Dynamic analysis of physicochemical characteristics and microbial communities of Aspergillus-type douchi during fermentation

Dynamic Correlation Between Bacterial Communities and Volatile Compounds During Douchiba Fermentation

Douchiba is a traditional bacteria-fermented soybean product in Guizhou, refined through the following steps of soaking, steaming, koji-making, salt sprinkling, fermentation, pounding, drying, molding, and after-ripening. However, the dynamic alterations of microbiota and volatile compounds of Douchiba were seldom reported. In this work, the bacterial communities and volatile compounds during the fermentation process of Douchiba were explored by high-throughput sequencing and headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) techniques, respectively. Furthermore, the correlation between microbial communities and volatile compounds was analyzed with Spearman's method. The findings revealed that the diversity and evenness of bacteria increased during the fermentation process of Douchiba. The dominant bacteria genera included Bacillus, Staphylococcus, Tetragenococcus, Loigolactobacillus, and Virgibacillus. Bacillus dominated the bacterial communities throughout the fermentation process, and Staphylococcus, Tetragenococcus, Loigolactobacillus, and Virgibacillus also became the dominant genera in the fermentation and after-ripening stages. A total of 134 volatiles were identified. The main volatiles were ketones and alcohols in the koji-making stage, ketones and pyrazines in the fermentation stage, and acids in the after-ripening stage. In total, 26 compounds were selected as the main characteristic volatiles, including 2,3,5-trimethylpyrazine, 3-methyl-1-butanol, and indole, which endowed Douchiba with a specific flavor. Additionally, Bacillus was significantly positively correlated with isovaleraldehyde, benzaldehyde, and acetic acid. Staphylococcus was significantly positively correlated with indole, 3-methylbutanoic acid, and eucalyptol. Tetragenococcus, Loigolactobacillus, and Virgibacillus were significantly correlated with indole and estragole. The research establishes a theoretical foundation for better regulating the flavor quality of Douchiba products.

Revealing the intrinsic relationship between microbial communities and physicochemical properties during ripening of Xuanwei ham

To clarify the relationship between microorganisms and physicochemical indicators of Xuanwei ham. Six ham samples for the first, second and third year were selected, respectively. The changes of physicochemical properties, the free fatty acids and microbial communities of Xuanwei ham were investigated by GC-MS and high-throughput sequencing technology. Results showed that scores of colour, overall acceptability, texture, taste and aroma were the highest in the third year sample. With increasing ripening time, moisture content, water activity (Aw), lightness (L*), springiness, and resilience decreased continuously, and yellowness (b*) was the highest in the second year sample. 31 free fatty acids were detected, and unsaturated fatty acids such as palmitoleic acid, oleic acid, and linoleic acid were the major fatty acids. The content of palmitoleic acid, oleic acid and eicosenoic acid increased significantly during processing. At the phylum level, the dominant bacteria were Proteobacteria and Firmicutes, and fungi were Ascomycota. At the genus level, the dominant bacteria were Staphylococcus and Psychrobacter, and fungi were Aspergillus. Correlation analysis showed that water content and Aw were closely related to microorganisms, and most unsaturated fatty acids were significantly correlated with microorganisms. These findings showed that microorganisms played an important role in the quality of Xuanwei ham, and provided a scientific basis for the quality control of Xuanwei ham.

A Systematic Comparative Study on the Physicochemical Properties, Volatile Compounds, and Biological Activity of Typical Fermented Soy Foods

Fermented soy foods can effectively improve the unpleasant odor of soybean and reduce its anti-nutritional factors while forming aromatic and bioactive compounds. However, a differential analysis of characteristic flavor and function among different fermented soy foods has yet to be conducted. In this study, a systematic comparison of different fermented soy foods was performed using E-nose, HS-SMPE-GC×GC-MS, bioactivity validation, and correlation analysis. The results showed that soy sauce and natto flavor profiles significantly differed from other products. Esters and alcohols were the main volatile substances in furu, broad bean paste, douchi, doujiang, and soy sauce, while pyrazine substances were mainly present in natto. Phenylacetaldehyde contributed to the sweet aroma of furu, while 1-octene-3-ol played a crucial role in the flavor formation of broad bean paste. 2,3-Butanediol and ethyl phenylacetate contributed fruity and honey-like aromas to douchi, doujiang, and soy sauce, respectively, while benzaldehyde played a vital role in the flavor synthesis of douchi. All six fermented soy foods demonstrated favorable antioxidative and antibacterial activities, although their efficacy varied significantly. This study lays the foundation for elucidating the mechanisms of flavor and functionality formation in fermented soy foods, which will help in the targeted development and optimization of these products.

Microbiology of fermented soy foods in Asia: Can we learn lessons for production of plant cheese analogues?

The food industry is facing the challenge of creating innovative, nutritious, and flavored plant-based products, due to consumer's increasing demand for the health and environmental sustainability. Fermentation as a unique and effective tool plays an important role in the innovation of food products. Traditional fermented soy foods are popular in many Asian and African countries as nutritious, digestible and flavorful daily staples or condiments. They are produced by specific microorganisms with the unique fermentation process in which microorganisms convert the ingredients of whole soybean or soybean curd to flavorful and functional molecules. This review provides an overview on traditional fermented food produced from soy, including douchi, natto, tempeh, and sufu as well as stinky tofu, including the background of these products, the manufacturing process, and the microbial diversity involved in fermentation procedures as well as flavor volatiles that were identified in the final products. The contribution of microbes to the quality of these five fermented soy foods is discussed, with the comparison to the role of cheese ripening microorganisms in cheese flavor formation. This communication aims to summarize the microbiology of fermented soy foods in Asia, evoking innovative ideas for the development of new plant-based fermented foods especially plant-based cheese analogues.

Flavor Characterization of Traditional Fermented Soybean Pastes from Northeast China and Korea

This study compares the physicochemical properties, taste, and volatile compounds of Northeastern Chinese dajiang (C) and Korean doenjang (K) and distinguishes the discriminant volatile metabolites between them. The result revealed that compared to group C, group K exhibited more similar physicochemical properties and had lower pH, moisture, and amino acid nitrogen content, while demonstrating higher titratable acidity, salt content, and reduced sugar content. The electronic tongue analysis showed that the saltiness and umami of soybean pastes had high response values, enabling clear differentiation of the overall taste between the two types of soybean pastes. A total of 71 volatile substances from the soybean pastes were identified through solid-phase microextraction gas chromatography-mass spectrometry. Furthermore, orthogonal partial least squares discriminant analysis revealed 19 volatile compounds as differentially flavored metabolites. Our study provides a basis for explaining the differences in flavor difference of Northeastern Chinese dajiang and Korean doenjang from the perspective of volatile metabolites.

Bioactive Ingredients in Traditional Fermented Food Condiments: Emerging Products for Prevention and Treatment of Obesity and Type 2 Diabetes

Obesity and type 2 diabetes (T2D) are severe metabolic diseases due to inappropriate lifestyle and genetic factors and their prevention/treatment cause serious problems. Therefore, searching for effective and safe approaches to control obesity and T2D is an essential challenge. This study presents the knowledge regarding the possible use of traditional fermented condiments (TFC), a known major source of bioactive compounds (BACs), as an adjuvant treatment for obesity and T2D. Data on antiobesity, antidiabetic, and different mechanisms of BACs action of TFC were collected using a methodical search in PubMed, Scopus databases, Web of Science, SciELO, and the Cochrane Library. We discuss the mechanisms by which BCs prevent or treat obesity and T2D. The effects of TFC on obesity and T2D have been found both in animal, human, and clinical studies. The findings demonstrated that BACs in TFC confer potential promising antiobesity and antidiabetic effects. Because of the potential therapeutic significance of bioactive ingredients, the consumption of TFC could be recommended as a functional condiment. Nevertheless, further investigation is required in more clinical studies of TFC to support the formulation of functional fermented condiments and nutraceutical and pharmaceutical applications.

Succession and Diversity of Microbial Flora during the Fermentation of Douchi and Their Effects on the Formation of Characteristic Aroma

This study aims to understand the development and succession of the microbial community during the production of traditional Aspergillus-type Douchi as well as their effects on the formation and variation of characteristic aroma compounds. High-throughput sequencing technology, solid-phase microextraction, gas chromatography-mass spectrometry, and Spearman correlation analysis were conducted to study the changes in the microbial community and characteristic flavor during the fermentation process. Aspergillus spp. was dominant in the early stage of fermentation, whereas Staphylococcus spp., Bacillus spp., and Millerozyma spp. became dominant later. At the early stage, the main flavor compounds were characteristic soy-derived alcohols and aldehydes, mainly 1-hexanol, 1-octen-3-ol, and nonanal. In the later stage, phenol, 2-methoxy-, and 3-octanone were formed. Correlation analysis showed that six bacterial genera and nine fungal genera were significantly correlated with the main volatile components, with higher correlation coefficients, occurring on fungi rather than bacteria. Alcohols and aldehydes were highly correlated with the relative abundance of bacteria, while that of yeast species such as Millerozyma spp., Kodamaea spp., and Candida spp. was positively correlated with decanal, 3-octanol, 2-methoxy-phenol, 4-ethyl-phenol, 3-octanone, and phenol. The novelty of this work lies in the molds that were dominant in the pre-fermentation stage, whereas the yeasts increased rapidly in the post-fermentation stage. This change was also an important reason for the formation of the special flavor of Douchi. Correlation analysis of fungi and flavor substances was more relevant than that of bacteria. As a foundation of our future focus, this work will potentially lead to improved quality of Douchi and shortening the production cycle by enriching the abundance of key microbes.

Dynamic changes of bacteria communities in Moutai-flavor Daqu during storage analyzed by next generation sequencing

The quality of Moutai-flavor Baijiu is highly dependent on Moutai-flavor Daqu (MTDQ), which needs to be stored for six months before using. It brings abundant bacterium, which can metabolize various enzymes and favor compounds. But the reasonable storage time of MTDQ prepared in different seasons is still uncertain. To this end, the study revealed a detailed bacterial profile of storage MTDQ prepared in three different seasons (specifically, they were stored start from spring, summer and autumn) by using high-throughput sequencing approach (next generation sequencing). Results showed that major phyla of storage MTDQ were Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes, and Fusobacteria. The advantages of Firmicutes were Thermoactinomyces and Bacillaceae. Significant differences in bacterial community structures of MTDQ from different seasons and storage time were observed. Compared with summer and autumn MTDQ, the decrease of Thermoactinomyces and increase of Desmospora in spring MTDQ were the main differences and bacterial community structures of summer and autumn MTDQ were more similar. The variation trends of the bacteria community indicated the effective time of storage period were appropriately six months for spring MTDQ, two months for summer MTDQ and more than six months for autumn MTDQ. These results showed that the length of storage time was associated with the season, it's reasonable to adjust the storage time of MTDQ with the season.

Production and Optimization of Conjugated Linoleic and Eicosapentaenoic Acids by Bifidobacterium lactis in Cold-Pressed Soybean Cake

Background and Purpose

In regard to the biosynthesis of conjugated linoleic acid (CLA) and eicosapentaenoic acid (EPA) by some bacteria, the objective of this study was to evaluate the efficiency of solid-state fermentation based on soybean pressed cake (SPC) to produce CLA and EPA by Bifidobacterium lactis. The objective of this study was to evaluate the efficiency of solid-state fermentation based on SPC to produce CLA and EPA by B. lactis.

Methods

Process conditions including humidity, inoculation level, and temperature parameters were optimized by adopting the response surface methodology (RSM) method (response surface method) and the design expert software. Accordingly, a homogeneous SPC paste substrate at 60, 70, and 80% humidity was prepared with different inoculation levels at 30, 37, and 44°C to assess the strain behavior. The introduced SPC consisted of 60% humidity, 2% inoculation level at 37°C, and 60% humidity, and 4% inoculation level at 30 and 44°C; it also included 6% inoculation level at 37°C, 70% humidity at 2% inoculation level, at 30 and 44°C, and 4% inoculation level at 37°C. Also, SPC with 80% humidity at 2% and 4% inoculation levels, and at 30 and 44°C was obtained. To confirm the accuracy of the conditions, an experiment was conducted according to the defined requirements.

Results

The results were compared with the predicted data, which showed a significant difference. Under optimized conditions, with an inoculation level of 4% on the SPC medium with 70% humidity and at 37°C, B. lactis strains could yield 9cis-, 11 trans-linoleic and eicosapentaenoic at 0.18 and 0.39% of the total fatty acids.

Conclusion

So, the potential benefits of using SPC as an inexpensive substrate for the commercial production of CLA and EPA should be noted.

Dynamic Changes in Microbial Communities and Physicochemical Characteristics During Fermentation of Non-post Fermented Shuidouchi

Non-post fermented Shuidouchi is a Chinese spontaneously fermented soybean food with multifunctionality in human health. The functionality and safety of this plant-based food will be affected by the microorganisms during fermentation. In this study, microbial diversity was investigated using culture-dependent and culture-independent methods. The functional metabolites such as polyamines and alkylpyrazines were also determined at different time points during fermentation. We found that Bacillus was the most dominant microbe throughout the fermentation process, while the temperature was the most important influencing factor. During fermentation, the microbial diversity increased at a moderate temperature and decreased at a high temperature (52^°C). High temperature caused the prosperity of the spore-producing bacteria such as Bacillus (more than 90% relative abundance in bacteria) and Aneurinibacillus (2% or so relative abundance in bacteria), and the inhibition of fungi. Furthermore, it was found by correlation analysis that the relative abundances of Bacillus and Aneurinibacillus were positively correlated with the relative content of amino acid metabolism pathway and the content of most alkylpyrazines and biogenic amines. Meanwhile, the relative abundances of many non-dominant bacteria were negatively correlated with the content of biogenic amines and positively correlated with the relative content of carbohydrate metabolism pathway. These effects were helpful to control the biogenic amine contents under the safety limits, increasing the alkylpyrazine type and product functionality. A two-stage temperature control strategy—a moderate temperature (35–42^°C) first, then a high temperature (52^°C)—was concluded from the spontaneous fermentation of non-post fermented Shuidouchi. This strategy could improve the safety of product by inhibiting or sterilizing the thermolabile microbes. The non-post fermented Shuidouchi product is rich in functional compounds such as polyamines and alkylpyrazines.