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.

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.

Identification and control of gas-producing bacteria isolated from the swollen bagged soy sauce.

The swelling of soy sauce bags seriously affects product quality and causes food safety problems, which has become an urgent problem to solve in the condiment industry. Here, gas-producing bacteria in the swollen bagged soy sauce were isolated and identified to provide an effective control method for inhibiting their growth and solving the swelling of soy sauce bags. It was found that three gas-producing bacteria isolated from the swollen bagged soy sauce were confirmed as Bacillus amyloliquefaciens (G1), Bacillus sp. (G2) and Bacillus subtilis (P3) using 16S rDNA analysis. The strains' morphologies, growth rates, and physiological and biochemical characteristics were also compared. Further studies yielded the optimal growth time, temperature and pH for the three gas-producing bacteria (B. amyloliquefacien: 24 h, 37 °C, and pH 7; Bacillus sp.: 18 h, 30 °C, and pH 6.5-7.5; B. subtilis: 36 h, 30 °C, and pH 8). Bacillus sp. was more salt tolerant than the other two. Then the antibacterial effect of the combination was tested by the physicochemical index. The results showed that filtering through a 0.22 µm inorganic micro-filtration membrane, sterilizing at 121 °C for 2 min, and adding 1 g/kg potassium sorbate was effective methods to inhibit three gas-producing bacteria and control the swelling of soy sauce.

Comparisons of Physicochemical Properties, Bacterial Diversities, Isoflavone Profiles and Antioxidant Activities on Household and Commercial doenjang.

In this study, the physicochemical properties (pH, acidity, salinity, and soluble protein), bacterial diversities, isoflavone contents, and antioxidant activities of doenjang (fermented soy paste), household doenjang (HDJ), and commercial doenjang (CDJ), were assessed and compared. The values of pH 5.14-5.94 and acidity 1.36-3.03%, indicated a similar level in all doenjang. The salinity was high in CDJ at 12.8-14.6%, and the protein contents (25.69-37.54 mg/g) were generally high in HDJ. Forty-three species were identified from the HDJ and CDJ. The main species were verified to be Bacillus amyloliquefaciens (B. amyloliquefaciens), B. amyloliquefaciens subsp. plantarum, Bacillus licheniformis, Bacillus sp. and Bacillus subtilis. Comparing the ratios of isoflavone types, the HDJ has an aglycone ratio of >80%, and 3HDJ indicates a ratio of isoflavone to aglycone of 100%. In the CDJ, except 4CDJ, glycosides account for a high proportion of more than 50%. The results of antioxidant activities and DNA protection effects were variedly confirmed regardless of HDJs and CDJs. Through these results, it is judged that HDJs have a variety of bacterial species compared to CDJs, and these are biologically active and converted from glycoside to aglycone. Bacterial distribution and isoflavone contents could be used as basic data.

Correlation between bacterial diversity and flavor substances in Longgang soy sauce.

Longgang soy sauce is one of the traditional fermented condiments in China, but its bacterial community succession and its unique flavor development during the fermentation process are not well-investigated. This study evaluated the bacterial diversity, flavor changes, and their correlation during the fermentation of Longgang soy sauce. The results showed that Weissella was the dominant bacterial genus in the fermentation stage of sauce fermented grains. In the first 31 days of the moromi fermentation stage, a variety of bacterial genera such as Weissella, Halomonas, Bacteroides, Pseudomonas, and Tetragenococcus were the dominant bacteria. Our results showed that these bacteria have a significantly positive correlation with phenylethyl alcohol, ethyl acetate, and 3-methyl-1-butanol. As the fermentation progressed, a flora structure with Halomonas as the main bacterial genus was formed. This genus exhibited a significantly positive and positive correlation with 1-octanol, ethyl palmitate, heptanol, and 2-nonanol, which are the unique flavor components of Longgang soy sauce.

Ratio of Histamine-Producing/Non-Histamine-Producing Subgroups of Tetragenococcus halophilus Determines the Histamine Accumulation during Spontaneous Fermentation of Soy Sauce.

Strain specificity (within-species variation) of microorganisms occurs widely in nature. It might affect microbiome construction and function in a complex microbial environment. Tetragenococcus halophilus, a halophilic bacterium that generally is used in high salt food fermentation, consists of two histamine-producing and non-histamine-producing subgroups. It is unclear whether and how the strain specificity of histamine-producing capacity influences the microbial community function during food fermentation. Here, based on systematic bioinformatic analysis, histamine production dynamic analysis, clone library construction analysis, and cultivation-based identification, we identified that T. halophilus is the focal histamine-producing microorganism during soy sauce fermentation. Furthermore, we discovered that a larger number and ratio of histamine-producing subgroups of T. halophilus significantly contributed more histamine production. We were able to artificially decrease the ratio of histamine-producing to non-histamine-producing subgroups of T. halophilus in complex soy sauce microbiota and realized the reduction of histamine by 34%. This study emphasizes the significance of strain specificity in regulating microbiome function. This study investigated how strain specificity influenced microbial community function and developed an efficient technique for histamine control. IMPORTANCE Inhibiting the production of microbiological hazards under the assumption of stable and high-quality fermentation is a critical and time-consuming task for the food fermentation industry. For spontaneously fermented food, it can be realized theoretically by finding and controlling the focal hazard-producing microorganism in complex microbiota. This work used histamine control in soy sauce as a model and developed a system-level approach to identify and regulate the focal hazard-producing microorganism. We discovered that the strain specificity of focal hazard-producing microorganisms had an important impact on hazard accumulation. Microorganisms frequently exhibit strain specificity. Strain specificity is receiving increasing interest since it determines not only microbial robustness but also microbial community assembly and microbiome function. This study creatively explored how the strain specificity of microorganisms influenced microbiome function. In addition, we believe that this work provides an excellent model for microbiological hazard control which can promote future work in other systems.

A case of Bacillus subtilis var. natto bacteremia caused by ingestion of natto during COVID-19 treatment in a maintenance hemodialysis patient with multiple myeloma.

A 70-year-old woman, who started on hemodialysis 7 months before for end-stage renal disease due to diabetic nephropathy and was diagnosed with symptomatic multiple myeloma 1 month before, was admitted to our hospital with critical coronavirus disease 2019 and treated with long-term immunosuppressive therapy such as steroids and tocilizumab. During treatment, Bacillus subtilis was detected in the blood cultures. We could not exclude the association of natto (fermented soybeans) with B. subtilis var. natto, which the patient had been eating every day from 8 days after admission. She was prohibited from eating natto and treated with vancomycin. Later, B. subtilis detected in the blood culture was identified as B. subtilis var. natto, which was identical with those contained in the natto that the patient consumed daily using a next-generation sequencer. Gut dysbiosis due to old age, malignant tumor, diabetes mellitus, end-stage renal disease, and intestinal inflammation caused by severe acute respiratory syndrome coronavirus 2 increased intestinal permeability and the risk of bacterial translocation, causing B. subtilis var. natto bacteremia. Therefore, careful consideration might be given to the intake of fermented foods containing live bacteria in patients with severe immunocompromised conditions.

α-Glucosidase Inhibitory Activity of Fermented Okara Broth Started with the Strain Bacillus amyloliquefaciens SY07.

In this work, a new strain of Bacillus amyloliquefaciens SY07 isolated from a traditional fermented soybean food was reported to possess remarkable α-glucosidase inhibitor-producing ability. Different culture media were applied for the proliferation of B. amyloliquefaciens SY07, and it was found that fermented okara broth presented the highest α-glucosidase inhibitory activity, while Luria-Bertani medium showed a negative effect. The extract from fermented okara broth acted in a dose-dependent manner to inhibit α-glucosidase activity, with an IC50 value of 0.454 mg/mL, and main inhibitors in the fermentation extract presented a reversible, uncompetitive pattern according to Lineweaver-Burk plots. Moreover, 1-deoxynojirimycin, a recognized α-glucosidase inhibitor, was found in the extract. Results indicated that B. amyloliquefaciens SY07 could utilize okara, a by-product from the soy processing industry, to generate α-glucosidase inhibitors effectively, and be regarded as a novel excellent microbial candidate for safe, economical production of potential functional foods or ingredients with hypoglycemic effect.

Bacillus subtilis BN strain promotes Th1 response via Toll-like receptor 2 in polarized mouse M1 macrophage.

Bacillus subtilis BN strain (BN strain) was isolated from natto, a traditional Japanese fermented soybean food product. The present study investigated the Th1 responses of the BN strain on a mouse macrophage cell line, J774.1. In cell cultures, the BN strain (spore cell cultured in Schaeffer's sporulation media) significantly increased the production of interleukin (IL-)12 protein. The BN strain induced the mRNA expression of M1 polarization genes, such as inducible nitric oxide synthase and IL-12p40 mRNA, and suppressed the mRNA expression of intracellular marker genes of M2 polarization, such as arginase 1 mRNA. The BN strain downregulated the mRNA expression of Toll-like receptor 4 (TLR4), while it upregulated the mRNA expression of TLR2, MyD88, and nuclear factor kappa B (NF-κB). The production of IL-12 protein induced by the BN strain was decreased by inhibitors of MyD88, NF-κB, and IκB kinase. Moreover, the production of IL-12 was strongly suppressed by neutralizing antibody against TLR2. These results suggest that the BN strain promotes Th1 response via TLR2 signal in mouse M1 macrophage. PRACTICAL APPLICATIONS: Bacillus subtilis is known to have beneficial effects for the host. B. subtilis BN stain (BN strain) was isolated from natto, a traditional Japanese fermented soybean food product. The effects of the BN strain on the Th1 response in macrophage cell cultures were investigated in this work. We found that the spore cells of BN strain promoted the production of Th1-type cytokine, and induced macrophage M1 polarization via Toll-like receptor 2. This study can serve as a significant reference for the development of functional food and feed with immunostimulatory effects. Over time, new food and feed products containing the BN strain may emerge, such as Juice, powder, and tablet.

Effect of Tempeh on Gut Microbiota and Anti-Stress Activity in Zebrafish.

Rhizopus oryzae is a fungus used to ferment tempeh in Indonesia and is generally recognized as safe (GRAS) for human consumption by the USA FDA. We previously assessed the effect of a tempeh extract on cortisol levels in zebrafish but did not include behavioral studies. Here, we measured the GABA content in three strains of Rhizopus oryzae, two isolated by us (MHU 001 and MHU 002) and one purchased. We then investigated the effect of tempeh on cortisol and the gut microbiota in a zebrafish experimental model. GABA concentration was the highest in MHU 002 (9.712 ± 0.404 g kg-1) followed by our MHU 001 strain and the purchased one. The fish were divided into one control group fed a normal diet and three experimental groups fed soybean tempeh fermented with one of the three strains of Rhizopus oryzae. After two weeks, individual fish were subjected to unpredicted chronic stress using the novel tank diving test and the tank light-dark test. Next-generation sequencing was used to analyze gut microbial communities and RT-PCR to analyze the expression of BDNF (brain-derived neurotrophic factor) gene and of other genes involved in serotonin signaling/metabolism in gut and brain. Tempeh-fed zebrafish exhibited increased exploratory behavior (less stress) in both tank tests. They also had significantly reduced gut Proteobacteria (include E. coli) (51.90% vs. 84.97%) and significantly increased gut Actinobacteria (include Bifidobacterium spp.) (1.80% vs. 0.79%). The content of Bifidobacteriumadolescentis, a "psychobiotic", increased ten-fold from 0.04% to 0.45%. Tempeh also increases BDNF levels in zebrafish brain. Rhizopus oryzae MHU 001 greatly improved the anti-stress effect of tempeh and microbiota composition in zebrafish gut.

The effect of the use of commercial tempeh starter on the diversity of Rhizopus tempeh in Indonesia.

At present, only a single Rhizopus species, R. microsporus, can be found in fresh tempeh produced in Java, Indonesia. The loss of diversity of Rhizopus in tempeh has been associated with the widespread use of commercial tempeh starter in Indonesia since the 2000s. However, the identities of the previous Rhizopus strains associated with tempeh, which have been preserved in a culture collection in Indonesia, have not been verified. The present study aimed to verify the identities of 22 Rhizopus strains isolated from tempeh produced using the traditional tempeh starters from the 1960s to the 2000s. Phylogenetic analysis based on the ITS regions in the rRNA gene sequence data, revealed that the Rhizopus strains belonged to the species R. arrhizus (five strains); R. delemar (14 strains); and R. microsporus (three strains). Verification of the identities of these Rhizopus strains in the present study confirmed the loss of diversity of Rhizopus species in tempeh produced in Indonesia, particularly in Java. Our findings confirmed that the morphological changes in Rhizopus species isolated from tempeh as a result of centuries of domestication.

Cheonggukjang-Specific Component 1,3-Diphenyl-2-Propanone as a Novel PPARα/γ Dual Agonist: An In Vitro and In Silico Study.

BACKGROUND: Cheonggukjang is a traditional fermented soybean paste that is mostly consumed in Korea. However, the biological activities of Cheonggukjang specific compounds have not been studied. Thus, we aimed to discover a novel dual agonist for PPARα/γ from dietary sources such as Cheonggukjang specific volatile compounds and explore the potential role of PPARα/γ dual agonists using in vitro and in silico tools. METHODS: A total of 35 compounds were selected from non-fermented and fermented soybean products cultured with Bacillus subtilis, namely Cheonggukjang, for analysis by in vitro and in silico studies. RESULTS: Molecular docking results showed that 1,3-diphenyl-2-propanone (DPP) had the lowest docking score for activating PPARα (1K7L) and PPARγ (3DZY) with non-toxic effects. Moreover, DPP significantly increased the transcriptional activities of both PPARα and PPARγ and highly activated its expression in Ac2F liver cells, in vitro. Here, we demonstrated for the first time that DPP can act as a dual agonist of PPARα/γ using in vitro and in silico tools. CONCLUSIONS: The Cheonggukjang-specific compound DPP could be a novel PPARα/γ dual agonist and it is warranted to determine the therapeutic potential of PPARα/γ activation by dietary intervention and/or supplementation in the treatment of metabolic disorders without causing any adverse effects.

Characteristics of Bacterial Strains with Desirable Flavor Compounds from Korean Traditional Fermented Soybean Paste (Doenjang).

To identify and analyze the characteristics of the microorganisms involved in the formation of the desirable flavor of Doenjang, a total of 179 strains were isolated from ninety-four Doenjang collected from six regions in South Korea, and fourteen strains were selected through a sensory evaluation of the aroma of each culture. The enzyme activities of amylase, protease and lipase was shown in the various strains. Bacillus sp.-K3, Bacillus sp.-K4 and Bacillus amyloliquefaciens-J2 showed relatively high protease activity, at 317.1 U, 317.3 U and 319.5 U, respectively. The Bacillus sp.-K1 showed the highest lipase activity at 2453.6 U. In the case of amylase, Bacillus subtilis-H6 showed the highest activity at 4105.5 U. The results of the PCA showed that Bacillus subtilis-H2, Bacillus subtilis-H3, and Bacillus sp.-K2 were closely related to the production of 3-hydroxy-2-butanone (23.51%~43.37%), and that Bacillus subtilis-H5 and Bacillus amyloliquefaciens-J2 were significantly associated with the production of phenethyl alcohol (0.39% and 0.37%). The production of peptides was observed to vary among the Bacillus cultures such as Val-Val-Pro-Pro-Phe-Leu and Pro-Ala-Glu-Val-Leu-Asp-Ile. These peptides are precursors of related volatile flavor compounds created in Doenjang via the enzymatic or non-enzymatic route; it is expected that these strains could be used to enhance the flavor of Doenjang.

Novel probiotic yeast from Miso promotes regulatory dendritic cell IL-10 production and attenuates DSS-induced colitis in mice.

BACKGROUND: Yeasts are a type of fungi thought to have probiotic functions. In this study, we isolated a novel probiotic yeast (Zygosaccharomyces sapae strain I-6) from Miso (a traditional Japanese fermented food). We examined its effects on phenotypic changes in intestinal dendritic cells (DCs), and evaluated its anti-inflammatory effects in dextran sulfate sodium (DSS)-induced colitis. METHODS: A single colony was selected from homogenized Miso, based on its ability to produce interleukin (IL)-10 in CD11c+ bone marrow DCs (BMDCs) in vitro. The anti-inflammatory effects of strain I-6 on CD11c+ BMDCs and CD11c+ CD103+ DCs were analyzed in mouse mesenteric lymph nodes in vitro and in a DSS mouse model. RESULTS: The IL-10 concentrations in the co-culture BMDC supernatants treated with I-6 were dramatically higher than in those treated with Saccharomyces cerevisiae (Sc). IL-10 production is mediated by both TLR2 and Dectin-1. ß-Glucan extracted from I-6 also induced higher levels of IL-10 production in BMDCs than ß-glucan from Sc. The number of mesenteric lymph node CD11c+ CD103+ DCs was significantly increased by I-6 administration, compared with Sc administration. Strain I-6 showed strong anti-inflammatory effects on DSS-induced colitis compared to Sc. Moreover, the adoptive transfer of I-6-treated BMDCs showed anti-inflammatory effects on DSS-induced colitis in mice without oral administration of I-6 cells. CONCLUSIONS: Strain I-6 induced phenotypic changes in intestinal CD11c+ DCs characterized by high IL-10 production and exerted strong anti-inflammatory effects on DSS-induced colitis. Traditional Japanese fermented foods may be a valuable source of probiotic yeasts for effective IBD therapy and treatment.

Fermentation and the microbial community of Japanese koji and miso: A review.

Miso is a well-known traditional Japanese fermented food, with a characteristic savory flavor and aroma, known predominately as the seasoning in miso soup. Miso production involves a two-stage fermentation, where first a mold, such as Aspergillus oryzae, is inoculated onto a substrate to make koji. A subsequent fermentation, this time by bacteria and yeast, occurs when the koji is added to a salt and soybean mash, with the miso left to ferment for up to 2 years. The microbial community of miso is considered essential to the development of the unique taste, texture, and nutritional profile of miso. Despite the importance of microorganisms in the production of miso, very little research has been undertaken to characterize and describe the microbial process. In this review, we provide an overview of the two-stage fermentation process, describe what is currently known about the microbial communities involved and consider any potential health benefits associated with the consumption of miso, along with food safety concerns. As the popularity of miso continues to expand globally and is produced under new environmental conditions, understanding the microbiological processes involved will assist to ensure that global production of miso is safe as well as delicious.

Metagenomic insights into the bacteria responsible for producing biogenic amines in sufu.

Harmful levels of biogenic amines (BAs) are frequently identified in sufu. The microorganisms and mechanisms responsible for BA production in sufu, however, are not well documented. In this study, sufu samples were randomly obtained from various regions of China. Putrescine, tyramine, and histamine were quantitated as the most abundant BAs. According to the metagenome sequencing, the abundances and diversities of genes encoding the critical enzymes in BA production were acquired. The results showed that genes encoding arginine-, ornithine-, tryptophan-, and histidine decarboxylases were the predominant amino acid decarboxylase genes. Furthermore, 34 metagenome-assembled genomes (MAGs) were generated, of which 23 encoded at least one gene involved in BA production. Genetic analysis of MAGs indicated genera affiliated with Enterococcus, Lactobacillus-related, and Lactococcus were the major histamine-synthesizing bacteria, and tyrosine may be utilized by Bacillus, Chryseobacterium, Kurthia, Lysinibacillus, Macrococcus, and Streptococcus to product tyramine. The critical species involved in two putrescine-producing pathways were also explored. In the ornithine decarboxylase pathway, Lactobacillus-related and Veillonella were predicted to be the main performers, whereas Sphingobacterium and unclassified Flavobacteriaceae were the dominant executors in the agmatine deiminase pathway. The present study not only explained the BAs formation mechanism in sufu but also identified specific bacteria used to control BAs in fermented soybean products.

Effect of fermentation with single and co-culture of lactic acid bacteria on okara: evaluation of bioactive compounds and volatile profiles.

Okara is the main soybean by-product resulting from the processing of soy milk and tofu. Despite being a product with a lot of potential and rich in many bioactive compounds such as polyphenols, it presents an unpleasant, rancid aroma. For this reason its use in the food industry is limited. In this study, we have reported the integral use of okara in a solid state fermentation process, conducted with wild strains of lactic acid bacteria, to evaluate the effect of bacterial metabolism on the volatile and polyphenolic profiles. Strains belonging to Lactobacillus acidophilus, Lacticaseibacillus rhamnosus and Pediococcus acidilactici species were used in monoculture and, for the first time, in co-culture. The results showed an improvement in the aromatic fraction showing a decrease in hexanal, responsible for off-flavour, and an increase in ketones with fruity and buttery notes in fermented okara. Polyphenols were also affected, and, in particular, a bioconversion of glucoside isoflavones to the aglycone forms was highlighted in all fermented substrates. In addition, the appearance of both phenyllactic and p-hydroxyphenyllactic acids as well as the increase in indole-3-lactic acid was observed for the first time upon okara fermentation. Overall, the co-culture appears to be the most promising for biovalorization of okara, thereby opening the possibility of its use in the development of functional ingredients.

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.

Physicochemical, flavor and microbial dynamic changes during low-salt doubanjiang (broad bean paste) fermentation.

This study aimed to elaborate the roles of salt concentration on doubanjiang (broad bean paste) fermentation. Three sets of doubanjiang samples which had lower salt concentration than commercial doubanjiang were prepared and the physicochemical parameters, biogenic amines, flavor, microbial dynamics were analyzed during fermentation. The salt reduction showed significant effect on the dynamics of bacteria and fungi, thus leading to doubanjiang samples with different properties. Salt reduction during fermentation relieved the osmotic pressure towards microbes, which favored the accumulation of amino acid nitrogen, amino acids, and volatile flavor compounds. However, higher concentrations of total acids and biogenic amines and the existence of conditional pathogens, such as Klebsiella, Cronobacter and Acinetobacter genera, were observed in salt reduced doubanjiang samples, which was undesirable for doubanjiang quality. This study would deep our understanding of the roles of salt on doubanjiang fermentation.

A metabolomics approach to evaluate post-fermentation enhancement of daidzein and genistein in a green okara extract.

BACKGROUND: Okara is a major agri-industrial by-product of the tofu and soymilk industries. Employing food-wastes as substrates for the green production of natural functional compounds is a recent trend that addresses the dual concepts of sustainable production and a zero-waste ecosystem. RESULTS: Extracts of unfermented okara and okara fermented with Rhizopus oligosporus were obtained using ethanol as extraction solvent, coupled with ultrasound sonication for enhanced extraction. Fermented extracts yielded significantly better results for total phenolic content (TPC) and total flavonoid content (TFC) than unfermented extracts. A qualitative liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) analysis revealed a shift from glucoside forms to respective aglycone forms of the detected isoflavones, post-fermentation. Since the aglycone forms have been associated with numerous health benefits, a quantitative high-performance liquid chromatography (HPLC) analysis was performed. Fermented okara extracts had daidzein and genistein concentrations of 11.782 ± 0.325 µg mL-1 and 10.125 ± 1.028 µg mL-1 , as opposed to that of 6.7 ± 2.42 µg mL-1 and 4.55 ± 0.316 µg mL-1 in raw okara extracts, respectively. Lastly, the detected isoflavones were mapped to their metabolic pathways, to understand the biochemical reactions triggered during the fermentation process. CONCLUSION: Fermented okara may be implemented as a sustainable solution for production of natural bioactive isoflavonoids genistein and daidzein. © 2021 Society of Chemical Industry.