Characterization of bacterial community and flavor differences of different types of Douchi

Correlation between physicochemical properties, flavor characteristics and microbial community structure in Dushan shrimp sour paste

Dushan shrimp sour paste (DSSP), a traditional Guizhou condiment, and its unique flavor is determined by the fermentation microbiota. However, the relationship between the microbiota structure and its flavor remains unclear. This study identified 116 volatile flavor compounds using electronic nose and headspace solid-phase microextraction-gas chromatography mass spectrometry (HS-SPME-GC-MS) techniques, of which 19 were considered as key flavor compounds, mainly consisting of 13 esters and 1 alcohol. High-throughput sequencing technique, the bacterial community structure of nine groups of DSSPs was determined. Further analysis revealed Vagococcus, Lactococcus, and Tepidimicrobium as key bacteria involved in flavor formation. This study contributes to our understanding of the relationship between bacterial communities and the flavor formation, and provides guidance for screening starter culture that enhance the flavor of DSSP in industrial production.

Deciphering the core microbiota in open environment solid-state fermentation of Beijing rice vinegar and its correlation with environmental factors

BACKGROUND

Rice vinegar is a popular cereal vinegar worldwide and is typically produced in an open environment, and the ecosystem of solid-state fermentation is complicated and robust. The present study aimed to reveal the shaping force of the establishment of the ecosystem of Beijing rice vinegar, the core function microbiota and their correlation with critical environmental factors. [Correction added after first online publication on 29 May 2024; the word "worldwide" has been removed from the first sentence under the section Background.] RESULTS: The experimental findings revealed the changes in environmental factors, major metabolites and microbial patterns during Beijing rice vinegar fermentation were obtained. The major metabolites accumulated at the middle and late acetic acid fermentation (AAF) periods. Principal coordinates and t-test analyses revealed the specific bacterial and fungal species at corresponding stages. Kosakonia, Methlobacterium, Sphingomonas, unidentified Rhizobiaceae, Pseudozyma and Saccharomycopsis dorminated during saccharification and alcohol fermentation and early AAF, whereas Lactococcus, Acetobacter, Rhodotorula and Kazachstania dominated the later AAF stages. Canonical correspondence analysis of environmental factors with core microbiota. Temperature and total acid were the most significant factors correlated with the SAF bacterial profile (Pediococcus, Weissella, Enterococcus and Kosakonia). Ethanol was the most significant factor between AAF1 and AAF3, and mainly affected Acetobacter and Lactobacillus. Conversely, ethanol was the most significant factor in the SAF, AAF1 and AAF3 fungi communities; typical microorganisms were Saccharomyces and Malassezia. Furthermore, the predicted phenotypes of bacteria and their response to environmental factors were evaluated.

CONCLUSION

In conclusion, the present study has provided insights into the process regulation of spontaneous fermentation and distinguished the key driving forces in the microbiota of Beijing rice vinegar fermentation. © 2024 Society of Chemical Industry.

A novel ACE inhibitory peptide from Douchi hydrolysate: Stability, inhibition mechanism, and antihypertensive potential in spontaneously hypertensive rats

Angiotensin I-converting enzyme (ACE) regulates blood pressure through the renin-angiotensin system. Douchi, a traditional fermented soybean condiment, may have antihypertensive effects, but research on ACE inhibitory peptides from Douchi hydrolysates is limited. We hypothesized that enzymatic treatment could enhance ACE inhibitory peptide diversity and efficacy. We tested ten single enzymes and four combinations, finding pepsin-trypsin-chymotrypsin most effective. Hydrolysates were purified using Sephadex G-15 and reversed-phase HPLC, and peptides were identified via LC-MS/MS. Five peptides (LF, VVF, VGAW, GLFG, NGK) were identified, with VGAW as the most potent ACE inhibitor (IC50 46.6 ± 5.2 μM) showing excellent thermal and pH stability. Lineweaver-Burk plots confirmed competitive inhibition, and molecular docking revealed eight hydrogen bonds between VGAW and ACE. In hypertensive rats, VGAW significantly reduced blood pressure at 12.5, 25, and 50 mg/kg. These findings highlight Douchi as a source of ACE inhibitory peptides and suggest VGAW as a promising functional food ingredient.

Ultra-high-depth macrogenomic sequencing revealed differences in microbial composition and function between high temperature and medium-high temperature Daqu

Complex microorganisms in Daqu of different temperatures play a vital role in the taste, flavor and quality of Baijiu during fermentation. However, understanding the functional diversity of the whole microbial community between the Daqus of two different temperatures (high temperature Daqu, HD and medium-high temperature Daqu, MD) remains a major challenge. Here, a systematic study of the microbial diversity, functions as well as physiological and biochemical indexes of Daqu are described. The results revealed that the Daqu exhibited unique characteristics. In particular, the diversity of microorganisms in HD and MD was high, with 44 species including 14 novel species (Sphingomonas sp. is the main novel species) detected in all samples. Their profiles of carbohydrate-active enzymes and specific functional components supported the fact that these species were involved in flavor formation. The Daqu microbiome consisted of a high proportion of phage, providing evidence of phage infection/genome integration and horizontal gene transfer from phage to bacteria. Such processes would also regulate Daqu microbiomes and thus flavor quality. These results enrich current knowledge of Daqu and can be used to promote the development of Baijiu fermentation technology.

Research progress on the fibrinolytic enzymes produced from traditional fermented foods

Cardiovascular diseases (CVDs) are a global health problem and leading cause of death worldwide. Thrombus formation, one of the CVDs, is essentially the formation of fibrin clots. The existing thrombolytic agents have the disadvantages of high price, short half-life, and high bleeding risk; hence, there is an urgent need to find the alternative thrombolytic agents. In recent years, traditional fermented foods have been widely investigated for their outstanding effects in the prevention and treatment of thrombus formation. In this review, we have focused on fibrinolytic enzymes produced by microorganisms during the fermentation of traditional fermented foods and their potential use for treating CVDs. First, we discussed about the sources of fibrinolytic enzymes and microbial strains that produce those enzymes followed by the optimization of fermentation process, purification, and physicochemical properties of fibrinolytic enzymes. Finally, we have summarized the thrombolytic effects of fibrinolytic enzymes in humans and mice. Fibrinolytic enzymes produced by microorganisms during the fermentation of traditional fermented foods not only lyse thrombi but also acts as anti-atherosclerotic, anti-hyperlipidemia, and neuroprotection agents. Therefore, fibrinolytic enzymes from traditional fermented foods have great potential for the prevention and treatment of CVDs.

Quality evaluation of Sojae Semen Praeparatum by HPLC combined with HS-GC-MS

Sojae Semen Praeparatum is a popular fermented legume product in China, with a delicious flavour and health benefits. However, the quality control methods for Sojae Semen Praeparatum are now incomplete, and there are no standards for defining its degree of fermentation. In this study, we introduced colour, acid value, ethanol-soluble extractives and six flavonoid components' content to evaluate the quality of Sojae Semen Praeparatum comprehensively. Multiple linear regression was used to streamline the 11 evaluation indicators to 4 and confirm the evaluating feasibility of the four indicators. The degree of fermentation and odour of Sojae Semen Praeparatum were analyzed on headspace-gas chromatography-mass, and two types of odours, 'pungent' and 'unpleasant', could distinguish over-fermented Sojae Semen Praeparatum. Our research developed fermentation specifications and quality standards for Sojae Semen Praeparatum.

Effects of selected Bacillus strains on the biogenic amines, bioactive ingredients and antioxidant capacity of shuidouchi

The control of biogenic amines (BAs) is crucial to guarantee the safety of fermented soybean products. In this study, the BAs composition of eleven shuidouchi samples was analyzed, and the BAs degradation strains were selected from shuidouchi samples with a low BAs content. Then the influences of screened BAs degradation strains on BAs, total phenolics (TP), total flavonoids (TF), isoflavones and the antioxidant ability of fermented shuidouchi were evaluated. Results showed that the total BAs content of all shuidouchi samples was within the safe range, while the GZXQ, GZQY and GZMX samples had higher levels of tyramine. Meanwhile, 109 strains were isolated from the YNLJ, GZLG, GZMZ, GZDY, and YNHY sample. Bacillus tropicus A11, Bacillus siamensis D11, Bacillus subtilis T2, and B. subtilis U2 with higher BAs degradation capacity and lower BAs production ability were selected to ferment shuidouchi. These four Bacillus strains could effectively control the BAs concentration of fermented shuidouchi, especially B. tropicus A11 and B. siamensis D11. Furthermore, compared to naturally fermented shuidouchi, higher levels of antioxidant ability, TP, TF, daidzein, glyciein, and genistein were found in the shuidouchi fermented with selected strains. These findings demonstrated that these screened strains could be applied as potential candidates for the production of high quality shuidouchi.

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.

Bacterial communities in home-made Doushen with and without chili pepper

Doushen is a traditional Chinese fermented soybean product prepared with sterilizated soybeans under open conditions. However, little is known on the bacterial community and their influence on the flavor of Doushen. In the present study, Doushen samples with and without chili pepper were collected to reveal the bacterial community and assess a correlation between bacterial community and VFCs in the two kinds of Doushen samples. We identified four phyla and 97 bacterial genera in the two kinds of Doushen samples. In addition, a total of 17 significantly different OTUs were detected by LEfSe (Line Discriminant Analysis (LDA) Effect Size). Results of Principal coordinates analysis (PCoA), unweighted pair-group method (UPGMA) and functional and phenotypes prediction showed that bacterial communities in the two kinds of Doushen were significantly different. Spearman correlation analysis showed that all the dominant genera, except Clostridium Sensu stricto 1, were significantly correlated with the characteristic VFCs. This study provides a theoretical basis for improving the flavour quality of traditional homemade Doushen.

Novel green soybean shuidouchi fermented by Bacillus velezensis with multibioactivities

Soybeans are usually fermented by Bacillus subtilis to produce shuidouchi, which is a traditional fermentation soybean product in China. In the study, green soybeans were fermented by Bacillus velezensis to make a novel green soybean shuidouchi with multibioactivities. The processing conditions were optimized as follows: initial moisture content 75%, inoculum concentration 7 log CFU/g, and incubation time 24 h for prefermentation; water addition 50%, salt addition 6%, temperature 45°C, 3 days for postfermentation. The fermented green soybean shuidouchi (FGSS) showed 234.8 FU/g dry weight (DW) for the fibrinolytic activity and IC50 of 0.33 mg/ml for the anticoagulant activity. FGSS had higher contents of chemical components including 3.6 mg rutin (RE)/g DW of total flavonoids, 8.2 mg gallic acid (GAE)/g DW of total phenolics, 63.7 mg/g DW of reducing sugars, and 163.8 mg/g DW of peptides than the unfermented green soybean shuidouchi (UGSS). Moreover, it exhibited high antioxidant activities of 29.8, 85.1 μmol trolox equivalent (TE)/g DW, and 12.8 μmol Fe2+/g DW through 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS), and ferric reducing antioxidant power (FRAP) experiments. Thus, a novel green soybean shuidouchi fermented by B. velezensis owing to multibioactivities can provide a theoretical basis for the further development of functional shuidouchi.