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Aroma is an indispensable factor that substantially impacts the quality assessment of black tea. This study aims to uncover the dynamic alterations in the sweet and floral aroma black tea (SFABT) throughout various manufacturing stages using a comprehensive analytical approach integrating gas chromatography electronic nose, gas chromatography–ion mobility spectrometry (GC-IMS), and gas chromatography–mass spectrometry (GC-MS). Notable alterations in volatile components were discerned during processing, predominantly during the rolling stage. A total of 59 typical volatile compounds were identified through GC-IMS, whereas 106 volatile components were recognized via GC-MS throughout the entire manufacturing process. Among them, 14 volatile compounds, such as linalool, β-ionone, dimethyl sulfide, and 1-octen-3-ol, stood out as characteristic components responsible for SFABT with relative odor activity values exceeding one. This study serves as an invaluable theoretical platform for strategic controllable processing of superior-quality black tea. [ABSTRACT FROM AUTHOR]

The characteristic aroma of Chinese black tea (BT) produced in summer usually lacks intensity and persistence, reducing consumer acceptance and market demand. Strobilanthes tonkinensis Lindau (STL) possesses excellent biological characteristics, making it a promising novel tea ingredient. We investigated the effects of different addition methods and concentrations for the novel additive STL on the sensory quality of BT. A 20:1500 g/g addition to rolled tea leaves was identified as the best BT with STL (BoS) treatment. We identified 141 volatile metabolites (VMs) for the first time in STL, with high alcohol, ester, ketone, enyne, alkyne, and alkane contents. Partial least-squares discriminant analysis distinguished the samples and revealed 28, 26, and 14 differential VMs in STL vs. BoS, BT vs. STL, and BT vs. BoS comparisons, respectively. Using a combination of Venn, multiple experiment viewer, and odor activity value analysis, 16 key differential VMs were identified. Compared to BT, the 1-octen-3-ol, 1-hexanol, 1-dodecanol, (E)-3-hexen-1-ol, phenylethyl alcohol, and 2-methoxy-3-(2-methylpropyl)-pyrazine contents in BoS were 394.7%, 53.6%, 34.1%, 24.4%, 9.9%, and 5.7% higher, respectively. BoS combined the aromatic properties of BT and STL into a sweet and glutinous rice flavor. The results provide theoretical support for future research and development of novel BT-based products. [ABSTRACT FROM AUTHOR]

Aroma assessment remains difficult and uncertain in the present sensory assessment system. It is highly desirable to develop a new assessment method to discriminate the quality of various teas in the tea market. In the present work, based on linear discriminant analysis and principal component analysis, the aroma of dry and wet samples of different Xi‐hu Longjing and Pu‐erh teas were tested and differentiated by electronic noses (e‐nose). The results confirm that e‐nose can discriminate different priced Xi‐hu Longjing tea samples in the range of 80‐800 RMB/500 g and varying storage years of Pu‐erh tea samples. Furthermore, for the detection of both dry and wet samples of Longjing and Pu‐erh teas, the results reveal that all samples have specific aroma characteristics that e‐nose can recognize. More importantly, contribution analysis in sensors indicates that nitrogen oxides, methane and alcohols are the characteristic components that contribute to the fragrances of different priced Xi‐hu Longjing teas, while nitrogen oxides, aromatic benzene and amines make the fragrances of Pu‐erh teas with different storage years disparate. Practical Application: This work demonstrates that e‐nose can rapidly distinguish tea products with different price levels and varying storage years. With the advantages of ease of use, high portability and flexibility, e‐nose will be widely expanded and applied in refined processing and the development of flavored foods. [ABSTRACT FROM AUTHOR]

[Display omitted] • Volatiles in fresh scent green tea during processing were studied by volatolomics. • Significant changes in volatiles occurred during spreading and fixation stages. • A total of 10 key odorants were screened out in fresh scent green tea. • Lipid degradation and glycoside hydrolysis dominated aroma generation. Processing technology plays a crucial role in the formation of tea aroma. The dynamic variations in volatile metabolites across different processing stages of fresh scent green tea (FSGT) were meticulously tracked utilizing advanced analytical techniques such as GC-E-Nose, GC–MS, and GC × GC-TOFMS. A total of 244 volatile metabolites were identified by GC–MS and GC × GC-TOFMS, among which 37 volatile compounds were concurrently detected by both methods. Spreading and fixation stages were deemed as pivotal processes for shaping the volatile profiles in FSGT. Notably, linalool, heptanal, 2-pentylfuran, nonanal, β -myrcene, hexanal, 2-heptanone, pentanal, 1-octen-3-ol, and 1-octanol were highlighted as primary contributors to the aroma profiles of FSGT by combining odor activity value assessment. Furthermore, lipid degradation and glycoside hydrolysis were the main pathways for aroma formation of FSGT. The results not only elucidate the intricate variations in volatile metabolites but also offer valuable insights into enhancing the processing techniques for improved aroma quality of green tea. [ABSTRACT FROM AUTHOR]

In this study, a combination of quantitative drying and Maillard reaction was investigated by addition of theanine and sucrose during the final firing process to explore the mechanism of chestnut-like aroma formation. The influence of exogenous additives on the formation of chestnut-like flavor of green tea was characterized by infrared-assisted extraction coupled to headspace solid-phase microextraction (IRAE-HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS), physicochemical components as well as sensory evaluation. The addition of theanine or sucrose separately could improve the chestnut-like characteristics flavor, among which the chestnut-like aroma quality and comprehensive quality of green tea was significantly improved by the addition of theanine/dry tea (5‰ w/w). Significant difference (p < 0.05) was observed among different addition treatments on physicochemical components. In addition, the effect of different drying time (15–75 min) was investigated and the chestnuts-like aroma was significantly improved when the drying time reached 45 min. Moreover, the change trends of two key chestnut-like aroma compounds (methyl salicylate and α-ionone) were well consistent with the sensory evaluation and reached the highest at 45 min. The results would further enrich the basic theoretical system of chestnut-like fragrance and also provide a reference for the processing of chestnut-like aroma of green tea. • A combination of quantitative drying and Maillard reaction was adopted. • Theanine and sucrose were added to explore the mechanism of chestnut-like aroma. • The chestnut-like aroma was improved by addition of theanine/dry tea (5‰ w/w). • The intensity of chestnuts-like aroma reached the highest when drying for 45 min. [ABSTRACT FROM AUTHOR]

[Display omitted] • Variation of metabolites during black tea processing were explored by multi-omics. • A total of 178 volatile components and 103 non-volatile components were identified. • A total of 11 volatiles were regarded as key aroma-active components. • Significant changes in volatile metabolites were observed in withering stage. • Significant changes in non-volatile metabolites occurred in withering stage. Processing technology has an important effect on the flavor quality of black tea. However, the dynamic changes of volatile and non-volatile metabolites in black tea during processing are poorly understood. In this study, the volatile and non-volatile compounds during black tea processing were comprehensively characterized by integrated volatolomics and UHPLC-Q-Exactive/MS analysis. Volatile and non-volatile metabolites changed continuously throughout the processing process, especially during the withering stage. A total of 178 volatile metabolites and 103 non-volatile metabolites were identified. Among them, 11 volatile components with relative odor activity value greater than 1 (including dimethyl sulfide, 3-methylbutanal, 2-methylbutanal, β -myrcene, β -ocimene, linalool, methyl salicylate, β -cyclocitral, β -citral, citral, and β -ionone) were regarded as key aroma-active components responsible for finished black tea with sweet aroma. This study provides a comprehensive understanding of dynamic evolution trajectory of volatile and non-volatile metabolites during processing, which lays a theoretical foundation for the targeted processing of high-quality black tea. [ABSTRACT FROM AUTHOR]

[Display omitted] • Volatiles in floral aroma green tea during processing were studied by volatolomics. • A total of 184 volatile compounds were identified by integrated three techniques. • Significant changes in volatiles were observed in withering and fixation processes. • Seven key odorants were identified and verified by aroma recombination. To characterize the key odorants of floral aroma green tea (FAGT) and reveal its dynamic evolution during processing, the volatile metabolites in FAGT during the whole processing were analyzed by integrated volatolomics techniques, relative odor activity value (rOAV), aroma recombination, and multivariate statistical analysis. The volatile profiles undergone significant changes during processing, especially in the withering and fixation stages. A total of 184 volatile compounds were identified (∼53.26% by GC-MS). Among them, 7 volatiles with rOAV > 1 were identified as characteristic odorants of FAGT, and most of these compounds reached the highest in withering stage. According to the formation pathways, these key odorants could be divided into four categories: fatty acid-derived volatiles, glycoside-derived volatiles, amino acid-derived volatiles, and carotenoid-derived volatiles. Our study provides a comprehensive strategy to elucidate changes in volatile profiles during processing and lays a theoretical foundation for the targeted processing of high-quality green tea. [ABSTRACT FROM AUTHOR]

Aroma is an important factor in evaluating tea infusion quality. In this study, the aroma quality of 44 Dianhong Congou tea infusions was classified into high-quality group and non-high-quality group according to the sensory evaluation. The volatile components were investigated by using headspace solid phase microextraction combined with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry. A total of 258 volatile components were identified, of which the three component types with the highest relative percentages were alcohols (17.05%), aldehydes (15.12%), and heterocycles (15.12%). Clear discrimination was achieved by orthogonal partial least squares discrimination analysis (R2Y = 0.94, Q2 = 0.82). In addition, 69 important differential compounds were identified based on variable importance in the projection value (VIP >1.0) and one-way ANOVA (p < 0.05). Moreover, seven common key odorants with odor activity values (OAVs) > 1 were screened out, including (E, E) -2,4-heptadienal, linalool, 1-octene-3-one, geraniol, β -myrcene, (Z) -4-heptenal, and nonanal. Aroma character impact value indicated that linalool performed a positively supportive role in the aroma quality of Dianhong Congou tea infusions, while (E, E) -2,4-heptadienal negatively affected the aroma quality. These results contribute to providing a theoretical support for directional processing of high-quality black tea. [Display omitted] • A total of 258 volatile components were identified in tea infusions by GC × GC-TOFMS. • Two grades of tea infusions were well separated by OPLS-DA (R2Y = 0.94, Q2 = 0.82). • A total of 69 differential compounds were excavated based on VIP >1 and p < 0.05. • Seven common key odorants with OAVs >1 were screened out. [ABSTRACT FROM AUTHOR]

Fermentation is a crucial process in black tea processing; however, the effect of fermentation time on the quality of Yunnan Congou black tea has never been assessed. This study aimed to evaluate the quality of Yunnan Congou black tea by detecting quality components, artificial sensory evaluation, and objective attributes under different fermentation times (2, 3, 4, and 5 h). Partial least squares discriminant, odor active value, and least-significant difference analyses were used to identify key differences in its compounds. Overall, 36 non-volatile and 142 volatile compounds were detected. We found that 3 h was the optimal fermentation time for retaining several simple catechins, allowing formation of theaflavins (TFs) and thearubigins (TRs) and promoting formation and conversion of sugars and degradation of flavonoid glycosides. The volatile compounds were most abundant, and sweet and umami comprehensive sensor responses were stronger in the 3 h-fermented samples with the best sensory quality. Nine non-volatile (including TFs, TRs, theabrownins, caffeine, and glucose) and eight volatile (including linalool, phenylacetaldehyde, methyl salicylate, benzaldehyde, 2-pentyl-furan, and trans -β-ionone) markers were identified using multivariate statistical analysis. This study provides technical guidance for directed and standardized production and lays a theoretical foundation for the in-depth study of Yunnan Congou black tea. • Fermentation time significantly influences the quality of Yunnan Congou black tea. • Evaluation was done using sensory, objective attributes, and multivariate analyses. • Thirty-six non-volatile and 142 volatile compounds were detected among tea samples. • Fermentation for 3 h was determined as the optimum time for Yunnan congou black tea. • Nine non-volatile and 8 volatile key differential compounds were identified. [ABSTRACT FROM AUTHOR]

• The variable-temperature final firing process resulted in differential tea aromas. • Clear discrimination was achieved based on volatile metabolites of GC × GC-TOFMS. • Ninety-one volatile biomarkers were identified based on VIP > 1.0 and p < 0.05. • The e-nose can effectively distinguish the subtle aroma difference. The drying technology is crucial to the quality of Congou black tea. In this study, the aroma dynamic characteristics during the variable-temperature final firing of Congou black tea was investigated by electronic nose (e-nose) and comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS). Varying drying temperatures and time obtained distinctly different types of aroma characteristics such as faint scent, floral aroma, and sweet fragrance. GC × GC-TOFMS identified a total of 243 volatile compounds. Clear discrimination among different variable-temperature final firing samples was achieved by using partial least squares discriminant analysis (R2Y = 0.95, Q2 = 0.727). Based on a dual criterion of variable importance in the projection value (VIP > 1.0) and one-way ANOVA (p < 0.05), ninety-one specific volatile biomarkers were identified, including 2,6-dimethyl-2,6-octadiene and 2,5-diethylpyrazine with VIP > 1.5. In addition, for the overall odor perception, e-nose was able to distinguish the subtle difference during the variable-temperature final firing process. [ABSTRACT FROM AUTHOR]

• Novel fixation methods for green tea process were investigated and novel fixation used electromagnetic energy were discussed. • Volatile compounds in green tea under different fixation methods were compared. • Multivariate analyses and odor activity values were combined with sensory evaluations. • Roller-hot air–steam and roller-hot air fixation facilitate a chestnut-like odor. • Six compounds for differentiating chestnut and non-chestnut odor teas were identified. Fixation is the key process to ensure green tea quality; however, the effect of various fixation methods on the formation of green tea with a chestnut-like aroma and the evolution of key volatile compounds has not been assessed to date. In this study, we compared four types of fixation methods for green tea: roller-hot air–steam, roller-hot air, roller-steam, and single roller. Infrared-assisted headspace solid-phase microextraction and gas chromatography-tandem dual mass spectrometry technology were used to detect the volatile compounds of green tea samples during processing. Partial least-squares discriminant analysis (PLS-DA), multiple experiment viewer (MEV), odor activity value (OAV), and least-significant difference analyzes were then applied to clarify the best fixation method for forming a chestnut-like aroma and associated compounds, and to explore the change law of key volatile compounds using different green tea fixation processes. One hundred and eighty-four volatile compounds were detected in the processed samples, with roller-hot air fixation found as the optimal method for generating an intense and long-lasting chestnut-like aroma and floral taste, based on sensory evaluation. The PLS-DA model clearly distinguished the four kinds of fixation samples and obtained 32 differential volatile compounds. Combining OAVs with screening by MEV analysis, 2,6,10,10-tetramethyl-1-oxaspiro [4.5] dec-6-ene, linalool, cedrol, 3-methyl-butanal, trans -β-ionone, and τ-cadinol emerged as key differential volatile compounds between green teas with and without a chestnut-like aroma. The evolution of these six differential volatile compounds throughout the tea-making process confirmed that rolling-hot air coupling treatment is most conducive to produce a chestnut-like aroma, which is beneficial to form and transform 2,6,10,10-tetramethyl-1-oxaspiro[4.5] dec-6-ene, 3-methyl-butanal, and τ-cadinol with baking aromas and fruity substances. These results provide a theoretical basis and technical guidance for the precise and directional processing of high-quality green tea with a chestnut-like aroma. [ABSTRACT FROM AUTHOR]

Aroma is a crucial factor determining the tea quality. Tea aroma consists of numerous volatiles and is highly dynamic. Thus, it is significant to generate a comprehensive pattern capturing the dynamic information reflected by the temporal changes of tea volatiles occurring in a relatively short period such as during tea brewing. Herein, a highly time-resolved positive photoionization ion mobility spectrometry (PP-IMS) approach has been developed for real-time fingerprinting of the dynamic changes of tea volatiles. The influences of different ionization sources on the analytical performance were systematically explored. The optimal acquisition time window was determined based on the minimum humidity interference. As a proof of concept, this approach was applied to the assessment and comparison of five different types of green tea aromas. In combination with chemometric tools, five types of aromas were accurately distinguished by using their "dynamic" fingerprints. The RV coefficients (0.20–0.63) and discrimination result showed that the "dynamic" fingerprints contained additional different information on tea volatiles and enabled an improved discrimination of tea aromas, compared to the conventional "static" fingerprints. This study provides a useful tool towards a comprehensive assessment of tea aromas, which is promising to facilitate the quality evaluation and control of tea products. Image 1 • A novel method for real-time fingerprinting of the dynamic changes of tea volatiles. • A highly time-resolved positive photoionization ion mobility spectrometry was used. • This method offers a comprehensive assessment of tea aroma including its dynamics. • Dynamic fingerprints of tea volatiles enable an improved discrimination of aromas. [ABSTRACT FROM AUTHOR]