Characterization of the Key Aroma-Active Compounds in Yongchuan Douchi (Fermented Soybean) by Application of the Sensomics Approach

Volatile flavor profiles of douchis from different origins and varieties based on GC-IMS and GC-O-QTOF/MS analysis

The present study comprehensively characterized the flavor differences between different varieties of douchis from different origins using headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) coupled with gas chromatography-olfactometry-quadrupole time-of-flight mass spectrometry (GC-O-QTOF/MS). A total of 91 volatile organic compounds (VOCs) were identified using HS-GC-IMS and 70 VOCs were identified using GC-O-QTOF/MS, mainly including acids, aldehydes, esters and alcohols. Additionally, 23 key aroma-presenting compounds were screened in five douchi species using relative odor activity value (ROAV) and the aroma compounds that contributed the most to the aroma varied among the five douchi species. Comparative analysis of the GC-IMS and GC-O-QTOF/ MS results yielded 13 VOCs that were detected by both techniques. Nonanal, hexanal, eucalyptol, 1-octen-3-ol, isoamyl acetate, and 2-pentylfuran were identified as key VOCs in the douchi species using both methods. These findings will provide deeper insights for exploring flavor differences in douchi from different geographic sources.

Characterization and correlations of dominant microorganisms and volatile compounds in fermentation process of Yangjiang douchi

BACKGROUND

Yangjiang douchi (YD) is a traditional fermented soybean product, which is popular in Chinese cuisine for its unique flavor. However, due to its high salt content and unstable flavor, its competitiveness in the international market is gradually weakening. Microorganisms have a key role in the production process of YD because it is a fermented food but the effect of microorganisms on the volatile compounds of YD is also not currently clear.

RESULTS

In this paper, aroma compounds and microbial diversity in different fermentation stages of YD were analyzed using gas chromatography-mass spectrometry/olfactometry (GC-MS/O) and IlluminaMiseq system sequencing. A total of 78 aroma-active compounds were detected throughout the fermentation process and they influenced the formation of flavor in YD. Fungi flora were relatively single in YD, and bacteria were rich and varied. A total of 418 species of bacteria were present during fermentation, with unclassified_Staphylococcus, Staphylococcus_kloosii, and Bacillus_velezensis_Bacillus predominating. There were 25 species of fungi at the species level, and Aspergillus minisclerotigenes (OTU 4) played a dominant role in the whole fermentation process.

CONCLUSION

Staphylococcus and Bacillus in the bacterial genus were strongly correlated with most flavor compounds detected, and A. minisclerotigenes in the fungi were more relevant to flavor compounds. This research provides a theoretical basis for the enhancement of the flavor of traditional fermented douchi in China. © 2024 Society of Chemical Industry.

Insight into the chemical compositions of Anhua dark teas derived from identical tea materials: A multi-omics, electronic sensory, and microbial sequencing analysis

Anhua dark teas (DTs), including Tianjian tea, Qianliang tea, Hei brick tea, and Fu brick tea, are unique fermented teas from China's Anhua County; yet their chemical composition differences remain unclear. Herein, metabolomics, volatolomics, and electronic sensory assessments were employed to analyze and compare chemical compositions and sensory characteristics of five types of Anhua DTs. All of these teas were derived from identical tea materials. Chemical compositions differed significantly among Anhua DTs, with Tianjian tea remarkable. Long-lasting fermentation and complex processing methods led to transformation of multiple compounds, particularly catechins. Eighteen volatile compounds with OVA > 1 were key aroma contributors in Anhua DTs. Internal transcribed spacer and 16S ribosomal DNA sequencing showed that Eurotium, Pseudomonas, and Bacillus are dominant microorganisms in Anhua DTs. Furthermore, this study unveiled notable differences in chemical compositions between Anhua DTs and five other traditional types of tea. This research enhances our understanding of Anhua DTs processing.

Impact of aroma-enhancing microorganisms on aroma attributes of industrial Douchi: An integrated analysis using E-nose, GC-IMS, GC-MS, and descriptive sensory evaluation

In order to enhance the aromatic profile of industrial Douchi, a comprehensive investigation was undertaken to assess the impact of aroma-enhancing microorganisms on the sensory attributes of Douchi. This evaluation utilized a combination of analytical techniques, including electronic nose analysis, gas chromatography-ion mobility spectrometry (GC-IMS), gas chromatography-mass spectrometry (GC-MS), and descriptive sensory analysis (DA). Both GC-IMS and GC-MS revealed significant changes in the volatile composition of Douchi following the addition of aroma-enhancing microorganisms (p < 0.05). Partial least squares-discriminant analysis (PLS-DA) identified benzaldehyde, benzene acetaldehyde, 3-octanone, and ethyl 2-methylbutyrate as significant differentiating volatile compounds. Additionally, compared to the control group, the sensory attributes of sourness in Douchi were significantly reduced (p < 0.001), while the attributes of wine-like and sweetness were notably enhanced (p < 0.05) when the ratio of G. candidum to C. versatilis was 1:1 (GCC group). By calculating the odor-activity values (OAVs) of key volatiles, it can be hypothesized that this aroma improvement of Douchi may be attributed to an increase in the typical volatiles (3-methyl-1-butanol, 1-octen-3-ol, 3-octanol, and 3-octanone) and ethyl 2-methylbutanoate with high OAVs (2340849.64 ∼ 16695327.86), as well as to decreases in the musty acetophenone. In conclusion, the aroma profile of Douchi was significantly enhanced when G. candidum and C. versatilis were added at a ratio of 1:1. This study provides valuable insights into the development of aroma enhancers for improving the sensory profile of Douchi.

Characterization of key aroma-active compounds in different types of Douchi based on molecular sensory science approaches

To attain the differences in the flavor profile of Douchi, the key aroma-active compounds of three types of Douchi were investigated. The "Sauce-like", "Smoky", "Nutty", "Roast", "Caramel", and "Flower" of Douchi were favored by customers. Further, a total of 179 volatile compounds were identified using HS-SPME-GC-MS, and 29 aroma compounds were detected using GC-O-MS. Based on the quantification, 9, 13, and 10 compounds were regarded as aroma-active compounds in Yangjiang Douchi (YJ), Pingjiang Douchi (PJ), and Liuyang Douchi (LY), respectively. Moreover, the mixture of these aroma-active compounds successfully simulated the main aromas of PJ, LY, and YJ. And omission experiments confirmed that guaiacol was the key aroma compound for LY, benzene acetaldehyde, dimethyl trisulfide, and 2-acetyl pyrrole were important for YJ, benzene acetaldehyde and 3,5-diethyl-2-methyl pyrazine notably contributed to key aroma of PJ.

Identification of key aroma compounds of faba beans (Vicia faba) and their development during germination - a SENSOMICS approach

Faba beans are a promising source of valuable plant protein. However, their aroma impression is often a hindrance for the use in a broad range of food products. To develop mitigation strategies, a deeper insight into the faba bean aroma is required. Therefore, for the first time, the SENSOMICS concept was applied. First, 52 aroma active compounds in raw and malted faba beans were identified and semi-quantitatively preselected by aroma extract dilution analysis. Afterwards, the aroma compounds were quantified, odor activity values were calculated, and the 17 prominent odors were selected and used in the reconstitution of the faba bean aroma. Seven statistically significant key aroma compounds 3-methylbutanoic acid, (E)-non-2-enal, hexanal, methional, 3-methylbutanal, sotolon, and 2-methylbutan-1-ol were identified in omission experiments. Finally, their development upon malting was studied. To conclude, by knowing the key aroma compounds, specific mitigation strategies can be developed, which facilitates the broader use of faba beans.

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.

Identification of novel α-glucosidase and ACE inhibitory peptides from Douchi using peptidomics approach and molecular docking

In this study, the effect of Douchi extract (DWE) on α-glucosidase and angiotensin-converting enzymes (ACE) were investigated, and several novel peptides with inhibitory activity against α-glucosidase and ACE were identified using peptidomics approach based on UPLC-MS/MS. The average inhibition rates of DWE on α-glucosidase and ACE were 73.75-78.10% and 4.56-27.07%, respectively. In the DWE, a total of 710 peptides were detected. Two novel peptides with potential inhibitory activity against α-glucosidase were identified using the correlation analysis, database alignment and molecular docking methods. They were DVFRAIPSEVL and DRPSINGLAGAN, with the IC50 values of 0.121 and 0.128 mg/mL, respectively. Also, four novel peptides with potential inhibitory activity against ACE were identified: PSSPFTDLWD, EEQDERQFPF, PVPVPVQQAFPF and PSSPFTDL, with IC50 values of 1.388, 0.041, 0.761 and 0.097 mg/mL, respectively. These results indicated that combining peptidomics and molecular docking is an effective alternative strategy for rapidly screening numbers of novel bioactive peptides from foods.

Characterization of Key Odorants in Lingtou Dancong Oolong Tea and Their Differences Induced by Environmental Conditions from Different Altitudes

Lingtou Dancong oolong tea is a famous Chinese oolong tea due to its special honey-like aroma. However, little is known about its specific aroma profile and key contributors. Furthermore, whether the aroma characteristics of Lingtou Dancong oolong tea are affected by the environmental conditions at different altitudes is unknown. In this study, the aromas in Lingtou Dancong oolong tea were extracted and analyzed by stir-bar sorptive extraction (SBSE) combined with gas chromatography-olfactometry (GC-O) and GC-mass spectrometry (GC-MS), and the aroma profiles of tea plants grown at different altitudes were compared. We detected 59 odor compounds in Lingtou Dancong oolong tea. Eight compounds with honey and floral odors were identified as key components on the basis of GC-O, GC-MS, odor activity value, and flavor dilution analyses. Differences in the contents of precursor geranyl diphosphate and transcript levels of structural genes were found to be responsible for the differential accumulation of linalool and hotrienol among plants grown at different altitudes. This is the first report on the aroma characteristics and key contributors of Lingtou Dancong oolong tea and their differences, as affected by altitude. These results provide details of the chemical basis of the aroma quality of Lingtou Dancong oolong tea.

Role of Sulfur Compounds in Vegetable and Mushroom Aroma

At the base of the food pyramid is vegetables, which should be consumed most often of all food products, especially in raw and unprocessed form. Vegetables and mushrooms are rich sources of bioactive compounds that can fulfill various functions in plants, starting from protection against herbivores and being natural insecticides to pro-health functions in human nutrition. Many of these compounds contain sulfur in their structure. From the point of view of food producers, it is extremely important to know that some of them have flavor properties. Volatile sulfur compounds are often potent odorants, and in many vegetables, belonging mainly to Brassicaeae and Allium (Amaryllidaceae), sulfur compounds determine their specific flavor. Interestingly, some of the pathways that form volatile sulfur compounds in vegetables are also found in selected edible mushrooms. The most important odor-active organosulfur compounds can be divided into isothiocyanates, nitriles, epithionitriles, thiols, sulfides, and polysulfides, as well as others, such as sulfur containing carbonyl compounds and esters, R-L-cysteine sulfoxides, and finally heterocyclic sulfur compounds found in shiitake mushrooms or truffles. This review paper summarizes their precursors and biosynthesis, as well as their sensory properties and changes in selected technological processes.

The Enhancement of the Perception of Saltiness by Odorants Selected from Chinese Douchi in Salt Solution

Douchi is a traditional fermented soya bean product that is popular for its smelled saltiness and unique flavor. In order to look for the relationship between smelled saltiness of volatiles and their saltiness-enhancing properties, gas chromatography-olfactometry/associated taste was used to select odorants associated with saltiness in Yongchuan Douchi. The enhancement effects of saltiness intensity by selected odorants were further verified by sensory evaluation analyses of 2-alternative forced-choice and odor-induced saltiness enhancement in a follow-up study. A total of 14 odorant compounds were selected for their odor-associated saltiness perception. The compounds of 2-ethyl-3,5-dimethyl pyrazine, 2,5-dimethyl pyrazine, dimethyl trisulfide, 3-(methylthio) propanol and 3-(methylthio) propanal could significantly enhance saltiness perception in salt solution. Among them, 2-ethyl-3,5-dimethyl pyrazine was reported for the first time to be able to improve the salty taste. The study suggested that salty food is an ideal material for selecting saltiness-enhancing odorants, which could provide more direct theoretical support for salt reduction in the food industry.

Characterization of the Key Aroma Constituents in Fried Tilapia through the Sensorics Concept

The object of this study was tilapia fish that were fried in soybean oil. Volatile compounds were extracted from the fish by ASE-HVE and were studied by GC-O-MS and the AEDA analysis method. A total of 30 aroma compounds were initially determined, and these compounds contribute to the aroma of fried tilapias. The key volatile compounds in fried tilapia were quantitatively analyzed by GC-MS, and the volatile compounds in soybean-fried tilapia were studied by flavor recombination and deletion experiments. Trimethylamine, hexanal, 2,3-dimethylpyrazine, dimethyl trisulfide, trans-2-octenal, 2,3-dimethyl-5-ethylpyrazine, (E)-2-nonenal, 2-propyl-pyridine, and (E,E)-2,4-decadienal were finally determined to be the key volatile compounds in soybean-fried tilapia.