Genomic and functional features of yeast species in Korean traditional fermented alcoholic beverage and soybean products.

In this review, we describe the genomic and physiological features of the yeast species predominantly isolated from Nuruk, a starter for traditional Korean rice wines, and Jang, a traditional Korean fermented soy product. Nuruk and Jang have several prevalent yeast species, including Saccharomycopsis fibuligera, Hyphopichia burtonii, and Debaryomyces hansenii complex, which belong to the CUG clade showing high osmotic tolerance. Comparative genomics revealed that the interspecies hybridization within yeast species for generating heterozygous diploid genomes occurs frequently as an evolutional strategy in the fermentation environment of Nuruk and Jang. Through gene inventory analysis based on the high-quality reference genome of S. fibuligera, new genes involved in cellulose degradation and volatile aroma biosynthesis and applicable to the production of novel valuable enzymes and chemicals can be discovered. The integrated genomic and transcriptomic analysis of Hyphopichia yeasts, which exhibit strong halotolerance, provides insights into the novel mechanisms of salt and osmo-stress tolerance for survival in fermentation environments with a low-water activity and high-concentration salts. In addition, Jang yeast isolates, such as D. hansenii, show probiotic potential for the industrial application of yeast species beyond fermentation starters to diverse human health sectors.

Genomic features, aroma profiles, and probiotic potential of the Debaryomyces hansenii species complex strains isolated from Korean soybean fermented food.

Fermented soybean products are gaining attention in the food industry owing to their nutritive value and health benefits. In this study, we performed genomic analysis and physiological characterization of two Debaryomyces spp. yeast isolates obtained from a Korean traditional fermented soy sauce "ganjang". Both Debaryomyces hansenii ganjang isolates KD2 and C11 showed halotolerance to concentrations of up to 15% NaCl and improved growth in the presence of salt. Ploidy and whole-genome sequencing analyses indicated that the KD2 genome is haploid, whereas the C11 genome is heterozygous diploid with two distinctive subgenomes. Interestingly, phylogenetic analysis using intron sequences indicated that the C11 strain was generated via hybridization between D. hansenii and D. tyrocola ancestor strains. The D. hansenii KD2 and D. hansenii-hybrid C11 produced various volatile flavor compounds associated with butter, caramel, cheese, and fruits, and showed high bioconversion activity from ferulic acid to 4-vinylguaiacol, a characteristic flavor compound of soybean products. Both KD2 and C11 exhibited viability in the presence of bile salts and at low pH and showed immunomodulatory activity to induce high levels of the anti-inflammatory cytokine IL-10. The safety of the yeast isolates was confirmed by analyzing virulence and acute oral toxicity. Together, the D. hansenii ganjang isolates possess physiological properties beneficial for improving the flavor and nutritional value of fermented products.

Production of arabitol from enzymatic hydrolysate of soybean flour by Debaryomyces hansenii fermentation.

Arabitol is a low-calorie sugar alcohol with anti-cariogenic properties. Enzymatic hydrolysate of soybean flour is a new renewable biorefinery feedstock containing hexose, pentose, and organic nitrogen sources. Arabitol production by Debaryomyces hansenii using soybean flour hydrolysate was investigated. Effects of medium composition, operating conditions, and culture stage (growing or stationary phase) were studied. Production was also compared at different culture volumes to understand the effect of dissolved oxygen concentration (DO). Main factors examined for medium composition effects were the carbon to nitrogen concentration ratio (C/N), inorganic (ammonium) to organic nitrogen ratio (I/O-N), and sugar composition. Arabitol yield increased with increasing C/N ratio and a high I/O-N (0.8-1.0), suggesting higher yield at stationary phase of low pH (3.5-4.5). Catabolite repression was observed, with the following order of consumption: glucose > fructose > galactose > xylose > arabinose. Arabitol production also favored hexoses and, among hexoses, glucose. DO condition was of critical importance to arabitol production and cell metabolism. The yeast consumed pentoses (xylose and arabinose) only at more favorable DO conditions. Finally, arabitol was produced in fermentors using mixed hydrolysates of soy flour and hulls. The process gave an arabitol yield of 54%, volumetric productivity of 0.90 g/L-h, and specific productivity of 0.031 g/g-h.

Hydrolysis of soybean isoflavones by Debaryomyces hansenii UFV-1 immobilised cells and free ß-glucosidase.

An intracellular ß-glucosidase from Debaryomyceshansenii UFV-1 was produced in an YP medium with cellobiose as the carbon source. This enzyme was purified, characterised and presented a Mr of 65.15kDa. Yeast cells containing the intracellular ß-glucosidase were immobilised in calcium alginate. The free ß-glucosidase and immobilised cells containing the enzyme presented optima values of pH and temperature of 6.0 and 45°C and 5.5 and 50°C, respectively. The free enzyme maintained 62% and 47% of its original activity after 90days at 4°C and after 15days at room temperature, respectively. The immobilisation process resulted in higher enzyme thermostability at 45 and 50°C. Soy molasses treatment with the free enzyme and the immobilised cells containing ß-glucosidase, for 2h at 40°C, promoted efficient hydrolysis of isoflavone glicosides to their aglycon forms. The results suggest that this enzyme could be used in the food industry, in the free or immobilised forms, for a safe and efficient process to hydrolyse isoflavone glycosides in soy molasses.

Analysis of microbial communities in doenjang, a Korean fermented soybean paste, using nested PCR-denaturing gradient gel electrophoresis.

Doenjang is a traditional Korean fermented soybean paste that provides a major source of protein. The microbial diversity of 10 samples of doenjang (5 commercially manufactured products and 5 homemade products) was investigated using nested PCR-denaturing gradient gel electrophoresis (DGGE). In the first step, the nearly complete 16S rRNA and 18S rRNA genes were amplified using universal primers. Subsequently, these products were used as a template in a nested PCR to obtain fragments suitable for DGGE. The bacterial DGGE profile targeting the V3 region of the 16S rRNA gene indicated that lactic acid bacteria such as Leuconostoc mesenteroide, Tetragenococcus halophilus, and Enterococcus faecium were the predominant species. However, bands corresponding to Bacillus species, known to be the main organisms in doenjang, were not detected under the conditions described above. When selective PCR was conducted using a primer specific for Bacillus species, Bacillus subtilis and B. licheniformis were detected in several doenjang samples. In analysis of fungi, Mucor plumbeus, Aspergillus oryzae, and Debaryomyces hansenii were the most common species in the doenjang samples. On the basis of DGGE, a few differences in community structure were found for different samples. Also, cluster analysis of the DGGE profile revealed that the microbial diversity did not differ clearly between commercially manufactured and homemade products. The nested PCR-DGGE technique was used for the first time in this study to asses a microbial community in doenjang and proved to be effective in profiling microbial diversity.

Nutrient digestibilities of a corn-soybean meal diet as influenced by Bacillus products fed to finishing swine.

Twelve crossbred barrows (initial BW of 59.7 kg) were used in nutrient balance trials to investigate the influence of adding two Bacillus products (Biomate 2B and Pelletmate Livestock, Chr. Hansen's Biosytems) to a 14% CP corn-soybean meal diet (.64% lysine, .6% Ca and .5% P). A 3 x 3 Latin-square design with an extra period was used. Treatments were as follows: 1) basal diet; 2) basal + Biomate 2B (BAC1); and 3) basal + Pelletmate Livestock (BAC2). After a 7-d adaptation to metabolism crates, each 10-d period consisted of 5 d of diet adjustment followed by 4 d of total collection and 1 d for change-over. Both BAC1 and BAC2 were added at a level of .05% to supply approximately 3 million colony forming units per gram of diet. Pigs were fed twice daily at a daily rate of 3.2 to 3.5% of BW. Feeding BAC1 or BAC2 elevated (P < .001) fecal Bacillus spore counts at the end of each collection period, but the effect on number of coliforms and lactic acid bacteria was not as consistent; coliform counts tended to be decreased (P < .10) when BAC2 was fed, but not (P > .10) when BAC1 was fed. The number of lactic acid bacteria was increased (P < .05) when BAC1 was fed, but not (P > .10) when BAC2 was fed. Body weights were similar among all treatments for all periods. There was no carry-over or pretreatment effect (P = .50). Digestibility coefficients of DM, neutral detergent fiber, acid detergent fiber, ash, and N and retention of N were not affected (P = .40) by feeding Bacillus products.

A protein antigen of Mycobacterium leprae is related to a family of small heat shock proteins.

The gene encoding an immunologically important 18-kilodalton protein antigen of Mycobacterium leprae has been sequenced, and the amino acid sequence of the antigen has been deduced. The 18-kilodalton antigen is strikingly similar in size and sequence to a family of eucaryotic heat shock proteins.