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.

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.

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.

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.

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.

The fermentation properties and microbial diversity of soy sauce fermented by germinated soybean.

BACKGROUND: The quality of commercial soy sauce is variable at present. Technical work is needed to improve the quality and flavor of soy sauce, especially in China. Material is a factor for influencing soy sauce characters in fermentation. RESULTS: Germinated soybean sauce (fermented by germinated soybean) had a gamma aminobutyric acid (GABA) concentration of 6.83 µg mL-1 , whereas a control (a soy sauce fermented by soybean) had a GABA concentration of less than 2.42 µg mL-1 . Germinated soybean sauce also contained significantly higher levels of isoflavones, total polyphenol, and amino acid nitrogen than the control soy sauce. Microbial diversity results showed that Bacillus was the dominant bacteria in germinated soy sauce compared with the control. Aldehydes, alcohols, esters, and phenols were the major flavor components of germinated soybean sauce. CONCLUSION: A soy sauce with high levels of GABA, isoflavones, and total polyphenol was developed using germinated soybean. Stenotrophomonas, the typical pathogen found in the control, was reduced dramatically and replaced by Bacillus during fermentation with the germinated soybean. The germinated soybean sauce exhibited a better aroma and taste than the control. Soy sauce fermented by soybeans that germinated for 48 h exhibited greater advantages than soy sauce that germinated for 24 and 72 h. © 2020 Society of Chemical Industry.

Metabolite Profiling and Microbial Community of Traditional Meju Show Primary and Secondary Metabolite Differences Correlated with Antioxidant Activities.

Meju, a type of fermented soybean paste, is used as a starter in the preparation of various Korean traditional soybean-based foods. In this study, we performed Illumina-MiSeq paired-end sequencing for microbial communities and mass spectrometry analysis for metabolite profiling to investigate the differences between 11 traditional meju products from different regions across Korea. Even though the bacterial and fungal communities showed remarkable variety, major genera including Bacillus, Enterococcus, Variovorax, Pediococcus, Weissella, and Aspergillus were detected in every sample of meju. The metabolite profile patterns of the 11 samples were clustered into two main groups: group I (M1-5) and group II (M6-11). The metabolite analysis indicated a relatively higher amino acid content in group I, while group II exhibited higher isoflavone, soyasaponin, and lysophospholipid contents. The bioactivity analysis proved that the ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)) radical-scavenging activity was higher in group II and the FRAP (ferric reducing antioxidant power) activity was higher in group I. The correlation analysis revealed that the ABTS activity was isoflavonoid, lipid, and soyasaponin related, whereas the FRAP activity was amino acid and flavonoid related. These results suggest that the antioxidant activities of meju are critically influenced by the microbiome and metabolite dynamics.

Fermented Soy Paste Alleviates Lipid Accumulation in the Liver by Regulating the AMPK Pathway and Modulating Gut Microbiota in High-Fat-Diet-Fed Rats.

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of liver disease due to lipid accumulation in the hepatocyte. Diet, especially a high-fat diet, is one risk factor that leads to NAFLD. Many natural compounds such as isoflavones have antiobesity effects. Therefore, intake of these functional compounds through daily dietary choices is a method of improving health. Miso is a kind of fermented soy paste, which is rich in isoflavones and has a different biological activity. In this study, we investigated the effects of different concentrations of fermented soy paste on NAFLD in high-fat-diet (HFD)-fed Sprague-Dawley (SD) rats. The results showed that 2% fermented soy paste decreased serum triacylglycerol (TG) and alanine aminotransferase (ALT) and reduced lipid accumulation in the liver through induced fatty acid oxidation by activating the adenosine 5'-monophosphate -activated protein kinase (AMPK) pathway and increasing PGC1α and CPT1α protein expression. Furthermore, we found that 2% fermented soy paste increased the abundance of Prevotellaceae NK3B31 and Desulfovibrio. Taken together, fermented soy paste improved HFD-induced lipid accumulation in the liver by activating fatty acid oxidation and modulating gut microbiota.

Comparative aroma and taste profiles of oil furu (soybean curd) fermented with different mucor strains.

The effects of different mucor strains (Mucor racemosus, Actinomucor, and Mucor wutungkiao) on aroma and taste profiles based on proteolysis, lipolysis, and their catabolism in oil furu were studied. Gas chromatography-mass spectrometry and relative odor activity were used to monitor the changes of key volatile compounds and the differences in the characteristic aroma contents of oil furu. Using principal component analysis, the different fermentation strains had an effect on aroma profiles. The volatile compounds from metabolism of protein and fatty acid contributed to the aroma of oil furu with different contribution from the different strains, presumably due to their different enzymes. The electronic tongue and free amino acid profiles also showed strain differences of taste. Based on these results, optimization of the amount of each of the different mucor strains during cofermentation might achieve better flavor.

Reduction in biogenic amines in douchi fermented by probiotic bacteria.

Ecology studies showed that esophageal and gastric cancers are directly correlated with the consumption of processed foods. The carcinogenicity of traditional Chinese fermented foods such as douchi (fermented black beans or fermented black soybeans) is due to the presence of carcinogenic N-nitroso compounds, which are derived from biogenic amines. Among the various biogenic amines that can act as precursors of N-nitroso compounds, histamine and tyramine are considered to be the most toxic and are of public health concern when present in food. We have examined some douchi products on the market, and significant amounts of histamine and tyramine were found. The use of fermentation starters generated by subculturing fermented products with unknown microbiota would induce the risk of biogenic amines. As the microbiota used in fermentation is a crucial factor in determining the biogenic amines of fermented food, it is hypothesized that the possible harmful effects of douchi can be minimized through the use of fermentation starters composed of probiotic bacteria. This is the first study to investigate the potential of using probiotic bacteria in manufacturing douchi. Lactobacillus rhamnosus GG (LGG), Lactobacillus casei Shirota (LcS) and Escherichia coli Nissle 1917 (EcN) were used to ferment black beans in this study, and no tyramine was detected in black bean samples incubated with these three strains anaerobically at 37°C or 20°C. The starter culture strains, temperature and presence of oxygen during the incubation period were found to be critical to the generation of biogenic amines. The findings of this study can provide evidence-based insights and warrant further investigations on the potential of reducing the harmful compounds in food fermented with probiotic bacteria as well as the sensory evaluation of douchi fermented with probiotic bacteria.

Short-Term Fermented Soybeans with Bacillus amyloliquefaciens Potentiated Insulin Secretion Capacity and Improved Gut Microbiome Diversity and Intestinal Integrity To Alleviate Asian Type 2 Diabetic Symptoms.

We determined that consuming chungkookjang fermented by Bacillus subtilis (BS) or Bacillus amyloliquefaciens (BA) alleviated hyperglycemia in partially pancreatectomized (Px) rats, an Asian type 2 diabetic (T2D) animal model. Px rats had deteriorated glucose metabolism with decreased glucose-stimulated insulin secretion and insulin sensitivity. Insulin secretion capacity was improved in the ascending order of the Px-control, positive control (3 mg of metformin/kg of body weight), BS (4.5% BS diet), BA (4.5% BA diet), and normal-control (sham-operated rats). BA and BS increased ß-cell mass and decreased malondialdehyde contents and tumor necrosis factor α expression in the islets. BA increased hepatic peroxisome proliferator-activated receptor (PPAR)-α and PPAR-ß similar to the positive control. Bacillales, Lactobacillales, and Verrucomicrobiales (Akkermensia muciniphila) increased and Enterobacteriales decreased in the BA and BS compared to the Px-control. BA prevented the decrease in the villi area and the number of goblet cells in intestinal tissues. In conclusion, BA improved glucose regulation by potentiating insulin secretion and reducing insulin resistance while maintaining gut mucin contents by improving gut microbiota in lean T2D rats.

Evaluation of Cold Atmospheric Pressure Plasma (CAPP) and plasma-activated water (PAW) as alternative non-thermal decontamination technologies for tofu: Impact on microbiological, sensorial and functional quality attributes.

The efficacy of Cold Atmospheric Pressure Plasma (CAPP) for the inactivation of Salmonella enterica serovar Enteritidis, Salmonella enterica serovar Typhimurium, Listeria monocytogenes and Escherichia coli O157:H7 on tofu was evaluated. The potential of using Plasma Activated Water (PAW) as an immersion solution for controlling microbial growth in tofu throughout its shelf-life was also investigated. The effects of these strategies on the physical and functional properties of treated tofu were also studied. CAPP treatment of tofu caused a limited inactivation of microbial populations, with log10 reductions attained ranging from 0.2 to 0.6 log10 for S. Enteritidis and E. coli O157:H7, respectively, after a 15 min treatment. CAPP did not affect tofu's water holding capacity, but it dried it and gave rise to changes in color and texture, which were reverted by immersing the treated product in distilled water. Refrigerated storage of tofu using PAW as an immersion solution was effective in controlling microbial growth. Thus, total counts obtained after 28 days of storage were around 3 log10 units lower than those observed for tofu stored immersed in non-treated deionized water. In addition, this strategy led to a product with a higher functional value than thermally-treated commercial tofu, retaining up to 80% of the initial content of total polyphenols, with better texture properties, less hardness and springiness (approximately 20-30% lower) and with minor changes in its characteristic color. Overall, these results evidence that PAW is a promising non-thermal technology which can facilitate the control of pathogenic microorganisms on tofu while retaining its physical and functional properties.

Enhancing Activities of Salt-Tolerant Proteases Secreted by Aspergillus oryzae Using Atmospheric and Room-Temperature Plasma Mutagenesis.

Aspergillus oryzae 3.042 was mutagenized using atmospheric and room-temperature plasma (ARTP) technology to enhance its salt-tolerant proteases activity. Compared to the starting strain, mutant H8 subjected to 180 s of ARTP treatment exhibited excellent genetic stability (15 generations), growth rate, and significantly increased activities of neutral proteases, alkaline proteases, and aspartyl aminopeptidase during fermentation. Mutant H8 significantly enhanced the contents of 1-5 kDa peptides, aspartic acid, serine, threonine, and cysteine in soy sauce by 16.61, 7.69, 17.30, 8.61, and 45.00%, respectively, but it had no effects on the contents of the other 14 free amino acids (FAAs) due to its slightly enhanced acidic proteases activity. Analyses of transcriptional expressions of salt-tolerant alkaline protease gene (AP, gi: 217809) and aspartyl aminopeptidase gene (AAP, gi: 6165646) indicated that their expression levels were increased by approximately 30 and 27%, respectively. But no mutation was found in the sequences of AP and AAP expression cassettes, suggesting that the increased activities of proteases in mutant H8 should be partially attributed to the increased expression of proteases. ARTP technology showed great potential in enhancing the activities of salt-tolerant proteases from A. oryzae.

A Sustainable Graphene Aerogel Capable of the Adsorptive Elimination of Biogenic Amines and Bacteria from Soy Sauce and Highly Efficient Cell Proliferation.

A graphene aerogel (GA) with a three-dimensional (3D) structure, ultra-lightweight nature, and high hydrophobicity was simply fabricated by the one-step pyrolysis of glucose and ammonium chloride. The as-synthesized GA exhibited a 3D interconnected microporous architecture with a high surface area of ∼2860 m2 g-1 and pore volume of 2.24 cm3 g-1. The hydrophobic GA (10 mg 100 mL-1) demonstrated rapid and excellent adsorption performance for the removal of food toxins such as various biogenic amines (histamine, cadaverine, and spermine) and the hazardous bacterium Staphylococcus aureus (a food contaminant and a cause of poor wound healing) from a liquid matrix with a maximum simultaneous adsorption capacity for multiple biogenic amines of >85.19% (histamine), 74.1% (cadaverine), and 70.11% (spermidine) and a 100% reduction in the viable cell count of S. aureus within 80 min of interaction. The outstanding adsorption capacity can be attributed to a highly interconnected porous network in the 3D architecture and a high surface-to-volume ratio. A case study using soy sauce spiked with multiple biogenic amines showed successful removal of toxins with excellent recyclability without any loss in absorption performance. Biocompatibility of the GA in terms of cell viability was observed even at high concentrations (83.46% and 75.28% at 25 and 50 mg mL-1, respectively). Confirmatory biocompatibility testing was conducted via live/dead cell evaluation, and the morphology of normal lung epithelial cells was examined via scanning electron microscopy showed no cellular shrinkage. Moreover, GA showed excellent removal of live colonies of S. aureus from the food matrix and immunoblotting analysis showed elevated protein expression levels of ß-catenin and α-SMA (α-smooth muscle actin). The biocompatible sugar-based GA could simultaneously adsorb multiple biogenic amines and live bacteria and was easy to regenerate via simple separation due to its high floatability, hydrophobicity, surface area, and porosity without any structural and functional loss, making it especially relevant for food safety and biomedical applications.

Improvement of menaquinone-7 production by Bacillus subtilis natto in a novel residue-free medium by increasing the redox potential.

Bacillus subtilis natto is a GRAS bacterium. Nattokinase, with fibrinolytic and antithrombotic activities, is one of the major products of this organism. It is being gradually recognized that B. subtilis natto can also be used as a biosynthetic strain for vitamin K2, which has phenomenal benefits, such as effects in the prevention of cardiovascular diseases and osteoporosis along with antitumor effects. Knocking out of the aprN gene by homologous recombination could improve the redox potential and slightly increase the concentration of MK-7. By detecting the change in redox potential during the growth of B. subtilis natto, a good oxygen supply and state of the cell membrane were found to be beneficial to vitamin K2 synthesis. A two-step RSM was used to optimize the operation parameters and substrate concentration in the new residue-free fermentation culture. The optimal conditions for the residue-free medium and control were determined. The optimum concentrations of soybean flour, corn flour, and peptone were 78.9, 72.4, and 24.8 g/L, respectively. The optimum rotational speed and volume of the culture medium using a shaking flask were 117 rpm and 10%, respectively. The state and composition of the cell membranes were more stable when engineered bacteria were cultured in this residue-free fermentation medium. Finally, the concentration of MK-7 increased by 37% to 18.9 mg/L, and the fermentation time was shortened by 24 h.

Qualidade microbiológica e nutricional de bebida fermentada de soja / Microbiological and nutritional quality of fermented soybean drink

A soja apresenta propriedades benéficas à saúde como a redução dos níveis de colesterol e efeitos protetores contra a obesidade. Os indivíduos intolerantes à lactose podem utilizar produtos como a bebida fermentada de soja como alternativa em substituição ao leite de vaca. Diante deste contexto, este estudo almejou o desenvolvimento de uma bebida fermentada à base de soja adicionada de fibra dietética solúvel como a inulina e saborizada com polpa de goiaba. Os resultados da avaliação microbiológica das formulações estavam de acordo com os parâmetros vigentes na legislação brasileira, denotando que as boas práticas na sua produção estavam adequadas. Na análise de minerais observou-se que os teores de potássio (629mg à 652mg), ferro (1,44mg à 1,56mg) e fósforo (323mg à341,33mg) se apresentaram acima da quantidade presente no leite de vaca. Este produto desenvolvido pode ser uma alternativa saudável e atender à expectativa de consumidores intolerantes à lactose, quanto à saúde e bem-estar.

Strain Screening from Traditional Fermented Soybean Foods and Induction of Nattokinase Production in Bacillus subtilis MX-6.

The plasminogen-free fibrin plate assay method was used to isolate Bacillus subtilis MX-6, a strain with high production of nattokinase from Chinese douchi. The presence of aprN, a gene-encoding nattokinase, was verified with PCR method. The predicted amino acid sequence was aligned with homologous sequences, and a phylogenetic tree was constructed. Nattokinase was sublimated with ammonium sulfate, using a DEAE-Sepharose Fast Flow column, a CM-Sepharose Fast Flow column and a Sephadex G-75 gel filtration column. SDS-PAGE analysis indicated that the molecular weight of the purified nattokinase from Bacillus subtilis MX-6 was about 28 kDa. Fermentation of Bacillus subtilis MX-6 nattokinase showed that nattokinase production was maximized after 72 h; the diameter of clear zone reached 21.60 mm on the plasminogen-free fibrin plate. Nattokinase production by Bacillus subtilis MX-6 increased significantly after supplementation with supernatant I, supernatant II and soy peptone but decreased substantially after the addition of amino acids. This result indicated that the nattokinase production by B. subtilis MX-6 might be induced by soybean polypeptides. The addition of MgSO4 and CaCl2 increased B. subtilis MX-6 nattokinase production.

Isolation of nitrite-degrading strains from Douchi and their application to degrade high nitrite in Jiangshui.

BACKGROUND: Excessive nitrite in food is potentially harmful to human health because of carcinogenic effects caused by its nitroso-derivatives. Douchi, which widely distributed throughout the country, is a traditional solid fermented soybean food with low nitrite content. RESULTS: In this study, bacteria which can degrade nitrite were isolated from Douchi and identified from their 16S rDNA sequences. Acinetobacter guillouiae, Acinetobacter bereziniae, Bacillus subtilis, Bacillus tequilensis, Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus aryabhattai and Bacillus methylotrophicus were selected. It was shown that all strains were able to degrade nitrite to some extent, including Bacillus subtilis NDS1, which was able to degrade 99.41% of nitrite. The enzyme activities of these strains were determined at 24 and 48 h and were shown to correspond with their nitrite degradation rates. The strains were used to inoculate Jiangshui, a kind of traditional fermented vegetable from northwest China that often has a high nitrite content. Of the strains tested, Bacillus subtilis NDS1, Bacillus tequilensis NDS3, Acinetobacter bereziniae NDS4, Bacillus subtilis NDS6, and Bacillus subtilis NDS12 were able to degrade nitrite in Jiangshui more rapidly, with Acinetobacter bereziniae NDS4 degrading almost all nitrite in 48 h compared with 180 h of control. CONCLUSION: These results indicate that the selected strains have potential to be used as nitrite-degrading agents in food. © 2018 Society of Chemical Industry.

Ottowia konkukae sp. nov., isolated from rotten biji (tofu residue).

A Gram-negative, aerobic, non-motile, non-spore-forming and rod-shaped bacterial strain, designated SK3863T, was isolated from rotten biji (residue remaining after making tofu). This bacterium was characterized in order to determine its taxonomic position by using the polyphasic approach. Strain SK3863T grew well at 25-37 °C on Reasoner's 2A agar plates. On the basis of 16S rRNA gene sequence similarity, strain SK3863T belonged to the family Comamonadaceae and was related to Ottowia beijingensis GCS-AN-3T (96.5 % sequence similarity) and Ottowia pentelensis RB3-7T (96.4 %). Lower sequence similarities (96.2 %) were found to all of the other recognized members of the genus Ottowia. The G+C content of the genomic DNA was 65.8 mol%. The major respiratory lipoquinone was ubiquinone 8 and the major fatty acids were C16 : 1ω6c/C16 : 1ω7c, C16 : 0 and C18 : 1ω7c/C18 : 1ω6c. Strain SK3863T could be differentiated genotypically and phenotypically from the recognized species of the genus Ottowia. The isolate therefore represents a novel species, for which the name Ottowia konkukae sp. nov. is proposed, with the type strain SK3863T (=KCCM 43236T=DSM 105395T).