Korean Fermented Soybean Products Research Articles

Analysis of Oligosaccharides in Korean Fermented Soybean Products by the Combination of Mass Spectrometry and Gas Chromatography

Doenjang (fermented soybean paste) and ganjang (soy sauce) are traditional fermented foods that are widely consumed in Korea. The oligosaccharides found in soybean and its fermented foods have great potential to improve the quality of foods; however, their structural details have not been well studied. In this study, we used advanced mass spectrometry and gas chromatography to analyze oligosaccharides and their monomeric composition in two fermented soybean products. In both foods, oligosaccharides with a degree of polymerization ranging from 3 to 7 were found. Their constituent monosaccharides were characterized; galactose, xylose, arabinose, and rhamnose were the predominant constituents of the oligosaccharides, and fucose, fructose, mannose, glucose, and N-acetylglucosamine were also found. The great structural diversity of the oligosaccharides found suggests that soybean carbohydrates are hydrolyzed and/or transformed during fermentation and may yield novel oligosaccharides.

Simple chromatographic determination of aflatoxins in Korean fermented soybean products doenjang, ganjang, and gochujang, with comparison of derivatization methods.

Korean fermented soybean products doenjang, ganjang, and gochujang are vulnerable to contamination with aflatoxigenic fungi in the open fermentation environment. Therefore, simple and effective methods to determine aflatoxins (AFs) in these complex food matrices are needed. High-performance liquid chromatography with fluorescence detection using two derivatization methods for AF determination in three fermented soybean products was optimized and validated. Pre-column derivatization (preCD) of the AF extracts was performed using trifluoroacetic acid, and post-column derivatization (PCD) was performed in a photochemical reactor for enhanced detection. Both derivatization methods resulted in acceptable performances for linearity (R2 > 0.999), recovery (71-118%), and precision (< 10.6%) values. Recovery and precision with preCD and PCD were similar, but the limit of detection was superior with PCD. When these analytical methods were applied to commercially available fermented soybean products, the AF levels of all commercial products were ranged from not detected to 6.06μg/kg.

Characterization of Aspergillus sojae Isolated from Meju, Korean Traditional Fermented Soybean Brick.

Initially, we screened 18 Aspergillus sojae-like strains from Aspergillus spp. isolated from meju (Korean traditional fermented soybean brick) according to their morphological characteristics. Because members of Aspergillus section Flavi are often incorrectly identified because of their phylogenetic similarity, we re-identified these strains at the morphological and molecular genetic levels. Fourteen strains were finally identified as A. sojae. The isolates produced protease and α-amylase with ranges of 2.66-10.64 and 21.53-106.73 unit/g-initial dry substrate (U/g-IDS), respectively, which were equivalent to those of the koji (starter mold) strains employed to produce Japanese soy sauce. Among the isolates and Japanese koji strains, strains SMF 127 and SMF 131 had the highest leucine aminopeptidase (LAP) activities at 6.00 and 6.06 U/g-IDS, respectively. LAP plays an important role in flavor development because of the production of low-molecular-weight peptides that affect the taste and decrease bitterness. SMF 127 and SMF 131 appeared to be non-aflatoxigenic because of a termination point mutation in aflR and the lack of the polyketide synthase gene found in other A. sojae strains. In addition, SMF 127 and SMF 131 were not cyclopiazonic acid (CPA) producers because of the deletion of maoA, dmaT, and pks/nrps, which are involved in CPA biosynthesis. Therefore, A. sojae strains such as SMF 127 and SMF 131, which have high protease and LAP activities and are free of safety issues, can be considered good starters for soybean fermentations, such as in the production of the Korean fermented soybean products meju, doenjang, and ganjang.

Genetic Diversity and Antibiotic Resistance of Enterococcus faecalis Isolates from Traditional Korean Fermented Soybean Foods.

Eighty-five Enterococcus faecalis isolates collected from animals (40 isolates), meju (a Korean fermented soybean product; 27 isolates), humans (10 isolates), and various environmental samples (8 isolates) were subjected to multilocus sequence typing (MLST) to identify genetic differences between samples of different origins. MLST analysis resulted in 44 sequence types (STs), and the eBURST algorithm clustered the STs into 21 clonal complexes (CCs) and 17 singletons. The predominant STs, ST695 (21.1%, 18/85) and ST694 (9.4%, 8/85), were singletons, and only contained isolates originating from meju. None of the STs in the current study belonged to CC2 or CC9, which comprise clinical isolates with high levels of antibiotic resistance. The E. faecalis isolates showed the highest rates of resistance to tetracycline (32.9%), followed by erythromycin (9.4%) and vancomycin (2.4%). All isolates from meju were sensitive to these three antibiotics. Hence, MLST uncovered genetic diversity within E. faecalis, and clustering of the STs using eBURST revealed a correlation between the genotypes and origins of the isolates.

Occurrence of Toxigenic Bacillus cereus and Bacillus thuringiensis in Doenjang, a Korean Fermented Soybean Paste

This study determined the prevalence and toxin profile of Bacillus cereus and Bacillus thuringiensis in doenjang, a fermented soybean food, made using both traditional and commercial methods. The 51 doenjang samples tested were broadly contaminated with B. cereus; in contrast, only one sample was positive for B. thuringiensis. All B. cereus isolates from doenjang were positive for diarrheal toxin genes. The frequencies of nheABC and hblACD in traditional samples were 22.7 and 0%, respectively, whereas 5.1 and 5.1% of B. cereus isolates from commercial samples possessed nheABC and hblACD, respectively. The detection rate of ces gene was 10.8%. The predominant toxin profile among isolates from enterotoxigenic B. cereus in doenjang was profile 4 (entFM-bceT-cytK). The major enterotoxin genes in emetic B. cereus were cytK, entFM, and nheA genes. The B. thuringiensis isolate was of the diarrheagenic type. These results provide a better understanding of the epidemiology of the enterotoxigenic and emetic B. cereus groups in Korean fermented soybean products.

Incidence, Antibiotic Susceptibility, and Toxin Profiles of Bacillus cereus sensu lato Isolated from Korean Fermented Soybean Products.

Korean fermented soybean products, such as doenjang, kochujang, ssamjang, and cho-kochujang, can harbor foodborne pathogens such as Bacillus cereus sensu lato (B. cereus sensu lato). The aim of this study was to characterize the toxin gene profiles, biochemical characteristics, and antibiotic resistance patterns of B. cereus sensu lato strains isolated from Korean fermented soybean products. Eighty-eight samples of Korean fermented soybean products purchased from retails in Seoul were tested. Thirteen of 26 doenjang samples, 13 of 23 kochujang samples, 16 of 30 ssamjang samples, and 5 of 9 cho-kochujang samples were positive for B. cereus sensu lato strains. The contamination level of all positive samples did not exceed 4 log CFU/g of food (maximum levels of Korea Food Code). Eighty-seven B. cereus sensu lato strains were isolated from 47 positive samples, and all isolates carried at least one enterotoxin gene. The detection rates of hblCDA, nheABC, cytK, and entFM enterotoxin genes among all isolates were 34.5%, 98.9%, 57.5%, and 100%, respectively. Fifteen strains (17.2%) harbored the emetic toxin gene. Most strains tested positive for salicin fermentation (62.1%), starch hydrolysis (66.7%), hemolysis (98.9%), motility test (100%), and lecithinase production (96.6%). The B. cereus sensu lato strains were highly resistant to β-lactam antibiotics such as ampicillin, penicillin, cefepime, imipenem, and oxacillin. Although B. cereus sensu lato levels in Korean fermented soybean products did not exceed the maximum levels permitted in South Korea (<10(4) CFU/g), these results indicate that the bacterial isolates have the potential to cause diarrheal or emetic gastrointestinal diseases.

Prevalence, genetic diversity, and antibiotic resistance of Bacillus cereus isolated from Korean fermented soybean products.

Bacillus cereus contamination is a major food safety problem for Korean fermented soybean products, but few studies have assessed its potential to cause foodborne illness. The objectives of this study were to investigate the prevalence and characteristics of B. cereus isolated from Korean fermented soybean products. B. cereus was detected in 110 of 162 (67.9%) samples. The highest B. cereus frequency was observed in deonjang (68 of 93 samples, 73.1%) and cheonggukjang (18 of 25, 72.0%); however, nonhemolytic enterotoxin was detected only in 22 of 162 samples (13.6%). Although the tested B. cereus isolates showed diverse pulsotypes according to repetitive sequence-PCR banding patterns, they displayed similar antibiotic sensitivity spectra. The low frequency of enterotoxin detection suggests that the potential risk of B. cereus foodborne illness associated with Korean fermented soybean products is lower than generally presumed. However, considering the prevalence of B. cereus and the high content of fermented soybean products in the Korean diet, it is necessary to constantly monitor the level of contamination with B. cereus and its toxins in such Korean food products.

Genome Sequence of Lysinibacillus boronitolerans F1182, Isolated from a Traditional Korean Fermented Soybean Product

Lysinibacillus is a Gram-positive, rod-shaped, and round-spore-forming bacterial genus of the family Bacillaceae. We analyzed the genome sequence of Lysinibacillus boronitolerans F1182, isolated from a traditional Korean fermented soybean product. The genome sequence contained 4.46 Mbp with a G+C content of 37.5%. This is the first report of an L. boronitolerans genome.

Detection of Foodborne Pathogens and Analysis of Aflatoxin Levels in Home-made Doenjang Samples

Doenjang is a traditional Korean fermented soybean product that provides a major source of protein. In this study, a total of 18 different home-made doenjang samples were examined for the presence of foodborne pathogens and the total aflatoxin levels. Using an enzyme-linked immunosorbent assay to assess microbial quality and potential public health risk, we showed that total coliform levels in the doenjang samples ranged from 0 to 4.43±2.32 ×106 CFU/g, and the maximum limit of Bacillus cereus was 4.67±2.0×105 CFU/g. However, other foodborne pathogens, such as Staphylococcus aureus, Escherichia coli O157:H7 and Salmonella spp., were not detected among the tested samples. One of the samples (S3) showed a maximum limit of 42.2±9.1 μg/kg for aflatoxin levels, which was above the safety limit allowed by the Codex Alimentarius Commission (CAC) regulatory agency. Further research is necessary to determine whether and how doenjang safety can be improved via elimination/reduction of microbial contamination during fermentation and storage or using microbial starter cultures for its fermentation.

Antimicrobial Compounds Profile During Cheonggukjang Fermentation Against Xanthomonas oryzae pv. oryzae (Xoo)

Xanthomonas oryzae causes rice bacterial blight, which has been reported as one of the most destructive diseases of rice. Metabolites were identified through cheonggukjang, a traditional Korean fermented soybean product fermented by the Bacillus spp., to control the bacteria. HPLC, MS, and UPLC-Q-TOF-MS analyses were performed to identify metabolites responsible for antimicrobial activity. In this analysis, the m/z values of 253.0498, 283.0600, 269.0455, 992.6287, and 1,006.6436 were identified as daidzein, glycitein, genistein, surfactin B, and surfactin A, respectively. The levels of surfactin B and surfactin A were found to be high at 24 h (4.35 μg/ml) and 36 h (3.43 μg/ml) of fermentation, respectively.

The Anti-Inflammatory Action of Fermented Soybean Products in Kidney of High-Fat-Fed Rats

Soybean has many compounds with a variety of biological properties that potentially benefit human health; among them, isoflavones have inhibitory effects on lipid oxidation in adipose tissue. In this study, we examined two Korean traditional fermented soybean products--doenjang (DNJ) and cheonggukjang (CGJ)--for their ability to suppress redox-sensitive nuclear factor κB (NF-κB) activation in the kidney of rats fed a high-fat diet. Sprague-Dawley rats, 4 weeks old, were fed soybean, DNJ, or CGJ (1 g/kg/day) with a 20% fat diet for 6 weeks. Body weight and food intake were carefully monitored. NF-κB-related activities of genes for inflammatory proteins, such as inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and vascular cell adhesion molecule-1 (VCAM-1), were determined. The soybean products exhibited antioxidative action by maintaining redox regulation, suppressing NF-κB activation, and modulating the expression of genes for NF-κB-induced inflammatory proteins such as COX-2, iNOS, and VCAM-1. Based on these results, we conclude that Korean traditional soybean fermented products, especially CGJ, suppress the generation of reactive species, NF-κB activity, and NF-κB-related inflammatory genes.

Metabolomic Assessment of Fermentative Capability of Soybean Starter Treated with High Pressure

Meju, a brick of dried fermented soybean naturally inoculated with microorganisms, is a starter used for producing traditional Korean fermented soybean products such as soybean paste (doenjang) and soy sauce (ganjang). In order to reduce aging time during production of soybean paste and soy sauce, high pressure (HP) treatment was applied to the meju starter at 500 MPa of pressure for 10 min at 15 degrees C. Fermentative behaviors of normal and HP-treated meju were assessed and compared through physicochemical and (1)H NMR-based metabolomic analysis. All mejues were incubated for 3 weeks at 30 degrees C. At 1 week of incubation, total bacterial population decreased mainly due to a reduction of water content by spontaneous evaporation during the incubation period. As the incubation time increased, glutamate, proline, betain, choline, and phosphocholine levels increased in both normal and HP-treated mejues, indicating that microorganisms in the mejues synthesize these metabolites to endure intracellular hyperosmotic stress induced by the reduction in water content. Through 3 weeks of incubation, the amino-type nitrogen contents and neutral protease activities in HP-treated meju were significantly higher (p < 0.05) than in normal meju, even though total bacterial content in HP-treated meju was 2 or 3 times lower. Moreover, marked increases in glycerol, acetate, tyrosine, and choline levels were observed in HP-treated meju compared to normal meju. In particular, higher levels of tyrosine in HP-treated meju were consistent with the increased neutral protease activities compared to normal meju, indicating an improvement in enzyme stability with HP treatment. These findings highlight a new or better understanding of the influence of the HP or physical treatments on fermentative products in food processing, such as those associated with soybean paste and soy sauce, regarding metabolic behaviors in fermentative starter induced by HP treatment.

Purification and characterisation of Aspergillus sojae naringinase: The production of prunin exhibiting markedly enhanced solubility with in vitro inhibition of HMG-CoA reductase

Aspergillus sojae isolated from a traditional Korean fermented soybean product exhibited strong naringinase activity. The naringinase enzyme was purified and had a molecular weight of 70 kDa. The α- l-rhamnosidase activity of this enzyme was optimal at pH 6.0 and stable in the pH range of 5.5–8.0. The purified enzyme also had β- d-glucosidase activity, but the activity was relatively weak compared to the activity of the naringinase from Penicillium decumbens. The enzymatic bioconversion by A. sojae naringinase of naringin to prunin was efficiently performed with a 91% yield and a negligible amount of naringenin. The bioconversion was achieved by repetitive batch reactions with enzyme recycling. Prunin exhibited a markedly enhanced solubility compared to naringenin and naringin while maintaining the in vitro inhibition of HMG-CoA reductase. The results reported in this paper show that the naringinase produced by A. sojae will be useful in enhancing the potential bioavailability of naringin by efficiently converting it to prunin as a food component in citrus.

Antidiabetic effects of fermented soybean products on type 2 diabetes

Historically, the incidence of type 2 diabetes has been lower in Asian populations compared with those in Western countries. One possible reason for the lower incidence among Asians is that they consume fermented soybean products, which are unique to the traditional Asian diet. Some have hypothesized that dietary phytoestrogens and soy peptides in fermented soybean foods consumed in traditional Asian diets may help prevent and slow the progression of type 2 diabetes. This review evaluates the existing evidence from animal studies and clinical and epidemiologic investigations on fermented soybeans in the prevention and treatment of type 2 diabetes. Nutritional studies performed in animals and intervention studies with humans suggest that the ingestion of soy protein with isoflavones improves glucose control and reduces insulin resistance. Korean fermented soybean products such as doenjang, kochujang, and chungkookjang contain alterations in the structures and content of isoflavonoids and small bioactive peptides, which are produced during fermentation. Several studies revealed improvements in insulin resistance and insulin secretion with the consumption of these fermented products. Therefore, fermented soybean products may help prevent or attenuate the progression of type 2 diabetes. Although the lack of human intervention trials does not permit definitive conclusions, the evidence does suggest that fermented soy products may be better for preventing or delaying the progression of type 2 diabetes compared with nonfermented soybeans.

The metabolites of Korean traditional fermented foods and their healthy functions

The metabolomics approaches for Korean traditional fermented foods are very attracted because they give us two important informatics : microbial metabolomics during fermentation and physiological metabolomics during metabolic digestion. In Korea, recently metabolomics study was studied on the microorganism for Korea traditional fermented foods such as kimchi, sool, chungkukjang, meju/doenjang and kochujang and also we started metabolomics study of Korea traditional fermented foods on animals and humans. Another important metabolomic/metagenomic area in foods is metabolomic/genomic investigation of intestinal microbial flora in human bodies, but this area is not investigated in Korea although many scientists are interested. Here, we are introduced primary microbial metabolites identified from the Korea traditional fermented foods (chungkukjang, meju and kochujang). Kimchi is very most important items for metabolomic study, however, we did not studied due to some restrictions. Also we reported the health effect of Korean fermented soy bean products on anti‐obesity, anti‐inflammation, anti‐diabetes and other healthy effect. In few years, we can discussed physiological metabolites/metabolomes during digestion of Korea fermented foods and nutraceuticals.

Poly‐γ‐glutamate isolated from fermented soy products changes omega‐3 fatty acid contents of liver and brain in diet‐induced obese rats

The study was carried out to evaluate the effects of poly‐gamma‐glutamate (γ‐PGA) on the omega‐fatty acids of liver and brain in diet‐induced obese rats. The gamma‐PGA isolated from a Korean fermented soybean product, Cheongkukjang is an anionic biopolymer. Ten‐weeks‐old Sprague‐Dawley male rats (n=64) were divided into two groups and induced obesity by providing the low 10% fat control and high 45% fat diets for 4 weeks. Then, they were randomly blocked into four groups in each fat diet and provided four different diets containing no PGA control, PGA, PGA‐Ca, and PGA‐Mg. The gamma‐PGA content of the diets was 0.1% that was determined as appropriate by previous studies. After 4 week feeding, rats were decapitated and the eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) contents of liver and brain were analyzed by gas chromatography. The low fat groups fed with three different types of PGA showed higher liver DHA content than the control and the high fat groups with PGA showed higher liver EPA content (p&lt;0.05). In the brain, the high fat groups fed with PGA showed significantly higher EPA contents in cerebellum except in cerebrum and brain stem, and showed higher DHA contents in all three brain regions. The results suggest that gamma‐PGA accumulates EPA and DHA in liver and brain. The binding forms of PGA may not influence the omega‐fatty acid accumulation. (This study was supported by 2007 Seoul R&amp; D Program).

Cross‐Cultural Comparisons among the Sensory Characteristics of Fermented Soybean Using Korean and Japanese Descriptive Analysis Panels

One of the most important initial steps in exporting a food product to another country from the R&D perspective is to describe and translate the sensory characteristics of a food product appropriately into the language of the target country. The objectives of this study were to describe and compare the sensory characteristics of Korean and Japanese style fermented soybean products, and to cross-culturally compare the lexicons of the identical product generated by the Korean and Japanese panelists. Four types of Korean and 4 types of Japanese style fermented soybean consisting of whole bean type and paste type were analyzed. Ten Korean and 9 Japanese panelists were recruited in Korea. Two separate descriptive analyses were conducted, with the panelists differing in their country of origin. Each group was trained, developed lexicon, and conducted descriptive analysis independently. Analysis of variance and various multivariate analyses were applied to delineate the sensory characteristics of the samples and to compare the cross-cultural differences in the usage of lexicon. The Korean and Japanese panelists generated 48 and 36 sensory attributes, respectively. Cross-cultural consensus was shown for evaluating the whole bean type fermented soybean and white miso, which were relatively distinctive samples. However, for the less distinctive samples, the panelists tend to rate higher in negative attributes for the fermented soybeans that originated from the other country. The Japanese panelists grouped the samples by their country of origin and soy sauce flavor was the main attribute for cross-cultural differentiation. However, the Korean panelists did not make a cross-cultural distinction among the samples.

Enhancement of γ-aminobutyric acid production in Chungkukjang by applying a Bacillus subtilis strain expressing glutamate decarboxylase from Lactobacillus brevis

For a foreign glutamate decarboxylase (GAD) to be expressed in Bacillus host system, a recombinant DNA (pLip/LbGAD) was constructed by ligating an LbGAD gene from Lactobacillus brevis OPK-3 into Escherichia coli-Bacillus shuttle vector, pLip. The pLip/LbGAD construct was then transformed into Bacillus subtilis. The culture of the transformed Bacillus strain with the pLip/LbGAD construct had higher GAD activity and gamma-aminobutyric acid (GABA) concentration than those of untransformed Bacillus counterpart. In addition, Chungkukjang, a traditional Korean fermented soybean product prepared by the transformed Bacillus subtilis, contained a significantly higher level of GABA than conventional ones. Thus, by introducing a foreign GAD gene, Bacillus strains have been genetically engineered to produce high levels of GAD and GABA.

된장의 혈전용해효소 활성과 미생물 분포와의 상관관계

된장의 혈전용해효소 활성과 미생물 분포와의 상관관계