Effect of incubation temperature on variations in bacterial communities grown in fermenting meju and the nutritional quality of soy sauce

Taxonomic Variations of Bacterial and Fungal Communities depending on Fermentation Temperature in Traditional Korean Fermented Soybean Food, Doenjang

Meju, a fermented soybean brick, is a key component in soybean foods like doenjang and ganjang, harboring a variety of microorganisms, including bacteria and fungi. These microorganisms significantly contribute to the nutritional and sensory characteristics of doenjang and ganjang. Amplicon-based next-generation sequencing was applied to investigate how the microbial communities of meju fermented at low and high temperatures differ and how this variation affects the microbial communities of doenjang, a subsequently fermented soybean food. Our metagenomic data showed distinct patterns depending on the fermentation temperature. The microbial abundance in the bacterial community was increased under both temperatures during the fermentation of meju and doenjang. Weissella was the most abundant genus before the fermentation of meju, however, it was replaced by Bacillus at high temperature-fermented meju and lactic acid bacteria such as Weissella and Latilactobacillus at low temperature-fermented meju. Leuconostoc, Logiolactobacillus, and Tetragenococcus gradually took over the dominant role during the fermentation process of doenjang, replacing the previous dominant microorganisms. Mucor was dominant in the fungal community before and after meju fermentation, whereas Debaryomyces was dominant under both temperatures during doenjang fermentation. The dominant fungal genus of doenjang was not affected regardless of the fermentation temperature of meju. Strong correlations were shown for specific bacteria and fungi linked to specific fermentation temperatures. This study helps our understanding of meju fermentation process at different fermentation temperatures and highlights different bacteria and fungi associated with specific fermentation periods which may influence the nutritional and organoleptic properties of the final fermented soybean foods doenjang.

Exploring the core functional microbiota related with flavor compounds in fermented soy sauce from different sources

Flavor, the most important quality index of soy sauce, is mostly influenced by the microbiota in fermented food ecosystem, however, the association between microorganisms and soy sauce flavor is still poorly understood. Therefore, the bacterial and fungal profiles, physicochemical parameters, and flavor compounds (9 organic acids, 17 free amino acids and 97 volatile flavor compounds) of 5 different source soy sauce were investigated using high-throughput sequencing, HPLC, amino acid analyzer and SPME/LLE-GC-MS, and their correlations were explored. A total of 3 fungal genera and 12 bacterial genera were identified as potential flavor-producing microorganisms by multivariate data and correlation analysis. Notably, Lactobacillus and Tetragenococcus were strongly positively correlated with succinic acid and lactic acid, respectively. Moreover, not only fungi, but also bacteria were found to be closely correlated with volatiles. Finally, 5 screened potential flavor-producing microorganisms were validated using a rapid fermentation model, with multiple strains showing the potential to improve the soy sauce flavor, with Lactobacillus fermentum being the most significant. Our research will provide a theoretical basis for the regulation and enhancement of soy sauce flavor.

Nutritional Contributions and Health Associations of Traditional Fermented Foods

The growing interest in the consumption and study of traditionally fermented food worldwide has led to the development of numerous scientific investigations that have focused on analyzing the microbial and nutritional composition and the health effects derived from the consumption of these foods. Traditionally fermented foods and beverages are a significant source of nutrients, including proteins, essential fatty acids, soluble fiber, minerals, vitamins, and some essential amino acids. Additionally, fermented foods have been considered functional due to their prebiotic content, and the presence of specific lactic acid bacterial strains (LAB), which have shown positive effects on the balance of the intestinal microbiota, providing a beneficial impact in the treatment of diseases. This review presents a bibliographic compilation of scientific studies assessing the effect of the nutritional content and LAB profile of traditional fermented foods on different conditions such as obesity, diabetes, and gastrointestinal disorders.

Effect of sulfite addition and pied de cuve inoculation on the microbial communities and sensory profiles of Chardonnay wines: dominance of indigenous Saccharomyces uvarum at a commercial winery

The microbial consortium of wine fermentations is highly dependent upon winemaking decisions made at crush, including the decision to inoculate and the decision to add sulfur dioxide (SO2) to the must. To investigate this, Chardonnay grape juice was subjected to two inoculation treatments (uninoculated and pied de cuve inoculation) as well as two SO2 addition concentrations (0 and 40 mg/L). The bacterial communities, fungal communities and Saccharomyces populations were monitored throughout fermentation using culture-dependent and culture-independent techniques. After fermentation, the wines were evaluated by a panel of experts. When no SO2 was added, the wines underwent alcoholic fermentation and malolactic fermentation simultaneously. Tatumella bacteria were present in significant numbers, but only in the fermentations to which no SO2 was added, and were likely responsible for the malolactic fermentation observed in these treatments. All fermentations were dominated by a genetically diverse indigenous population of Saccharomyces uvarum, the highest diversity of S. uvarum strains to be identified to date; 150 unique strains were identified, with differences in strain composition as a result of SO2 addition. This is the first report of indigenous S. uvarum strains dominating and completing fermentations at a commercial winery in North America.

Analyses of microbial community of naturally homemade soybean pastes in Liaoning Province of China by Illumina Miseq Sequencing

Traditional Chinese soybean pastes are homemade using natural fermentation and are quite common and popular in Liaoning Province. In this study, we investigated microbial diversity by collecting 23 samples from 10 cities and sequenced them using 2 × 300 bp Illumina Miseq Sequencing. 16S and ITS primers were used to amplify the V3-V4 region of the bacterial 16S rRNA gene and the ITS1 region of the fungal ITS rDNA gene, respectively. In total, 687,888 filtered bacterial sequences were obtained from nineteen samples and 1,091,649 filtered fungal sequences were obtained from twenty samples. Among the bacterial sequences, Firmicutes (74.77%), Proteobacteria (22.61%), and Actinobacteria (2.55%) were the predominant phyla, with Staphylococcus making up most of the Firmicutes. Among the fungal sequences, Ascomycota, Basidiomycota and Zygomycota accounted for 94.88%, 3.29% and 1.77%, respectively, while Glomeromycota and Chytridiomycota accounted for the remaining 0.06%. Most of the species from Ascomycota were unclassified Trichocomaceae and Debaryomyces, including 404578 and 187827 sequences, respectively. The microbial community in each sample was unique, most likely due to the geographical differences and external factors including the environment and manufacturing process during the fermentation. Soybean paste is the result of fermentation involving a great diversity of microorganisms, which include not only bacteria but also fungi.

Making soy sauce using direct fermentation of defatted soybean meal without the meju (soybean Koji) preparation process

Soy sauce prepared via direct fermentation of defatted soybean meal (DFSM) using halophiles without addition of dried, fermented soybeans or meju was evaluated. DFSM was fermented using single and mixed cultures of Oceanobacillus kimchii and Bacillus pumilus under 18% salinity conditions. Amounts of total organic nitrogen, free amino acids, and organic acids in soy sauce prepared with the mixed culture were slightly higher than sauces prepared with single culture. The ingredient content was higher in soy sauce prepared via direct fermentation of DFSM than soy sauce prepared with meju. Microorganisms detected in DFSM fermentation were not detected in the meju culture, except for the 2 halophiles, based on metagenomic analysis. Direct fermentation of DFSM is better than using meju for preparation of soy sauce.