauerkraut. Elucidating the correlations among microbiota and metabolites will help guide future improvements in sauerkraut fermentation processes.

Influence of Different Ratios of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus on Fermentation Characteristics of Yogurt

Lactic acid bacteria (LAB) are industrially important bacteria that are widely used in the fermented food industry, especially in the manufacture of yogurt. The fermentation characteristics of LAB are an important factor affecting the physicochemical properties of yogurts. Here, different ratios of L. delbrueckii subsp. bulgaricus IMAU20312 and S. thermophilus IMAU80809 were compared with a commercial starter JD (control) for their effects on viable cell counts, pH values, titratable acidity (TA), viscosity and water holding capacity (WHC) of milk during fermentation. Sensory evaluation and flavour profiles were also determined at the end of fermentation. All samples had a viable cell count above 5.59 × 10⁷ CFU/mL at the end of fermentation, and a significant increase in TA and decrease in pH were observed. Viscosity, WHC and the sensory evaluation results of one treatment ratio (A3) were closer to the commercial starter control than the others. A total of 63 volatile flavour compounds and 10 odour-active (OAVs) compounds were detected in all treatment ratios and the control according to the results from solid-phase micro-extraction-gas chromatography-mass spectrometry (SPME-GC-MS). Principal components analysis (PCA) also indicated that the flavour characteristics of the A3 treatment ratio were closer to the control. These results help us understand how the fermentation characteristics of yogurts are affected by the ratio of L. delbrueckii subsp. bulgaricus to S. thermophilus in starter cultures; this is useful for the development of value-added fermented dairy products.

Evaluation of Chemical and Sensory Characteristics of Sauerkraut Juice Powder and its Application in Food

Sauerkraut juice is rich in bioactive compounds; however, it is considered a byproduct of the production process. An innovative solution was found through the process of spray-drying to obtain sauerkraut juice powder. The aim of this study was to evaluate chemical and sensory characteristics of sauerkraut juice powder (SJP) and its application in foodstuffs. For SJP, total phenol content, antiradical activity, and nutritional value were determined, and the results showed that SJP is rich in minerals, especially calcium and potassium, as well as organic acids and vitamin C. SJP contains 12% NaCl and a total phenol content of 359.54 mg GAE 100 g^-1 dw. SJP has umami attributes, such as sweet, sour, and salty. Sensory tests-descriptive, rate-all-that-apply, overall liking, and volatile profile determination-were carried out separately in SJP experimental samples with olive oil and sour cream. Among the sweet, sour, and salty flavours, garlic, yogurt, and mayonnaise were also mentioned. In the detection of volatile compounds, leafy and grassy green aromas with light almond were identified in the samples with olive oil and butter and rancid cheese and fishy/amine odours were identified in samples with sour cream. There were significant differences in the overall likability of samples, but the experimental samples with SJP were more popular than control samples; therefore, SJP may be used as a salt alternative in food applications.

Effect of Autochthonous Lactic Acid Bacteria-Enhanced Fermentation on the Quality of Suancai

The lactic acid bacteria (LABs) used for fermentation have an extremely vital impact on the quality of Suancai, a fermented vegetable. The bacterial diversity and metabolites of inoculated Suancai with LABs, including Lactiplantibacillus plantarum (Lb. plantarum), Levilactabacillus brevis (Lb. brevis), and Leuconostoc mesenteroides (Leu. mesenteroides), were investigated. The inoculation of LABs significantly decreased the pH and the content of nitrite. The Suancai inoculated with LABs had a higher content of the total titratable acidity (TTA) and organic acids than spontaneous fermentation. The LABs inoculation significantly influenced the bacterial community structures, which directly or indirectly caused changes of metabolites. The bacterial community profiles of Suancai inoculated with Lb. plantarum were more similar to spontaneous fermentation. The inoculation of Lb. plantarum, Lb. brevis, and Leu. mesenteroides could increase its abundance in Suancai. Whatever the species inoculated, Lb. plantarum was always the predominant bacterium in Suancai after fermentation. The inoculated LABs were positively correlated with most volatile compounds and amino acids. The inoculated LABs significantly improved the volatile compounds and amino acid content of Suancai. This study could contribute to understanding the function of starters in Suancai fermentation and promote the selection of applicable starters for high-quality Suancai production.

How Microbiome Composition Correlates with Biochemical Changes during Sauerkraut Fermentation: a Focus on Neglected Bacterial Players and Functionalities

This study provided a new perspective on the bacterial community succession during sauerkraut fermentation, and on resulting metabolic functions. While culture-dependent methods confirmed the key role of the well-known core microbiome species, metagenomic approach (shotgun) revealed Secundilactobacillus malefermentans as a species of the core microbiome, especially during the last weeks of fermentation. Although the potentiality of S. malefermentans has not yet fully explored, it held core functional genes usually attributed to others lactic acid bacteria driving sauerkraut fermentation. Based on our results it is arguable that S. malefermentans might have a key a role during sauerkraut fermentation carried out at low temperature. Under our experimental conditions, the profile of phenolic compounds changed throughout sauerkraut fermentation. The amount of free phenolics, including free phenolic acids, increased at the beginning of the fermentation, whereas the conversion of phenolic acids into microbial derivatives was consistent during the last part of the sauerkraut fermentation. We pioneered correlating changes in the phenolics profile to changes in the microbiome, although the framework presented is still fragmentary. Annotated genes linked to the phenolic compounds metabolism (VprA and padA) were found in many core species during the whole process. A high metabolic potential for phenolics bioconversion emerged for lactobacilli and Pediococcus spp. through correlation analysis between microbiome composition and phenolics profile. IMPORTANCE Our study was not limited to describe the succession pattern of the microbial community during sauerkraut fermentation, but also revealed how some neglected bacterial players belong to the core species during sauerkrauts processing, especially at low temperature. Such species might have a role as potential starters to optimize the fermentation processes and to obtain sauerkrauts with improved and standardized nutritional and sensory features. Furthermore, our correlations between microbiome composition and phenolics profile might also represent new references for sauerkraut biotechnology, aiming to identify new metabolic drivers of potential sauerkraut functionalities. Finally, sauerkraut ecosystem is a tractable model, although with high level of complexity, and resultant ecological information might be extended to other plant ecosystems.

Screening of Lactiplantibacillus plantarum with High Stress Tolerance and High Esterase Activity and Their Effect on Promoting Protein Metabolism and Flavor Formation in Suanzhayu, a Chinese Fermented Fish

In this study, three Lactiplantibacillus plantarum, namely 3-14-LJ, M22, and MB1, with high acetate esterase activity, acid, salt, and high-temperature tolerance were selected from 708 strains isolated from fermented food. Then, L. plantarum strains MB1, M22, and 3-14-LJ were inoculated at 107 CFU/mL in the model and 107 CFU/g in actual Suanzhayu systems, and the effects during fermentation on the physicochemical properties, amino acid, and volatile substance were investigated. The results showed that the inoculated group had a faster pH decrease, lower protein content, higher TCA-soluble peptides, and total amino acid contents than the control group in both systems (p < 0.05). Inoculation was also found to increase the production of volatile compounds, particularly esters, improve the sour taste, and decrease the bitterness of the product (p < 0.05). L. plantarum M22 was more effective than the other two strains in stimulating the production of isoamyl acetate, ethyl hexanoate, and ethyl octanoate. However, differences were discovered between the strains as well as between the model and the actual systems. Overall, the isolated strains, particularly L. plantarum M22, have good fermentation characteristics and have the potential to become excellent Suanzhayu fermenters in the future.

Flavour Generation during Lactic Acid Fermentation of Brassica Vegetables—Literature Review

Fermentation is a method of food preservation that has been used for centuries. Lactic acid fermentation, apart from extending the shelf-life of vegetables, affects significantly the flavour of food products. In this review, the formation of flavour, including both taste and aroma, in fermented Brassica vegetables is summarized. The flavour-active compounds are generated in various metabolic pathways from many precursors present in raw materials used for fermentation. In Brassica vegetables, a unique group of chemicals, namely glucosinolates, is present, which significantly influence the flavour of fermented products. In this summary, we took a closer look at the flavour of two of the most commonly eaten worldwide fermented Brassica products, which are sauerkraut and kimchi. Finally, the needs and directions for future studies were addressed.

Microbial Diversity and Quality-Related Physicochemical Properties of Spicy Cabbage in Northeastern China and Their Correlation Analysis

Chinese spicy cabbage (CSC) is a popular special fermented food in Northeast China. The bacterial community and quality of CSC from different regions of northeastern China (Group_J: Jilin province, Group_L: Liaoning province, Group_H: Heilongjiang province) at retail (Group_P) and home-made (Group_C) were investigated in this study. The determination of the microbial community was achieved using high-throughput sequencing and the quality-related physicochemical characteristics included pH, salinity, total acid (TA), amino acid nitrogen (AAN), reducing sugar (RS), nitrite, and biogenic amines (BAs). Based on OPLS-DA analysis, there was a difference between the quality of Group_C and Group_P. No significant difference was observed in province grouping. Proteobacteria and Firmicutes were the dominant phyla, and the dominant genera were Lactobacillus, Pantoea, Weissella, and Pseudomonas. All groups had significant differences in community structure (p < 0.05). Compared with Group_C, the relative abundance of opportunistic pathogens (Pseudomonas and Serratia) in Group_P was lower. Pseudomonas and Serratia were the biomarkers in Group_H. At the genus level, Lactobacilluss and Weissella had a positive correlation with pH, Cadaverrine, and salinity (p < 0.05), however, they were negatively related to tryptamine. Pseudomonas was negatively correlated with salinity (p < 0.05). Bacterial community and physicochemical parameters of CSC, as well as the correlation between them, were discussed in this study, providing a reference for future studies on CSC inoculation and fermentation.

Bioactive Properties, Volatile Compounds, and Sensory Profile of Sauerkraut Are Dependent on Cultivar Choice and Storage Conditions

Sauerkraut is produced by cabbage fermentation either spontaneously or by adding lactic acid bacteria. Although commercial cabbage cultivars are more desirable due to their higher yield and uniformity, traditional cultivars are highly prized for their unique sensory characteristics and suitability for fermentation. The aim of this study was to investigate the properties of sauerkrauts from traditional cabbage cultivars ('Brgujski' and 'Žminjski') compared to commercial samples, and to unravel the effects of ambient (18 °C) and cold storage (4 °C) on sauerkraut properties. Higher total phenolic contents and total antioxidant capacities measured by both FRAP and DPPH methods were observed for sauerkrauts from traditional cultivars. In total, 32 volatile compounds were identified, and differences in the volatile profile were observed among the investigated sauerkrauts. The sensory properties of traditional cabbage cultivars were on par, or even better, compared to those of commercially available sauerkraut products. The cold storage conditions characteristic of commercial environments preserved the total antioxidant capacity, the red to green color ratio (a), as well as the lightness (L) of sauerkraut compared to the ambient temperatures characteristic of domestic conditions, indicating the preservation of bioactive compounds responsible for the purple cabbage head coloration of the investigated traditional cultivars.

Effects of Lactobacillus plantarum C7 and Staphylococcus warneri S6 on flavor quality and bacterial diversity of fermented meat rice, a traditional Chinese food

Fermented meat rice (FMR) is a traditional Chinese fermented food with special flavor and abundant microorganisms. Lactobacillus and Staphylococcus species have been found to be excellent strains in FMR during fermentation. However, their roles in FMR flavor formation remain yet to be elucidated. Here, we investigated the correlation between physicochemical properties and volatile flavor components, as well as the microbial community during FMR fermentation. First, we determined pH, total titratable acids (TTA), proteins, total lipids, organic acids, free amino acids (FAAs), and volatile flavor compounds (VFCs). With increasing fermentation time, inoculation with Lactobacillus plantarum C7+ Staphylococcus warneri S6 (LP + SW) accelerated the decrease in pH, increased TTA, and reduced protein and total lipid content of FMR. In addition, LP + SW inoculation resulted in significantly (P < 0.05) higher contents of β-eudesmol, nerolidol, ethyl caproate, citronellal, lactic acid, and most FAAs (aspartic acid, glutamic acid, alanine, and lysine) in FMR compared to natural fermentation. Second, inoculated fermentation promoted the growth of Lactobacillus plantarum and/or Staphylococcus warneri and inhibited the growth of some potentially pathogenic microorganisms such as Acinetobacter and Enhydrobacter. Lactobacillus and Staphylococcus were found to be highly correlated with the physicochemical properties and VFCs (P < 0.05) of FMR as indicated by redundancy analysis (RDA) and partial least squares (PLS, VIP > 1.0) analysis. Finally, Spearman's correlation (| r | ≥ 0.7, P < 0.05) analysis of SPSS was visualized by the Cytoscape software. The findings suggest that inoculation with L. plantarum C7 and/or S. warneri S6 can significantly improve the flavor quality of FMR.

Effect of starter cultures mixed with different autochthonous lactic acid bacteria on microbial, metabolome and sensory properties of Chinese northeast sauerkraut

Effects of mixed cultures composed of any two of four autochthonous lactic acid bacteria on fermentation of Chinese northeast sauerkraut were investigated in this study. Results indicated that different mixed cultures inoculation generated diversified physicochemical, microbiological and flavor quality of sauerkraut. Compared to spontaneous fermentation, mix-culture fermentation showed significant higher population of lactic acid bacteria and lower amounts of undesirable microorganisms. Free amino acids increased by 2- to 5-fold from initial level in spontaneous and mix-culture fermentation, with the lowest production by spontaneous fermentation. Moreover, mix-culture fermentation promoted the flavor formation based on the analysis of HS-SPME/GC-MS, E-nose, E-tongue and sensory evaluation, especially for the mixed culture of Leu. mesenteroides and L. plantarum. These results highlighted that using a mixed culture made up with Leu. mesenteroides and L. plantarum could be a potential way to improve the quality of sauerkraut, which could provide an alternative way to meet consumers' requirement.

Improving the quality of Suancai by inoculating with Lactobacillus plantarum and Pediococcus pentosaceus

The quality characteristics of Suancai fermented with Lactobacillus plantarum CGMCC No.20193 (Lb. plantarum) and Pediococcus pentosaceus CGMCC No. 20192 (P. pentosaceus) were investigated. Their inoculation affected the bacterial communities revealed by Pacbio Sequel platform. After fermentation, the dominant phylum and genus in inoculation and spontaneous fermented Suancai were Firmicutes and Lactobacillus. Compared with single inoculation, the co-inoculation of Lb. plantarum and P. pentosaceus had a higher bacterial diversity. The Suancai co-inoculated with Lb. plantarum and P. pentosaceus had a more similar VCs profile with spontaneous fermented Suancai. The inoculation of Lb. plantarum and P. pentosaceus increased the content of organic acids, such as lactate, acetate, citrate, succinate, malate and tartrate. The most amino acids content in Suancai fermented with Lb. plantarum and P. pentosaceus were higher than that in spontaneous fermented Suancai. Compared single inoculation, the Suancai co-inoculated with Lb. plantarum and P. pentosaceus had a higher similarity of organoleptic tastes with spontaneous fermented Suancai. These results may facilitate the understanding of the starters' effects on the Suancai fermentation and the selection of applicable starters to manipulate the flavor.

Effect of ripening and variety on the physiochemical quality and flavor of fermented Chinese chili pepper (Paojiao)

This work monitored the effect of ripening and variety on the physiochemical quality and flavor of fermented Chinese chili pepper (Paojiao). Three commercial varieties of chili pepper (Capsicum frutescens Linn.) at three ripening stages were selected. Physiochemical quality (color, texture, and vitamin C) and flavor properties [capsaicinoids, free amino acid (FAA), and aroma] were determined and compared by multivariate data analysis. The hardness and chewiness decreased, while the contents of vitamin C, capsaicin, and taste-active FAAs increased in Paojiao with ripening. More volatiles were found in green peppers. Fingerprinting and multivariate data analysis revealed that ester, aldehydes, and terpenes were discriminant volatiles that significantly changed in Paojiao during ripening. In general, ripening and variety greatly affect the physiochemical and flavor quality of peppers and their effects intensify after fermentation.