Biochemical, textural and microstructural changes in whole-soya bean cotyledon sufu during fermentation

Investigation into the potential mechanism of Bacillus amyloliquefaciens in the fermentation of broad bean paste by metabolomics and transcriptomics

Pixian broad bean paste is a renowned fermented seasoning. The fermentation of broad bean is the most important process of Pixian broad bean paste. To enhance the flavor of tank-fermented broad bean paste, salt-tolerant Bacillus amyloliquefaciens strain was inoculated, resulting in an increase in total amount of volatile compounds, potentially leading to different flavor characteristics. To investigate the fermentation mechanism, monoculture simulated fermentation systems were designed. Metabolomics and transcriptomics were used to explore Bacillus amyloliquefaciens' transcriptional response to salt stress and potential aroma production mechanisms. The results highlighted different metabolite profiles under salt stress, and the crucial roles of energy metabolism, amino acid metabolism, reaction system, transportation system in Bacillus amyloliquefaciens' hypersaline stress response. This study provides a scientific basis for the industrial application of Bacillus amyloliquefaciens and new insights into addressing the challenges of poor flavor quality in tank fermentation products.

Evaluation of Sufu Fermented Using Mucor racemosus M2: Biochemical, Textural, Structural and Microbiological Properties

The quality and safety of sufu fermented using Mucor racemosa M2 was studied and compared with naturally fermented sufu. After 90 days post-fermentation, both naturally fermented and inoculated fermented sufu reached the maturity standard of sufu, and the degree of protein hydrolysis of natural sufu (WP/TP: 34% ± 1%; AAN/TN: 33% ± 1%) was slightly higher than that of the inoculated sufu (WP/TP: 28.2% ± 0.4%; AAN/TN: 27% ± 1%). The hardness and adhesiveness of inoculated sufu (Hadness: 1063 g ± 211 g; Adhesiveness: -80 g ± 47 g) were significantly greater than those of natural sufu (Hadness: 790 g ± 57 g; Adhesiveness: -23 g ± 28 g), and the internal structure of natural sufu was denser and more uniform than that of inoculated sufu. A total of 50 aroma compounds were detected in natural and inoculated sufu. The total number of bacterial colonies in naturally fermented sufu was significantly higher than that in inoculated sufu, and the pathogenic bacteria in both types of fermented sufu were lower than the limit of pathogenic bacteria required in fermented soybean products. The content of biogenic amines in sufu was determined by high performance liquid chromatography (HPLC), and the results showed that the content of biogenic amines (Putrescine, Cadaverine, Histamine, Tyramine, etc.) in naturally fermented sufu was significantly higher than that in inoculated fermented sufu. Especially the histamine content, after 90 days of fermentation, was found to be 64.95 ± 4.55 for inoculated fertilization and 44.24 ± 0.71 for natural fertilization. Overall, the quality of inoculated sufu was somewhat better than that of natural sufu, and the M2 strain can be used to ferment sufu.

Microbiology, flavor formation, and bioactivity of fermented soybean curd (furu): A review

Soybeans are an important plant-based food but its beany flavor and anti-nutritional factors limit its consumption. Fermentation is an effective way to improve its flavor and nutrition. Furu is a popular fermented soybean curd and mainly manufactured in Asia, which has been consumed for thousands of years as an appetizer because of its attractive flavors. This review first classifies furu products on the basis of various factors; then, the microorganisms involved in its fermentation and their various functions are discussed. The mechanisms for the formation of aroma and taste compounds during fermentation are also discussed; and the microbial metabolites and their bioactivities are analyzed. Finally, future prospects and challenges are introduced and further research is proposed. This information is needed to protect the regional characteristics of furu and to regulate its consistent quality. The current information suggests that more in vivo experiments and further clinical trials are needed to confirm its safety and the microbial community needs to be optimized and standardized for each type of furu to improve the production process.

HS-SPME-GC × GC/MS combined with multivariate statistics analysis to investigate the flavor formation mechanism of tank-fermented broad bean paste

With the advancement of industrialization, tank fermentation technology is promising for Pixian broad bean paste. This study identified and analyzed the general physicochemical factors and volatile metabolites of fermented broad beans in a thermostatic fermenter. Headspace solid-phase microextraction (HS-SPME)-two-dimensional gas chromatography-mass spectrometry (GC × GC-MS) was applied to detect the volatile compounds in fermented broad beans, while metabolomics was used to explore their physicochemical characteristics and analyze the possible metabolic mechanism. A total of 184 different metabolites were detected, including 36 alcohols, 29 aldehydes, 26 esters, 21 ketones, 14 acids, 14 aromatic compounds, ten heterocycles, nine phenols, nine organonitrogen compounds, seven hydrocarbons, two ethers, and seven other types, which were annotated to various branch metabolic pathways of carbohydrate and amino acid metabolism. This study provides references for subsequent functional microorganism mining to improve the quality of the tank-fermented broad beans and upgrade the Pixian broad bean paste industry.

Fermentation characteristics of Pixian broad bean paste in closed system of gradient steady-state temperature field

A closed system of gradient steady-state temperature field (GSTF) was constructed to ferment Pixian broad bean paste (PBP). The contents of physicochemical factors and organic acids in the fermentation under GSTF (FG) were closer to those in the traditional fermentation (TF). The taste intensities of 8 free amino acids in the FG were higher than those in the constant temperature fermentation (CTF), but 14 in the TF showed the highest among the processes of FG, CTF and TF. The FG product had the most volatiles with 87, and its flavor properties were more stable. The FG produced great effects on the microbe evolutions especially improved the fungal diversity. Bacillus were identified as the core microbes in the FG while the roles of Staphylococcus, Lactobacillus and Pantoea were strengthened. The results indicated that the fermentation characteristics in the FG had been further improved compared with the CTF.

The fermentation-time dependent proteolysis profile and peptidomic analysis of fermented soybean curd

The proteolysis and peptidomic profiles and potential bioactivities of fermented soybean curd (furu) during fermentation were studied. The degree of protein hydrolysis (DH) and peptide content significantly increased with fermentation time (p < 0.05), and reached the highest levels after ripening for 90 days. The variety and abundance of bioactive peptides in furu samples were fermentation-time dependent, and furu ripening for 30 and 90 days showed the highest similarity. An ACE-inhibitor and antioxidant peptides were the two main bioactive peptide components, and their abundance and bioactivities exhibited a significant increase with fermentation and reached the maximum levels at 90 days. All these results indicated that microbial fermentation is an effective way to obtain bioactive peptides with soy-based fermented products, and their effects on health might be explored in future studies. PRACTICAL APPLICATION: This work indicated that microbial fermentation is an effective way to obtain bioactive peptides with soy-based fermented products.

High-Throughput Sequencing and Metabolomics Reveal Differences in Bacterial Diversity and Metabolites Between Red and White Sufu

Sufu is a traditional fermented soybean food produced in China. However, the microbial compositions and metabolites of different types of sufu have not been studied in detail. Accordingly, in this study, we evaluated the differences in bacterial communities and metabolites between commercial red sufu (RS) and white sufu (WS). Principal coordinate analysis and the unweighted pair group method with arithmetic means analysis of 16S rRNA genes revealed that the bacterial community structures of RS and WS differed dramatically. At the phylum level, the relative abundances of Firmicutes and Proteobacteria were significantly different between RS and WS (P < 0.01). Moreover, the abundances of Lactococcus and Tetragenococcus genera were significantly different between RS and WS (P < 0.01). Among metabolites, most free amino acids, few of volatile flavor compounds, and some organic acids showed significant differences between RS and WS (P < 0.05). Additionally, correlations between microbiota and metabolites were determined. Aggregated boosted tree analysis showed that formic acid had the highest relative influence (20.27%) on bacterial community diversity (Chao 1), following by arginine (5.38%), propanol (4.57%), oxalic acid (4.46%), and hexanol (4.43%). Moreover, Streptococcaceae and Moraxellaceae had the highest relative influence on the concentration of formic acid (12.84% and 8.75%, respectively). The profiles obtained in this study improve our understanding of the relationships between bacterial flora and metabolites in different types of sufu. These findings may help us interpret the roles of bacterial communities in the flavor and characteristics of sufu.

High-throughput sequencing approach to characterize dynamic changes of the fungal and bacterial communities during the production of sufu, a traditional Chinese fermented soybean food

Red sufu is a traditional food produced by the fermentation of soybean. In this study, sufu samples were periodically collected during the whole fermentation to investigate the dynamic changes of fungal and bacterial communities using high-throughput sequencing technology. The overall process can be divided into pre- and post-fermentation. During post-fermentation, the pH value showed a gradual decrease over time while the amino nitrogen content increased. Trichosporon, Actinomucor and Cryptococcus were the main genera in pre-fermentation while Monascus and Aspergillus were dominant in post-fermentation. This huge shift in fungal composition was caused by process procedure of pouring dressing mixture. However, the bacterial composition was not greatly changed after pouring dressing mixture, the Acinetobacter and Enterobacter were the predominant genera throughout the whole process. Furthermore, Bacillus species were first detected after adding dressing mixture, but declined abruptly to a very low level (0.07%) by the end of the fermentation. Our work demonstrates the dynamic changes of physicochemical properties and microbial composition in every fermentation stage, the knowledge of which could potentially serve as a foundation for improving the safety and quality of sufu in the future.

Effect of microwave sterilization on maturation time and quality of low-salt sufu

The objective of this study was to reduce the microorganism number and salt content in pehtze by microwave sterilization. The maturation time and quality of low-salt sufu were evaluated. The microorganism inactivation rate, moisture content and water activity of the pehtze, which was used for the growth of the starter culture, showed that 4,250 W for 30 s was suitable for the preparation of low-salt sufu. With regard to the physicochemical properties of sufu, 120-day sufu samples obtained by traditional high-salt (14%) fermentation and 75-day sufu samples obtained by low-salt (4%) fermentation met the standard requirements. With regard to the sensory characteristics of sufu, the taste and after taste scores of 75-day low-salt sufu samples were significantly higher than those of 120-day high-salt sufu samples (p < .05).The overall acceptance score of low-salt sufu samples also was higher than that of high-salt sufu samples. The contents of free amino acids and the profiles of typical flavor compounds partly explained the sensory quality and shorter ripening time of sufu manufactured. The total biogenic amine contents were reduced by 46%.

Volatile flavour components, microbiota and their correlations in different sufu, a Chinese fermented soybean food

AIM

To investigate the volatile flavour components (VFCs), microbiota and their correlations of three categories of sufu, a Chinese fermented soybean food.

METHODS AND RESULTS

The VFCs were analyzed by headspace solid-phase micro-extraction (HS-SPME) combined with gas chromatography and mass spectrometry. A total of 141 VFCs were tentatively identified, in which 12 esters, eight aldehydes, five alcohols and nine miscellaneous compounds were recognized as the characteristic VFCs through the relative odour activity value. The complex microbial community was revealed by Illumina MiSeq sequencing. Among the total 202 bacteria and 125 fungi species identified, 16 bacteria and 7 fungi species were revealed as dominant community members. Furthermore, the VFC-microbiota correlation was characterized by Spearman's rank correlation coefficients (ρ). Based on the positive VFC-microbiota correlation, two bacterial species and three fungal species were selected as potential flavour-producing microbiota.

CONCLUSIONS

A variety of VFCs and complicated microbiota were observed in the three categories of sufu. Lactococcus lactis, Sphingobacterium sp., Pichia fermentans, Kodamaea ohmeri and Saccharomyces rouxii were the potential flavour-producing microbiota.

SIGNIFICANCE AND IMPACT OF THE STUDY

The preliminary results would be useful for designing starter cultures to produce sufu with desirable sensory properties, consistent flavour and shorter ripening time. Furthermore, these results will also provide a new insight to improve the flavour quality of traditional fermented soybean food.