The fermentation of traditional vinegar is a spontaneous and complex process that involves interactions among various microorganisms. Here, we used a microbiome approach to determine the effects of networks, such as fermentation temperature, location, physicochemical and sensory characteristics, and bacterial profile, within traditional grain vinegar samples collected from various regions of Korea. Acetic acid and lactic acid were identified as the major metabolites of grain vinegar, and sourness and umami were determined as taste fingerprints that could distinguish between vinegar samples. Acetobacter ghanensis and Lactobacillus acetotolerans were the predominant bacterial species, and the functional composition of the microbiota revealed that the nucleotide biosynthesis pathway was the most enriched. These results reveal that vinegar samples fermented outdoors are more similar to each other than vinegar samples fermented at 30 °C, when comparing the distance matrix for comprehending bacterial networks among samples. This study may help obtain high-quality vinegar through optimized fermentation conditions by suggesting differences in sensory characteristics according to the fermentation environment.
Several types of fermented soybean food are consumed in Korea and representative examples are ganjang (soy sauce) and doenjang (soybean paste). The traditional production of ganjang and doenjang starts from the manufacture of meju. Meju is made by soaking, steaming, crushing, and molding soybeans into blocks, followed by spontaneous fermentation for 2-3 months. The ripened meju is mixed with brine and ripened for a further 2-3 months, then the liquid portion of the mixture is separated, resulting in a traditional type of ganjang. The remaining solid portion is subsequently mashed and fermented for >6 months and becomes quality doenjang [1]. Ripened meju is used as a starter culture as well as a nutrient and flavor source for fermented food production in Korea [2].Understanding of traditional fermented soybean foods has long been a research theme of food scientists in Korea. Several studies including microbial community analysis have provided basic insight for accelerated ripening, quality assurance, and flavor enhancement of fermented soybean foods. Early microbial studies isolated and identified microorganisms exhibiting strong amylase, protease, and lipase activities that can contribute to degradation of soybean macromolecules [3][4][5][6]. More recent culture-independent microbial community analysis techniques have revealed the presence of a wider variety of microorganisms in the food matrices [7][8][9][10][11][12][13][14][15]. However, regardless of the analytical methods used, most microbial studies reported that the bacterial genus Bacillus and the fungal genus Aspergillus were the most populous microorganisms.Recently, molecular biology techniques and sequence databases have contributed to identification, characterization, and typing of bacteria and increased the number of novel bacterial species [16]. Rapid advances in whole-genome sequencing technologies and analysis pipelines have further enhanced the resolution power of bacterial species and influenced the taxonomic status of closely related identities. This advanced bacterial identification methodology has affected the consolidation and assignment of new taxa in the genus Bacillus [17][18][19]. In this context, we isolated and identified Bacillus spp. from 12 meju samples collected from five regions of Korea to determine the predominant Bacillus species in meju based on current bacterial taxonomic standards [20]. One hundred and fifty-one Bacillus isolates were identified, in the following order of predominance: B. velezensis, B. sonorensis, B. subtilis, and B. licheniformis. Strains of four Bacillus spp. were respectively inoculated into sterilized soybeans and the free amino acid profiles of the resulting cultures were analyzed to discern their metabolic traits. After 30 days of culture, B. licheniformis showed the highest production of serine, threonine, and glutamic acid; B. subtilis exhibited the highest production of alanine, asparagine, glycine, leucine, proline, tryptophan, and lysine. B. velezensis increased the γ-aminobutyric acid (GABA) ...
Traditional grain vinegar is fermented using multiple acetic acid bacteria (AAB) at various temperatures. A single AAB showed high acid-producing ability at 30 °C with a 5% alcohol concentration and an initial pH adjusted to 4.0. Multiple AAB were similar to a single AAB; however, the optimal initial pH was 3.0. Acid production ability according to the type of AAB was higher in multiple AAB than in single AAB. That is, using multiple AAB helped increase the titratable acidity of traditional grain vinegar. In addition, increasing the titratable acidity and content of volatile flavor compounds was advantageous when two, rather than four, AAB types were mixed and used. The titratable acidity was high at medium temperatures (30 °C); however, volatile flavor compounds increased at low temperatures (20 °C) under multiple AAB. A 16S rDNA-based microbiome taxonomic profiling analysis identified differences in beta diversity due to multiple AAB and fermentation temperatures. In particular, beta diversity analysis revealed a specific pattern when a mixture of Acetobacter ascedens GV–8 and Acetobacter pasteurianus GV–22 was fermented at a low temperature (20 °C). Therefore, we propose the application of multiple AAB with acidic and flavor-producing properties in traditional grain vinegar.
We evaluated the antibiotic minimum inhibitory concentrations (MICs) of 123 Bacillus velezensis strains predominantly isolated from fermented soybean foods from Korea. When the 2018 European Food Safety Authority breakpoint values for Bacillus spp. were applied, all the strains were sensitive to chloramphenicol, clindamycin, erythromycin, gentamicin, kanamycin, tetracycline, and vancomycin, and eight strains (6.5%) were resistant to streptomycin. The population distribution in MIC tests with streptomycin was continuous and the profile was clearly different from that expected for acquired antibiotic resistance. As of October 25th 2021, there were 181 complete published genomes of B. velezensis strains; 175 (96.7%) and 136 (75.2%) of these strains respectively possess potential tetracycline and streptomycin resistance genes tetL and ant(6) in the chromosome. In B. licheniformis, SpeG confers resistance to clindamycin and there is an ‘speG’ gene annotated in the genomes of 180 B. velezensis strains; however, the gene products exhibit ≤ 26.6% amino acid identity with that from B. licheniformis DSM 13T. All the potential antibiotic resistance genes in the 181 B. velezensis strains were intrinsic, and traits of lateral gene transfer were not found. In this context, B. velezensis may not present a high risk in terms of antibiotic resistance in food fermentation or human use.
Traditional yeast (Saccharomyces cerevisiae) has been used for its benefits in various fermentation processes; the benefits of non-Saccharomyces yeast as a material for food, feed, and pharmaceuticals have been studied recently. This study evaluated the anti-inflammatory activity and extracellular functional characteristics of wild-type yeasts isolated from traditional fermented foods (doenjang (common name: soybean paste) and nuruk) in Korea. The viability of the yeast and lipopolysaccharide (LPS)-stimulated RAWBlue™ cells was improved, similar to unstimulated RAWBlue™ cells, and the isolates demonstrated NF-κB inhibitory activity. Yeast suppressed the nitric oxide production in LPS-stimulated RAWBlue™ cells, which was attributed to the inhibition of iNOS or COX-2 mRNA expression depending on the strain. Although there were differences depending on the strain, the production of anti-inflammatory cytokines was reduced in the yeast and LPS-stimulated RAWBlue™ cells, some of which were demonstrated at the mRNA level. In addition, the isolates exhibited high antioxidant and antihypertensive activities (similar to the positive control), which varied depending on the strain. This suggests that yeast can be used for fermentation with enhanced antioxidant and antihypertensive activities. Furthermore, the isolates inhibited the growth of pathogenic Gram-negative bacteria, indicating that yeast can inhibit food spoilage and the growth of pathogenic bacteria during fermentation. Consequently, utilizing raw materials to cultivate yeast strains could be a promising avenue for developing functional foods to prevent and treat inflammatory reactions; such foods may exhibit antioxidant, antihypertensive, and antibacterial properties.
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