Exploring the Health Benefits of Yeast Isolated from Traditional Fermented Foods in Korea: Anti-Inflammatory and Functional Properties of Saccharomyces and Non-Saccharomyces Strains.

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.

Microbiome Analysis of Traditional Grain Vinegar Produced under Different Fermentation Conditions in Various Regions in Korea.

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.

Antibiotic susceptibility of Bacillus velezensis.

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 25 October 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 Bacillus 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.

Safety and Technological Characterization of Staphylococcus xylosus and Staphylococcus pseudoxylosus Isolates from Fermented Soybean Foods of Korea.

We evaluated the antibiotic susceptibilities, hemolytic activities, and technological properties of 36 Staphylococcus xylosus strains and 49 S. pseudoxylosus strains predominantly isolated from fermented soybean foods from Korea. Most of the strains were sensitive to chloramphenicol, erythromycin, gentamycin, kanamycin, lincomycin, oxacillin, tetracycline, and trimethoprim. However, 23 strains exhibited potential phenotypic acquired resistance to erythromycin, lincomycin, and tetracycline. Based on breakpoint values for staphylococci from the Clinical and Laboratory Standards Institute, >30% of the isolates were resistant to ampicillin and penicillin G, but the population distributions in minimum inhibitory concentration tests were clearly different from those expected for acquired resistance. None of the strains exhibited clear α- or ß-hemolytic activity. S. xylosus and S. pseudoxylosus exhibited salt tolerance on agar medium containing 20% and 22% (w/v) NaCl, respectively. S. xylosus and S. pseudoxylosus strains possessed protease and lipase activities, which were affected by the NaCl concentration. Protease activity of S. pseudoxylosus was strain-specific, but lipase activity might be a characteristic of both species. This study confirms the potential of both species for use in high-salt soybean fermentation, but the safety and technological properties of strains must be determined to select suitable starter candidates.

Genetic Background Behind the Amino Acid Profiles of Fermented Soybeans Produced by Four Bacillus spp.

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) concentration to >200% of that in the control samples. B. sonorensis produced a somewhat similar amino acid profile with B. licheniformis. Comparative genomic analysis of the four Bacillus strains and the genetic profiles of the produced free amino acids revealed that genes involved in glutamate and arginine metabolism were not common to the four strains. The genes gadA/B (encoding a glutamate decarboxylase), rocE (amino acid permease), and puuD (γ-glutamyl-γ-aminobutyrate hydrolase) determined GABA production, and their presence was species-specific. Taken together, B. licheniformis and B. velezensis were respectively shown to have high potential to increase concentrations of glutamic acid and GABA, while B. subtilis has the ability to increase essential amino acid concentrations in fermented soybean foods.