The effect of salt concentrations on the fermentation of doenjang, a traditional Korean fermented soybean paste

A combination of omics-based analyses to elucidate the effect of NaCl concentrations on the metabolites and microbial dynamics during the ripening fermentation of Pixian-Douban

The study investigated the effect of different sodium chloride (NaCl) concentrations (10%, 15%, and 20%) on the ripening fermentation of Pixian-Douban, a traditional fermented condiment. The results showed that NaCl affected the dynamics of physicochemical parameters, volatile components, fatty acids, amino metabolites, organic acids, and microbial composition, and their dynamic modes were different. After 253 days fermentation, the 10% NaCl Pixian-Douban had significantly (p < 0.05) higher levels of total organic acids (20,308.25 mg/kg), amino metabolites (28,144.96 mg/kg), and volatiles (3.36 mg/kg) compared to 15% and 20% NaCl Pixian-Douban. Notably, the possible health risk associated with high concentration of biogenic amines in 10% NaCl Pixian-Douban is of concern. Moreover, correlation analyses indicated that the effect of NaCl on the quality of Pixian-Douban may be mainly related to bacteria. This study deepens the knowledge about the role of NaCl in ripening fermentation of Pixian-Douban and contributes to develop low-NaCl Pixian-Douban product.

Impact of salt content on Douchi metabolites: biogenic amines, non-volatile compounds and volatile compounds

BACKGROUND

The excessive salt intake associated with Douchi has become a topic of controversy. Addressing this concern and enhancing its market competitiveness necessitates the application of salt reduction fermentation in Douchi. Therefore, to promote the application of salt reduction fermentation in Douchi, a comprehensive study was undertaken aiming to investigate the differences in biogenic amines, volatile compounds and non-volatile compounds in Douchi with varying salt content.

RESULTS

The findings unequivocally demonstrate that salt hampers the formation of metabolites in Douchi. As the salt content increased, there was a significant decrease (P < 0.05) in the levels of total acid, amino-type nitrogen and free amino acids in Douchi. Notably, when the salt content exceeded 80 g kg-1, there was a substantial reduction (P < 0.05) in putrescine, lactic acid and malic acid levels. Similarly, when the salt content surpassed 40 g kg-1, β-phenethylamine and oxalic acid levels exhibited a significant decline (P < 0.05). Furthermore, the results of E-nose and principal component analysis based on headspace solid phase microextraction gas chromatography-mass spectrometry revealed notable discrepancies in the volatile compound content between Douchi samples with relatively low salt content (40 and 80 g kg-1) and those with relatively high salt content (120, 160 and 200 g kg-1) (P < 0.05). By employing partial least squares discriminant analysis, eight distinct volatile compounds, including o-xylene, benzaldehyde and 1-octen-one, were identified. These compounds exhibited higher concentrations in Douchi samples with relatively low salt content (40 and 80 g kg-1). The sensory results showed that Douchi samples with lower salt content exhibited higher scores in the soy sauce-like and Douchi aroma attributes.

CONCLUSION

In conclusion, this study significantly enhances our understanding of the impact of salt on metabolites in Douchi and provides invaluable insights for the development of salt reduction fermentation in this context. © 2024 Society of Chemical Industry.

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.

Developing a High-Umami, Low-Salt Soy Sauce through Accelerated Moromi Fermentation with Corynebacterium and Lactiplantibacillus Strains

The traditional fermentation process of soy sauce employs a hyperhaline model and has a long fermentation period. A hyperhaline model can improve fermentation speed, but easily leads to the contamination of miscellaneous bacteria and fermentation failure. In this study, after the conventional koji and moromi fermentation, the fermentation broth was pasteurized and diluted, and then inoculated with three selected microorganisms including Corynebacterium glutamicum, Corynebacterium ammoniagenes, and Lactiplantibacillus plantarum for secondary fermentation. During this ten-day fermentation, the pH, free amino acids, organic acids, nucleotide acids, fatty acids, and volatile compounds were analyzed. The fermentation group inoculated with C. glutamicum accumulated the high content of amino acid nitrogen of 0.92 g/100 mL and glutamic acid of 509.4 mg/100 mL. The C. ammoniagenes group and L. plantarum group were rich in nucleotide and organic acid, respectively. The fermentation group inoculated with three microorganisms exhibited the best sensory attributes, showing the potential to develop a suitable fermentation method. The brewing speed of the proposed process in this study was faster than that of the traditional method, and the umami substances could be significantly accumulated in this low-salt fermented model (7% w/v NaCl). This study provides a reference for the low-salt and rapid fermentation of seasoning.

Application effects of NaCl substitute on the fermentation profile of Pixian douban (broad bean paste)

The effects of a reduced-salt substitute (composed of NaCl, sodium gluconate, KCl, L-histidine, and L-lysine) applied in the fermentation of traditional Pixian douban (PXDB) were explored in this study according to sensory quality, physicochemical characteristics, color, colony count, and the contents of free amino acids (FAAs), organic acids, and volatile flavor compounds. The results showed that the PXDB with a 15% salt substitution had the most attractive reddish-brown color, a mellow fragrance, and the lowest total colony count of the three pastes. The fermentation quality of the 15% salt substitute PXDB was superior to that of the control groups, its sensory quality was more readily accepted, and the contents of its amino acid nitrogen, FAAs and organic acids had increased by 0.1050, 0.3290, and 3.9068 mg/g, respectively. Moreover, the concentrations of the main aroma compounds in the PXDB containing the salt substitute were higher than those of the control. These included phenylethanol, 3-methylthiopropanol, isoamyl alcohol, furfural, benzaldehyde, phenylacetaldehyde, nonanal, isoamyl aldehyde, 4-ethylphenol, and, particularly, 2,6-dimethylpyrazine, which had increased as much as 100 times. Correlation analysis showed that Glu, Phe, Tyr, Gly, Leu, Val, Asp, Ile, citric acids, and succinic acids were all positively correlated with the main aroma and contributed to the generation of PXDB's characteristic flavor, and main aroma substances in turn positively influence PXDB flavor sensory attributes. Overall, these results showed the application of the 15% salt substitute during PXDB fermentation improved the quality of the paste and, thus, would benefit the development of reduced-salt PXDB.

Characterization of key aroma-active compounds in different types of Douchi based on molecular sensory science approaches

To attain the differences in the flavor profile of Douchi, the key aroma-active compounds of three types of Douchi were investigated. The "Sauce-like", "Smoky", "Nutty", "Roast", "Caramel", and "Flower" of Douchi were favored by customers. Further, a total of 179 volatile compounds were identified using HS-SPME-GC-MS, and 29 aroma compounds were detected using GC-O-MS. Based on the quantification, 9, 13, and 10 compounds were regarded as aroma-active compounds in Yangjiang Douchi (YJ), Pingjiang Douchi (PJ), and Liuyang Douchi (LY), respectively. Moreover, the mixture of these aroma-active compounds successfully simulated the main aromas of PJ, LY, and YJ. And omission experiments confirmed that guaiacol was the key aroma compound for LY, benzene acetaldehyde, dimethyl trisulfide, and 2-acetyl pyrrole were important for YJ, benzene acetaldehyde and 3,5-diethyl-2-methyl pyrazine notably contributed to key aroma of PJ.

Comparison of microbial diversity and metabolites on household and commercial doenjang

In this study, the microbial diversity, free amino acid (FAA), and biological activities of household doenjang (HDJ) from four different regions and commercial doenjang (CDJ) four manufacturers were analyzed. And volatile flavor compound (VFC) and isoflavone profiles were analyzed using gas chromatograph-mass spectrometer (GC-MS) and high performance liquid chromatography (HPLC), respectively. The major bacterial genus in 1HDJ and 2HDJ was Bacillus (97.5%), while in 3HDJ and 4HDJ, it was Enterobacter (47.5%) and Pseudomonas (80%), respectively. Tetragenococcus was the main bacterial genus of CDJ. The Zygosaccharomyces genus among yeast was comparatively high in all samples. In all samples, glutamic acid predominated among the FAAs, and the 3-methyl butanal, benzeneacetaldehyde, and diallyl disulphide were major VFCs. CDJ contained higher levels of isoflavone-glycoside and total phenolics. Except for 3HDJ and 4CDJ, the isoflavone-aglycone and total flavonoid contents were higher in HDJ. The correlation between bacterial genus and metabolited of doenjang showed that Tetragenococcus was closely related to glutamic acid, Bacillus was related to aglycones and ammonia, and Pseudomonas was highly related to isovaleric acid. While, correlation between yeast genus and metabolited of doenjang confirmed that Candida, Hanseniaspora, and Saccharomyces were related with furfural, benzeneacetaldehyde, and 3-methyl butanal, respectively. The results of this study can be utilized as basic data for the industrialization and development of doenjang.

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.

Unraveling the carbohydrate metabolic characteristics of Leuconostoc mesenteroides J18 through metabolite and transcriptome analyses

The metabolic characteristics of Leuconostoc mesenteroides subsp. mesenteroides J18, which is mainly responsible for kimchi fermentation, on various carbon sources were investigated through carbon utilization, metabolite, and transcriptome analyses at different culture conditions (10 and 30 °C with/without 2.5% NaCl). The metabolic features of strain J18 were relatively similar across the four culture conditions. However, the metabolic characteristics of strain J18 showed significant variations depending on the carbon source. These distinct metabolic traits of strain J18 on various carbon sources were validated through transcriptomic analyses and the reconstruction of metabolic pathways. The transcriptional expression of the metabolic pathways in response to each carbon source consistently correlated with the production profiles of metabolites, including ethanol, acetoin, diacetyl, and riboflavin, in each carbon source. Our findings suggests that the abundance of Leu. mesenteroides during fermentation and the taste and flavor of fermented food products can be controlled by altering the carbon sources.

Microbial-derived salt-tolerant proteases and their applications in high-salt traditional soybean fermented foods: a review

Different microorganisms can produce different proteases, which can adapt to different industrial requirements such as pH, temperature, and pressure. Salt-tolerant proteases (STPs) from microorganisms exhibit higher salt tolerance, wider adaptability, and more efficient catalytic ability under extreme conditions compared to conventional proteases. These unique enzymes hold great promise for applications in various industries including food, medicine, environmental protection, agriculture, detergents, dyes, and others. Scientific studies on microbial-derived STPs have been widely reported, but there has been little systematic review of microbial-derived STPs and their application in high-salt conventional soybean fermentable foods. This review presents the STP-producing microbial species and their selection methods, and summarizes and analyzes the salt tolerance mechanisms of the microorganisms. It also outlines various techniques for the isolation and purification of STPs from microorganisms and discusses the salt tolerance mechanisms of STPs. Furthermore, this review demonstrates the contribution of modern biotechnology in the screening of novel microbial-derived STPs and their improvement in salt tolerance. It highlights the potential applications and commercial value of salt-tolerant microorganisms and STPs in high-salt traditional soy fermented foods. The review ends with concluding remarks on the challenges and future directions for microbial-derived STPs. This review provides valuable insights into the separation, purification, performance enhancement, and application of microbial-derived STPs in traditional fermented foods.

Safety Analysis of Korean Cottage Industries' Doenjang, a Traditional Fermented Soybean Product: A Special Reference to Biogenic Amines

The typical Korean diet contains a significant quantity of doenjang owing to its unique taste and health benefits. However, the presence of anti-nutritional and toxic substances, such as biogenic amines and microbial pathogens, in doenjang has resulted in a loss of revenue and poor consumer health. The present study focused on the identification and quantification of different biogenic amines, pathogenic Bacillus cereus, and yeast counts in 36 doenjang products (designated as De-1 to De-36, 500 g each) procured from the different cottage industries situated in different parts of the Republic of Korea. The results indicated, only three samples were contaminated with B. cereus, exceeding the recommended limit (4 log CFU/g) suggested by the national standards of Korea. A total of six distinct yeasts were identified in different doenjang samples, whose comprehensive enzymatic profiling suggested the absence of harmful enzymes such as N-acetyl-β-glucosaminidase, α-chymotrypsin, and β-glucuronidase. The biogenic amines were detected in the range of 67.68 mg/kg to 2556.68 mg/kg and classified into six major groups based on hierarchical cluster analysis. All doenjang samples contained tryptamine, putrescine, cadaverine, histamine, and tyramine, while 94.44% were positive for spermidine and spermine. The results documented the analysis of traditional cottage industry doenjang and suggest the need for constant monitoring to ensure the safety of food for the consumer.

Exploring the Profile Contributions in Meyerozyma guilliermondii YB4 under Different NaCl Concentrations Using GC-MS Combined with GC-IMS and an Electronic Nose

Using Meyerozyma guilliermondii YB4, which was isolated and screened from southern Sichuan pickles in the laboratory, as the experimental group, we investigated the changes in growth, total ester content, and volatile flavor substances of M. guilliermondii YB4 under different NaCl concentrations. The growth of M. guilliermondii YB4 was found to be inhibited by NaCl, and the degree of inhibition increased at higher NaCl concentrations. Additionally, the total ester content of the control group (CK) was significantly lower compared to the other groups (p < 0.05). The application of NaCl also resulted in distinct changes in the volatile profile of YB4, as evidenced by E-nose results. Gas chromatography-mass spectrometry (GC-MS) and gas chromatography-ion mobility spectrometry (GC-IMS) were employed to analyze the volatile compounds. A total of 148 and 86 volatiles were detected and identified using GC-MS and GC-IMS, respectively. Differential volatiles among the various NaCl concentrations in YB4 were determined by a variable importance in projection (VIP) analysis in partial least squares-discriminant analysis (PLS-DA). These differentially expressed volatiles were further confirmed by their relative odor activity value (ROAV) and odor description. Ten key contributing volatiles were identified, including ethanol, 1-pentanol, nonanal, octanal, isoamyl acetate, palmitic acid ethyl ester, acrolein, ethyl isobutanoate, prop-1-ene-3,3'-thiobis, and 2-acetylpyrazine. This study provides insights into the specificities and contributions of volatiles in YB4 under different NaCl concentrations. These findings offer valuable information for the development of aroma-producing yeast agents and the subsequent enhancement in the flavor of southern Sichuan pickles.

Probiotic Properties and Safety Evaluation of Lactobacillus plantarum HY7718 with Superior Storage Stability Isolated from Fermented Squid

The aim of this study was to identify new potential probiotics with improved storage stability and to evaluate their efficacy and safety. Sixty lactic acid bacteria strains were isolated from Korean traditional fermented foods, and their survival was tested under extreme conditions. Lactobacillus plantarum HY7718 (HY7718) showed the greatest stability during storage. HY7718 also showed a stable growth curve under industrial conditions. Whole genome sequencing revealed that the HY7718 genome comprises 3.26 Mbp, with 44.5% G + C content, and 3056 annotated Protein-coding DNA sequences (CDSs). HY7718 adhered to intestinal epithelial cells and was tolerant to gastric fluids. Additionally, HY7718 exhibited no hemolytic activity and was not resistant to antibiotics, confirming that it has probiotic properties and is safe for consumption. Additionally, we evaluated its effects on intestinal health using TNF-induced Caco-2 cells. HY7718 restored the expression of tight junction proteins such as zonular occludens (ZO-1, ZO-2), occludin (OCLN), and claudins (CLDN1, CLDN4), and regulated the expression of myosin light-chain kinase (MLCK), Elk-1, and nuclear factor kappa B subunit 1 (NFKB1). Moreover, HY7718 reduced the secretion of proinflammatory cytokines such as interleukin-6 (IL-6) and IL-8, as well as reducing the levels of peroxide-induced reactive oxygen species. In conclusion, HY7718 has probiotic properties, is safe, is stable under extreme storage conditions, and exerts positive effects on intestinal cells. These results suggest that L. plantarum HY7718 is a potential probiotic for use as a functional supplement in the food industry.

Flavor Characterization of Traditional Fermented Soybean Pastes from Northeast China and Korea

This study compares the physicochemical properties, taste, and volatile compounds of Northeastern Chinese dajiang (C) and Korean doenjang (K) and distinguishes the discriminant volatile metabolites between them. The result revealed that compared to group C, group K exhibited more similar physicochemical properties and had lower pH, moisture, and amino acid nitrogen content, while demonstrating higher titratable acidity, salt content, and reduced sugar content. The electronic tongue analysis showed that the saltiness and umami of soybean pastes had high response values, enabling clear differentiation of the overall taste between the two types of soybean pastes. A total of 71 volatile substances from the soybean pastes were identified through solid-phase microextraction gas chromatography-mass spectrometry. Furthermore, orthogonal partial least squares discriminant analysis revealed 19 volatile compounds as differentially flavored metabolites. Our study provides a basis for explaining the differences in flavor difference of Northeastern Chinese dajiang and Korean doenjang from the perspective of volatile metabolites.

Monitoring and risk assessment of biogenic amines in Korean commercial fermented seasonings

Fermented seasonings are widely used in Korean cuisine; however, some contain high levels of biogenic amines (BAs). In this study, in order to estimate the potential BA risk from fermented seasoning, the BA contents in 50 commercial brands (n = 292) of five seasonings (soy sauce, Gochujang, Doenjang, Ssamjang, and Cheonggukjang) and their changes due to different cooking methods were evaluated by high-performance liquid chromatography. The risk assessment for consumer exposure was evaluated by computing the estimated daily intake (EDI), histamine (HIS) intake, and tyramine (TYR) intake. Maximum contents of HIS detected in Cheonggukjang, soy sauce, Doenjang, and Ssamjang were 318.46, 148.15, 123.65, and 114.07 mg/kg, respectively. However, even in the worst-case scenario, the EDI value and HIS intake results demonstrated that the seasonings had a limited impact on the risk of HIS poisoning due to their low consumption. Cheonggukjang exhibited the highest TYR content (312.89 mg/kg), and the TYR exposure results implied that those taking classical antidepressant monoamine oxidase inhibitors should pay attention to Cheonggukjang. After stir-frying, the total BA retentions in soy sauce and Gochujang were only 51.45% and 57.08%, respectively, which may be caused by high temperature. Based on the results of this study, the five seasonings contained various BAs, which can be influenced by the cooking process, and all five seasonings are safe for the general population in terms of the risk of BAs.

Screening lactic acid bacteria and yeast strains for soybean paste fermentation in northeast of China

Soybean paste was a traditional fermented product in northeast China, mainly fermented by molds, yeast, Bacillus, and lactic acid bacteria. In this study, the safety and fermentation ability of lactic acid bacteria and yeast strains isolated from traditional soybean paste in northeast China were evaluated, and the dynamic changes of biogenic amines, aflatoxin, total acids, amino acid nitrogen, and volatile compounds were investigated during the fermentation of the traditional soybean paste. Among the tested strains, Lactiplantibacillus plantarum DPUL-J8 could decompose putrescine by 100%, and no biogenic amine was produced by Pichia kudriavzevii DPUY-J8. Lactiplantibacillus plantarum DPUL-J8 and P. kudriavzevii DPUY-J8 with strong biogenic amine degrading capacities were inoculated into the soybean paste. After 30 days of fermentation, the content of biogenic amines and aflatoxin in the fermented soybean paste declined by more than 60% and 50%, respectively. At the same time, compared with the control group without inoculation, the contents of total acid (1.29 ± 0.05 g/100 g), amino acid nitrogen (0.82 ± 0.01 g/100 g), and volatile compounds in soybean paste fermented by L. plantarum DPUL-J8 and P. kudriavzevii DPUY-J8 were significantly increased, which had a good flavor. These results indicated that the use of L. plantarum DPUL-J8 and P. kudriavzevii DPUY-J8 as starter cultures for soybean paste might be a good strategy to improve the safety and flavor of traditional Chinese soybean paste.

Comprehensive investigation on volatile and non-volatile metabolites in low-salt doubanjiang with different fermentation methods

Doubanjiang is a well-known fermented condiment in China, but the high-salt concentration in its traditional manufacture process greatly lengthens the fermentation time, and leads to potential health risks. Here, the effects of salt reduction and co-inoculated starters (Tetragenococcus halophilus and Zygosaccharomyces rouxii) on the volatile metabolites (VMs) and non-volatile metabolites (NVMs) of doubanjiang were investigated using metabolomics technology and chemometrics analysis. Results showed that 75 VMs were identified, and 12 of them had significant aroma contribution (ROVAs ≥ 1). In addition, 106 NVMs were defined as significantly different metabolites (p < 0.05; VIP ≥ 1). Salt reduction could significantly increase the concentrations of VMs, but this strategy also promoted some undesirable odors like 2-phetylfuran and hexanoic acid, which could be totally suppressed by inoculation of starter. Moreover, the two starters improved amino acid, ester, and acid metabolites. This study provides a deeper insight into the development of low-salt fermented foods.

In-depth genome and pan-genome analysis of a metal-resistant bacterium Pseudomonas parafulva OS-1

A metal-resistant bacterium Pseudomonas parafulva OS-1 was isolated from waste-contaminated soil in Ranchi City, India. The isolated strain OS-1 showed its growth at 25-45°C, pH 5.0-9.0, and in the presence of ZnSO₄ (upto 5 mM). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain OS-1 belonged to the genus Pseudomonas and was most closely related to parafulva species. To unravel the genomic features, we sequenced the complete genome of P. parafulva OS-1 using Illumina HiSeq 4,000 sequencing platform. The results of average nucleotide identity (ANI) analysis indicated the closest similarity of OS-1 to P. parafulva PRS09-11288 and P. parafulva DTSP2. The metabolic potential of P. parafulva OS-1 based on Clusters of Othologous Genes (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) indicated a high number of genes related to stress protection, metal resistance, and multiple drug-efflux, etc., which is relatively rare in P. parafulva strains. Compared with other parafulva strains, P. parafulva OS-1 was found to have the unique β-lactam resistance and type VI secretion system (T6SS) gene. Additionally, its genomes encode various CAZymes such as glycoside hydrolases and other genes associated with lignocellulose breakdown, suggesting that strain OS-1 have strong biomass degradation potential. The presence of genomic complexity in the OS-1 genome indicates that horizontal gene transfer (HGT) might happen during evolution. Therefore, genomic and comparative genome analysis of parafulva strains is valuable for further understanding the mechanism of resistance to metal stress and opens a perspective to exploit a newly isolated bacterium for biotechnological applications.

Physicochemical, microbiological, and sensory characteristics of "Sui Wu'u" traditional pork products from Bajawa, West Flores, Indonesia

Background and Aim

Sui Wu'u is a traditional meat preservation product from Bajawa, a region in East Nusa Tenggara. It is made by mixing pork with salt and corn flour, which is then stored in a bamboo container (tuku) for months. After 6 months of storage, this study examined the physicochemical, microbiological, and sensory properties of Sui Wu'u.

Materials and Methods

Sui Wu'u products were prepared using the traditional recipe from the Bajawa community. Fresh pork (pork belly and backfat), corn flour, and salt were purchased from local/traditional markets at proportions of 65%, 30%, and 5%, respectively. The physicochemical, amino acid, fatty acid profile, microbiological, and sensory properties of Sui Wu'u were evaluated after being stored for 6 months in a bamboo container (tuku).

Results

The results indicated that these Sui Wu'u were mainly characterized by high-fat levels, followed by protein. The pH value, salt content, moisture content, and water activity were 4.72%, 1.72%, 6.11%, and 0.62%, respectively. Minerals (K, P, Se, and Zn) and vitamin B6, as well as amino acids, such as leucine, phenylalanine, lysine (essential amino acids), glycine, proline, glutamic acid, and alanine (non-essential amino acids), are present in Sui Wu'u. The fatty acid profile was dominated by monounsaturated fatty acids (MUFA) (21.69%), saturated fatty acids (SFA) (17.78%), and polyunsaturated fatty acids (PUFA) (5.36%). Monounsaturated fatty acids, oleic acid (C18:1n9) was the most abundant fatty acid in Sui Wu'u, followed by palmitic acid SFA (C16:0); MUFA stearic acid (C18:0); and PUFA linoleic (C18:2n-6). The microbiological characteristics of Sui Wu'u showed no detectable microorganisms (<10 CFU/g) for Salmonella, total E. coli and total Staphylococcus, and average values of 4.4 × 105 CFU/g for total microbes, which were still below the maximum limit of microbial contamination according to the regulations of the Food and Drug Supervisory Agency of the Republic of Indonesia. The sensory assessment indicated that panelists highly preferred (rated as very like) Sui Wu'u for all sensory attributes.

Conclusion

The physicochemical, microbiological, and sensory characteristics of Sui Wu'u after 6 months of storage indicated that it still provides essential nutrients for the body and is quite safe for consumption. The stability of Sui Wu'u's shelf life can be attributed to the appropriate combination of pork, salt, corn flour, bamboo packaging (tuku), and storage temperature. The high-fat content in Sui Wu'u can be reduced by increasing the proportion of lean meat. Ensuring strict sanitation during the manufacturing process, using high-quality pork, salt, corn flour, and proper packaging with bamboo can further improve the safety of Sui Wu'u for consumption.

Moromi mash dysbiosis trigged by salt reduction is relevant to quality and aroma changes of soy sauce

Health concerns related to excessive salt consumption have increased the demand for foods with reduced salt content. However, it is a challenge to perform low salt fermentation of high salt liquid-state (HSL) soy sauce due to the interplay between salt and microorganisms. In this study, ≤12 % (w/v) NaCl led to failed fermentation of HSL soy sauce. At 9 % (w/v) NaCl, amino acid nitrogen decreased to 0.31 g/100 mL, total acid increased to 10.1 g/L, and biogenic amines increased to 904.49 mg/L. With reduced salt, the total number of bacteria (1-2 orders of magnitude) and spoilage bacteria (Bacillus, Kurthia, Staphylococcus saprophyticus, and Lactobacillus pobuzihii) increased, and the total number of functional microorganisms (Weissella, Zygosaccharomyces, and Candida) decreased. Unacceptable volatiles contents were higher in reduced-salt soy sauce than in normal salt soy sauce. Most of the unacceptable volatiles were positively correlated with spoilage bacteria.

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.

Effect of Salt Concentration on Flavor Characteristics and Physicochemical Quality of Pickled Brassica napus

This study aimed to elaborate on the role of salt concentration on pickled Brassica napus leaf and stem (BLS); it also contributed to the development of low-salt and healthy Brassica napus products in the harvest period. Five sets of pickled BLS samples were prepared, and the physicochemical parameters, free amino acids (FAAs), and the volatile flavor components (VFCs) were analyzed after fermentation. Results showed that some antioxidants, FAAs, and VFCs underwent dynamic changes during fermentation. Nitrite increased with an increase in the salt concentration used for fermentation. Pickled BLS contained a wide range of FAAs; a total of 23 were detected, which might be used as a source of amino acid supplementation. The VFCs were analyzed via headspace solid-phase micro-extraction (HS-SPME) combined with gas chromatography and mass spectrometry (GC-MS). A total of 51 VFCs were tentatively identified. The contribution to flavor could be expressed by the relative odor activity value (ROAV). Salt is one of the important factors affecting the quality of vegetable fermentation. Therefore, for large-scale pickled BLS production, a key issue is to balance the low salt concentration and high fermentation quality. Under the action of salt and microorganisms, the fresh BLS fermented via dry pickling, which not only improved its FAAs and VFCs, endowed the production with a unique flavor, but also prolonged the shelf life.

Effects of Low-Temperature and Low-Salt Fermentation on the Physicochemical Properties and Volatile Flavor Substances of Chinese Kohlrabi Using Gas Chromatography–Ion Mobility Spectrometry

To explore the effect of low-temperature and low-salt fermentation on the volatile flavor substances of Chinese kohlrabi, low-temperature and low-salt fermented Chinese kohlrabi (LSCK) and traditional high-salt fermented Chinese kohlrabi (HSCK) were produced. The physicochemical and texture properties of the two kinds of Chinese kohlrabies were evaluated. Headspace gas chromatography-ion mobility spectrometry (GC-IMS) and electronic nose (E-nose) were used to analyze the volatile flavor substances of the kohlrabi. The results showed that the total acid content significantly decreased (p < 0.05), while protein and reducing sugar contents significantly increased (p < 0.05) by low-temperature and low-salt fermentation. A total of 114 volatile flavor substances were identified. The alcohol, ketone, pyrazine, ether, and nitrile contents in LSCK were significantly higher than those in HSCK (p < 0.05). Moreover, the unpleasant flavor from the 3-methylbutyric acid formation was effectively depressed in LSCK. The principal component analysis (PCA) and orthogonal partial least squares discrimination analysis (OPLS-DA) models established by multivariate statistical analysis significantly distinguished the two types of kohlrabies. Multivariate statistical analysis suggested that 16 volatile flavor substances with VIP >1, including tetrahydrothiophene, ethyl 3-(methylthio)propanoate, 3-methylbutyric acid, hexanenitrile, and 3-methyl-3-buten-1-ol, could be used as potential biomarkers for identifying LSCK and HSCK. The E-nose analysis further demonstrated that there was a significant difference in overall flavor between the LSCK and HSCK. The present study provides support for the development of green processing technology and new low-salt Chinese kohlrabi products.

Patterns of biogenic amine during broad bean paste fermentation: microbial diversity and functionality via Bacillus bioaugmentation

BACKGROUND

Broad bean paste is a high nitrogen and high salt traditional Chinese condiment, which triggers biosynthesis of nitrogen hazards like biogenic amines (BAs). Mechanisms of association and applied research of functional safety and community assembly within multiple-microbial fermentation are currently lacking. Here, bioaugmentation was performed based on the profiles of BAs accumulation and microbial succession to evaluate the functional variation within broad bean paste fermentation.

RESULTS

Putrescine, spermine, and spermidine were the main BAs during traditional broad bean paste fermentation. Staphylococcus, Streptococcus, Lactococcus, Lactobacillus, Leuconostoc, and Bacillus were the predominant bacteria, whereas Aspergillus and Zygosaccharomyces dominated in fungal species, and community structure shifted upon salt exposure. PICRUSt software uncovered that Bacillus contributed significantly (>1%) to the amine oxidase gene family. Bacillus amyloliquefaciens 1-G6 and Bacillus licheniformis 2-B3 were screened to perform the bioaugmentation of broad bean paste, which achieved a 29% and 16% BA decrease respectively. Interaction network analysis showed that Cronobacter and Lactobacillus were significantly negatively correlated with Bacillus (ρ = -0.829 and ρ = -0.714, respectively, P < 0.05) in the B. amyloliquefaciens 1-G6 group, and Staphylococcus and Buttiauxella were inhibited by Bacillus (ρ = -0.657 and ρ = -0.543, respectively, P < 0.05) in the B. licheniformis 2-B3 group.

CONCLUSION

The synergism of amine oxidase activity and microbial interactions led to the decline of BAs. Thus, this study improves our understanding of the underlying mechanisms of microbial succession and functional variation to further facilitate the optimization of the fermented food industry.

Reduced formation of biogenic amines in low-salt Zhacai via fermentation under CO2-modified atmosphere

Reducing sodium salt content in traditional fermented vegetables and developing low-salt fermented products have attracted increasing attention.However, low-salt fermented vegetables are prone to accumulate toxic biogenic amines (BAs) caused by the undesirable metabolism of spoilage microorganisms. This study aimed to investigate the impact of a CO₂-modified atmosphere (MA) approach to the fermentation of low-salt Zhacai and the accumulation of BAs. The results show CO₂-MA effectively suppressed the production of excessive BAs in low-salt Zhacai, as evidenced by a decrease in the total BA content from 63.66 to 161.41 mg/ kg under natural air conditions to 1.88-24.76 mg/ kg under CO₂-MA. Overall, the mechanism of hindering BA formation was closely related to the change in the microbial community and the downregulation of BA-producing enzymes. Lactic acid bacteria, including Lactiplantibacillus plantarum, Weissella spp., and Pediococcus spp., were enriched under CO₂-MA, whereas amine-producing microorganisms (e.g., Halomonas spp., Psychrobacter spp., Corynebacterium spp., and Levilactobacillus brevis) were greatly inhibited. Moreover, metagenomic analysis revealed that genes encoding amino acid decarboxylase, amine deiminase, and amine synthase were downregulated, which could be the fundamental reason for BA reduction. This study provides an alternative method for reducing BA production in fermented food.

Insights into the flavor perception and enhancement of sodium-reduced fermented foods: A review

Salt (sodium chloride, NaCl) is a vital ingredient in fermented foods, which affects their safety, texture, and flavor characteristics. Recently, the demand for reduced-sodium fermented foods has increased, as consumers have become more health-conscious. However, reducing sodium content in fermented foods may negatively affect flavor perception, which is a critical quality attribute of fermented foods for both the food industry and consumers. This review summarizes the role of salt in the human body and foods and its role in the flavor perception of fermented foods. Current sodium reduction strategies used in the food industry mainly include the direct stealth reduction of NaCl, substituting NaCl with other chloride salts, and structure modification of NaCl. The odor-induced saltiness enhancement, application of starter cultures, flavor enhancers, and non-thermal processing technology are potential strategies for flavor compensation of sodium-reduced fermented foods. However, reducing sodium in fermented food is challenging due to its specific role in flavor perception (e.g., promoting saltiness and volatile compound release from food matrices, inhibiting bitterness, and changing microflora structure). Therefore, multiple challenges must be addressed in order to improve the flavor of low-sodium fermented foods. Future studies should thus focus on the combination of several strategies to compensate for the deficiencies in flavor resulting from sodium reduction.

Reduction of sodium chloride: a review

Sodium chloride (NaCl) is an enjoyable condiment. However, evidence is accumulating to indicate that an excessive intake of Na⁺ in food may lead to an increased risk of cardiovascular and cerebrovascular diseases. Previous systematic reviews have focused on replacing NaCl with other metal salts (e.g. KCl). However, new salty flavor enhancers (yeast extract, taste peptides, and odor compounds) have yet to be reviewed. This systematic review evaluates the methods for, and feasibility, of NaCl reduction. It defines NaCl reduction and considers the methods used for this purpose, especially the use of flavor enhancers (yeast extract, taste peptides, and odor compounds). © 2022 Society of Chemical Industry.

Probiotic potential of Tetragenococcus halophilus EFEL7002 isolated from Korean soy Meju

BACKGROUND

Probiotic starters can improve the flavor profile, texture, and health-promoting properties of fermented foods. Tetragenococcus halophilus is a halophilic lactic acid bacterium that is a candidate starter for high-salt fermented foods. However, the species is known to produce biogenic amines, which are associated with neurotoxicity. Here, we report a probiotic starter strain of T. halophilus, EFEL7002, that is suitable for use in high-salt fermentation.

RESULTS

EFEL7002 was isolated from Korean meju (fermented soybean) and identified as T. halophilus, with 99.85% similarity. The strain is safe for use in food as it is a non-hemolytic and non-biogenic amine producer. EFEL7002 is tolerant to gastrointestinal conditions and can adhere to Caco-2 cells. This strain showed antioxidant, anti-inflammatory, and protective effects against the human gut epithelial barrier. EFEL7002 grew well in media containing 0-18% NaCl showing maximum cell densities in 6% or 12% NaCl.

CONCLUSIONS

T. halophilus EFEL7002 can be used as a health-promoting probiotic starter culture for various salty fermented foods.

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.

Insight into the protein degradation during the broad bean fermentation process

Broad bean fermentation is of vital importance in PixianDouban (PXDB) production, as well as a key process for microorganisms to degrade protein, which lays the foundation for the formation of PXDB flavor. In this study, two fungi and bacteria were screened, and their morphology, molecular biology, growth, and enzyme production characteristics were analyzed, and then they were applied to the broad bean fermentation simulation system. The protein, peptide, amino acid, amino nitrogen, and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) in the system were evaluated. The results showed that the four microorganisms were Aspergillus oryzae, Aspergillus jensenii, Staphylococcus gallinarum, and Enterobacter hormaeche. Aspergillus oryzae had the highest protease activity at pH 7.0, while the other three strains had better enzyme activity stability under neutral acidic conditions. And the total protein (F1 and F2 were 18.32 g/100 g, 19.15 g/100 g, respectively), peptides (11.79 ± 0.04 mg/g and 12.06 ± 0.04 mg/g), and amino acids (55.12 ± 2.78 mg/g and 54.11 ± 1.97 mg/g) of the fungus experimental groups (F) were higher than the bacterial experimental groups (B). In addition, the enzyme system produced by fungi exhibited a stronger ability for albumin (20 kDa) and glutenin (<30 kDa) deterioration in neutral conditions, while the bacterial enzyme system was more efficient in degrading albumin (<30 kDa) and glutenin (20–30 kDa) in acidic conditions, as indicated by SDS‐PAGE. These findings showed that both bacteria and fungi played an important role in the degradation of protein in different fermentation stages of broad bean fermentation.

Impact of salt concentration on bacterial diversity and changes in biogenic amines during fermentation of farmhouse soybean paste in Northeast China

Farmhouse soybean paste in Northeast China is a traditional fermented product made from soybean, and more than 11% (w/w) salt is usually added during production to control the fermentation process. In this study, the variations in bacterial diversity, biogenic amines(BAs) and physicochemical properties during the natural fermentation of soybean paste with different salt concentrations (8%, 9%, 10%, 11%, and 12%) were studied. The results show that at 0 days (0 d) of fermentation in soybean paste, the dominant genera included Staphylococcus, unidentified Clostridiales, and Sporolactobacillus. During fermentation from 30 d to 90 d, the dominant genera were Tetragenococcus and Staphylococcus. However, the proportions of the dominant genera were different depending on the salt concentration. Putrescine(Put), tryptamine(Try), β-phenethylamine(Phe), cadaverine(Cad), histamine(His), and tyramine(Tyr) showed negative correlations with salt concentration. The amino type nitrogen(ANN), titratable acidity(TTA) and total number of colonies were also negatively correlated with salt concentration. Analysis of the correlation between genera and BAs showed that 12 genera were positively correlated with BAs, and 4 genera were negatively correlated with BAs. The results of this study indicated that salt has a significant impact on bacterial diversity during the fermentation of soybean paste, which in turn affects the changes in bacterial metabolites. From the perspective of food safety, the amount of salt added in the soybean paste can be reduced to 10% under the existing fermentation conditions.

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The effect of salt concentration on soybean paste was studied.

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Salt concentration affected the bacterial diversity and BAs in soybean paste.

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There was a species succession process in the initial 30 days of fermentation.

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There was correlation between the BAs and some bacteria in soybean paste.

Effects of Salt Treatment Time on the Metabolites, Microbial Composition, and Quality Characteristics of the Soy Sauce Moromi Extract

Salt is one of the most important factors for fermented foods, but the effect of salt treatment time on the quality of fermented foods has rarely been studied. In this study, the effect of different salt treatment times (0, 48, and 96 h) after the start of fermentation on the quality of the soy sauce moromi extract (SSME) was investigated. As the salt treatment time was delayed, the population of Aspergillus oryzae, Lactobacillaceae, and Enterococcaecea in SSME increased, whereas the population of Staphylococcaceae and Bacillaceae decreased, leading to changes in the enzymatic activity and metabolite profiles. In particular, the contents of amino acids, peptides, volatile compounds, acidic compounds, sugars, and secondary metabolites were significantly affected by the salt treatment time, resulting in changes in the sensory quality and appearance of SSME. The correlation data showed that metabolites, bacterial population, and sensory parameters had strong positive or negative correlations with each other. Moreover, based on metabolomics analysis, the salt treatment-time-related SSME metabolomic pathway was proposed. Although further studies are needed to elucidate the salt treatment mechanism in fermented foods, our data can be useful to better understand the effect of salt treatment time on the quality of fermented foods.

The microbial community, biogenic amines content of soybean paste, and the degradation of biogenic amines by Lactobacillus plantarum HM24

Soybean paste was a traditional fermented product in Northeast China, mainly fermented by molds, yeast, Bacillus, and lactic acid bacteria. This study investigated the dynamic changes of the microbial community and biogenic amine content during the fermentation of the traditional soybean paste. The microbial diversity of soybean paste in different regions was analyzed by MiSeq sequencing technology. The results showed that Penicillium and Tetragenococcus were the dominant microorganisms responsible for the fermentation of soybean paste. Biogenic amine was found in the traditional soybean paste at different fermentation stages, putrescine, and tyramine were the mainly biogenic amines and their content increased with the extension of fermentation time. Serratia in the soybean paste was positively correlated with the formation of spermine, cadaverine (p < .01), and β-phenethylamine (p < .05), Leuconostoc was negatively correlated with tyramine formation (p < .05), and Enterococcus was positively correlated with the formation of histamine, tryptamine and cadaverine (p < .01). Lactobacillus fermentum HM22, Lactobacillus plantarum HM24, and Enterococcus faecalis YF10042 with strong biogenic amine degrading capacity were inoculated into the koji. After 20 days of fermentation, the degradation rates of tryptamine, β-phenylethylamine, putrescine, cadaverine, histamine, and tyramine in soybean paste inoculated with L. plantarum HM24 were 35.31%, 43.14%, 30.18%, 33.44%, 32.74%, and 39.91%, respectively, indicating that the use of L. plantarum HM24 as a starter culture in soybean paste fermentation might be a good strategy for biogenic amines reduction.

Bacterial Diversity of Sun-Dried Spanish Mackerel in Dalian and Application of Lactobacillus plantarum X23 as a Biopreservative

ABSTRACT

Sun-dried Spanish mackerel is a common food in Dalian and made by adding salt and sun drying, which has special physical, chemical, and microbiological properties. In this study, the physicochemical properties and microbial composition of commercially available sun-dried Spanish mackerel in Dalian were assessed, and some Lactobacillus strains were screened as a biopreservative for sun-dried Spanish mackerel preparation. The results showed that the total volatile base nitrogen content in the traditional sun-dried Spanish mackerel samples from Dalian was within 30 mg/100 g, the histamine content was 7 to 17 mg/kg, and the dominant bacteria at the genus level were Lactobacillus, Psychrobacter, and Ralstonia. A strain with biopreservative potential was isolated from a sun-dried Spanish mackerel sample, identified as L. plantarum species by 16S rDNA sequencing, and assigned as L. plantarum X23. Fresh Spanish mackerel flesh was treated with 16% brine and L. plantarum X23 at a dose of 107 CFU/mL and then dried in the sun. The sun-dried Spanish mackerel flesh treated with 16% brine and L. plantarum X23 showed a decreased histamine and acid value, increased free amino acid content, and a higher sensory score compared with the sun-dried Spanish mackerel without L. plantarum X23 treatment (P < 0.05). In conclusion, the sun-dried Spanish mackerel purchased from the supermarkets in Dalian were safely edible, and L. plantarum X23 can significantly reduce the content of histamine and putrescine in self-made, low-salt, sun-dried Spanish mackerel and has potential as a biopreservative for sun-dried Spanish mackerel preparation.

HIGHLIGHTS

Bacterial Community and Anti-Cerebrovascular Disease-Related Bacillus Species Isolated from Traditionally Made Kochujang from Different Provinces of Korea

Traditionally made Kochujang (TMK) is a long-term fermented soybean and rice mixture with red pepper and salts. The ambient bacteria in rice straw and nutrient components of Kochujang influence the bacteria community. We aimed to investigate the bacterial composition and quality of TMK from different provinces of Korea: Chungcheung (CC), Jeolla (JL), Kyungsang (KS), and GeongGee plus Kangwon (GK) provinces, and Jeju island (JJ). Furthermore, Bacillus spp. isolated from TMK were studied to have anti-cerebrovascular disease activity and probiotic properties. Seventy-three TMK samples from different regions were collected to assess the biogenic amine contents, bacteria composition using next-generation methods, and bacterial functions using Picrust2. Bacillus spp. was isolated from the collected TMK, and their antioxidant, fibrinolytic, and angiotensin I conversion enzyme (ACE) inhibitory activities and probiotic properties were examined. KS TMK had lower sodium contents than the other TMK. There were no significant differences in histamine and tyramine contents among the TMK samples in different provinces. The predominant bacteria in TMK was Bacillus spp., but KS included much less Bacillus spp. and higher Enterococcus and Staphylococcus than the other TMK. Gene expression related to lipopolysaccharide biosynthesis was higher in KS TMK than the other TMK in Picrust2. The predominant Bacillus spp. isolated from TMK was B. subtilis and B. velezensis. B. subtilis SRCM117233, SRCM117245, and SRCM117253 had antioxidant activity, whereas B. subtilis had higher fibrinolytic activity than other Bacillus spp. Only B. velezensis SRCM117254, SRCM117311, SRCM117314, and SRCM117318 had over 10% ACE inhibitory activity. In conclusion, KS had less Bacillus related to lower sodium contents than the other TMK. The specific strains of B. subtilis and B. velezensis had antioxidant, fibrinolytic, and ACE inhibitory activity, and they can be used as a starter culture to produce better quality controlled Kochujang with anti-cerebrovascular disease activities.

Korean traditional foods as antiviral and respiratory disease prevention and treatments: A detailed review

BACKGROUND

Korean traditional food (KTF), originated from ancestral agriculture and the nomadic traditions of the Korean peninsula and southern Manchuria, is based on healthy food that balances disease prevention and treatment. Fermented foods that include grains, herbs, fruits, and mushrooms are also an important practice in KTF, providing high levels of Lactobacilli, which confer relevant health benefits, including antiviral properties. Some of these probiotics may also protect against the Influenza virus through the modulation of innate immunity.

SCOPE AND APPROACH

The emerging of the COVID-19 pandemic, in addition to other diseases of viral origin, and the problems associated with other respiratory disorders, highlight how essential is a healthy eating pattern to strengthen our immune system.Key Findings and Conclusions: The present review covers the information available on edible plants, herbs, mushrooms, and preparations used in KTF to outline their multiple medicinal effects (e.g., antidiabetic, chemopreventive, antioxidative, anti-inflammatory, antibacterial), emphasizing their role and effects on the immune system with an emphasis on modulating properties of the gut microbiota that further support strong respiratory immunity. Potential functional foods commonly used in Korean cuisine such as Kimchi (a mixture of fermented vegetables), Meju, Doenjang, Jeotgal, and Mekgeolli and fermented sauces, among others, are highlighted for their great potential to improve gut-lung immunity. The traditional Korean diet and dietary mechanisms that may target viruses ACE-2 receptors or affect any step of a virus infection pathway that can determine a patient's prognosis are also highlighted. The regular oral intake of bioactive ingredients used in Korean foods can offer protection for some viral diseases, through protective and immunomodulatory effects, as evidenced in pre-clinical and clinical studies.

Characterization and correlation of microbial communities and metabolite and volatile compounds in doenjang fermentation

To investigate the general fermentation features of doenjang, a traditional Korean fermented soybean paste, eleven batches of doenjang were prepared. The bacterial and fungal communities and the metabolites such as free sugars, organic acids, amino acids, and volatile compounds were analyzed during fermentation. Tetragenococcus, Aspergillus, and Debaryomyces were the most common microbes; galactose, fructose, and glucose were the major sugars; and lactate and acetate were the major organic acids. Spearman correlation analyses showed that the quantity of meju was correlated with only Pediococcus and Halomonas abundance, while solar salt concentration was correlated with the relative abundance of many microbial taxa and the amount of glycerol and total volatile compounds. The abundance of heterolactic acid bacteria, such as Tetragenococcus, Pediococcus, Weissella, and Enterococcus, was positively correlated with the levels of lactate, acetate, and ethanol, suggesting that heterolactic acid fermentation may be a major metabolism pathway during the fermentation of doenjang. The abundance of Weissella, Hyphopichia, and Wickerhamomyces was positively correlated with ethyl acetate levels, whereas the abundance of Staphylococcus and Bacillus was positively correlated with the concentration of major volatile compounds, 3-methylbutanoic acid and tetramethylpyrazine, respectively, suggesting that they may play important roles in the production of flavor compounds during fermentation.

Metabolic Features of Ganjang (a Korean Traditional Soy Sauce) Fermentation Revealed by Genome-Centered Metatranscriptomics

The taste and quality of soy sauce, a fermented liquid condiment popular worldwide, is greatly influenced by microbial metabolism during fermentation. To investigate the fermentative features of ganjang (a Korean traditional soy sauce), ganjang batches using meju (fermented soybean) bricks and solar salts were prepared, and organic compounds, microbial communities, metagenomes, and metatranscriptomes of ganjang were quantitively analyzed during fermentation. Polymeric compound analysis in the ganjang treated with/without microbial inhibitors revealed that indigenous enzymes of meju bricks might be primarily responsible for degrading polymeric compounds. Through metagenome binning and microbe sequencing, 17 high-quality genome sequences representing all major ganjang microbiota were obtained, and their transcriptional expressions were quantitatively analyzed by mapping metatranscriptome reads normalized by spike-in RNA sequencing to the 17 genomes, which revealed that microbial metabolism might primarily occur while meju bricks are in the ganjang solution and decrease significantly after the removal of meju bricks. Metabolic pathways for carbohydrates, proteins, and lipids of the major ganjang microbiota were reconstructed, and their metabolic genes were transcriptionally analyzed, revealing that facultative lactic acid fermentation by Tetragenococcus was the major fermentation process active in the ganjang fermentation and that aerobic respiration by facultatively aerobic bacteria such as Chromohalobacter, Halomonas, and Marinobacter was also an important metabolic process during fermentation. Although the abundances of Fungi and the corresponding transcriptional expression levels were generally much lower than those of Bacteria, our analysis suggests that yeasts such as Debaryomyces and Wickerhamomyces might be in large part responsible for producing biogenic amines and flavors.

IMPORTANCE The taste and quality of soy sauce, a popular fermented liquid condiment worldwide, is greatly influenced by microbial metabolism during fermentation. Spontaneous fermentation of ganjang (a Korean traditional soy sauce) in a nonsterile environment leads to the growth of diverse bacteria and fungi during fermentation, making it difficult to understand the mechanism of ganjang fermentation. Genome-centered metatranscriptomic analysis, combined with organic compound analysis, quantitative metagenome and metatranscriptome analyses, and metabolic pathway reconstruction and expressional analysis of the major ganjang microbiota during fermentation, would provide comprehensive insights into the metabolic features of ganjang fermentation.

Sodium Reduction in Traditional Fermented Foods: Challenges, Strategies, and Perspectives

Sodium salt is a pivotal ingredient in traditional fermented foods, but its excessive consumption adversely affects human health, product quality, and production efficiency. Therefore, reducing sodium salt content in traditional fermented foods and developing low-sodium fermented foods have attracted increasing attention. Given the essential role of sodium salt in the safety and quality of fermented foods, appropriate approaches should be applied in the production of low-sodium fermented foods. In this review, the challenges of sodium reduction in traditional fermented foods are presented, including the possible growth of pathogenic bacteria, the formation of hazardous chemicals, flavor deficiency, and texture deterioration. Physical, chemical, and biological strategies are also discussed. This review provides references for improving the quality and safety of low-sodium fermented foods.