Partial substitution of wheat flour with soybean and gluten powder: impact on flavor characteristics of Pixian Douban-Meju and its quality.

BACKGROUND: In this study, different proportions of soybean flour and gluten flour were used as partial replacements for wheat flour for the fermentation of Pixian Douban-Meju (PXDB). The aim was to study the effects of soybean flour/gluten flour on the quality improvement of PXDB. RESULTS: In comparison with the control group (CT) (0% substitution of wheat flour), substitution of wheat flower with 12.5% soybean flour (the H2 group), 7.5% gluten flour (G2), and 10% gluten flour (G3) improved the amino acid nitrogen content by 3.8%, 5.6%, and 9.4% respectively. The mixtures of wheat flour and gluten flour (G2 or G3) increased the organic acid and free amino acid content. The results of two-dimensional gas chromatography mass spectrometry (GC × GC-MS) showed that the amount of key aroma substances increased about sixfold in comparison with the CT group (194.61 g.kg-1 ), achieving 1283.67, 1113.883, and 1160.19 g.kg-1 in the H2, G2, and G3 groups, respectively. There were also more aldehydes and pyrazines in all the substitution groups. Quantitative descriptive analysis indicated that the G3 sample presented the best organoleptic quality with a reddish-brown color and a more mellow aroma than the control sample. CONCLUSION: In conclusion, the fermentation of G3 resulted in higher quality PXDB-meju, showing that partial substitution of wheat flour with gluten improved the quality of PXDB. © 2023 Society of Chemical Industry.

Fermentative features of Bacillus velezensis and Leuconostoc mesenteroides in doenjang-meju, a Korean traditional fermented soybean brick.

To investigate the fermentative characteristics of Bacillus and lactic acid bacteria, the key microbes known to be involved in doenjang-meju (a Korean traditional fermented soybean brick) fermentation, we prepared and analyzed two sets of doenjang-meju inoculated with either Aspergillus oryzae and Bacillus velezensis (BDM) or A. oryzae and Leuconostoc mesenteroides (LDM). A large decrease in pH was observed during the early fermentation period in LDM, whereas the pH remained relatively constant in BDM. Although observed in higher levels in BDM during the early fermentation period, free sugar and amino acid contents and Aspergillus abundance were higher in LDM thereafter, which aligned with α-amylase and protease activity profiles in LDM and BDM, suggesting their association with Aspergillus. Higher levels of isoflavone aglycones and glycerol along with greater ß-glucosidase and lipase activities in LDM and BDM, respectively, were suggestive of the characteristics of Leuconostoc and Bacillus, respectively. More diverse and higher amounts of volatile compounds were observed in BDM than in LDM. The α-amylase, lipase, protease, ß-glucosidase, and antimicrobial activities of A. oryzae, B. velezensis, and L. mesenteroides were examined through genomic analyses and in vitro assays, which well supported the results of their fermentative characteristics in LDM and BDM.

Dynamics of microbial communities and metabolites in ganjang, a traditional Korean fermented soy sauce, during fermentation.

Six different ganjang batches were prepared and the microbial communities in the ganjang samples and raw materials (meju and solar salts), as well as the metabolites generated during fermentation were analyzed. The varying amounts of raw materials used differentially affected the microbial communities. Halophilic or halotolerant microbes derived from solar salts were abundant during middle or late fermentation. By contrast, non-halophilic microbes derived from meju were abundant mainly during early fermentation. Debaryomyces, Tetragenococcus, and Staphylococcus were abundant in all ganjang batches, which suggested that these may be the most common microbes involved in ganjang fermentation. The salt concentrations did not affect the abundance of Debaryomyces, which was abundant in all ganjang batches. Tetragenococcus was abundant in low salt ganjang, whereas Staphylococcus was abundant in high salt ganjang. Metabolite analysis revealed that carbohydrate concentrations were high in ganjang prepared using high amounts of meju. The level of lactate, which may be largely produced by Tetragenococcus, in low salt ganjang was high because of high microbial activity. The amino acid concentrations of the ganjang batches were mainly associated with meju quantity, but not salt concentration. These results indicated that the production of amino acids may be associated with indigenous proteases in meju, but not microbial activities during ganjang fermentation.

Anti-obesity effects of gochujang products prepared using rice koji and soybean meju in rats.

The Korean traditional hot sauce gochujang has been reported to have biological activities. Different kinds of gochujang products were prepared based on combinations of a fungal rice koji with two kinds of bacterial soybean mejus. Diets that included gochujang products were fed to rats and anti-obesity effects were investigated. Gochujang products reduced body weight gains, epididymal fat weights, and triglyceride levels in the serum and the liver. Effects were exerted by the diet that included the non-fermented gochujang mixture, increased using a fungal rice koji, and further enhanced using a bacterial soybean meju. Dietary effects were apparently induced via inhibition of the lipogenic enzymes fatty acid synthase, malic enzyme, and lipoprotein lipase by gochujang products in epididymal adipose tissues, and inhibition of glucose-6-phosphate dehydrogenase in the liver. High levels of capsaicin and genistein in gochujang products are considered to contribute to anti-obesity effects.

Hypolipidemic and antiinflammation activities of fermented soybean fibers from meju in C57BL/6 J mice.

Meju, a naturally fermented soy block used to produce soy paste and soy sauce in Korea, is suggested to exhibit hypolipidemic and antiinflammatory activities; however, its mechanisms of action are elusive. Here, we report that the water-soluble fibers but not the amino acids and peptides from meju exhibited hypolipidemic activity in vivo. Feeding of fermented soybean fibers (FSF) from meju reduced plasma cholesterol, triglyceride, adipocyte size, and hepatic lipid accumulation in C57BL/6 J mice. FSF treatment reduced HMG-CoA reductase expression, whereas the expression of genes in the fatty acid uptake and subsequent beta-oxidation were significantly induced in the livers. Hepatic lipogenic genes, including Srebp1c and Lxrα, were unaltered. Feeding with the fermented soybean peptides and amino acids (FSPA) induced the expression of lipogenic genes, which may have canceled the induction of low-density lipoprotein receptor and Cyp7a1 gene expressions in FSPA livers. The plasma concentrations of C-reactive protein, TNF-α, and interlukin-6 were significantly reduced in the FSF, FSPA, and meju groups compared with the control groups, suggesting that both of the fibers and peptides/amino acids from meju may be beneficial. These findings suggest that soluble fibers from meju are critical hypolipidemic components that regulate hepatic gene expressions and reduce proinflammatory cytokines in vivo.

Anti-obesity effects of traditional and standardized meju in high-fat diet-induced obese C57BL/6J mice.

The aim of the study was to evaluate the anti-obesity effects of two types of meju in diet induced obese C57BL/6J mice. Animals were randomly divided into 4 dietary group (n = 10); normal diet, high fat diet with 30% soybean, high fat diet with 30% traditional meju, high fat diet with 30% standardized meju. After 16 weeks, after animals were sacrificed. It was observed that the high fat diet with 30% traditional meju and high fat diet with 30% standardized meju significantly reduced body weight gain, epididymal fat weight, serum triglyceride along with serum insulin and leptin levels compared to the high fat diet with 30% soybean. And also, the expression levels of hepatic lipid anabolic genes were significantly decreased in the high fat diet with 30% traditional meju and high fat diet with 30% standardized meju compared to the high fat diet with 30% soybean. In conclusion, the assessment of all the obesity markers strongly advocate the anti-obesity effect of traditional as well as standardized meju in diet induce obesity conditions.

Enzymatic Activity and Amino Acids Production of Predominant Fungi from Traditional Meju during Soybean Fermentation.

To investigate the effect of the predominant fungal species from Korean traditional meju and doenjang on soybean fermentation, the enzymatic activity and amino acid production of twenty-two fungal strains were assessed through solid- and liquid-state soybean fermentation. Enzymatic activity analyses of solid-state fermented soybeans revealed different enzyme activities involving protease, leucine aminopeptidase (LAP), carboxypeptidase (CaP), glutaminase, γ-glutamyl transferase (GGT), and amylase, depending on the fungal species. These enzymatic activities significantly affected the amino acid profile throughout liquid-state fermentation. Strains belonging to Mucoromycota, including Lichtheimia, Mucor, Rhizomucor, and Rhizopus, produced smaller amounts of total amino acids and umami-producing amino acids, such as glutamic acid and aspartic acid, than strains belonging to Aspergillus subgenus circumdati. The genera Penicillium and Scopulariopsis produced large amounts of total amino acids and glutamic acid, suggesting that these genera play an essential role in producing umami and kokumi tastes in fermented soybean products. Strains belonging to Aspergillus subgenus circumdati, including A. oryzae, showed the highest amino acid content, including glutamic acid, suggesting the potential benefits of A. oryzae as a starter for soybean fermentation. This study showed the potential of traditional meju strains as starters for soybean fermentation. However, further analysis of processes such as the production of G-peptide for kokumi taste and volatile compounds for flavor and safety is needed.

Taxonomic Variations of Bacterial and Fungal Communities depending on Fermentation Temperature in Traditional Korean Fermented Soybean Food, Doenjang.

Meju, a fermented soybean brick, is a key component in soybean foods like doenjang and ganjang, harboring a variety of microorganisms, including bacteria and fungi. These microorganisms significantly contribute to the nutritional and sensory characteristics of doenjang and ganjang. Amplicon-based next-generation sequencing was applied to investigate how the microbial communities of meju fermented at low and high temperatures differ and how this variation affects the microbial communities of doenjang, a subsequently fermented soybean food. Our metagenomic data showed distinct patterns depending on the fermentation temperature. The microbial abundance in the bacterial community was increased under both temperatures during the fermentation of meju and doenjang. Weissella was the most abundant genus before the fermentation of meju, however, it was replaced by Bacillus at high temperature-fermented meju and lactic acid bacteria such as Weissella and Latilactobacillus at low temperature-fermented meju. Leuconostoc, Logiolactobacillus, and Tetragenococcus gradually took over the dominant role during the fermentation process of doenjang, replacing the previous dominant microorganisms. Mucor was dominant in the fungal community before and after meju fermentation, whereas Debaryomyces was dominant under both temperatures during doenjang fermentation. The dominant fungal genus of doenjang was not affected regardless of the fermentation temperature of meju. Strong correlations were shown for specific bacteria and fungi linked to specific fermentation temperatures. This study helps our understanding of meju fermentation process at different fermentation temperatures and highlights different bacteria and fungi associated with specific fermentation periods which may influence the nutritional and organoleptic properties of the final fermented soybean foods doenjang.

Revealing the formation mechanisms of key flavors in fermented broad bean paste.

Pixian Douban (PXDB) is a popular Chinese condiment for its distinctive flavor. Broad bean fermentation (Meju) is the most important process in the formation of flavor substances. Key flavors were analyzed qualitatively and quantitatively, and metagenomic technology was applied to study the microbial diversity during broad bean fermentation. In addition, the main metabolic pathways of key flavors were explored. Results indicated that Staphylococcus_gallinarum was the main microorganism in the microbial community, accounting for 39.13%, followed by Lactobacillus_agilis, accounting for 13.76%. Aspergillus_flavus was the fungus with the highest species abundance, accounting for 3.02%. The KEGG Pathway enrichment analysis showed that carbohydrate metabolism and amino acid metabolism were the main metabolic pathways. Glycoside hydrolase and glycosyltransferase genes were the most abundant, accounting for more than 70% of the total number of active enzyme genes. A total of 113 enzymes related to key flavors and 39 microorganisms corresponding to enzymes were annotated. And Staphylococcus_gallinarum, Lactobacillus_agilis, Weissella_confusa, Pediococcus_acidilactici, Staphylococcus_kloosii, Aspergillus_oryzae, and Aspergillus_flavus played a key role in the metabolic pathway. This study reveals the formation mechanism of key flavors in fermented broad bean, it is important for guiding the industrial production of PXDB and improving product quality.

Fermentative metabolic features of doenjang-meju as revealed by genome-centered metatranscriptomics.

Fermentative features of doenjang-meju, a traditional Korean soybean brick, were investigated over 45 days via genome-centered metatranscriptomics. The pH value rapidly decreased within 10 days and successively increased after 20 days, along with an initial bacterial growth, including lactic acid bacteria, and subsequent fungal growth, suggesting their association. Polysaccharides and lipids underwent degradation, and amino acids, free sugars, and organic acids increased during the early stage. Metagenome analysis identified Aspergillus, Bacillus, Enterococcus, Staphylococcus, and Leuconostoc as major microbes, which were isolated and genome-sequenced. Metatranscriptomic analysis revealed the major roles of Bacillus and Enterococcus during the early period, shifting to Aspergillus dominance after 10 days. Metabolic pathway reconstruction and transcriptional analysis reveal that Aspergillus primarily decomposed polysaccharides to free sugars; Aspergillus and Bacillus metabolized lipids, free sugars, and organic acids generated by Enterococcus; and Aspergillus and Bacillus were instrumental in amino acid metabolism: their contributions varied by compounds and pathways.

Correlation between monosaccharide, oligosaccharide, and microbial community profile changes in traditional soybean brick (meju) fermentation.

Meju is essential for making diverse traditional fermented soybean foods in Korea. To understand the changes in carbohydrates during fermentation, we aimed to identify autochthonous microorganisms from spontaneously fermented meju and compare the alterations in monosaccharides and oligosaccharides throughout the fermentation process. Microbial diversity was determined using a metabarcoding approach, and monosaccharide and oligosaccharide profiles were obtained by HPLC-Q-TOF MS and HPLC-MS/MS analyses, respectively. The dominant bacterial genera were Weissella, Lactobacillus, and Leuconostoc, while Mucor was highly abundant in the fungal community. The total monosaccharide content increased from Day 0 to Day 50, with the highest amount being 4.37 mg/g. Oligosaccharide profiling revealed the degradation of soybean dietary fiber during fermentation, and novel oligosaccharide structures were also discovered. Correlation analysis revealed that the fungus Mucor was positively related to pentose-containing oligosaccharides, galactose, and galacturonic acid, indicating that Mucor may degrade soybean dietary fibers such as xylogalacturonan, arabinogalactan, and rhamnogalacturonan. The negative relationships between the abundances of Weissella and oligo- and monosaccharides suggested that the bacteria may utilize saccharides for fermentation. These findings provide insights into the mechanisms underlying carbohydrate degradation and utilization; the key components involved in saccharide transformation that contribute to the characteristics of traditional meju were subsequently identified.

Microbial communities in the fermentation of Meju, a Korean traditional soybean brick.

Meju is a traditional Korean soybean brick characterized by diverse microbial communities. The microbial communities in Meju were identified at the phylum and genus levels using high-throughput sequencing. During Meju fermentation, diverse factors such as total bacterial cell numbers, moisture content, salinity, pH, enzyme activities, and free amino acids were monitored. After 30 days of fermentation, microbial adaptation and increased protease activity resulted in significant changes, including an increase in pH and alterations in free amino acid content by day 70. Bacterial community analysis revealed significant changes in Bacillus, Lactococcus, and Enterococcus levels as fermentation progressed. The decrease in pH during fermentation was influenced by lactic acid bacteria, which affected bacterial dynamics. At the end of fermentation, the fungal community was dominated by Monascus, Aspergillus, and Scopulariopsis, which affected the free amino acid levels. These results indicate that pH and moisture content may be significant factors in determining microbial communities.

ComQXPA quorum-sensing systems contribute to enhancing the protease activity of Bacillus velezensis DMB05 from fermented soybeans.

Bacillus velezensis DMB05, isolated from traditionally fermented soybean, meju, exhibited no protease activity on a TSA plate containing skim milk. To shed light on the genetic background behind this phenotypic non-protease activity, we analyzed the complete genome sequence of strain DMB05 and compared it with those of two B. velezensis strains which did exhibit protease activity. Comparative genome analyses showed no significant difference in the kind or number of proteases between the genomes of the three strains and that all strains possessed the degSU two-component system involved in the gene regulation of protease. However, strain DMB05 possessed a truncated comP which is part of the comQXPA operon that regulates the expression of degQ involved in the activation of DegSU. When the entire comQXPA operon derived from DMB06 was introduced into DMB05, the recombinant expressed proteolytic activity. The results of this experimental study provide evidence for the presence of regulatory genes involved in protease activity, one of several important factors involved in fermentation.

Novel Starter Strain Enterococcus faecium DMEA09 from Traditional Korean Fermented Meju.

The Enterococcus faecium strain DMEA09 was previously isolated from traditional Korean fermented meju. The objective of the current study was to investigate the traits of E. faecium strain DMEA09 as a starter candidate, focusing on its safety and technological properties. Regarding its safety, the DMEA09 strain was found to be sensitive to nine antibiotics (ampicillin, chloramphenicol, erythromycin, gentamicin, kanamycin, streptomycin, tetracycline, tylosin, and vancomycin) by showing lower minimum inhibitory concentrations (MICs) than the cut-off values suggested by the European Union Food Safety Authority for these nine antibiotics. However, its MIC value for clindamycin was twice as high as the cut-off value. A genomic analysis revealed that strain DMEA09 did not encode the acquired antibiotic resistance genes, including those for clindamycin. The DMEA09 strain did not show hemolysis as a result of analyzing α- and ß-hemolysis. It did not form biofilm either. A genomic analysis revealed that strain DMEA09 did not encode for any virulence factors including hemolysin. Most importantly, multilocus sequence typing revealed that the clonal group of strain DMEA09 was distinguished from clinical isolates. Regarding its technological properties, strain DMEA09 could grow in the presence of 6% salt. It showed protease activity when the salt concentration was 3%. It did not exhibit lipase activity. Its genome possessed 37 putative protease genes and salt-tolerance genes for survivability under salt conditions. Consequently, strain DMEA09 shows safe and technological properties as a new starter candidate. This was confirmed by genome analysis.

The differences between broad bean koji fermented in laboratory and factory conditions by an efficient Aspergillus oryzae.

Broad bean paste-meju was fermented by a mixture of broad bean koji and saline; koji fermentation is an essential process for the production of broad bean paste-meju. Aspergillus oryzae was the most widely used in sauce fermentation. The purpose of this study was to research the factory adaptability of the highly efficient A. oryzae PNM003 and further evaluate the effect of fermentation conditions and fermentation strains on koji. A. oryzae PNM003 was compared with the widely used strain HN 3.042 not only in the laboratory but also in factory conditions (large scale). Results showed that the koji made with the same starter in the factory had a greater amount of fungi than that in the laboratory. Bacteria and yeast levels in HN_L koji were higher than in PN_L koji. As for fungi constitution, almost only Aspergillus survived in the end through the microorganism self-purification process during koji fermentation. As for the bacterial constitution, koji was grouped by fermentation conditions instead of fermentation starter. PN koji had higher protease activity and a higher content of total acids, amino acid nitrogen, amino acids, and organic acids in the laboratory conditions. Nevertheless, in factory conditions, PN koji and HN koji had similar indexes. As for volatile flavor compounds, koji made with the two starters in the same condition was grouped together. As for the same starter, there were more flavor compounds metabolized in the factory condition than in the laboratory condition, especially esters and alcohols. The results showed PN was a highly efficient strain to ferment koji, but the advantages were expressed more remarkably in laboratory conditions. In brief, the fermented condition had a greater influence than the fermentation starter for broad bean koji.

Inhibitory effects of meju prepared with mixed starter cultures on azoxymethane and dextran sulfate sodium-induced colon carcinogenesis in mice.

BACKGROUNDS: Meju is the main ingredient and the starter culture of traditional Korean fermented soybean foods; these fermented soybean products are well-known for their various health benefits, including anticancer effects. We developed the grain-type meju using probiotic mixed starter cultures to improve the qualities and functionalities of fermented soybean products, as well as the meju itself. In this study, the inhibitory effects of the grain-type meju were investigated in azoxymethane (AOM) and dextran sulfate sodium (DSS)-induced colon carcinogenesis mice model. MATERIALS AND METHODS: AOM and DSS colon carcinogenesis was induced in female C57BL/6 mice and meju was orally administered for 4 weeks. The body weight, colon length, and colon weight of mice were determined, and colonic tissues were histologically observed. The serum levels of proinflammatory cytokines and the levels of inflammation- and apoptosis-related genes in colonic tissue were also analyzed. RESULTS: The administration of meju using probiotic mixed starter cultures ameliorated the symptoms of colon cancer and reduced number of neoplasia, and reduced serum proinflammatory cytokine levels and iNOS and COX-2 expression levels in colonic tissue. It increased Bax and reduced Bcl-2 expression levels and increased p21 and p53 expression in colonic tissues. CONCLUSION: The meju showed inhibitory effects on the progression of colon cancer induced by AOM and DSS by ameliorating the symptoms of colon cancer, reducing the number of neoplasias and regulating proinflammatory cytokine levels and the expressions of inflammation- and apoptosis-related genes in the colonic tissue.

Characterization of Nonaflatoxigenic Aspergillus flavus/oryzae Strains Isolated from Korean Traditional Soybean Meju.

Filamentous fungi that could be classified into Aspergillus flavus/oryzae were isolated from traditionally fermented meju commercially available in Korea. The samples were analyzed for aflatoxin B1 and ochratoxin A contamination by HPLC; however, no toxin was detected. In addition, fungal and bacterial metagenomic sequencing were performed to analyze the microbial distribution in the samples. The results revealed that the distribution and abundance of fungi and bacteria differed considerably depending on the production regions and fermentation conditions of the meju samples. Through morphological analysis, ITS region sequencing, and assessment of the aflatoxin-producing ability, a total of 32 A. flavus/oryzae strains were identified. PCR analysis of six regions with a high mutation frequency in the aflatoxin gene cluster (AGC) revealed a total of six types of AGC breaking point patterns. The A. flavus/oryzae strains did not exhibit the high amylase activity detected in the commercial yellow koji strain (starter mold). However, their peptidase and lipase activities were generally higher than that of the koji isolates. We verified the safety of the traditionally fermented meju samples by analyzing the AGC breaking point pattern and the enzyme activities of A. flavus/oryzae strains isolated from the samples. The isolated strains could possibly be used as starter molds for soybean fermentation.

Dynamics and correlation of microbial communities and metabolic compounds in doenjang-meju, a Korean traditional soybean brick.

To investigate the general fermentation characteristics of doenjang-meju (a Korean traditional soybean brick), they were periodically collected from eight different manufacturers during all fermentation stages, and their microbial communities and metabolic compounds (metabolites and volatile compounds) were analyzed. Bacillus and/or lactic acid bacteria (LAB, mainly Enterococcus) and Aspergillus were abundant during fermentation. Fructose and glucose; glycerol; acetate and lactate; and cadaverine, putrescine, tyramine, and histamine were identified as the major sugars, carbon compound, organic acids, and biogenic amines, respectively. Tetramethylpyrazine, butyric acid, butyl butyrate, butanol, acetic acid, 2-methylbutyrate, acetoin, 2,3-butandiol, and nonadecane were the major volatile compounds. However, the profiles of microbial communities, metabolites, and volatile compounds during fermentation varied significanlty among samples. Principal component analysis revealed that doenjang-meju had two differentiated fermentation features, Bacillus-dominated fermentation and LAB (mainly Enterococcus)-dominated fermentation, each having different metabolite and volatile compound profiles. Particularly, fewer volatile compounds were detected in LAB-dominated doenjang-meju samples. Correlation analysis showed a strong negative correlation between Bacillus and LAB, and bacteria and fungi were less correlated with each other. Enterococcus, LAB, and Bacillus were positively correlated with lactate, flavonoid aglycones, and putrescine, respectively, suggesting that they might be mainly responsible for producing the compounds during fermentation. This study provides insights into the general fermentation characteristics of doenjang-meju.

Metabolomic analysis of meju during fermentation by ultra performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC-Q-TOF MS).

Changes in the water-soluble metabolites of meju during fermentation were analysed by ultra performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC-Q-TOF MS), and the resultant data were statistically processed by partial least squares-discriminant analysis (PLS-DA). Various metabolites, including amino acids, small peptides, nucleosides, urea cycle intermediates, and organic acids, which are responsible for the unique taste and nutritional and functional quality of fermented soy foods, were clearly altered by increasing the fermentation period. Changes in these metabolites allowed discrimination among meju samples with different fermentation periods (0, 10, 20, 40, and 60d) on a PLS-DA score plot, and the fermentation was mainly processed between 10 and 40d of fermentation. Twenty-two metabolites (phenylalanine, glutamic acid, leucine, adenine, citrulline, arginine, glutamine, γ-aminobutyric acid, proline, acetylornithine, valine, pipecolic acid, methionine, citric acid, xanthine, tyrosine, isoleucine, Glu-Tyr, Ser-Pro, tryptophan, Glu-Phe, and Leu-Val-Pro-Pro) with high PLS-DA values of over 1.00 were determined as the major compounds contributing to the discrimination of meju samples. These metabolites, which were positively related to the sensory quality of meju, can be used as fermentation biomarkers for the production of meju and to construct the meju fermentation metabolic pathway. Therefore, our results indicate that monitoring the changes in metabolites during meju fermentation might be important for producing meju-related foods with good nutritional and sensory quality.

Comparative Evaluation of Quality and Metabolite Profiles in Meju Using Starter Cultures of Bacillus velezensis and Aspergillus oryzae.

The production of good Meju soybean paste primarily depends on the selection of raw materials and fermenting microorganisms, which together influence its characteristic metabolites, taste, and aroma. In this study, we analyzed the relationship between properties and metabolites in Meju samples fermented by Aspergillus oryzae alone or with Bacillus velezensis. We developed fast-stable processing techniques to obtain Meju from A. oryzae and B. velezensis using the inoculation method, thereby ensuring safety in the production of soybean paste. The amino-type nitrogen content increased from an initial 180-228 mg% to a final 226-776 mg% during fermentation and was higher in Meju inoculated separately with the fungi and bacteria (C group) than in Meju co-inoculated with both the starters concurrently (D group). The levels of metabolites such as glucose, myo-inositol, glycerol, and fatty acids (palmitic, stearic, oleic, and linoleic acids) in Meju fermented by A. oryzae with B. velezensis were higher than those in Meju fermented by A. oryzae alone. Fungal growth was affected by the inoculated bacteria, which often occurs during the fermentation of co-inoculated Meju.