Differences of characteristic aroma compounds in Rougui tea leaves with different roasting temperatures analyzed by switchable GC-O-MS and GC × GC-O-MS and sensory evaluation

Characterization and metabolism pathway of volatile compounds in blueberries of different varieties and origins analyzed via HS-GC-IMS and HS-SPME-GC-MS

This study comprehensively identified 10 blueberry varieties from 3 regions using headspace gas chromatography ion mobility spectrometry (HS-GC-IMS) and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). The former identified 70 volatile organic compounds, while the latter identified 618. The blueberry varieties, Bluecrop, Reka, and Northland in Northeast China have significant advantages in fresh and sweet flavors were found through HS-GC-IMS. HS-SPME-GC-MS found that terpenes, esters, and heterocyclic are the main volatile components in blueberry (47.09 %), with nine volatile organic metabolites (benzene, 1,3-dimethyl, etc.) serving as potential biomarkers for distinguishing blueberry varieties from the three regions. In addition, the top 10 aromatic compounds in different blueberry varieties were screened, among which 5-ethyl-3-hydroxy-4-methyl-2 (5H) - furanone had the highest rOAV value. These findings provide theoretical support for exploring the key flavor characteristics of different varieties of blueberries and effectively distinguishing blueberries from various production areas.

Formation Mechanisms and Kinetic Modeling of Key Aroma Compounds During Qidan Tea Roasting

Understanding the changes in tea aroma and non-volatile substances during roasting is essential for optimizing tea processing and enhancing tea quality. In this study, the Carbon Module Labeling (CAMOLA) technique was employed to simulate the roasting conditions of Qidan, thereby elucidating the formation pathway of the theanine-glucose Maillard system. Combined with sensory evaluation, the results indicated that the floral and fruity aromas of Qidan tea decreased, while the woody, roasted, smoky, and herbal aromas increased with prolonged roasting time. Kinetic modeling demonstrated that higher temperatures favored the production of benzaldehyde, which was directly proportional to the heating temperature. In contrast, pyrazines exhibited zero-order kinetics, influenced by both temperature and time. An increasing trend in furans was observed with rising temperature and extended heating time. The kinetic equations effectively describe the changes in aroma compounds associated with merad, highlighting the differences in the production patterns of aroma compounds under varying roasting conditions. This study provides a theoretical foundation for optimizing roasting parameters to enhance tea quality.

Discovery and identification of novel color compound formed from EGCG upon heating: Integrated multispectral, sensory evaluation, metabolomics, and nuclear magnetic resonance

(-)-Epigallocatechin gallate (EGCG) is the major catechin in tea. However, its transformation mechanisms into sensory-active compounds during tea roasting remain unclear. LC-MS-based metabolomics and multispectral analysis discovered a variety of novel color compounds (NCCs) formed from EGCG during high-temperature heating, and these compounds were positively correlated with color indexes. The critical NCC1 was identified, with a color dilution factor of 14 and taste thresholds for bitterness and astringency at 35.61 μM. The effects of substrate ratio, temperature, time, and pH on NCC1 content were explored, revealing that (-)-epigallocatechin (EGC) contributed to its formation. The NCC1 content ranged from 0.03 to 448.03 μM under different in vitro conditions. The content of NCC1 in tea roasted for different times ranged from 1.25 to 3.59 μM. The present study provides a basis for exploring how sensory-active compounds are formed from catechins in tea during high-temperature roasting, and for evaluating their properties.

Insight into the mechanism of roasting-induced characteristic aroma formation in Wuyi rock tea using an "in-leaf" model with isotopic labeling

Wuyi Rock Tea (WRT) undergoes complex chemical transformations during roasting that significantly influence its aroma. This study explores the mechanisms involved in the formation of key aroma compounds, specifically alkylpyrazines and furans. Using HS-SPME-GC-O-MS and aroma dilution analysis, we identified 15 odor-active compounds, including three alkylpyrazines (2,6-diethyl-pyrazine, 2-ethyl-3,5-dimethyl-pyrazine, and 2-methyl-3,5-diethyl-pyrazine) and two furans (furfural and 5-methyl-2-furancarboxaldehyde), with odor-active values exceeding 1. An "in-leaf" labeling approach utilizing isotopically labeled alanine ([15N]-Ala) and glucose ([U13C6]-Glc) was employed to explore the contributions of tea leaf matrix and soluble compounds. Results indicated that the incorporation of two nitrogen atoms from alanine was the predominant pathway for alkylpyrazine formation, while five or six carbon atoms from glucose were primarily responsible for furan formation. Additionally, the insoluble tea leaf matrix contributed 13 % to 32 % of alkylpyrazines and 12 % to 25 % of furans. These findings enhance our understanding of the Maillard reaction's role in WRT's flavor development.

Characterization of key aroma in Huangjincha black tea processed from four different cultivars

Huangjincha (HJC) is a cultivar rich in amino acids making it ideal for producing high-quality black tea. In this study, the aroma composition of HJC black tea from four different cultivars (HJC1, HJC2, HJC18, and HJC168) was analyzed by aroma sensory evaluation combined with volatile compound analysis. Among 271 identified volatiles, with 39 compounds as key odorants contributing to the diverse aromas of HJC black teas. The OAV and GC-O results indicated that geraniol and benzeneacetaldehyde (HJC1), 3-methylbutanal and 1-penten-3-ol (HJC2), (E, E)-2,4-hexadienal and damascenone (HJC18), as well as methyl salicylate and citral (HJC168) were the most significant aroma compounds. Furthermore, PLS analysis revealed four odorants contributed to floral characteristic, three were related to fruity attribute, four were associated with green attribute, three were connected to fresh attribute, three were linked to nutty profile, and three were tied to the sweet profile.

Effects of fermented tea by Aspergillus cristatus on the characteristic aroma and non-volatile components of Jiang-flavor baijiu

BACKGROUND

Fu Brick tea (FBT) extract has been demonstrated to lower blood lipids, protect liver, and prevent obesity. Despite these benefits, there are no products on the market that combine FBT with other foods or beverages.

RESULT

In this study, we developed a novel product by combining FBT with high-alcohol Jiang-flavor baijiu, resulting in FBT-baijiu. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis revealed that FBT-baijiu contains health-promoting alkaloids, including eurocristatine (13.60 ± 0.13 mg/L), (-)-neoechinulin A (10.26 ± 0.09 mg/L), neoechinulin D (7.89 ± 0.05 mg/L), variecolorin G (6.94 ± 0.05 mg/L), and echinulin (25.46 ± 0.27 mg/L), which are known to be present in FBT. The aroma compounds of the FBT-baijiu and the base baijiu were analyzed using comprehensive gas chromatography-olfactometry-mass spectrometry (GC-O-MS) technology. The major volatile compounds of two baijiu samples were identified using relative odor activity values (r-OAVs) analysis. The FBT-baijiu showed a significant reduction in ester content, but a remarkable enhancement in aromatic properties. The findings show that combining FBT with baijiu not only offers functional components but also enhances the flavor profile.

CONCLUSION

This study highlights the potential of utilizing FBT as a functional food ingredient or additive, paving the way for the development of new health-promoting products. © 2024 Society of Chemical Industry.

Improving the Sensory Quality of Black Tea by Blending Varieties During Processing

Tea blending technology is based on finished tea. Blending fresh leaves during processing has not been proposed and investigated anywhere. This study investigates the impact of blending fresh leaves from different varieties on the flavor quality of black tea. The main taste components, including catechins, theaflavins, and free amino acids, were analyzed using HPLC, while the volatile components were analyzed using GC-MS. The results show that adding fresh Jinguanyin or Jinxuan leaves to Fudingdabai can regulate the ratio of esterified to non-esterified catechins, increase the content of theaflavins and amino acids, and positively impact the strength and freshness of the black tea. The sensory evaluation results show that the taste scores of FJG (black tea made from the blend of fresh Fudingdabai and Jinguanyin tea leaves) (92.14 ± 0.41 b) and FJX (black tea made from the blend of fresh Fudingdabai and Jinxuan tea leaves) (93.80 ± 0.19 a) are significantly higher than those of Fudingdabai (90.05 ± 0.31 d), Jinguanyin (86.10 ± 0.45 e), and Jinxuan (91.03 ± 0.26 c). Furthermore, adding fresh Jinguanyin or Jinxuan leaves to Fudingdabai can also enhance the floral compounds in the black tea, specifically phenylacetaldehyde, linalool, benzyl alcohol, and oxidized linalool (linalool-type pyran), which make important contributions to the floral aroma of the black tea. Conclusions: Blending fresh leaves for processing can enhance the sensory quality of black tea. This work proposes new insights and methods to enhance black tea sensory quality via the blending of fresh tea leaves with different varieties during processing.

Effect of shaking and piling processing on improving the aroma quality of green tea

Aroma plays a crucial role in the quality of pure green tea beverage. However, there are limited methods to improve their aroma. In this study, green tea produced using shaking and piling process (SPGT) demonstrated a notable improvement in aromatic intensity, particularly in floral, fruity, and sweet notes. A total of 58 volatile compounds were detected, with SPGT exhibiting the highest concentration of aroma compounds among the tested green teas. Eight key aroma compounds were selected based on a relative odor activity value (ROAV) greater than 1 in SPGT: dimethyl sulfide (71.14, cooked corn-like), 2-methylbutanal (3.17, cereal), octanal (1.31, fruity), linalool (5.25, floral), nonanal (5.00, floral), (E)-2-nonenal (2.81, cucumber), decanal (22.90, fruity), and β-ionone (60.51, floral). The concentration of aroma compounds, especially for floral and fruity key volatile compounds significantly increased during the shaking and piling process (p < 0.05), and their formation pathways help explained these changes. Our results provided a new theoretical foundation and practical guidelines for producing the high-aroma green tea.

Maillard reaction inducing amino acids degradation can adjust the flavour characteristic of black tea

Drying is the step that is to be used to adjust and control the formation of flavour and quality in black tea processing. In the present work, the comprehensive two-dimensional gas chromatography with mass spectrometry (GC × GC-MS) and gas chromatography olfactometry with mass (GC-O-MS) were used to determine the dynamic change of the volatile compounds in black tea during drying at 90, 120, 150 °C for 1 h. Results showed that the ratio of esters and aldehydes largely declined when temperature was elevated from 90 °C to 150 °C, while the ratio of heterocycles was increased to 22.4 % from 16.5 %. A total of 15 key aroma activity volatiles were screened out in three temperature dried samples, therein 11 volatiles were connected with the Maillard reaction, meaning these volatiles were highly relevant to the degradation of amino acids during the drying process. We detected that 21 amino acids were decreased with enhanced temperature and extended the drying time, which promoted the Maillard-derived volatiles formation. Therefore, it was suggested that to control the degradation of amino acids adjust the flavour profiles of black tea by changing the drying temperature and time.

Characterization of the volatile compounds in tea (Camellia sinensis L.) flowers during blooming

Tea flower, with characteristic flavor formed during blooming, are a significant tea resource. However, studies on the volatile compounds of tea flower and their aroma characteristics during flowering are scarce. In this study, the odor characteristics of tea flower during blooming were comprehensively investigated by GC-MS, PCA, ACI determination and sensory evaluation. The tea flower of unopened buds (TF-S1) contained the highest alcohol amounts, while fully opened tea flowers (TF-S3) had the highest heterocyclic compounds. Half-opened tea flowers (TF-S2) had the most volatile compounds, including high levels of linalool and its oxides, and low levels of (Z)-3-hexen-1-ol. Acetoin and cosmene were first identified in TF-S1 and TF-S2, respectively. The major ACI components differed, with linalool being prominent exhibiting ACI above 27 in all samples. Acetophenone, unique to TF-S2 with ACI of 57.35, contributed to sweet odor. Furthermore, PCA analysis and sensory evaluation revealed distinct aroma characteristics among the samples. Overall, TF-S2 and TF-S3 had higher volatile amounts and better aroma properties with floral, powdery or almond-like odors. These results advance the understanding of aroma properties of tea flower during blooming, and provide a reference for resource utilization and promotion of the application in food or cosmetics industries.

Identification of aroma active compounds in Shanxi aged vinegar and tracing the source in the entire production process

The aroma-active compounds (AACs) of traditional vinegars are formed through complexed pathways. Moreover, their source is not clear yet. The composition of AACs throughout the entire process of Shanxi aged vinegar (SAV) production from the raw materials, alcohol fermentation (AF), acetic acid fermentation (AAF), fumigation and aging stages were analyzed. A total of 121 AACs were determined by GC × GC-O-TOF-MS, of which 88 were identified by GC-MS/MS. There were 27 and 41 AACs (FD ≥ 400) detected in before-aging and after-aging SAV, respectively. Furthermore, it can be concluded the AAF and fumigation were the main sources of AACs. Also, the AAF was the main source of the compounds with caramel, creamy, floral, fruity, sour, cheesy notes, while the compounds owned roasted, nutty, spicy and woody aromas mainly came from fumigation. Finally, the potential transformation pathway of AACs was mapped and discussed. Overall, GC × GC-O-TOF-MS was a useful technique to enrich the AACs of SAV.

Tea Quality: An Overview of the Analytical Methods and Sensory Analyses Used in the Most Recent Studies

Tea, one of the world's most consumed beverages, has a rich variety of sensory qualities such as appearance, aroma, mouthfeel and flavor. This review paper summarizes the chemical and volatile compositions and sensory qualities of different tea infusions including black, green, oolong, dark, yellow, and white teas based on published data over the past 4 years (between 2021 and 2024), largely focusing on the methodologies. This review highlights the relationships among the different processing methods of tea and their resulting chemical and sensory profiles. Environmental and handling factors during processing, such as fermentation, roasting, and drying are known to play pivotal roles in shaping the unique flavors and aromas of different types of tea, each containing a wide variety of compounds enhancing specific sensory characteristics like umami, astringency, sweetness, and fruity or floral notes, which may correlate with certain groups of chemical compositions. The integration of advanced analytical methods, such as high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS), with traditional sensory analysis techniques was found to be essential in the evaluation of the chemical composition and sensory attributes of teas. Additionally, emerging approaches like near-infrared spectroscopy (NIRS) and electronic sensory methods show potential in modern tea evaluation. The complexity of tea sensory characteristics necessitates the development of combined approaches using both analytical methods and human sensory analysis for a comprehensive and better understanding of tea quality.

Characterization of volatile compounds and identification of key aroma compounds in different aroma types of Rougui Wuyi rock tea

In this study, we characterized the aroma profiles of different Rougui Wuyi rock tea (RGWRT) aroma types and identified the key aroma-active compounds producing these differences. The roasting process was found to have a considerable effect on the aroma profiles. Eleven aroma compounds, including linalool, β-ionone, geraniol, indole, and (E)-nerolidol, strongly affected the aroma profiles. An RGWRT aroma wheel was constructed. The rich RGWRT aroma was found to be dominated by floral, cinnamon-like, and roasty aromas. Human olfaction was correlated with volatile compounds to determine the aromatic characteristics of these compounds. Most key aroma-active compounds were found to have floral, sweet, and herbal aromas (as well as some other aroma descriptors). The differences in key compounds of different aroma types were found to result from the methylerythritol phosphate, mevalonic acid and shikimate metabolic pathways and the Maillard reaction. Linalool, geraniol, and (E,E)-2,4-heptadienal were found to spontaneously bind to olfactory receptors.

Dynamic changes and interaction between different aroma types during low-temperature roasting of bud green tea

As an important process for enhancing aroma of Wuyi rock tea, roasting has gradually been applied to the processing of bud green tea (BGT). However, there is a lack of comprehensive research on the impact of roasting on BGT aroma. This research provides a detailed analysis of the changes in aroma perception and compounds during the low-temperature roasting process (105°C, 90 minutes) of BGT. First, the changes in aroma perception were studied using quantitative descriptive analysis (QDA). The aroma perception of BGT transformed from fresh to chestnut like. Next, headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis was conducted to characterize the volatile compounds during roasting. A total of 313 volatile compounds were identified, among which 72 showed significant differences. Compounds such as linalool, benzyl alcohol, ionone, and ethyl salicylate (floral aroma) and 2,6-dimethylpyrazine, 2,3-dimethylpyrazine, 2-acetylpyrrole, and 3-furfural (caramel-like aroma) were confirmed to be involved in the formation of the chestnut-like aroma during roasting process. In addition, representative aroma compounds with different characteristics were selected based on monomolecular olfactory results to simulate sensory-level aroma interactions. The results showed that fresh and tender aromas exhibited mutual enhancement at low concentrations, while sweet and chestnut-like aromas showed mutual enhancement at all concentrations.

Characterization of odor profiles of pea milk varieties and identification of key odor-active compounds by molecular sensory science approaches using soybean milk as a reference

This study investigated the odor profiles of four pea milk varieties based on sensory evaluation, electronic nose (E-nose), and gas chromatography-mass spectrometry (GC-MS) with soybean milk as a reference. Compared to soybean milk, pea milk exhibited lower intensity of beany, oil-oxidation, and mushroom flavors as well as higher intensity of grassy/green and earthy flavors. ZW.6 pea milk was selected for further identification of key odor-active compounds using molecular sensory science approaches. Using headspace solid phase microextraction (HS-SPME), solvent-assisted flavor evaporation (SAFE), and dynamic headspace sampling (DHS) combined with comprehensive gas chromatography-olfactometry-mass spectrometry (GC × GC-O-MS), 102 odor-active compounds were detected in ZW.6 pea milk. Among these, 19 compounds exhibiting high flavor dilution (FD) factors were accurately quantitated. Ten key odor-active compounds were ultimately identified through aroma recombination and omission experiment. Aldehydes and alcohols significantly contribute to the odor profile of pea milk.

Enhancing Odor Analysis with Gas Chromatography-Olfactometry (GC-O): Recent Breakthroughs and Challenges

Gas chromatography-olfactometry (GC-O) has made significant advancements in recent years, with breakthroughs in its applications and the identification of its limitations. This technology is widely used for analyzing complex odor patterns. The review begins by explaining the principles of GC-O, including sample preparation, separation methods, and olfactory evaluation techniques. It then explores the diverse range of applications where GC-O has found success, such as food and beverage industries, environmental monitoring, perfume and aroma development, and forensic analysis. One of the major breakthroughs in GC-O analysis is the improvement in separation power and resolution of odorants. Techniques like rapid GC, comprehensive two-dimensional GC, and multidimensional GC have enhanced the identification and quantification of odor-active chemicals. However, GC-O also has limitations. These include the challenges in detecting and quantifying trace odorants, dealing with matrix effects, and ensuring the repeatability and consistency of results across laboratories. The review examines these limitations closely and discusses potential solutions and future directions for improvement in GC-O analysis. Overall, this review presents a comprehensive overview of the recent advances in GC-O, covering breakthroughs, applications, and limitations. It aims to promote the wider usage of GC-O analysis in odor analysis and related industries. Researchers, practitioners, and anyone interested in leveraging the capabilities of GC-O in analyzing complex odor patterns will find this review a valuable resource. The article highlights the potential of GC-O and encourages further research and development in the field.

Unveiling the aromatic intricacies of Wuyi Rock Tea: A comparative study on sensory attributes and odor-active compounds of Rougui and Shuixian varieties

The distinctive fragrance of Wuyi Rock Tea (WRT) has garnered high attention in recent years. Herein, we conducted a comprehensive comparison of the sensory attributes and odor-active compounds (OACs) between two quintessential WRTs, namely Rougui (RGT) and Shuixian (SXT). Sensory analysis revealed that RGT exhibited a more pronounced fruity aroma, while SXT had a more complex and intricate sensory profile. By using gas chromatography-olfactory mass spectrometry (GC-O-MS) and two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOF-MS) analyses, 26 OACs were identified. Among them, 12 compounds with odor activity values > 1 were recognized as key OACs. Noteworthily, eight compounds, including 6-methyl-5-hepten-2-one, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, linalool, methyl salicylate, geraniol, (E)-β-ionone, and (E)-nerolidol, were shared by both teas. The unique compounds for RGT were (E)-linalool oxide and (Z)-jasmone, while those for SXT were β-cyclocitral and α-ionone. These findings offer valuable insights for better understanding the flavor differences between the two most important types of WRT.

Contents of ɑ-dicarbonyl compounds in commercial black tea and affected by the processing

The species and contents of ɑ-dicarbonyls in commercial black tea were examined, along with the effects of the manufacturing process and drying temperature on the formation of ɑ-dicarbonyls. Ten ɑ-dicarbonyls were quantified in commercial and in-process black tea samples by using UPLC-MS/MS and their derived quinoxalines. The ɑ-dicarbonyls content in commercial black tea decreased significantly (p < 0.05) in the following order: 3-deoxyglucosone > glucosone > 3-deoxypentosone = threosone > galactosone ≥ methylglyoxal = glyoxal ≥ 3-deoxygalactosone = 3-deoxythreosone = diacetyl. Except for 3-deoxyglucosone and 3-deoxygalactosone, a further eight ɑ-dicarbonyls were identified in all manufacturing steps of black tea. Except for the drying step, the rolling and fermenting played important roles in the formation of ɑ-dicarbonyls. The total contents of ɑ-dicarbonyls in black tea infusion ranged from 16.48 to 75.32 μg/g based on our detected ten ɑ-dicarbonyls.

From heat to flavor: Unlocking new chemical signatures to discriminate Wuyi rock tea under light and moderate roasting

Roasting is crucial for the distinct flavor of Wuyi rock tea (WRT). This study applied untargeted metabolomics to investigate the effects of roasting on 139 WRT samples roasted at light fire (LF) or moderate fire (MF) intensities. Compared to LF, MF roasting led to a decrease in the cis/trans flavanol ratio by 56% and theanine by 85%, while increasing the levels of N-ethyl-2-pyrrolidione-substituted flavanols (EPSFs), flavonol aglycones and flavone C-glycosides. Two new roast markers, 3-p-coumaroyl 1,5-lactone and 4-p-coumaroyl 1,5-lactone, were identified in WRT and their formation increased with roasting temperature. MF roasting facilitated the formation of diverse heterocycles (e.g., pyrazines) and aldehydes (e.g., (Z)-4-heptenal and (E,E)-2.4-decadienal) that contributed to the augmented roasted and fatty odors in WRT. Additionally, the Maillard product furfuryl methyl ether was solely detected in MF samples. These findings provide novel insights into roast markers in WRT with implications for improving quality control measures during tea roasting.

Comprehensive applications of metabolomics on tea science and technology: Opportunities, hurdles, and perspectives

With the development of metabolomics analytical techniques, relevant studies have increased in recent decades. The procedures of metabolomics analysis mainly include sample preparation, data acquisition and pre-processing, multivariate statistical analysis, as well as maker compounds' identification. In the present review, we summarized the published articles of tea metabolomics regarding different analytical tools, such as mass spectrometry, nuclear magnetic resonance, ultraviolet-visible spectrometry, and Fourier transform infrared spectrometry. The metabolite variation of fresh tea leaves with different treatments, such as biotic/abiotic stress, horticultural measures, and nutritional supplies was reviewed. Furthermore, the changes of chemical composition of processed tea samples under different processing technologies were also profiled. Since the identification of critical or marker metabolites is a complicated task, we also discussed the procedure of metabolite identification to clarify the importance of omics data analysis. The present review provides a workflow diagram for tea metabolomics research and also the perspectives of related studies in the future.

Characterization of key volatile compounds in jasmine tea infusion with different amount of flowers

The quality of jasmine tea is related to the volatiles of its infusion. In this study, the volatiles of jasmine tea infusion were extracted under the optimal conditions with a 50/30 μm DVB/CAR/PDMS fiber, tea/water ratio of 1:25 and extraction time of 5 min. A total of 204 volatiles were analyzed by comprehensive two-dimensional gas chromatography-quadrupole time-of-flight mass spectrometry (GC × GC-Q-TOF-MS). Twenty-five compounds were identified as the key volatile compounds by fold change (FC), orthogonal partial least squares discriminant analysis (OPLS-DA), and two-way orthogonal partial least squares analysis (O2PLS). Then optimal amount of flowers (80%-120%) was obtained by the equation describing key volatiles and quality of jasmine tea infusion. And 80% amount of flowers was more appropriate considering the production cost and more pleasant taste. This study laid a foundation for the extraction and research of volatiles of tea infusion and guided the reasonable amount of flowers to produce jasmine tea.

Decoding the Chemical Signatures and Sensory Profiles of Enshi Yulu: Insights from Diverse Tea Cultivars

Enshi Yulu, a renowned Chinese steamed green tea, is highly valued for its unique sensory attributes. To enhance our comprehensive understanding of the metabolic variation induced by steaming fixation, we investigated the overall chemical profiles and organoleptic quality of Enshi Yulu from different tea cultivars (Longjing 43, Xiapu Chunbolv, and Zhongcha 108). The relationships between sensory traits and non-volatiles/volatiles were evaluated. A total of 58 volatiles and 18 non-volatiles were identified as characteristic compounds for discriminating among the three tea cultivars, and the majority were correlated with sensory attributes. The "mellow" taste was associated with L-aspartic acid, L-asparagine, L-tyrosine, L-valine, EGC, EC, and ECG, while gallic acid and theobromine contributed to the "astringent" taste. "Kokumi" contributors were identified as L-methionine, L-lysine, and GCG. Enshi Yulu displayed a "pure" and "clean and refreshing" aroma associated with similar volatiles like benzyl alcohol, δ-cadinene, and muurolol. The composition of volatile compounds related to the "chestnut" flavor was complex, including aromatic heterocycles, acids, ketones, terpenes, and terpene derivatives. The key contributors to the "fresh" flavor were identified as linalool oxides. This study provides valuable insights into the sensory-related chemical profiles of Enshi Yulu, offering essential information for flavor and quality identification of Enshi Yulu.

Analysis of Volatile Profile and Aromatic Characteristics of Raw Pu-erh Tea during Storage Based on GC-MS and Odor Activity Value

Volatile constituents are critical to the flavor of tea, but their changes in raw Pu-erh tea (RAPT) during storage have not been clearly understood. This work aimed to investigate the volatile composition and their changes at various storage durations. The volatile profile of RAPT was determined using headspace solid-phase microextraction in combination gas chromatography-mass spectrometry. A total of 130 volatile compounds were identified in RAPT samples, and 64 of them were shared by all samples. The aroma attributes of RAPT over a storage period ranging from 0 to 10 years were assessed through the combination of odor activity value (OAV), aroma characteristic influence(ACI) value, and multivariate statistical analysis. The results revealed that RAPT exhibited a distinct floral and fruity aroma profile after storage for approximately 3-4 years. A notable shift in aroma was observed after 3-4 years of storage, indicating a significant turning point. Furthermore, the likely notable shift after 10 years of storage may signify the second turning point. According to the odor activity value (OAV ≥ 100), eight key volatile compounds were identified: linalool, α-terpineol, geraniol, trans-β-ionone, α-ionone, (E,E)-2,4-heptadienal, 1-octanol, and octanal. Combining OAV (≥100) and ACI (≥1), five compounds, namely linalool, (E,E)-2,4-heptadienal, (Z)-3-hexen-1-ol, 2,6,10,10-tetramethyl-1-oxaspiro [4.5]dec-6-ene, and octanal, were identified as significant contributors to the aroma. The results offer a scientific foundation and valuable insights for understanding the volatile composition of RAPT and their changes during storage.

Contribution of theanine to the temperature-induced changes in aroma profile of Wuyi rock tea

Theanine is a distinctive amino acid in tea that plays a vital role in tea flavor during the roasting process. Model thermal reactions of total amino acids and sugars with different roasting conditions (low-fire, middle-fire, and high-fire) showed theanine competitively inhibited the formation of indole, skatole, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, and Strecker aldehydes, while greatly stimulated the production of roasty pyrazines. In addition, highest amounts of pyrazines were obtained under high-fire degree. Quantification of these reaction products in Wuyi rock tea (WRT) was realized in different roasted Dahongpao teas by means of sensomics approach. The quantitative data revealed the biggest influence of roasting temperatures on the formation of reaction products among indole, lipid oxidation products, and pyrazines, while other reaction products were only slightly affected. The findings of this study provide a fresh perspective on the impact of theanine on aroma formation during the roasting process, which will help to explore the formation of key odorants during tea production.

Enantiomeric separation and precise quantification of chiral volatiles in Wuyi rock teas using an efficient enantioselective GC × GC-TOFMS approach

Chiral volatiles play important roles in the formation of aroma quality of foods. To date, enantiomeric characteristics of chiral volatiles in Wuyi rock tea (WRT) and their aroma contributions are still unclear. In this study, an efficient enantioselective comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (Es-GC × GC-TOFMS) approach to separate and precisely quantitate 24 pairs of chiral volatiles in WRTs was established, and the enantiomeric distribution and aroma contribution of chiral volatiles among WRTs from four representative cultivars were investigated. Enantiomeric ratio (ER) of R-α-ionone (80%) in Dahongpao (DHP), ER of S-α-terpineol (57%) in Jinfo (JF), ERs of R-γ-heptanolactone (69%), S-γ-nonanolactone (55%), (2R, 5S)-theaspirane B (91%), concentration of S-(E)-nerolidol (313.37 ng/mL) in Rougui (RG) and concentration of R-α-ionone (33.01 ng/mL) in Shuixian (SX) were unique from other types of WRTs, which were considered as the potential chemical markers to distinguish WRT cultivars. The OAV assessment determined 7 volatile enantiomers as the aroma-active compounds, especially R-α-ionone and R-δ-octanolactone in SX, as well as S-(E)-nerolidol and (1R, 2R)-methyl jasmonate in RG contribute much to aroma formation of the corresponding WRTs. The above results provide scientific references for discrimination of tea cultivars and directed improvement of the aroma quality of WRT.

Aroma Identification and Classification in 18 Kinds of Teas (Camellia sinensis) by Sensory Evaluation, HS-SPME-GC-IMS/GC × GC-MS, and Chemometrics

Tea (Camellia sinensis) is one of the most popular beverages worldwide. Many types of tea products continuously emerge in an endless stream; so, the classification of tea becomes more difficult. Aroma is a vital indicator of tea quality. The present study deals with the identification of aroma compounds in 18 different kinds of tea belonging to three typical tea varieties, including green tea, oolong tea, and black tea, using GC-IMS and GC × GC-O-MS. Moreover, the clustering of all 18 tea samples and the in depth correlation analysis between sensory evaluation and instrumental data were performed using the PCA and OPLS-DA. The results revealed that in all 18 kinds of tea, a total of 85 aroma compounds were detected by GC-IMS, whereas 318 were detected by GC × GC-O-MS. The PCA result revealed that green tea, oolong tea, and black tea could be clearly separated based on their peak areas. The OPLS-DA result showed that a total of 49 aroma compounds with VIP value > 1.0 could be considered as the potential indicators to quickly classify or verify tea types. This study not only compared the aroma differences across different types of teas, but also provided ideas for the rapid monitoring of tea quality and variety.

Flavor perception and health benefits of tea

As one of the most consumed non-alcoholic beverages in the world, tea is acclaimed for its pleasant flavor and various health benefits. Different types of tea present a distinctive flavor and bioactivity due to the changes in the composition and proportion of respective compounds. This article aimed to provide a more comprehensive understanding of tea flavor (including aroma and taste) and the character of tea in preventing and alleviating diseases. The recent advanced modern analytical techniques for revealing flavor components in tea, including enrichment, identification, quantitation, statistics, and sensory evaluation methodologies, were summarized in the following content. Besides, the role of tea in anti-cancer, preventing cardiovascular disease and metabolic syndrome, anti-aging and neuroprotection, and regulating gut microbiota was also listed in this article. Moreover, questions and outlooks were mentioned to objectify tea products' flavor quality and health benefits on a molecular level and significantly promote our understanding of the comprehensive value of tea as a satisfactory health beverage in the future.

Odor changes in breast milk during different storage temperatures and times using GC × GC-O-MS

Breastfeeding is generally the preferred way that most mothers will choose. It is common to store expressed breast milk in the refrigerator in many families. However, there is a phenomenon that infants may refuse to consume stored breast milk, presumably due to changes in odor. Thus, the odor changes in breast milk stored at 4 °C for 72 h and at -20 °C for 60 d were studied. Compared with fresh breast milk, 7 and 16 odor compounds were newly detected by SPME and GC × GC-O-MS when breast milk was stored at 4 and -20 °C, respectively. The concentration of (E)-2-decenal, octanal, hexanal, 1-octen-3-ol, 2-pentylfuran, lauric acid, decanoic acid and hexanoic acid significantly increased after storage at 4 °C for 36 h and -20 °C for 30 d. In addition, the proportion of acids increased, whereas that of aldehydes decreased during storage. Chemometric analysis with OPLS-DA suggested that breast milk should be stored at 4 °C for less than 36 h and at -20 °C for less than 30 d for maximum preservation of the original odors.

Metabolomics integrated with machine learning to discriminate the geographic origin of Rougui Wuyi rock tea

The geographic origin of agri-food products contributes greatly to their quality and market value. Here, we developed a robust method combining metabolomics and machine learning (ML) to authenticate the geographic origin of Wuyi rock tea, a premium oolong tea. The volatiles of 333 tea samples (174 from the core region and 159 from the non-core region) were profiled using gas chromatography time-of-flight mass spectrometry and a series of ML algorithms were tested. Wuyi rock tea from the two regions featured distinct aroma profiles. Multilayer Perceptron achieved the best performance with an average accuracy of 92.7% on the training data using 176 volatile features. The model was benchmarked with two independent test sets, showing over 90% accuracy. Gradient Boosting algorithm yielded the best accuracy (89.6%) when using only 30 volatile features. The proposed methodology holds great promise for its broader applications in identifying the geographic origins of other valuable agri-food products.

Discovery and Flavor Characterization of High-Grade Markers in Baked Green Tea

Green tea is a popular beverage around the world and possesses a unique flavor. The flavor qualities of green tea are closely related to its grade and this relationship has not yet been studied. Three baked green teas with similar flavor were studied, namely, Huangshan Maofeng, Taiping Houkui, and Shucheng Xiaolanhua. A total of 34 odor compounds were identified by solid phase microextraction (SPME) combined with two-dimensional comprehensive gas chromatography–olfactometry–mass spectrometry analysis (GC×GC-O-MS). The results of the clustering analysis showed that the content of D-limonene and linalool in the high-grade (Grade A) tea was much higher than the content in other grades, so they were identified as odor markers of Grade A baked green tea. The taste components of different grades of green tea infusion were analyzed by high-performance liquid chromatography–mass spectrometry (HPLC–MS) and HPLC. A combination of clustering analysis, principal component analysis (PCA), and orthogonal partial least squares discrimination analysis (OPLS-DA) indicated that galloylglucose, digalloylglucose, trigalloyglucose, strictinin, and gallic acid could be used as taste markers of Grade A baked green tea. Therefore, the results in this paper reveal the substances responsible for the odor and taste markers of high-grade baked green tea.

Antioxidant effects and reaction volatiles from heated mixture of soy protein hydrolysates and coconut oil

Soy protein hydrolysates (SPHs) are prepared from soybean meal using commercially available protease enzymes and acid/alkali treatment. The antioxidant properties of SPHs were evaluated by measuring headspace oxygen consumption and conjugated diene formation in oil-in-water (O/W) emulsions. In addition, volatile profiles were analyzed for the heated mixture of SPHs and the coconut oil (SPHCO). Total amino acid content was the highest in double proteases. SPHs prepared from enzymes acted as better antioxidants than those prepared from acid/alkali treatments in O/W emulsions. SPHs prepared from double proteases generated the highest amounts of total volatiles and nitrogen-containing compounds in SPHCO. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, 2-methyl-butanal, benzeneacetaldehyde, and 2,6-dimethylpyrazine were the major volatiles in SPHCO. Enzymatic SPHs act as natural antioxidants in the O/W emulsion matrix, and thermal reaction products from SPHCO may contribute to the production of a unique volatile flavor in plant protein-based foods.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01189-7.

Variation of Aroma Components of Pasteurized Yogurt with Different Process Combination before and after Aging by DHS/GC-O-MS

Pasteurized yogurt is a healthy yogurt that can be stored in ambient temperature conditions. Dynamic headspace sampling (DHS) combined with gas chromatography-olfactory mass spectrometry (GC-O-MS), sensory evaluation, electronic nose (E-nose), and partial least squares discriminant analysis (PLS-DA) were used to analyze the flavor changes of pasteurized yogurt with different process combinations before and after aging. The results of odor profiles showed that the sensory descriptors of fermented, sweet, and sour were greatly affected by different process combinations. The results of odor-active compounds and relative odor activity value (r-OAV) showed that the combination of the production process affected the overall odor profile of pasteurized yogurt, which was consistent with the sensory evaluation results. A total of 15 odor-active compounds of 38 volatile compounds were detected in pasteurized yogurt samples. r-OAV results revealed that hexanal, (E)-2-octenal, 2-heptanone, and butanoic acid may be important odor-active compounds responsible for off-odor in aged, pasteurized yogurt samples. PLS-DA and variable importance of projection (VIP) results showed that butanoic acid, hexanal, acetoin, decanoic acid, 1-pentanol, 1-nonanal, and hexanoic acid were differential compounds that distinguish pasteurized yogurt before and after aging.

Aroma characteristics of Wuyi rock tea prepared from 16 different tea plant varieties

Wuyi rock tea (WRT) is famous for its long history and unique characteristic of floral, fruity and nutty flavors. This study investigated the aroma characteristics of WRTs prepared from 16 different oolong tea plant varieties. The sensory evaluation results showed that all WRTs had an 'Yan flavor' taste, and the odor was strong and lasting. Roasted, floral and fruity odors were the prime aroma profiles for WRTs. Furthermore, a total of 368 volatile compounds were detected using HS-SPME-GC-MS and analyzed with OPLS-DA and HCA methods. The volatile compounds heterocyclic compounds, esters, hydrocarbons, terpenoids and ketones were the major aromatic components of the WRTs. Specifically, the volatile profiles among newly selected cultivars were comparatively analyzed, and 205 differential volatile compounds were found with variable importance in the projection (VIP) values above 1.0. These results indicated that the aroma profiles of WRTs were mainly dependent on the cultivar specificities of volatile compounds.

Comparative study of the volatile fingerprints of roasted and unroasted oolong tea by sensory profiling and HS-SPME-GC-MS

Roasting plays important roles in shaping the volatile profile of oolong tea. In this study, the sensory attributes and volatile compositions of 153 roasted or unroasted oolong tea samples, belonging to four typical types, namely, High Mountain oolong tea (HMT), Tieguanyin tea (TGYT), Dongding oolong tea (DDT) and Wuyi rock tea (WRT), were studied in detail. Based on the sensory evaluation by tea evaluation experts, their respective sensory profiles were established and compared. Unroasted teas had more pronounced fresh and green flavors, while roasted teas had higher scores in pungent and caramel flavors. In particular, WRT demonstrated a unique fragrance of floral fruity flavors. By using HS-SPME-GC-MS analysis, a total of 128 compounds were identified across all samples. Notably, it was found that roasting largely increased the variety of volatile compounds in oolong tea. Furthermore, the characteristic volatile compounds of each type of tea were identified by PLS-DA modeling. Linalool and geraniol were the characteristic volatiles of HMT. Four volatiles, including (E)-nerolidol, jasmin lactone, benzeneacetaldehyde, and 4-methyl benzaldehyde oxime were identified as the characteristic volatiles of TGYT. Seven volatiles, including N-ethyl pyrrole, 3-(hydroxy methyl) pyridine, 4-pyridylcarbinol, 1-methyl pyrrole-2-carboxaldehyde, 2-ethyl-3,5-dimethyl pyrazine, 4-amino-2,3-xylenol, and 4,6-dimethyl pyrimidine were the characteristic volatiles of DDT. For WRT, 2,2,6-trimethyl cyclohexan-1-one, hexanoic acid, benzaldehyde, benzyl alcohol, β-cyclocitral, (E)-β-ionone, α-ionone, and octanoic acid were the characteristic volatiles. These findings expand our knowledge of the volatile fingerprints of oolong tea.

Insights into Characteristic Volatiles in Wuyi Rock Teas with Different Cultivars by Chemometrics and Gas Chromatography Olfactometry/Mass Spectrometry

Wuyi rock tea (WRT) is one of the most famous subcategories of oolong tea, exhibiting distinct aroma characteristics with the application of different cultivars. However, a comprehensive comparison of the characteristic volatiles among WRTs with different cultivars has rarely been carried out. In this study, non-targeted analyses of volatile fragrant compounds (VFCs) and targeted aroma-active compounds in WRTs from four different cultivars were performed using chemometrics and gas chromatography olfactometry/mass spectrometry (GC-O/MS). A total of 166, 169, 166, and 169 VFCs were identified for Dahongpao (DHP), Rougui (RG), Shuixian (SX), and Jinfo (JF), respectively; and 40 components were considered as the key differential VFCs among WRTs by multivariate statistical analysis. Furthermore, 56 aroma-active compounds were recognized with predominant performances in "floral & fruity", "green & fresh", "roasted and caramel", "sweet", and "herbal" attributes. The comprehensive analysis of the chemometrics and GC-O/MS results indicated that methyl salicylate, p-cymene, 2,5-dimethylpyrazine, and 1-furfurylpyrrole in DHP; phenylethyl alcohol, phenethyl acetate, indole, and (E)-β-famesene in RG; linalool, phenethyl butyrate, hexyl hexanoate, and dihydroactinidiolide in JF; and naphthalene in SX were the characteristic volatiles for each type of WRT. The obtained results provide a fundamental basis for distinguishing tea cultivars, recombination, and simulation of the WRT aroma.

Characterization of Key Odor-Active Off-Flavor Compounds in Aged Pasteurized Yogurt by Sensory-Directed Flavor Analysis

The purpose of this study was to determine the key odor-active compounds contributing to the off-flavor of aged pasteurized yogurt (APY) using sensory-directed flavor analysis. Additionally, different extraction methods were compared to determine their effects on the volatile compounds, including dynamic headspace sampling (DHS), solid-phase microextraction, and stir bar sorptive extraction, and DHS was found to be suitable for this study. The results showed that comprehensive two-dimensional gas chromatography-olfactometry-mass spectrometry analysis (GC × GC-O-MS) had more advantages in separating and identifying the volatile compounds than the traditional GC-O-MS. A total of 17 odor-active compounds were determined in the fresh pasteurized yogurt and APY samples by DHS coupled with GC × GC-O-MS. The dynamic headspace dilution analysis demonstrated that 2-heptanone and hexanal were the most vital components in APY with the highest flavor dilution factor. Furthermore, the spiking and omission experimental results revealed that the odor-active compounds, such as 2-heptanone, butanoic acid, pentanoic acid, hexanal, and (E)-2-heptenal, were the key odor-active off-flavor contributors in APY. Therefore, these compounds could be used as potential indicators to determine the freshness of pasteurized yogurt.

The stress-induced metabolites changes in the flavor formation of oolong tea during enzymatic-catalyzed process: A case study of Zhangping Shuixian tea

To interpret the environmental stresses induced dynamic changes of volatile and non-volatile constitutes in oolong tea leaves during enzymatic-catalyzed processes (ECP), metabolomic and proteomic studies were carried out using the processed leaf samples collected at the different stages of ECP for Zhangping Shuixian tea manufacture. Non-processed leaves were applied as control. Out of identified 980 non-volatiles and 157 volatiles, 40 non-volatiles and 8 volatiles were screened out as biomarkers, respectively. The integrated analysis on metabolites-proteins showed that phenylpropanoid biosynthesis, flavonoid biosynthesis, and phenylalanine metabolism were significantly enriched and highly correlated to the dynamic changes of key metabolites during ECP stage. A biological pathway network was constructed to illuminate the enzymatic-catalyzed production of critical flavoring compounds, including carbohydrates, amino acids, flavonoids, and volatile phenylpropanoids/benzenoids. The electronic-sensory analyses indicated leaf dehydration and mechanical wounding occurred over the sun-withering and turning-over steps are indispensable to form characteristic flavor of Shuixian tea.

Comparison of Different Volatile Extraction Methods for the Identification of Fishy Off-Odor in Fish By-Products

This study was conducted to analyze volatile odor compounds and key odor-active compounds in the fish soup using fish scarp and bone. Five extraction methods, including solid-phase microextraction (SPME), dynamic headspace sampling (DHS), solvent-assisted flavor evaporation (SAFE), stir bar sorptive extraction (SBSE), liquid-liquid extraction (LLE), were compared and SPME was finally selected as the best extraction method for further study. The volatile odor compounds were analyzed by gas chromatography-olfactometry-mass spectrometry (GC-O-MS) and comprehensive two-dimensional gas chromatography-olfactometry-mass spectrometry (GC × GC-O-MS) techniques, and the key odor-active compounds were identified via aroma extract dilution analysis (AEDA) and relative odor activity value (r-OAV) calculation. A total of 38 volatile compounds were identified by GC-O-MS, among which 10 were declared as odor-active compounds. Whereas 39 volatile compounds were identified by GC × GC-O-MS, among which 12 were declared as odor-active compounds. The study results revealed that 1-octen-3-one, 2-pentylfuran, (E)-2-octenal, 1-octen-3-one, hexanal, 1-octen-3-ol, 6-methylhept-5-en-2-one, (E,Z)-2,6-nondienal and 2-ethyl-3,5-dimethylpyrazine were the key odor-active compounds in the fish soup.

Flavor of tea (Camellia sinensis): A review on odorants and analytical techniques

Tea is among the most consumed nonalcoholic beverages worldwide. Understanding tea flavor, in terms of both sensory aspects and chemical properties, is essential for manufacturers and consumers to maintain high quality of tea products and to correctly distinguish acceptable or unacceptable products. This article gives a comprehensive review on the aroma and off-flavor characteristics associated with 184 odorants. Although many efforts have been made toward the characterization of flavor compounds in different types of tea, modern flavor analytical techniques that affect the results of flavor analysis have not been compared and summarized systematically up to now. Thus, the overview mainly provides the instrumental flavor analytical techniques for both aroma and taste of tea (i.e., extraction and enrichment, qualitative, quantitative, and chemometric approaches) as well as descriptive sensory analytical methodologies for tea, which is helpful for tea flavor researchers. Flavor developments of tea evolved toward time-saving, portability, real-time monitoring, and visualization are also prospected to get a deeper insight into the influences of different processing techniques on the formation and changes of flavor compounds, especially desired flavor compounds and off-flavor substances present at (ultra)trace amounts in tea and tea products.

Decoding the Specific Roasty Aroma Wuyi Rock Tea (Camellia sinensis: Dahongpao) by the Sensomics Approach

Aroma extract dilution analysis was performed on volatile fractions extracted from a freshly prepared Dahongpao (DHP) tea infusion using solvent-assisted flavor evaporation, yielding 65 odor-active domains with flavor dilution factors ranging between 32 and 32,768. In addition, six aromatic substances were captured by headspace analysis. Quantitation of 54 compounds by an internal standard method and stable isotope dilution assays revealed that the concentrations of 32 odorants exceeded their respective orthonasal odor threshold values in tea infusion. The results of odor activity values (OAVs) suggested that 2-metylbutanal (malty) and γ-hexalactone (coconut-like) had the highest OAVs (248 and 154). Eight odorants including γ-hexalactone (OAV 154), methyl 2-methylbutanoate (59), phenylacetic acid (7.2), acetylpyrazine (5.7), 2-methoxyphenol (3.4), p-cresol (2.7), 2,6-diethylpyrazine (2.7), and vanillin (1.8) were newly identified as key odorants in DHP tea infusion. An aroma recombination model in a non-volatile matrix extracted from tea infusion satisfactorily mimicked the overall aroma of DHP tea infusion, thereby confirming the identification and quantitative experiments. Omission experiments verified the obvious significance of 6-methyl-5-hepten-2-one (OAV 91), 2-ethyl-3,5-dimethylpyrazine (19), 4-hydroxy-2,5-dimethylfuran-3(2H)-one (13), and acetylpyrazine (5.7) as key odorants for the special roasty and caramel-like aroma of DHP tea.