Functional properties of soy sauce and metabolism genes of strains for fermentation

Changes in Metabolite Profiles of Chinese Soy Sauce at Different Time Durations of Fermentation Studied by 1H-NMR-Based Metabolomics

Fermentation parameters, especially the duration, are important in imparting a peculiar taste and flavor to soy sauce. The main purpose of this research was to monitor metabolic changes occurring during the various time intervals of the fermentation process. NMR-based metabolomics was used to monitor the compositional changes in soy sauce during fermentation. The 1H-NMR spectra of the soy sauce samples taken from the fermentation tanks at 0 to 8 months were analyzed using 1H-NMR spectroscopy, and the obtained spectra were analyzed by multivariate statistical analysis. The Principal Component Analysis (PCA) and Partial Least Square Discriminate analysis (PLSDA) revealed the separation of samples fermented for various time durations under identical conditions. Key metabolites shown by corresponding loading plots exhibited variations in amino acids (lysine, threonine, isoleucine, etc.), acetate, glucose, fructose, sucrose, ethanol, glycerol, and others. The levels of ethanol in soy sauce increased with longer fermentation durations, which can be influenced by both natural fermentation and the intentional addition of ethanol as a preservative. The study shows that the variation in metabolite can be very efficiently monitored using 1H-NMR-based metabolomics, thus suggestion to optimize the time duration to get the soy sauce product with the desired taste and flavor.

Draft genome sequence of Candida versatilis and osmotolerance analysis in soy sauce fermentation

BACKGROUND

The salt-tolerant yeast strain Candida versatilis is usually added to high-salt, liquid-state soy sauce fermentation. The genome of C. versatilis was sequenced in our previous study but the reason for its high-osmolarity ability was not clear.

RESULTS

The 9.7 Mbp genome of C. versatilis contained 4711 CDS. Candida versatilis was the closest to another yeast, Zygosaccharomyces rouxii, added to soy sauce fermentation. The protein sequence of the whole genome was divided into 4338 groups, accounting for 92.1% of all the predicted protein of C. versatilis using OrthoMCL. Mitogen-activated protein kinase (MAPK) signal pathways, including high osmolarity and cell integrity, were predicted and proved by investigating the expression changes of the key genes CvHOG1, CvGPD1, and CvFPS1 in a high osmotic environment and by testing the variations of intracellular glycerol and extracellular glycerol.

CONCLUSION

Candida versatilis exhibited strong osmotolerance because it could synthesize intracellular glycerol and absorb glycerol from the environment cooperated with the shut down of glycerol efflux channel in membrane. © 2018 Society of Chemical Industry.

Isolation, identification and application on soy sauce fermentation flavor bacteria of CS1.03

Bacillus is a common bacterial genus in Chinese traditional sun-brewed moromi. Some Bacillus species can metabolize sauce flavour and aroma substances. To address the insufficiency of flavour microbes in soy sauce fermentation, we used 16S rDNA sequence analysis to identify the CS1.03 strain, which was isolated from moromi produced through the traditional and natural sun brewing methods. A Box-Behnken design was used to optimize the addition technology of CS1.03, and ammoniacal nitrogen content and sensory evaluation were adopted as determination indices. GC-MS analysis was also performed to analyse the flavour components. Results identified CS1.03 as Bacillus subtilis. The optimal conditions yielded 10.7 g/L ammoniacal nitrogen in fermented soy sauce with rich aroma and flavour, and a sensory evaluation score of 90.5. GC-MS analysis revealed that the contents of phenol, aldehyde and ketone are all increased. These results demonstrated that CS1.03 could improve the flavour of soy sauce and shows good potential for application in soy sauce fermentation.

Bioactivity of soy-based fermented foods: A review

For centuries, fermented soy foods have been dietary staples in Asia and, now, in response to consumer demand, they are available throughout the world. Fermentation bestows unique flavors, boosts nutritional values and increases or adds new functional properties. In this review, we describe the functional properties and underlying action mechanisms of soy-based fermented foods such as Natto, fermented soy milk, Tempeh and soy sauce. When possible, the contribution of specific bioactive components is highlighted. While numerous studies with in vitro and animal models have hinted at the functionality of fermented soy foods, ascribing health benefits requires well-designed, often complex human studies with analysis of diet, lifestyle, family and medical history combined with long-term follow-ups for each subject. In addition, the contribution of the microbiome to the bioactivities of fermented soy foods, possibly mediated through direct action or bioactive metabolites, needs to be studied. Potential synergy or other interactions among the microorganisms carrying out the fermentation and the host's microbial community may also contribute to food functionality, but the details still require elucidation. Finally, safety evaluation of fermented soy foods has been limited, but is essential in order to provide guidelines for consumption and confirm lack of toxicity.

Complete mitochondrial genome sequence of Aspergillus oryzae RIB 127 and its comparative analysis with related species

Here, we determined the complete sequence and annotation of the mitochondrial genome of A. oryzae (strain RIB 127). The complete mitochondrial genome is 29,202 base pairs (bp), with low GC content of 26.2%. Conserved genes identified include 26 transfer RNAs, the small and large ribosomal RNA subunits, and 14 protein-coding genes. Phylogenetic analysis based on the complete mitochondrial genome revealed that RIB 127 formed a single clade with two other A. oryzae species.

Comparison and analysis of the genomes of two Aspergillus oryzae strains

A. oryzae 3.042 (China) and A. oryzae RIB40 (Japan) used for soy sauce fermentation show some regional differences. We sequenced the genome of A. oryzae 3.042 and compared it to A. oryzae RIB40 in an attempt to understand why different features are shown by these two A. oryzae strains. We predict 11,399 protein-coding genes in A. oryzae 3.042. The genomes of these two A. oryzae strains are collinear revealed by MUMmer analysis, indicating that the differences are not obvious between them. Several strain-specific genes of two strains are identified by genome sequences' comparison, and they are classified into some groups, which have the relationship with cell growth, cellular response and regulation, resistance, energy metabolism, salt tolerance, and flavor formation. A. oryzae 3.042 showed stronger potential for mycelial growth and environmental stress resistance, such as the genes of chitinase and quinone reductase. Some genes unique to A. oryzae RIB40 were related to energy metabolism and salt tolerance, especially genes for Na(+) and K(+) transport, while others were associated with signal transduction and flavor formation. The genome sequence of A. oryzae 3.042 will facilitate the identification of the genetic basis of traits in A. oryzae 3.042, and accelerate our understanding of the different genetic traits of the two A. oryzae strains.