Fermentation of Chinese sauerkraut in pure culture and binary co-culture with Leuconostoc mesenteroides and Lactobacillus plantarum

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.

An innovative way to treat cash crop wastes: The fermentation characteristics and functional microbial community using different substrates to produce Agricultural Jiaosu

With the increase of global demand for cash crops, a large of cash crop waste was produced and caused severe environmental issues. To produce Agricultural Jiaosu (AJ) using these wastes is a sustainable waste disposal method. However, the fermentation mechanism, metabolites, and microbial characteristics of AJ fermented with different substrates remain unclear. In this study, the effects of different substrates (fruit and vegetable waste and Chinese herbal medicine waste) on the fermentation characteristics of AJ, including metabolites and microbial community properties, were investigated. The results revealed that AJ fermentation was a process of converting organic matter into organic acids and other metabolites, mainly including hydrolysis, acidogenesis, and maturation stages. At the genus level, Lactobacillus, Acetobacter, Hydrogenibacillus, Halomonas, and Prevotella_1 were the dominant bacteria in the fermentation system. The bacterial diversity of composite substrate AJ was higher than that of single substrate AJ. The organic acids and secondary metabolites concentration and the composition of key microorganisms depended on the substrate type. Furthermore, AJ's potential functional genes were mainly concentrated in cofactors and vitamin, carbohydrate, and amino acid metabolism. The findings of this study indicated that AJ is an innovative eco-friendly technology that can convert cash crop wastes into sustainable eco-products, and that its characteristics depend on the substrate type. Therefore, the substrate used to produce AJ should be carefully selected according to the application field.

Enhancement of nutritional, sensory and storage stability by lactic fermentation of Auricularia auricula

BACKGROUND

Auricularia auricula is of important nutritional value, although its utilization or consumption are mainly under the original form with no further processing. Indeed, its liquid or other fermented products contribute to improved digestion and absorption of nutrients.

RESULTS

The present study used Lactiplantibacillus plantarum to ferment A. auricula juice after an initial processing comprising superfine grinding and high-pressure homogenization. The content of probiotic bacteria in the juice of A. auricula reached 8.48 log colony-forming units mL^-1 after 24 h of fermentation under 37 °C, with the addition of 3% carbon and 0.3% nitrogen source. Meanwhile, the antioxidant activity was increased approximately two-fold, as well as the enriched volatile flavors, both effectively cover up the unwelcoming earthy smell of A. auricula. Furthermore, the storage stability was also strengthened up to 28 days.

CONCLUSION

In summary, the introduced fermentation process not only realized the purpose of improving the nutritional value of A. auricula, but also effectively upgraded the sensory evaluation of A. auricula products. © 2022 Society of Chemical Industry.

Two-species community design of lactic acid bacteria for optimal production of lactate

Microbial communities that metabolise pentose and hexose sugars are useful in producing high-value chemicals, resulting in the effective conversion of raw materials to the product, a reduction in the production cost, and increased yield. Here, we present a computational analysis approach called CAMP (Co-culture/Community Analyses for Metabolite Production) that simulates and identifies appropriate communities to produce a metabolite of interest. To demonstrate this approach, we focus on the optimal production of lactate from various Lactic Acid Bacteria. We used genome-scale metabolic models (GSMMs) belonging to Lactobacillus, Leuconostoc, and Pediococcus species from the Virtual Metabolic Human (VMH; https://vmh.life/) resource and well-curated GSMMs of L. plantarum WCSF1 and L. reuteri JCM 1112. We analysed 1176 two-species communities using a constraint-based modelling method for steady-state flux-balance analysis of communities. Flux variability analysis was used to detect the maximum lactate flux in the communities. Using glucose or xylose as substrates separately or in combination resulted in either parasitism, amensalism, or mutualism being the dominant interaction behaviour in the communities. Interaction behaviour between members of the community was deduced based on variations in the predicted growth rates of monocultures and co-cultures. Acetaldehyde, ethanol, acetate, among other metabolites, were found to be cross-fed between community members. L. plantarum WCSF1 was found to be a member of communities with high lactate yields. In silico community optimisation strategies to predict reaction knock-outs for improving lactate flux were implemented. Reaction knock-outs of acetate kinase, phosphate acetyltransferase, and fumarate reductase in the communities were found to enhance lactate production.

Health-Promoting Constituents and Selected Quality Parameters of Different Types of Kimchi: Fermented Plant Products

The aim of this study was to evaluate the quality and health-promoting constituents of several variants of kimchi obtained from Chinese cabbage, kohlrabi, white radish, and cucumbers. The level of dry matter, total soluble solids, ash, total acidity, pH, dietary fiber, and vitamins C, B₁, and B₂, as well as total polyphenols (TP) and antioxidant activity AA (ABTS, DPPH) in kimchi, were determined. In addition, color parameters were determined (L∗, a∗, b∗, C∗, and h^o). Kimchi with the highest proportion of Chinese cabbage (63%) had the highest levels of dry matter (11.01 g), ash (2.57 g), and vitamins: C, B₁, and B₂ (51 mg, 52 μg, and 242 μg, respectively), expressed per 100 g of fresh weight. In addition, this product showed the highest total AA of 132.3 μmol Tx/g (ABTS) and 49.7 μmol Tx/g (DPPH) due to its high level of TP (194 mg/100 g). Cucumber-derived kimchi (85%) also had a high content of TP (147 mg/100 g) and high AA of 88.7 μmol Tx/g (ABTS) and 36.3 μmol Tx/g (DPPH). Additionally, stuffed kimchi from kohlrabi (88%) had the highest amounts of total dietary fiber, 3.65 g/100 g fresh weight. In all products, red (a∗) and yellow (b∗) were the dominant colors, with values of L∗ ranging between 32.63 and 53.16. In general, our studies have shown that depending on the raw materials used, kimchi is a good source of dietary fiber but also vitamins and polyphenols.

Effect of Lactobacillus plantarum enriched with organic/inorganic selenium on the quality and microbial communities of fermented pickles

Lactobacillus enriched with organic/inorganic selenium and pickles fermented with the Lactobacillus plantarum R were prepared. The results showed that selenium-enriched Lactobacillus plantarum R enhanced the antioxidant capacity, inhibition rate of advanced glycation end-products (AGEs), nitrite degradation, and the organic acid production of fermented pickles, while Lactobacillus plantarum R enriched with inorganic selenium (R-Se-IN) showed the best performance. Twenty-three aroma-active substances and seven characteristic compounds were detected in the R-Se-IN group. Moreover, the bacterial community result revealed that Lactococcus, Lactobacillus, and Leuconostoc were predominant in the R-Se-IN group, while the other groups contained Enterobacter, Halomonas, and Klebsiella. Furthermore, the correlations between environmental factors, differential flavor substances, and microbial communities were explored based on multivariate statistical analysis. These results indicate that the addition of Lactobacillus plantarum R enriched with organic/inorganic selenium influenced the environmental factors, differential flavor substances, and microbial communities of the fermented pickles.

Nutrient consumption patterns of Lactobacillus plantarum and their application in suancai

The purpose of the present study was to control the fermentation time and nitrite content of suancai prepared with Lactobacillus plantarum. According to analyses of the consumption amount and rate of nutrients, growth-stimulating nutrients, essential nutrients and nutrients accelerating the fermentation process of suancai, Asp, Thr, Glu, Cys, Tyr, Mg²⁺, Mn²⁺ and inosine were selected as additions to suancai prepared with L. plantarum. The fermentation time and nitrite content of suancai supplemented with nutrients and prepared with L. plantarum were shortened by 2 days and 5 days and reduced by approximately 0.1-fold and 0.7-fold, respectively, compared with unsupplemented suancai prepared with L. plantarum at 25 °C and 10 °C. The fermentation time and nitrite content of suancai supplemented with nutrients and prepared with L. plantarum were shortened by 6 days and 15 days and reduced by approximately 0.17-fold and 0.8-fold, respectively, compared with suancai undergoing spontaneous fermentation at 25 °C and 10 °C. Furthermore, no significant differences were observed in sensory properties in suancai. The results of this study indicated that certain nutrients accelerated the growth of L. plantarum and reduced the fermentation time and nitrite content of suancai prepared with L. plantarum. These findings help to establish a foundation for the practical use of nutrients to control the fermentation of suancai.

Fermentation characteristics and bacterial dynamics during Chinese sauerkraut fermentation by Lactobacillus curvatus LC-20 under varied salt concentrations reveal its potential in low-salt suan cai production

Salt profoundly affects the physicochemical properties and microbial abundance of fermented foods such as suan cai, a popular traditional fermented food in China. It is vital to systematically investigate the effects of salt concentrations on fermented suan cai for high fermentation quality and large-scale production. We elucidated the effects of salt concentrations on Lactobacillus curvatus (LC-20) and suan cai during fermentation, and found that salt (0-1%) favoured an increase in LC-20 growth and a decrease in pH (salt: 0-2%). For suan cai fermentation, the results from sensory scoring judged 1% salt treatment the highest. Salt concentration also affected the nitrite content of the fermentation system with peak nitrite values in low salt treatments being significantly higher on the first day, and gradually decreasing to similar levels. After fermentation, the total titratable acid and lactic acid concentrations in the 0-1% treatments were higher (p < 0.05) than those in 2-5% treatments. The colony forming units of lactic acid bacteria increased initially and then decreased after 6 d of fermentation. At the phylum level, Firmicutes and Proteobacteria were predominant in all treatments, and at the genus level, Lactobacillus dominated the fermentation. Other lactic acid bacteria such as Lactococcus and Weissella were also detected. Quantitative PCR showed DNA concentration of LC-20 at 0.5-2% salt treatments were higher than that in other treatments and L. curvatus was the dominant microorganism during fermentation. Hence, we conclude that L. curvatus could be used for suan cai product at low salt concentrations.

Fermentation of blueberry and blackberry juices using Lactobacillus plantarum, Streptococcus thermophilus and Bifidobacterium bifidum: Growth of probiotics, metabolism of phenolics, antioxidant capacity in vitro and sensory evaluation

In this study, three potential probiotic strains were selected to ferment blueberry and blackberry juices. The viable cell counts of selected strains were increased by 0.4-0.7 log CFU/mL in berry juices environments after 48-h fermentation. Meanwhile, the contents of cyanindin-3-glucoside and peonidin-3-glucoside decreased over 30%. Heatmap presented an upgrade trend of syringic acid, ferulic acid, gallic acid and lactic acid during fermentation. However, the contents of p-coumaric acid, protocatechuic acid, chlorogenic acid, critic acid and malic acid showed downgrade trend. The metabolism of phenolics probably contributed to the enhancement of the ABTS radical scavenging activity (40%-60%) in fermented berry juices. Moreover, the three strains presented different capacities on changing the quality of berry juices according to the PCA and LDA analysis. The contents of individual organic acids had positive correlations with sensory quality, especially for sourness. Overall, probiotic fermentation could improve the sensory quality of berry juices.

Analysis of the Microbial Diversity and Characteristics of Fermented Blueberry Beverages from Different Regions

In this study, high-throughput sequencing methods were used to analyze the composition and diversity of the microbial communities of three different traditional fermented blueberry beverages (Jiaosu A, Jiaosu B, and Jiaosu C) produced in three different regions. Lactic acid bacteria and yeast counts, total soluble solids, total titration acid, total phenols, total flavonoids, total anthocyanin, superoxide dismutase, and antioxidant activity were analyzed in all samples. The results showed that at the phylum level, the bacteria in all samples were predominantly Firmicutes and Proteobacteria, while the majority of fungus belonged to Ascomycota. At the genus level, Lactobacillus, Gluconobacter, and Acetobacter were the dominant bacteria, and Dekkera and Issatchenkia were the dominant fungi. Our data show that the lactic acid bacteria counts in Jiaosu A were the lowest of the three products, in the range of 4.31–10.9 log CFU/mL, while yeast counts ranged from 6.71 to 7.35 log CFU/mL. The antioxidant activities of Jiaosu C were greater than those of Jiaosu A and Jiaosu B, and Spearman correlation analysis showed that the relative abundance of Lactobacillus and Dekkera was significantly positively correlated with total phenolics, total anthocyanin, total flavonoids, and antioxidant index.

Effects of temperature on paocai bacterial succession revealed by culture-dependent and culture-independent methods

Paocai is a widely consumed Chinese traditional fermented vegetable product. To understand the effect of temperature on paocai fermentation flora, the bacterial community structure of paocai fermented at 10 °C, 15 °C, 25 °C and 35 °C was analyzed by culture-dependent and culture-independent methods. The results showed that increasing the fermentation temperature in a certain range is beneficial for rapid paocai acid production and shortening of the maturity period. Illumina Miseq sequencing was performed on 56 samples at different fermentation process temperatures using a culture-independent method. A total of 1,964,231 high-quality reads of 16S rRNA V3-V4 regions were obtained, and they were divided into 405 operational taxonomic units (OTUs) and identified as 213 bacterial genera. The bacterial diversity decreased with the progression of fermentation, and some spoiled samples had an increased diversity. The culture-independent method found that at 10 °C, Lactococcus appeared at the start of fermentation, Leuconostoc and Weissella appeared in the middle of fermentation, and Lactobacillus and Leuconostoc dominated fermentation in the late stage. At 15 °C, Lactococcus started fermentation, Leuconostoc appeared in the middle stage, and Lactobacillus was dominant in the late stage. At 25 °C, Lactococcus started fermentation, Weissella and Lactobacillus appeared in the middle stage, and Lactobacillus dominated fermentation in the late stage. Finally, at 35 °C, Lactococcus, Weissella, and Lactobacillus started fermentation, Weissella and Lactobacillus appeared in the middle stage, and Lactobacillus dominated fermentation in the late stage. A total of 647 strains of bacteria were isolated by culture-dependent methods and were divided into 12 genera and 19 species by randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) and 16S ribosomal RNA gene (rDNA) sequencing technology. More types of bacteria were isolated in the early stage of fermentation. At 10 °C, Lactococcus lactis began fermentation, and Lactobacillus brevis and Leuconostoc mesenteroides dominated acid production in the middle and late stages of paocai fermentation. At 15 °C, L. lactis initiates fermentation, while Lactobacillus plantarum dominates the acid fermentation of paocai. At 25 °C and 35 °C, there were a large number of Enterobacteriaceae bacteria in the start-up fermentation stage, and L. plantarum was dominant after 1-2 days of fermentation. Redundancy analysis (RDA) found that the lower the temperature, the more bacterial species that are produced, and the higher the temperature and the longer the time, the more obvious are the effects of L. plantarum on paocai. The results of dominant bacteria studied by culture-dependent and culture-independent methods are similar. The results indicate that most of the dominant microorganisms in the paocai fermentation system are culturable. This discovery can provide data and physical support for modernization and regulation of different types of paocai production.

Bacterial community dynamics and physicochemical characteristics in natural fermentation of jiang-shui, a traditional food made in northwest China

BACKGROUND

Chinese jiang-shui is fermented food without salt. In consideration of the few studies of the bacterial community and dynamics of jiang-shui fermentation, the aim of this study was to investigate the microbial diversity and dynamics of jiang-shui fermentation using high-throughput sequencing (HTS), denaturing gradient gel electrophoresis (DGGE) and the culture-dependent method.

RESULTS

The culture-dependent method showed that pathogenic bacteria (Staphylococcus aureus, Salmonella and Escherichia coli) and yeast mainly existed in the early stage and lactic acid bacteria dominated until the end stage. HTS and DGGE revealed that Serratia marcescens, Serratia sp., Lactobacillus curvatus, Lactococcus lactis, uncultured bacterium and Bacillus thuringiensis started the fermentation, followed by the middle stage with Lactococcus lactis, Weissella sp. and Bacillus arthracis as the predominant species. The end stage was characterized with Lactobacillus pentosus, Weissella cibaria and Weissella sp. as the major bacteria.

CONCLUSIONS

The results showed that genera Serratia, Lactococcus, Weissella and Lactobacillus dominated the whole process of jiang-shui fermentation. This study provided a good analysis of the bacterial changes of jiang-shui fermentation, and future studies should consider the relationships among the sensory characteristics, microbial communities and metabolites. © 2019 Society of Chemical Industry.

Influence of oxygen exposure on fermentation process and sensory qualities of Sichuan pickle (paocai)

The physicochemical and microbial changes, volatile profile, texture and appearance were investigated in three groups of Sichuan pickles differing in oxygen exposure during a 64 day fermentation process.

Characterization of a probiotic starter culture with anti-Candida activity for Chinese pickle fermentation

A probiotic starter can be used for Chinese pickle fermentation and the resulting product may be a promising anti-Candida probiotic.

Dynamic changes of bacterial communities and nitrite character during northeastern Chinese sauerkraut fermentation

Northeastern Chinese sauerkraut is a well-known traditional fermented vegetable in China. Incomplete identification of the microorganisms' (bacteria in spontaneous fermentation) diversity and accumulation of nitrite make it difficult to normalize the fermentation process and product qualities of northeastern Chinese sauerkraut. Conventional culturing and polymerase chain reaction-denaturing gradient gel electrophoresis methods were combined to describe microbial structure and diversity. Lactobacillus, Leuconostoc, Enterobacter, Accumulibacter, Thermotoga, Pseudomonas, Clostridium, Rahnella and Citrobacter were predominant microorganisms in different fermentation periods. The pH value and nitrite concentration presented a certain relevance to the amount of lactic acid bacteria. Lactobacillus and Leuconostoc had the ability to decrease nitrite by inhibiting nitrate-reducing bacteria such as Enterobacter. Therefore, Northeastern Chinese sauerkraut should not be eaten until 4 weeks of fermentation for the safety and quality of fermented foods. Northeastern Chinese sauerkraut is rich in lactic acid bacteria, which demonstrate its ability as an excellent probiotic for applications in functional foods.

Bacterial diversity and community structure during fermentation of Chinese sauerkraut with Lactobacillus casei 11MZ-5-1 by Illumina Miseq sequencing

The bacterial diversity and community structure involved in Chinese sauerkraut is one of the most important factors shaping the final characteristics of traditional foods. In this research, Lactobacillus casei 11MZ-5-1 was applied in Chinese sauerkraut fermentation as a starter culture. Illumina Miseq sequencing analysis was used to reveal the bacterial diversity and community structure during Chinese sauerkraut fermentation. A total of 177 283 high-quality reads of 16S rRNA V4 regions were obtained. The inoculation of L. casei 11MZ-5-1 decreased considerably the bacterial richness and bacterial diversity. This inoculum led to the replacement of Lactococcus by Lactobacillus. The levels of Pseudomonas and Enterobacter bacteria decreased. These findings reveal the evolution of important bacterial groups that are involved in fermentation and will facilitate improvements in the Chinese sauerkraut fermentation process.

SIGNIFICANCE AND IMPACT OF THE STUDY

This research thoroughly revealed the effects of Lactobacillus casei 11MZ-5-1 starter cultures on bacterial communities during Chinese sauerkraut fermentation. Illumina Miseq sequencing was effective technique to monitor the bacterial diversity and community structure. The inoculation of L. casei 11MZ-5-1 led to the decline of bacterial richness and diversity together with a consistent predominance of Lactobacillus during spontaneous fermentation. The result collectively suggested L. casei 11MZ-5-1 is a promising starter in Chinese sauerkraut manufacturing.

Suitability of various DNA extraction methods for a traditional Chinese paocai system

Traditional paocai brine (PB), which is continuously propagated by back-slopping and contains various species of lactic acid bacteria (LAB), is critical for the flavor of paocai. Culture-independent approaches are commonly used to investigate the microbial communities of fermented food. To evaluate the influence of different DNA (DNA) extraction methods on estimates of bacterial community profiles from 4 PBs, the lysis efficiency, DNA yield, purity and denaturing gradient gel electrophoresis (DGGE) profiles of V3 region of a 16S ribosomal ribonucleic acid gene were acquired. The cell lysis pattern of SDS + beads and Lysing matrix E+ beads (methods 3 and 4) showed higher cell lysis efficiency than SDS and SDS + Lysozyme (methods 1 and 2) in all PBs. SDS + beads obtained the largest DNA yield of the 4 methods. Moreover, methods 3 and 4 resulted in higher H' values and generated more global bacteria profiles than other methods. Overall, our results demonstrate that the properties of PB significantly affect the efficiency of DNA extraction methods. Methods 3 and 4 were both suitable for DNA extraction from PB. Method 3 is more economic, simple and rapid than method 4 for large-scale studies of the bacterial profiles of PB.

Selection of Taste Markers Related to Lactic Acid Bacteria Microflora Metabolism for Chinese Traditional Paocai: A Gas Chromatography-Mass Spectrometry-Based Metabolomics Approach

Traditional paocai brine (PB) is continuously propagated by back-slopping and contains numerous lactic acid bacteria (LAB) strains. Although PB is important for the quality of paocai (Chinese sauerkraut), the taste features, taste-related compounds of PB-paocai and the effects of LAB communities from PB on the taste compounds remain unclear. An electronic tongue was used to evaluate the taste features of 13 PB-paocai samples. Umami, saltiness, bitterness, sweetness, and aftertaste astringency were the main taste features of PB-paocai. A total of 14 compounds were identified as discriminant taste markers for PB-paocai via gas chromatography-mass spectrometry (GC-MS)-based multimarker profiling. A LAB co-culture (Lactobacillus plantarum, Lactobacillus buchneri, and Pediococcus ethanoliduran) from PB could significantly increase glutamic acid (umami), sucrose (sweetness), glycine (sweetness), lactic acid (sourness), and γ-aminobutyric acid in PB-paocai, which would endow it with important flavor features. Such features could then facilitate starter screening and fermentation optimization to produce paocai-related foods with better nutritional and sensory qualities.

Multiple roles of lactic acid bacteria microflora in the formation of marker flavour compounds in traditional chinese paocai

Traditional paocai brine (PB), which is continuously propagated by back-slopping and contains multiple species of lactic acid bacteria (LAB), is critical for the flavour of paocai.