Biogenic amines content and assessment of bacterial and fungal diversity in stinky tofu – A traditional fermented soy curd

Bioconversion of lignans in flaxseed cake by fermented tofu microbiota and isolation of Enterococcus faecium strain ZB26 responsible for converting secoisolariciresinol diglucoside to enterodiol

Human intestinal microbiota plays a crucial role in converting secoisolariciresinol diglucoside, a lignan found in flaxseed, to enterodiol, which has a range of health benefits: antioxidative, antitumor, and estrogenic/anti-estrogenic effects. Given the high secoisolariciresinol diglucoside content in flaxseed cake, this study investigated the potential of co-fermenting flaxseed cake with fermented soybean product to isolate bacterial strains that effectively convert secoisolariciresinol diglucoside to enterodiol in a controlled environment (in vitro). The co-fermentation process with stinky tofu microbiota significantly altered the lignan, generating 12 intermediate lignan metabolites as identified by targeted metabolomics. One particular promising strain, ZB26, demonstrated an impressive ability to convert secoisolariciresinol diglucoside. It achieved a conversion rate of 87.42 ± 0.33%, with secoisolariciresinol and enterodiol generation rates of 94.22 ± 0.51% and 2.91 ± 0.03%, respectively. Further optimization revealed, under specific conditions (0.5 mM secoisolariciresinol diglucoside, pH 8, 30 °C for 3 days), ZB26 could convert an even higher percentage (97.75 ± 0.05%) of the secoisolariciresinol diglucoside to generate secoisolariciresinol (103.02 ± 0.16%) and enterodiol (3.18 ± 0.31%). These findings suggest that the identified strains ZB26 have promising potential for developing functional foods and ingredients enriched with lignans.

Effect of salt concentration on the quality and microbial community during pickled peppers fermentation

This work aimed to investigate the effect of salt concentration on the quality and microbial community of pickled peppers during fermentation, and the cross-correlation between microorganisms and quality was also revealed. The results showed that 9 volatile flavor compounds were unique to the low salt concentration group (D group), which also contained higher content of FAA, lactic acid and acetic acid than high salt concentration group (G group). Meanwhile, the samples of D2 group have a better texture properties. Firmicutes, Proteobacteria, Ascomycota, Lactobacillus, Pectobacterium, and Pseudomonas were detected as the main microbial community during the fermentation with different salt concentrations. Furthermore, the correlations analysis results indicated that the salt concentration has a significant effect on the microbial community of pickled peppers (p < 0.001), and Pediococcus, Lactobacillus, Cedecca, Issatchenkia, Pichia, Kazachstania, and Hanseniaspora were significantly correlated with flavors, which played crucial roles in the unique flavor formation of pickled peppers.

Effect of precursors and stress factors on yeast isolated from fermented maesil extract and their biogenic amine formation

Biogenic amines are produced during fermentation and can act as harmful substances. Strains related to the fermentation of maesil extract were identified and Clavispora lusitaniae and Pichia kluyveri were selected to investigate the relationship between biogenic amines and precursors, NaCl or ethanol. Biogenic amines were analyzed by high-performance liquid chromatography. Among precursors added, arginine was most effective for the biogenic amines formation. After 24 h incubation, the content of total biogenic amines increased from 37.60 to 51.75 mL/L for C. lusitaniae and from 2.60 to 33.30 mL/L for P. kluyveri in arginine-added medium. The number of yeast decreased in both NaCl- and ethanol-YM broth added with arginine, but there was no correlation between the number of yeast and biogenic amines. These results suggested that the formation of biogenic amines by yeast was affected by various factors and their interactions rather than a single factor, such as decarboxylase activity and stress factor.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01328-8.

Microbiology of fermented soy foods in Asia: Can we learn lessons for production of plant cheese analogues?

The food industry is facing the challenge of creating innovative, nutritious, and flavored plant-based products, due to consumer's increasing demand for the health and environmental sustainability. Fermentation as a unique and effective tool plays an important role in the innovation of food products. Traditional fermented soy foods are popular in many Asian and African countries as nutritious, digestible and flavorful daily staples or condiments. They are produced by specific microorganisms with the unique fermentation process in which microorganisms convert the ingredients of whole soybean or soybean curd to flavorful and functional molecules. This review provides an overview on traditional fermented food produced from soy, including douchi, natto, tempeh, and sufu as well as stinky tofu, including the background of these products, the manufacturing process, and the microbial diversity involved in fermentation procedures as well as flavor volatiles that were identified in the final products. The contribution of microbes to the quality of these five fermented soy foods is discussed, with the comparison to the role of cheese ripening microorganisms in cheese flavor formation. This communication aims to summarize the microbiology of fermented soy foods in Asia, evoking innovative ideas for the development of new plant-based fermented foods especially plant-based cheese analogues.

Evaluation of Body Changes and the Anti-Obesity Effect after Consumption of Korean Fermented Food, Cheonggukjang: Randomized, Double-Blind Clinical Trial

Cheonggukjang is a traditional Korean fermented soybean food with potential health benefits. For this reason, Cheonggukjang is consumed in the form of pills in addition to being used as a food ingredient. There are few clinical studies that have evaluated changes in various health indicators through blood and stool tests before and after consumption of Cheonggukjang. In this study, symptoms and hematological changes were analyzed before and after the intake of traditional Cheonggukjang pills containing high-dose (n = 19) or low-dose (n = 20) beneficial bacteria and commercial Cheonggukjang pills (n = 20). Anti-obesity effects and body composition changes were determined before and after Cheonggukjang consumption. Lastly, the changes in microorganisms and short-chain fatty acids in the stool were compared. No changes in obesity and inflammation-related indicators were observed before and after Cheonggukjang consumption. The Firmicutes/Bacteroidetes ratio, associated with obesity, decreased in all three groups after Cheonggukjang consumption, but no statistical significance was indicated. Cheonggukjang contained various BAs, but they did not adversely affect symptoms and hematological changes in the participants. BAs generated during the manufacturing process of Cheonggukjang did not have any adverse effects in this randomized, double-blind clinical trial. Further research is needed in future concerning the anti-obesity effect or regarding changes in the microbiome and short-chain fatty acids in feces.

Characterisation of the Aroma Profile and Dynamic Changes in the Flavour of Stinky Tofu during Storage

Stinky tofu is a traditional Chinese food with wide consumption in China. Nevertheless, the dynamic changes in the flavour of stinky tofu during storage have yet to be investigated. In this study, the flavour changes of stinky tofu over six different storage periods were comprehensively analysed through sensory, electronic nose and gas chromatography-mass spectrometry (GC-MS) analyses. The results of the sensory and electronic nose analyses confirmed the changes in the flavour of stinky tofu across different storage periods. In the GC-MS analysis, 60 volatile compounds were detected during storage, and the odour activity values indicated that 29 of these 60 compounds significantly contributed to the aroma profile. During storage, the alcohol concentration of the stinky tofu gradually decreased while the acid and ester concentrations increased. According to a partial least squares analysis, 2-phenylethyl acetate, 2-phenylethyl propanoate, p-cresol, and phenylethyl alcohol, which were detected after 10 days of storage, promoting the release of an overripe apple-like odour from the stinky tofu. Findings regarding the flavour changes and characteristics of stinky tofu during different storage periods can provide a potential reference for recognising the quality of these products.

Development of novel fermented stinky sea bass and analysis of its taste active compounds, flavor compounds, and quality

This paper developed novel fermented stinky sea bass (FSSB) products and reports the first analysis of its taste active compounds, flavor compounds, and quality. The FSSB with Xian Hen stinky tofu (F-XH) had the best sensory quality. After fermentation, the texture of FSSB improved, and the umami amino and sweet amino acid contents significantly increased, whereas that of the bitter amino acids decreased. Moreover, the IMP content and EUC in FSSB increased significantly. Of the six key volatile flavor compounds distinguished, the key volatile flavor compounds of F-XH are Ethyl Acetate, Propan-2-ol, alpha-pinene, 2-methylbutanal, acetol, 4-Methylpentan-2-one. Ethyl Acetate and 2-propanol were thought to give F-XH its unique wine flavor after cooking. The quality evaluation results demonstrated that the six FSSB complied with the Chinese Standard (GB10136-2015) (2015) animal aquatic products. Six types of FSSB products with unique flavors were developed, and a reference was provided for their industrial application.

Microbial community succession and volatile compounds changes during spontaneous fermentation of Cabernet Sauvignon (Vitis vinifera L.) under rain-shelter cultivation

Microbiota succession in spontaneous fermentation of Cabernet Sauvignon cultivated under the rain-shelter was characterized, with open-field cultivation as the control. For both cultivation modes, Saccharomyces, Starmerella, and Mycosphearella were the principal fungi, and Tatumella, Gluconobacter, and Acinetobacter were the prevailing bacteria. Rain-shelter reduced the abundance of Hanseniaspora, Candida, Starmerella, Gluconobacter, and Lactococcus. During fermentation, fungal microbiota diversity in samples from the rain-shelter cultivation decreased more drastically than the control (p < 0.05). In terms of the correlation between microbiota and volatile compounds production, the abundance of Hanseniaspora uvarum, Candida apicola, Starmerella bacillaris, Gluconobacter oxydans, and Lactococcus lactis were positively correlated with the production of esters and higher alcohols. Instead of bacterial microbiota, fungal community succession exhibited a positive correlation with the final wine volatiles under the rain-shelter cultivation. These findings demonstrated rain-shelter cultivation influences the succession pattern of microbial communities and in turn impacts the wine aromas and flavors.

The interaction between Lactobacillus plantarum SC-5 and its biogenic amine formation with different salt concentrations in Chinese Dongbei Suancai

Dongbei Suancai (DBSC) - a Chinese cabbage-based sauerkraut is a traditional fermented food which is popular in Asian countries. The biogenic amines that are usually generated during spontaneous fermentation have raised public health concern, while inoculation technology may solve this problem. In the current research, the biogenic amines, as well as their interactions with the microbial community in DBSC inoculated with Lactobacillus plantarum SC-5 or spontaneously fermented without inoculation were systematically investigated throughout 60 d fermentation. High-performance liquid chromatography analysis showed that the predominant biogenic amines in DBSC including putrescine, tyramine, spermidine, cadaverine and histamine increased during fermentation. Inoculated DBSC had a significantly lower content of total biogenic amines than the spontaneously fermented DBSC (216.72-237.33 mg/kg vs. 234.62-266.81 mg/kg) during 60 days' fermentation (P < 0.05). High throughput sequencing based on 16S rDNA identified 70 species in the bacterial community belonging to 7 genera of lactic acid bacteria, of which Lactobacillus, Leuconostoc and Lactococcus were dominant. Furthermore, six common genera of bacteria were positively correlated with biogenic amines based on Spearman's rank correlation test. Notably, the abundance of Lactobacillus plantarum SC-5 was negatively correlated with the content of biogenic amines in DBSC. In conclusion, inoculation of the proper starter like Lactobacillus plantarum SC-5 can reduce total biogenic amines in DBSC possibly by modifying the microbial communities in the fermented sauerkraut, which provides practical guidance for industrial production of high quality DBSC.

Propionic Acid and Sodium Benzoate Affected Biogenic Amine Formation, Microbial Community, and Quality of Oat Silage

Investigating the microbial communities and biogenic amine (BA) formation in silage is of vital for improving the quality and safety of oat silage. The present study evaluated the effects of propionic acid (P) and sodium benzoate (SB) on the quality properties, microbial communities, and BA formation in oat silage. Oat was harvested at boot stage and ensiled using P and SB as additives in mini silos, followed by 14 days of aerobic exposure. The results showed that P and SB improved fermentation quality of oat silage, increased the lactic acid content, and decreased pH value and ammonia nitrogen content. Putrescine, cadaverine, and tyramine were the dominant BAs in oat silage; spermidine and spermine were not detected. The control silage had the highest content of total biogenic amine (TBA, 2506.7 mg kg^–1 DM), and decreased by 51.1 and 57.7% after adding P and SB, respectively. Moreover, a lower putrescine, cadaverine, and tyramine content and undesirable microbes, such as Caproiciproducens, Stenotrophomonas, Herbinix, and Enterobacter genera, were observed in P and SB silages, which was beneficial for oat silage quality. The fungal community of P silage was dominated by Monascus fuliginosus, and the temperature, pH and ammonia nitrogen content increased after exposure to air. Sedimentibacter, Herbinix, Caproiciproducens, Enterobacter, and Escherichia-Shigella were found to be positively correlated with BA formation in oat silage. Overall, P and SB effectively inhibit the undesirable microbes and BA formation in oat silage, the P silage exhibited lower aerobic stability than the SB silage.

Correlation between bacterial community succession and propionic acid during gray sufu fermentation

In order to explore the correlation between the production of propionic acid (PA) and the succession of bacterial community during the fermentation of gray sufu, high-throughput sequencing and HPLC (High Performance Liquid Chromatography) were used to monitor the changes of bacterial community and metabolite content. The abundance and metabolite concentration of Propionibacterium increased rapidly in the early stage of fermentation. In the middle stage, the abundance of Lactobacillus began to increase, while the pH decreased rapidly. In the late stage, the concentration of PA began to decrease, but it remained at a high level at the end of fermentation. Correlation analysis showed that Lactobacillus and Bacillus had a strong negative correlation with PA and its precursor. The results showed that Fusobacterium, Providencia, Lactobacillus and Bacillus could be the key factors to reduce the PA content. This study provides a new idea for the quality control of traditional fermented food.

Assessment of the Distribution and Safety of Tetragenococcus muriaticus for Potential Application in the Preparation of Chinese Grasshopper Sub Shrimp Paste

The bacterial profiles of 63 grasshopper sub shrimp paste samples collected from seven typical regions around the Bohai Sea were investigated by high-throughput sequencing. Tetragenococcus muriaticus was found to be the prevailing species present in all the samples, and the presence of T. muriaticus also weakly correlated with the histamine content in the samples. Six T. muriaticus strains with low biogenic amine (BA)-producing ability and deficient in histamine production were identified and subjected to safety assessment. All six strains displayed weak resistance to fifteen known antibiotics as based on the Enterococcus breakpoint values. None of the strains exhibited hemolytic activity or biofilm formation. All strains exhibited were able to grow on MRS agar containing 21% NaCl and expressed amine oxidase and strain-specific proteases and lipases. Most of the strains exhibited acid production at 18% NaCl. Moreover, three of the strains (designated as SG, TS, and QH) with histamine degradation ability were inoculated into separate shrimp paste samples to determine their effect on BA accumulation. The results indicated that the addition of T. muriaticus to shrimp pastes not only led to a significant reduction of BA content in the pastes but also improved the flavor of the pastes. Consequently, these strains may be used as potential candidates for controlling the content of histamine in fermented foods.

Role of lactic acid bacteria in flavor development in traditional Chinese fermented foods: A review

Traditional Chinese fermented foods are favored by consumers due to their unique flavor, texture and nutritional values. A large number of microorganisms participate in the process of fermentation, especially lactic acid bacteria (LAB), which are present in almost all fermented foods and contribute to flavor development. The formation process of flavor is complex and involves the biochemical conversion of various food components. It is very important to fully understand the conversion process to direct the flavor formation in foods. A comprehensive link between the LAB community and the flavor formation in traditional Chinese fermented foods is reviewed. The main mechanisms involved in the flavor formation dominated by LAB are carbohydrate metabolism, proteolysis and amino acid catabolism, and lipolysis and fatty acid metabolism. This review highlights some useful novel approaches for flavor enhancement, including the application of functional starter cultures and metabolic engineering, which may provide significant advances toward improving the flavor of fermented foods for a promising market.

Primary and Secondary Succession Mediate the Accumulation of Biogenic Amines during Industrial Semidry Chinese Rice Wine Fermentation

The use of exogenous functional microorganisms to regulate biogenic amine (BA) content is a common approach in fermentation systems. Here, to better understand the microbial traits of succession trajectories in resource-based and biotic interference systems, the BA-related primary and secondary succession were tracked during industrial semidry Chinese rice wine (CRW) fermentation. Dominant abundance and BA-associated microbial functionality based on phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) indicated that Citrobacter, Acinetobacter, Lactobacillus, Exiguobacterium, Bacillus, Pseudomonas, and Enterobacter spp. prominently contributed to the decarboxylase gene family in CRW. The expression levels of tyrosine decarboxylase (tyrDC), ornithine decarboxylase (odc), and agmatine deiminase (aguA) genes were assessed by quantitative PCR (qPCR). The transcription levels of these genes did not correlate with the BA formation rate during postfermentation, indicating that acidification and carbon source depletion upregulated the expression and microbes launch the dormancy strategy to respond to unfavorable conditions. Furthermore, microbial interference with CRW fermentation by Lactobacillus plantarum (ACBC271) and Staphylococcus xylosus (CGMCC1.8382) coinoculated at a ratio of 1:2 exhibited the best synergetic control of BA content. Spearman correlations revealed that Lactobacillus and Staphylococcus exhibited influence on BA-associated microbiota (|ρ| > 0), Exiguobacterium and Pseudomonas were strongly suppressed by Lactobacillus (ρ = -0.867 and ρ = -0.782, respectively; P < 0.05), and Staphylococcus showed the strongest inhibitory effect toward Lactobacillus (ρ = -0.115) and Citrobacter (ρ = -0.188) in the coinoculated 1:2 group. The high inhibitory effect of exogenous added strains on specific bacteria presented evidence for the obtained BA-associated contributors. Overall, this work provides important insight into the microbial traits that rely on resource usage and functional microbiota within food microbial ecology.IMPORTANCE Understanding the shifting patterns of substance usage and microbial interactions is a fundamental objective within microbiology and ecology. Analyses of primary and secondary microbial succession allow for determinations of taxonomic diversity, community traits, and functional transformations over time or after a disturbance. The kinetics of BA generation and the patterns of resource consumption, functional metagenome prediction, and microbial interactions were profiled to elucidate the equilibrium mechanism of microbial systems. Secondary succession after a disturbance triggers a change in resource usage, which in turn affects primary succession and metabolism. In this study, the functional potential of exogenous microorganisms under disturbance synergized with secondary succession strategies, including rebalancing and dormancy, which ultimately reduced BA accumulation. Thus, this succession system could facilitate the settling of essential issues with respect to microbial traits that rely on resource usage and microbial interactions that occur in natural ecosystems.

The Impact of Microbial Diversity on Biogenic Amines Formation in Grasshopper Sub Shrimp Paste During the Fermentation

Biogenic amines (BAs) and microbial diversity are important factors affecting food quality and safety in fermented foods. In this study, the bacterial and fungal diversity in grasshopper sub shrimp paste taken at different fermentation times were comprehensively analyzed, while the pH, colony counts, salinity, total volatile base nitrogen (TVB-N) and BA contents were quantitatively determined. In addition, the correlations among the samples with respect to microbial communities and the different parameters investigated especially BAs were also established. By combining the results of spearman correlation heatmap with the contents of BAs produced by the 102 halotolerant bacteria isolated from the grasshopper sub shrimp paste, six major genera of bacteria (Jeotgalibaca, Jeotgalicoccus, Lysinibacillus, Sporosarcina, Staphylococcus, and Psychrobacter) were found to be positively correlated with BA production level, suggesting that these bacteria might have a strong tendency to produce BAs. Other bacteria such as Lentibacillus, Pseudomonas, and Salinicoccus were considered as poor BA producers. The grasshopper sub shrimp paste was characterized by a relatively high abundance of Tetragenococcus, which was the dominant genus during the fermentation process, and it also produced a relatively high level of BAs but the spearman correlation heatmap revealed a negative correlation between T. muriaticus and BA level. Analysis of the species relevance network in grasshopper sub shrimp explained that the actual production of BAs by a certain strain was closely related to other species present in the complex fermentation system.

High-Throughput Sequencing and Metabolomics Reveal Differences in Bacterial Diversity and Metabolites Between Red and White Sufu

Sufu is a traditional fermented soybean food produced in China. However, the microbial compositions and metabolites of different types of sufu have not been studied in detail. Accordingly, in this study, we evaluated the differences in bacterial communities and metabolites between commercial red sufu (RS) and white sufu (WS). Principal coordinate analysis and the unweighted pair group method with arithmetic means analysis of 16S rRNA genes revealed that the bacterial community structures of RS and WS differed dramatically. At the phylum level, the relative abundances of Firmicutes and Proteobacteria were significantly different between RS and WS (P < 0.01). Moreover, the abundances of Lactococcus and Tetragenococcus genera were significantly different between RS and WS (P < 0.01). Among metabolites, most free amino acids, few of volatile flavor compounds, and some organic acids showed significant differences between RS and WS (P < 0.05). Additionally, correlations between microbiota and metabolites were determined. Aggregated boosted tree analysis showed that formic acid had the highest relative influence (20.27%) on bacterial community diversity (Chao 1), following by arginine (5.38%), propanol (4.57%), oxalic acid (4.46%), and hexanol (4.43%). Moreover, Streptococcaceae and Moraxellaceae had the highest relative influence on the concentration of formic acid (12.84% and 8.75%, respectively). The profiles obtained in this study improve our understanding of the relationships between bacterial flora and metabolites in different types of sufu. These findings may help us interpret the roles of bacterial communities in the flavor and characteristics of sufu.

Shelf life prediction and food safety risk assessment of an innovative whole soybean curd based on predictive models

The aim of the present study is to predict the shelf life and evaluate the risk profile of an innovative whole soybean curd (WSC). Two main spoilage strains were isolated from spoiled WSC and identified as B. subtilis and B. cereus. The origin analysis confirmed that B. subtilis and B. cereus originated from soybean materials and survived in soybean curd. For microbial contamination analysis, thermotolerant coliforms, E. coli and S. aureus were not detected in soybean curd. The predicted shelf life of WSC and okara-filtered curd that was stored at 10 °C were 141.95 h (5.91 d) and 206.25 h (8.59 d), respectively. Moreover, the models applied in this study exhibited great fitting goodness and the predicted growth parameters were fail-safe. To conclude, introduction of okara into soybean curd reinforced the initial contamination level but didn't significantly increase the risk profile of WSC.

Dynamic Detection of Biogenic Amines as a Quality Indicator and Their Relationship with Free Amino Acids Profiles in Large Yellow Croaker (Pseudosciaena crocea)

The production of biogenic amines (BAs) set considerable obstacles in seafood preservation. However, the characteristic BAs and their roles in the spoilage profiles in large yellow croaker were still poorly understood. The BAs contents, free amino acids (FAAs) contents, aerobic bacterial count, sensory evaluation and several characteristic physicochemical indexes were monitored during storage at 4 °C. It's forcefully uncovered that the putrescine and cadaverine were the main BAs and the sum value of them could be used as a novel quality indicator instead of BAI. The reasonable limitation for unaccepted corruption was suggested be around 60 mg/kg. The regression model (r > 0.8, P < 0.05) at 4 °C indicated a significant correlation between the main BAs and total volatile basic nitrogen (TVB-N), protein hydrolysis index (P.I.%) as well as pH value, offering a new interpretation form for the physiochemical properties of BAs in aquatic products. Additionally, the evolution of FAAs show the predominant role of lysine, proline, histidine, glycine, and alanine during the whole storage and it can be concluded that BAs biosynthesis in large yellow croaker were moderately related with their precursor substance. This work provides a preliminary insight into the origin of BAs in large yellow croaker. PRACTICAL APPLICATION: It was proposed that the sum value of putrescine and cadaverine which were the main BAs can be used as a novel quality indicator instead of BAI in large yellow croaker. And the regression models of BAs and other physiochemical indexes provided a new perspective for comprehending the spoilage profiles involving BAs biosynthesis. The study may potentially contribute to improving the evaluation of seafood freshness and provide new target site for seafood preservation.