Flavor Formation Mechanism Research Articles

Changes of physicochemical and volatile flavor compounds of dry-cured Diqing Tibetan pig hams during fermentation

This study aimed to explore the flavor formation mechanism of Diqing Tibetan pig hams by investigating changes of their physicochemical and volatile flavor compounds during fermentation (0, 30, 90, 180, 360, and 540d) using amino acid analyzer , texture profile analysis, and gas chromatography-ion mobility spectroscopy (GC-IMS). During fermentation, the hams significantly decreased in moisture and centrifugal loss, while increased in chewiness, hardness, and proteolysis index, with their free amino acids content reaching the maximum at 360d and significantly decreasing at 540d. GC-IMS identified 78 volatile organic compounds, with the highest total content of alcohols and aldehydes at 180d, ketones and heterocycles at 360d, and esters at 540d. PLS-DA screened 24 volatile flavor markers, with aldehyde (2-methyl-2-propenal), ketone (2-heptanone-D), alcohol (3-methylbutanol-D), ester (ethyl3-methylbutanoate-M), and heterocyclic substances (2,3-dimethylpyrazine-M) as the main VFMs at 360d. The unique flavor of 540d Diqing Tibetan pig hams was attributed to their higher content of 3-methyl-2-butenal, 3-(methylthio) propanal, ethyl caproate and 2-butanone. These findings provide a scientific basis for the flavor formation mechanism of hams which favoring the further development processing strategies for Diqing Tibetan pig.

Integrated volatolomics and lipidomics analysis reveal the characteristic flavor formation mechanism in steamed large yellow croaker (Pseudosciaena crocea)

The internal relationship between lipid composition and characteristic flavor in the steamed large yellow croaker (LYC) was investigated using volatolomics, lipidomics, and electronic sensory systems. Compared to fresh LYC, the concentrations of five key volatile flavor compounds detected after steaming exceeded human sensory thresholds. Notably, nonanal, hexanal, and 1-octen-3-ol significantly influenced the flavor of the cooked meat. Steaming at 70 °C enhanced the LYC flavor profile, with the strongest flavor observed at 80 °C. The content of three key volatile flavor compounds peaked, especially hexanal, which reached 54.55 μg/kg. Phosphatidylcholines, triacylglycerols, and fatty acids were closely associated with the volatile flavor profile of steamed LYC. The oxidation of FA 22:6 was identified as a crucial source of flavor in LYC. This study aimed to improve consumer experience by exploring the nutritional quality and flavor formation mechanisms in the thermal processing of LYC.

Microbiomics and metabolomics insights into the microbial regulation on the formation of flavor components in the traditional fermentation process of Chinese Hongqu aged vinegar

This study aimed to investigate microbial succession and metabolic dynamics during the traditional fermentation of Hongqu aged vinegar, and explore the core functional microbes closely related to the formation of flavor components. Microbiome analysis demonstrated that Lactobacillus, Acetobacter, Bacillus, Enterobacter, Lactococcus, Leuconostoc and Weissella were the predominant bacterial genera, while Aspergillus piperis, Aspergillus oryzae, Monascus purpureus, Candida athensensis, C. xylopsoci, Penicillium ochrosalmoneum and Simplicillium aogashimaense were the predominant fungal species. Correlation analysis revealed that Acetobacter was positively correlated with the production of tetramethylpyrazine, acetoin and acetic acid, Lactococcus showed positive correlation with the production of 2-nonanone, 2-heptanone, ethyl caprylate, ethyl caprate, 1-hexanol, 1-octanol and 1-octen-3-ol, C. xylopsoci and C. rugosa were positively associated with the production of diethyl malonate, 2,3-butanediyl diacetate, acetoin, benzaldehyde and tetramethylpyrazine. Correspondingly, non-volatile metabolites were also detected through ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. A variety of amino acids and functional dipeptides were identified during the traditional brewing of Hongqu aged vinegar. Correlation analysis revealed that Lactobacillus was significantly associated with DL-lactate, indolelactic acid, D-(+)-3-phenyllactic acid, pimelic acid, pregabalin and 3-aminobutanoic acid. This study is useful for understanding flavor formation mechanism and developing effective strategies for the suitable strains selection to improve the flavor quality of Hongqu aged vinegar.

Analysis of the microbial community structure and characteristic flavor of traditional fermented bean paste.

Bean paste is a traditional Chinese fermented condiment, which is loved by consumers for its pleasant flavor and nutritional properties. However, the microbial communities and related flavor compounds in bean paste remain unclear. We studied the correlation between the core functional microorganisms and flavor compounds in bean paste samples at different fermentation stages. Bacterial and fungal communities changed significantly during fermentation. The results indicated that the dominant bacterial genera were Staphylococcus, Lactococcus, and Bacillus. The dominant fungi were Aspergillus and Lichtheimia. During the early and late stages of bean paste fermentation, alcohols, hydrocarbons, esters, and phenols were the main flavor compounds detected. The types and proportions of alcohols and esters in the bean pastes fermented for different durations were similar, whereas the relative contents of phenols and hydrocarbons were higher in the later stages of fermentation. Correlation analysis revealed that core functional microorganisms played a key role in the fermentation process, and the potential correlation between bacterial genera and flavors was stronger than that of fungal genera. Staphylococcus abundance was significantly correlated with the flavor levels of ethyl oleate, ç-pinene, diallyl disulfide, á-myrcene, D-limonene, and tetradecanoic acid, ethyl ester. The abundance of Aspergillus and Lichtheimia was significantly correlated with the flavor levels of á-myrcene, ç-pinene, and DL-3-phenyllactic acid. This study explored the relationship between microorganisms and flavor compounds in bean paste to deepen our understanding of the mechanism of flavor formation for bean paste.

Flavoromics Analysis of Passion Fruit-Roasted Chicken.

Currently, research on the flavor components and their dynamic changes in roasted chicken with a special flavor is rare. In this study, a passion fruit-roasted chicken was prepared, its characteristic flavor components were profiled by flavoromics, and their evolution patterns and precursors were determined. The results showed that the characteristic flavor component with the highest contribution rate was ethyl butyrate (50.44%). In particular, some unique flavor compounds were identified compared with other roasted chicken products available. The main volatile flavor components in all stages of processing were alcohols, esters, and hydrocarbons, 15 to 30 min of roasting is an important stage for establishing the aroma system, and at the end, hydrocarbons were the main volatile compounds. During the 30-day storage period, the characteristic flavor components included ethyl butyrate, ethyl maltol, β-caryophyllene, and guaiacene. In conclusion, passion fruit-roasted chicken contained many characteristic flavor components, which were mainly formed within 15 to 30 min of roasting and were basically stable during the 30-day storage period. In a word, this work prepared a novel roasted chicken and revealed its mechanism of flavor formation at different baking stages and storage periods, which provided references for industrial production.

Comprehensive insights into the mechanism of flavor formation driven via inoculation with mixed starter cultures in dry-fermented tilapia sausages: Integration of macrogenomics, volatilomics, and lipidomics

To investigate the mechanisms of flavor formation in dry-fermented tilapia sausages, the volatiles, bacterial community, and lipid composition during fermentation were analyzed using gas chromatography-ion mobility spectrometry, 16S high throughput sequencing, and ultra-performance liquid chromatography-mass spectrometer. Pediococcus pentosaceus, Staphylococcus xylosus, and Staphylococcus carnosus became dominant bacteria during the fermentation. A total of 66 volatiles and 293 lipids (48 differential lipids) were identified. PC and PE content decreased. Aldehyde and 1-octen-3-ol content decreased. Most esters and ketones content increased during fermentation. Six metabolic pathways associated with differential lipids were identified by enrichment analysis. Glycerophospholipid metabolism was the main metabolic pathway. Correlation analysis revealed that PC and PE were precursors for volatiles, including PC 16:0/18:2 and PE 18:0/22:6. The dominant bacteria facilitate the hydrolysis of PC and PE, leading to the formation of esters and ketones. This study provides a theoretical basis for the targeted regulation of fermented sausage flavors.

Flavor formation by amino acid catabolism in low-salt sufu paste, a Chinese fermented soybean food

In this study, the low-salt sufu paste was fermented enhanced by a mixed starter (Pichia fermentans, Kodamaea ohmeri and Lactococcus lactis subsp.) and α-ketoglutarate. Multispecies microbial community is crucial for the flavor formation of sufu paste during post-ripening. Consequently, the primary biochemical pathways of the flavor formation were analyzed using a metagenomic approach in conjunction with gas chromatography mass spectrometry (GC-MS). After post-ripening for 15 d, a total of 86 volatile flavor compounds (VFCs) were tentatively identified, in which 6 compounds were recognized as the main characteristic VFCs. The metagenomics revealed that Actinomucor elegans, Lactobacillus fermentum, Lactococcus lactis subsp., Pichia fermentans, Lactobacillus delbrueckii and Propionibacterium acidipropionici were the dominant species. According to the functional annotation, amino acid metabolisms were identified as the predominant pathways for flavor formation. Among them, aromatic amino acids metabolisms accounted for the highest proportion, up to 41.3%. The VFCs formation pathways mainly involved transamination, decarboxylation, dehydrogenation and oxidation reaction. The amino acid transamination was proposed as a crucial step in VFCs formation, and the corresponding aminotransferases were the key rate-limiting enzymes. These findings have implications for enhancing the flavor quality of sufu paste and elucidating the mechanism of flavor formation in traditional soybean fermented food.

Comprehensive analysis of spatial heterogeneity reveals the important role of the upper-layer fermented grains in the fermentation and flavor formation of Qingxiangxing baijiu

Different spatial positions lead to inconsistent fermentation effects and flavors, however, the spatial heterogeneity of Qingxiangxing (QXX) Baijiu remains unknown. We investigated the microbes, flavors, and physicochemical properties of different layers in fermented grains of QXX Baijiu using Illumina HiSeq sequencing, two-dimensional gas chromatography–mass spectrometry (GC × GC–MS) and ultra-high performance liquid chromatography-mass (UHPLC-MS). A total of 79 volatiles, 1596 metabolites, 50 bacterial genera, and 52 fungal genera were identified. The contents distribution followed the order: upper layer > bottom layer > middle layer. Organic acids and derivatives were the main differential metabolites across the three layers. Starch, pH, and reducing sugar levels increased from the upper to bottom layer. Saccharomyces and Lactobacillus were dominant microbes. Pediococcus, the biomarker of upper layer, showed positive correlations with formic acid, ethyl lactate, acetic acid, ethyl linoleate, and ethyl oleate. These findings deepen our understanding of the fermentation and flavor formation mechanisms of QXX Baijiu.

Effects of electrohydrodynamics on drying characteristics and volatile profiles of goji berry (Lycium barbarum L.)

In this study, the changes in drying characteristics and volatile profiles of goji berries under different AC voltages (14, 18, 22, 26, and 30 kV) were investigated using an electrohydrodynamic (EHD) needle-plate electrode system. The results showed that increasing voltage significantly increased the drying rate, rehydration capacity, and lightness value of goji berry, decreased the drying time and browning degree (BI). The ordered structure in the secondary structure of goji berry proteins increased with increasing voltage. A total of 87 volatile compounds were identified in the dried goji berry under different drying voltages. Alcohols were the main volatile compounds. The short drying time can effectively reduce microbial contamination, resulting in the lowest content of alcohols in the dried goji berry products after drying at 30 kV. These findings reveal the drying characteristics and flavor formation mechanism of goji berries during electrohydrodynamic drying.

Effects of different curing concentrations and drying times on the microbial community structure and metabolites of dried Spanish mackerel

Cured Spanish mackerel has a promising market owing to its nutritious nature as well as ease of transportation and preservation. However, the nutritional and flavor formation mechanism of Spanish mackerel after curing and drying is unclear. To overcome this problem, the effects of different processing conditions on the free amino acid, microbial community, and flavor of Spanish mackerel were explored. Staphylococcus and Cobetia are the main microorganisms in cured mackerel and are closely associated with the formation of their quality. Compared with fresh mackerel, cured mackerel contains increased levels of protein, fat, and chloride, contributing to its distinctive flavor. The contents of free amino acids in the BA64 group were substantially higher than those in other groups, particularly the contents of threonine, glycine, and tyrosine. These findings will contribute to the development of high-quality cured Spanish mackerel products and cured aquatic products.

Identification and validation of core microbes for the formation of the characteristic flavor of fermented oysters (Crassostrea gigas)

Self-fermented oyster homogenates were prepared to investigate core microbes and their correlations with flavor formation mechanisms. Five bacterial and four fungal genera were identified. Correlation analysis showed that Saccharomyces cerevisiae, Kazachstania, and L. pentosus were core species for the flavor of fermented products. Four core microbes were selected for inoculation into homogenates. Twelve key aroma compounds with odor activity values >1 were identified by gas chromatography–mass spectrometry. L. plantarum and S. cerevisiae were beneficial for producing key aroma compounds such as 1-octen-3-ol, (E,Z)-2,6-nonadienal, and heptanal. Fermentation with four microbes resulted in significant increases in contents of Asp, Glu, Lys, inosine monophosphate, and guanosine monophosphate, which provided freshness and sweetness. Fermentation with four microbes resulted in high digestibility, antioxidant abilities, and zinc contents. This study has elucidated the mechanism of flavor formation by microbial action and provides a reference for targeted flavor control in fermented oyster products.

Comprehensive analysis of flavor formation mechanisms in the mechanized preparation Cantonese soy sauce koji using absolute quantitative metabolomics and microbiomics approaches

Based on the widespread application and under-research of mechanized preparation Cantonese soy sauce koji (MP), absolute quantitative approaches were utilized to systematically analyze the flavor formation mechanism in MP. The results indicated that the enzyme activities increased greatly during MP fermentation, and 4 organic acids, 15 amino acids, and 2 volatiles were identified as significantly different flavor actives. The flavor parameters of MP4 were basically identical to those of MP5. Furthermore, microorganisms were dominated by Staphylococcus, Weissella, and Aspergillus in MP, and their biomass demonstrated an increasing trend. A precise enumeration of microorganisms exposed the inaccuracy of relative quantitative data. Concurrently, Staphylococcus and Aspergillus were positively correlated with numerous enzymes and flavor compounds, and targeted strains for enhancing MP quality. The flavor formation network comprises pathways including carbohydrate metabolism, lipid metabolism and oxidation, and protein degradation and amino acid metabolism. In summary, the fermentation period of MP can be substantially shortened without compromising the product quality. These findings lay the groundwork for refining parameters in modern production processes.

Impacts of Aspergillus oryzae 3.042 on the flavor formation pathway in Cantonese soy sauce koji

To investigate the mechanism of flavor formation during the traditional preparation Cantonese soy sauce koji (TP), the changes of microorganisms, physicochemical properties, and flavor compounds in TP were comprehensively and dynamically monitored by absolute quantitative methods. Results demonstrated that inoculating Aspergillus oryzae 3.042 in TP was crucial role in enhancing enzyme activity properties. Absolute quantification of flavor combined with multivariate statistical analysis yielded 5 organic acids, 15 amino acids, and 2 volatiles as significantly different flavors of TP. Amplicon sequencing and RT-qPCR revealed that the dominant genera were Staphylococcus, Weissella, Enterobacter, Lactic streptococci, Lactobacillus, and Aspergillus, which exhibited a increasing trend in TP. Correlation analysis exhibited that Staphylococcus and Aspergillus were the pivotal genera contributing to the enzyme activities and flavor of TP. The flavor formation network involved lipid and protein degradation, carbohydrate metabolism and other pathways. Simultaneously, TP can appropriately increase the fermentation time to improve product quality.

Metatranscriptomics unravel the formation mechanism of key flavors during the natural fermentation of suansun, a Chinese traditional fermented bamboo shoot

Suansun is a naturally fermented vegetable with unique flavor that depends on metabolic activities of microbiota. However, the formation mechanism of the key flavor driven by active microbiota during suansun fermentation is unclear. In this study, metatranscriptomics and metabolomics were used to analyze the key flavor profiles as well as the core functional microorganisms for flavor formation. HS-SPME-GC-MS and UPLC-Q-TOF/MS identified that organic acids, esters, alcohols, aldehydes, phenols and small peptides exert an important influence on the flavor formation of suansun. Based on the metatranscriptomic data, the metabolic network related to the formation of key flavors of suansun was reconstructed. Functional annotation further indicated that 5 genera (including Lactococcus, Enterococcus, Leuconostoc, Lactiplantibacillus and Weissella), which can actively produce enzymes that related to flavor synthesis, were the core functional microorganisms for flavor formation of suansun. These findings contributed to a better understanding of the flavor formation mechanism in suansun and other naturally-fermented foods.

Genomic basis of metabolome-mediated cultivar-specific flavor formation in juice sacs of the pomelo (Citrus grandis (L.) Osbeck) cultivars Shatian and Guanxi honey

Shatian pomelo (Citrus grandis (L.) Osbeck cv. Shatian) (ST) is one of the main cultivars of pomelo, and its flavor, aroma and mastication traits exhibit marked specificity compared to those of another major pomelo cultivar, Guanxi honey pomelo (Citrus grandis (L.) Osbeck cv. Guanxi honey) (BR). As parents, both cultivars generated many offspring cultivars with excellent quality. However, the limited study of pomelo flavor-specific metabolites and their metabolic pathways has hindered the understanding of pomelo flavor diversity. In this work, genome resequencing and metabolome analyses were performed to reveal the differences in cultivar-specific flavor metabolic pathways and cultivar-specificity formation molecular bases in taste flavor, aroma and mastication. A total of 397,056 and 427,885 SNP-InDels were found, with 53.67% and 54.76% of the SNP-InDels located in the gene intervals in ST and BR, respectively. 148 candidate genes distributed in carbohydrate, amino acid, flavonoid, lipid, terpene and lignin metabolism pathways were screened to uncover the molecular basis of flavor, aroma and mastication trait formation biological processes. Overall, revealing the origin of the cultivar-specific flavor of ST and BR may provide novel insight into the pomelo flavor formation mechanism and genetic resources for pomelo genetic breeding.

Identification of characteristic flavor compounds and small molecule metabolites during the ripening process of Nuodeng ham by GC-IMS, GC–MS combined with metabolomics

To investigate effects of metabolites and volatile compounds on the quality of Nuodeng ham, gas chromatography-mass spectrometry (GC–MS), ultra-high performance liquid chromatography-Q exactive orbitrap-mass spectrometry (UHPLC-QE-MS), and gas chromatography-ion transfer spectroscopy (GC-IMS) were used to analyze the differences of free fatty acids, small molecule metabolites and volatile compounds of Nuodeng ham at different ripening stages (the first, second and third year sample). 40 free fatty acids were detected. 757 and 300 metabolites were detected in positive and negative ion modes, respectively. 48 differential metabolites (VIP ≥ 1.5, P < 0.05) might important components affecting flavor differences of Nuodeng ham. Metabolic pathways revealed that fermenting-ripening of ham was associated with 31 metabolic pathways, among, 19 pathways were significant (Impact > 0.01, P < 0.05). 58 volatile compounds were identified, combined with PCA and PLS-DA, 15 flavor markers were screened out. These findings provide a scientific basis for further research on the flavor formation mechanism of Nuodeng ham.

Evolution behavior of volatile components of shiitake mushrooms during infrared-assisted spouted bed drying

The present study aimed to investigate the effect of different drying temperatures and airflow speeds on the number and species of volatile components in infrared-assisted spouted bed dried (IRSBD) Shiitake mushrooms. The dynamics changes in volatile components (determined by HS-SPME-GC-MS) during drying under optimal conditions were also monitored. Results revealed that the maximum number of volatile components (69 species) was observed at a temperature of 55 °C and airflow speed of 8.0 m/s, of which the volatile components in Shiitake mushrooms varied significantly over the drying process at this condition. Fresh Shiitake mushrooms mainly composed of volatile substances such as alcohols, ketones and acids. During the early drying stage (0–40 min), the levels of alcohols and ketones gradually decreased, while the species and levels of aldehydes, esters, and volatile sulfur-containing compounds (VSCs) increased. In the middle stage (40–120 min), levels of alcohols, esters, aldehydes, acids, and alkanes species increased, while the levels of VSCs decreased. For the last stage (120–200 min), the levels of sulfur-containing heterocyclic compounds, aldehydes, esters, acids, pyrazines, and alkanes were all increased. The findings of this study provide insights into the flavor formation mechanism during IRSBD of Shiitake mushrooms and offer a theoretical reference for the production of industrial flavorful dried goods.

Insights into major pigment accumulation and (non)enzymatic degradations and conjugations to characterized flavors during intelligent black tea processing

Intelligently processed black teas (BT) possess premium quality but there is a lack in comprehensive understanding of flavor formation mechanism. In this study, the accumulation of carotenoids, flavonoids, and Maillard products and (non)enzymatic degradations and conjugations to characterized flavors were comprehensively studied. Significant decrease was observed that flava-3-ols were heavily oxidised from > 240 mg·g−1 in fresh leaves (FL) to < 30 mg·g−1, while other 21 flavonoids decreased by < 30% in BT, accompanied by a sweet aftertaste. Carotenes and xanthophylls, significantly accumulated during withering compared to FL (from 641 ± 39.7 μg·g−1 to 728 ± 44.9 μg·g−1) but decreased in BT. Strong correlations were confirmed between the 218 primary metabolites, carotenoids, and flavonoids, and their contributions to BT sweet tastes were elucidated. Furthermore, 45 floral/sweet volatiles with VIP > 1 originating from carotenoids, lipids, and amino acids were screened. An integrated illustration of pigments thermal- and enzymatic-dominated contributions to BT flavour was comprehensively conducted.

Extracellular proteolytic enzyme-mediated amino exposure and β-oxidation drive the raspberry aroma and creamy flavor formation.

The fermentation-driving ability of Daqu has been widely reported, while the potential influence of substances in Daqu on Baijiu flavor formation has attracted increasing interest. Pseudo-targeted metabolomics integrated proteomics combined with sensory evaluation strategy was applied to investigate the correlation between flavor characteristics and metabolic profiling of Daqu, and the mechanism of flavor formation was also elucidated. The 4-hydroxy-2,5-dimethylfuran-3-one (3.5mgkg-1) and 2,3-dihydro-1h-inden-5-ol (894.3μgkg-1) were identified as the unique substances in qingcha qu, which were vital for raspberry flavor formation and associated with the up-regulation of amino acid metabolism. The dec-9-enoic acid (37.4mgkg-1) was screened out as the substance related to the formation of cream flavor in hongxin qu produced through the shortening of fatty acid carbon chains and unsaturated modification of long chain fatty and acceleration of carbon metabolism in hongxin qu mediated by filamentous Aspergillus spp. was related to the smoky aroma enhancement.

Chemometrics-based investigation of non-volatiles/volatiles flavor of tencha (Camellia sinensis cv. Yabukita, Longjing 43 and Baiye 1)

The increasing demand for tea consumption calls for the development of more products with distinct characteristics. The sensory quality of tencha is significantly determined by innate differences among tea cultivars. However, the correlations between the chemical composition and sensory traits of tencha are still unclear. To enhance the understanding of the flavor formation mechanism in tencha and further to develop new cultivars resources, we investigated non-volatiles and volatile metabolites as well as sensory traits in tencha from different tea cultivars (Camellia sinensis cv. Yabukita, Longjing 43 and Baiye 1); the relationships between the flavor traits and non-volatiles/volatiles were further evaluated by partial least squares - discriminate analysis (PLS-DA), multiple factor analysis (MFA) and multidimensional alignment (MDA) analysis. A total of 64 non-volatiles and 116 volatiles were detected in all samples, among which 71 metabolites were identified as key flavor-chemical contributors involving amino acids, flavonol glycosides, flavones, catechins, ketones, alcohols, hydrocarbons, aldehydes, esters and acids. The levels of taste-related amino acids, flavonol glycosides and gallic acid varied significantly among the tencha samples made from different tea cultivars. All the samples exhibited typical quality characteristics of tencha. The tencha from Camellia sinensis cv. Longjing 43 and Camellia sinensis cv. Baiye 1 (cultivated in the open) exhibited higher levels of amino acids and gallic acid, which were associated with the umami taste and mellow taste of tea infusion. Abundant flavonol glycosides were related to the astringency, while partial tri-glycosides specifically quercetin-3-O-galactoside-rhamnoside-glucoside and total of flavonol galactoside-rhamnoside-glucoside were associated with mellow taste. The floral alcohols were identified as significant contributors to the refreshing aroma traits of tencha. The green, almond-like, acidic and fruity odorants were associated with a green and fresh aroma, while the green, cheesy and waxy odorants such as ketones, esters, acids and hydrocarbons were associated with seaweed-like aroma. This study provides insight into sensory-related chemical profiles of tencha from different tea cultivars, supplying valuable information on flavor and quality identification for tencha.