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Abstract: The signaling pathways that control the hypoxia/reoxygenation (H/R)-induced cardiomyocyte apoptosis have not been fully defined. In this study, we investigated whether extracellular signal-regulated kinase1/2 (ERK1/2) plays a role in NO’s anti-apoptotic effect against H/R injury. Primary cultures of adult rat ventricular myocytes (ARVMs) were exposed to 3h of hypoxia followed by 30, 60, 90 and 120min of reoxygenation in presence of a vehicle, NO donor (GSNO, 50μmol/L) and inhibitors of ERK1/2 (PD98059, 10μmol/L). GSNO protected the cardiomyocyte from reoxygenation injury, as evidenced by decreased apoptosis, and this protective effect was inhibited by co-treatment with PD98059 during reoxygenation. Consistent with this, when administered with adenoviral vector encoding dominant negative ERK (Ad-dnERK), GSNO’s effect was also blocked. Western blotting revealed that GSNO increased the ERK phosphorylation during reoxygenation. Furthermore, H/R-induced activation of caspase-3 and -9 were attenuated by GSNO. Interestingly, X-linked inhibitor of apoptosis protein (XIAP) protein levels decreased in myocytes subjected to reoxygenation, and ERK phosphorylation can improve XIAP expression, which involved inhibiting caspase-3, -7 and -9 activities. Overexpression experiment with adenoviral vector containing constitutively active ERK (Ad-caERK) alone acquired protection against apoptosis triggered by H/R injury and positively regulated XIAP expression compared with control adenovirus (Ad-LacZ). Our data demonstrated that, GSNO’s antiapoptotic effect against reoxygenation injury involves ERK signaling pathway. The activation of ERK increased XIAP expression and led to decreased caspase activation. [Copyright &y& Elsevier]

Catechins and theaflavins, as the primary bioactive constituents of black tea, have a significant impact on its color, aroma, and flavor profile. We developed a rapid and precise method using HPLC to detect catechins and theaflavins in black tea. The method employed 0.1% formic acid-acetonitrile (phase A) and 1% formic acid-water (phase B) as mobile phases. Separation occurred on an Agilent SB-C18 column (4.6 mm × 250 mm, 5 µm), with 20 μL injection volume. Detection took place at 30 °C with a flow rate of 1 mL/min for 55 min.Quantitative determination utilized the external standard method, exhibiting high sensitivity (limit of detection: 0.19 to 5.14 μg/mL) and a strong linear correlation (R2 ≥ 0.9993) between concentration range and peak area. Precision, repeatability, and stability were excellent, with relative standard deviations (RSDs) below 5% (n = 5). The average recovery rate of standard addition ranged from 98.02% to 102.57%, with an RSD of less than 3.17% (n = 5). In summary, this straightforward, efficient, and precise approach is well-suited for both qualitative and quantitative analysis of catechins and theaflavins in tea. It overcomes the limitations of previous methods, providing a valuable tool for evaluating the quality and composition of black tea. • A HPLC method has been developed for detection of both catechins and theaflavins. • This method detects 14 Catechins and theaflavins. • The method is a simultaneous, rapid, accurate and efficient approach. • The method was validated by analysis extract of Longgu black tea. [ABSTRACT FROM AUTHOR]

Fixation is crucial for green tea quality; previous studies were conducted on finished teas and focused on the volatile metabolites of green tea. However, non-volatile metabolites' (NVMs) evolution and formation mechanisms during fixation remain unclear. Here, fixated tea samples were collected at seven different time points during the green tea fixation stage, the dynamic changes and formation mechanisms of NVMs investigated via ultra-performance liquid chromatography-tandem mass spectrometry and enzymatic activity analyses. The results showed that fixation contained enzymatic activity thermal and non-enzymatic thermal stages. Moreover, 1196 NVMs (10 classes) were detected, and significant NVM variations were observed during the "enzymatic activity thermal" fixation stages, with increasing trends in lipids and amino acids, except alkaloids. Furthermore, 160 common differential NVMs were identified. KEGG analysis revealed that unsaturated fatty acid, linoleic acid phenylpropanoid, and flavonoid metabolism pathways were essential during fixation and influenced green tea aroma, taste, and color formation. These results provide a theoretical basis to regulate green tea fixation technology and enrich the chemical theory of green tea processing. • Fixation contained enzymatic activity thermal and non-enzymatic thermal stages. • Metabolites change dramatically during the enzymatic activity thermal stages. • 160 common differential NVMs were identified in the green tea-fixated samples. • Unsaturated fatty acid and linoleic acid metabolism is crucial for aroma formation. • Phenylpropanoid and flavonoid metabolism is crucial for taste and liquor formation. [ABSTRACT FROM AUTHOR]

• Effect of fermentation method on Congou black tea quality was examined firstly. • Novel dynamic fermentation (RFM) was superior to traditional fermentation method. • Black tea with RFM had higher amino acids, theaflavins and thearubigins. • Black tea with RFM had lower tea polyphenols, catechins and theabrownins. • Amino acids and tea pigments were the key fermentation differential substances. This study aimed to investigate the effects of a novel dynamic fermentation method (DFM) on the biochemical components change and sensory quality formation of Congou black tea. It was found that the most drastic changes in biochemical components took place within 30 min of fermentation. The a value (redness) of liquor color, the reduction degree of catechins, polyphenol oxidase activity, the formation rate and contents of theaflavins and thearubigins, as well the content of amino acids were significantly higher under DFM than the traditional fermentation method. Sensory quality was also superior under DFM with the highest scores for liquor color, aroma, and taste. Partial least squares discrimination analysis (PLS-DA) indicated significant differences between DFM and the other two methods. Moreover, the loadings scatter plot and variables important in the projection (VIP) showed that amino acids, catechins, and tea pigments were the key differential substances among the fermentation methods. These results are expected to provide a theoretical basis and technical guidance for the improvement of black tea quality. [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]

Fixation is a critical step in green tea quality formation. In this study, an integrated analysis of sensory evaluation, electronic tongue, quantitative analysis of major chemical constituents and metabolomics analysis was performed to investigate the effect of fixation temperature (205 °C, 215 °C, 225 °C) on the taste profile of Longjing green tea and the underlying non-volatile metabolites changes. A total of 17 major chemical constituents and 100 non-volatile metabolites were investigated. 31 key differential metabolites were screened. With the increase of fixation temperature, the content of cis -catechins (epicatechin) and dimeric catechins (theaflavin, theaflavin-3′-gallate, theaflavin-3,3′-gallate) were significantly decreased, which may reduce the bitterness. The astringency of tea infusions varied depending mainly on the content changes in flavonol glycosedes, along with trans -catechins (gallocatechin, catechin gallate, gallocatechin gallate). Besides, the contents of amino acids, phenolic acids and carbohydrates were also varied. These substances were altered possibly due to variations in epimerization, oxidative polymerization, and thermal degradation. Longjing tea treated with an appropriate fixation temperature of about 215 °C rendered optimal taste quality. This study could advance the understanding of the fixation regulation of green tea taste and its underlying mechanism. [Display omitted] • Fixation temperature affects the bitterness and astringency of Longjing tea. • Decreases in cis- catechins and theaflavins led to a decrease in bitterness. • Low levels of trans -catechins and flavonol glycosides led to low astringency. • Epimerization and oxidative polymerization of catechins were significantly impacted. • 31 key differential metabolites were screened in differently treated samples. [ABSTRACT FROM AUTHOR]

In the present work, a simple, rapid and reliable method using Micro-Chamber/Thermal Extractor (μ-CTE) combined with thermal desorption (TD) coupled to gas chromatography-mass spectrometry (TD-GC-MS) was developed for investigating the differences in aroma determinants among three chestnut flavor green teas (tender chestnut, chestnut, and cooked chestnut). The extraction parameters such as sample amount, extraction time, and chamber temperature were evaluated through orthogonal experimental design to achieve the maximum of extraction efficiency. Subsequently, the repeatability and precision of the method were confirmed under optimal conditions. A total of 97 volatile compounds were identified in 15 green tea samples. Furthermore, multivariate statistical analysis including partial least square-discrimination analysis (PLS-DA) and hierarchical clustering analysis (HCA) were conducted to reveal the detailed distinctions of three chestnut flavor green teas. Totally, 41 potential volatile markers were identified based on variable importance in projection (VIP) score > 1, which were responsible for the discrimination of green teas with three different flavor characteristics. The results suggest that the proposed strategy is a feasible and rapid technique to distinguish green teas and will provide scientific role on the special flavor quality assessment of green teas. [ABSTRACT FROM AUTHOR]

Drying plays an important role in the development of high-quality aroma black tea. In this study, changes in the volatile profiles of Congou black tea samples subjected to different drying times were comprehensively characterized via gas chromatography-electronic nose, gas chromatography-mass spectroscopy, and gas chromatography-ion mobility spectroscopy (GC-IMS) analyses. Different drying times generated different aroma types (e.g., floral and sweet aromas, etc.). Forty-five minutes of drying treatment was identified as a critical time point for the formation of tea aroma quality, since at this point additional drying caused a decline in aroma quality. Here we identified a total of 90 volatile organic compounds, mainly alcohols and aldehydes, using GC-IMS. Based on the volatile fingerprints generated by GC-IMS, an authentic orthogonal partial least squares discriminant analysis model with credible parameters (R2Y = 0.921, Q2 = 0.817) was established. Moreover, using variable importance in projection > 1.35 and p < 0.05 as filtering criteria, six variables including four identified key differential components were screened out. This study provides a new perspective for understanding the dynamic changes occurring during drying and lays a theoretical foundation for precise and quality-oriented processing of Congou black tea. [Display omitted] • Alcohols and aldehydes were the most abundant volatiles identified by GC-IMS. • Four differential components with VIP > 1.35 & p < 0.05 were identified and screened. • Significant changes in volatile components occurred under a drying time of 45-min. • Excellent separation of volatile components was achieved via GC-IMS. [ABSTRACT FROM AUTHOR]

Drying is an important process in black tea processing, at the same time, catechin is an important factor in determining the sensory quality of black tea. However, there is a lack of effective real-time detection methods for the detection of catechins in black tea drying process. Therefore, we analyzed the trends of catechins in black tea drying process under different drying conditions and further explored the quantitative prediction model of eight individual catechins in black tea drying process by Least squares support vector machine (LS-SVM) based on near-infrared spectroscopy (NIRS) and chemometrics methods. The results showed that the prediction accuracy of the eight monomeric catechins prediction models established based on the extraction of competitive adaptive reweighted sampling (CARS) and successive projections algorithm (SPA) feature spectra achieved the best results, and the correlation coefficient values of the prediction sets (R p) were all greater than 0.98, and the relative percentage deviation (RPD) values were all greater than 5. The gallocatechin gallate (GCG) with the highest prediction accuracy was 0.9977 and the RPD value was 14.8. This study shows that the method based on near-infrared spectroscopy and chemometrics has strong predictive power for catechins in black tea drying process, which is a guideline for controlling the sensory quality of black tea drying. • Different drying temperatures and times affect the catechin content of black tea. • Catechin during black tea drying was monitored using NIR spectroscopy. • Different quantitative prediction models were compared to accurate detection of catechins. • NIR spectroscopy can be used to monitor the drying process of black tea. [ABSTRACT FROM AUTHOR]

Rolling is a crucial step in congou black tea manufacturing. Herein, the influence of rolling time (50, 75, 100, 125 min) on the sensory quality and chemical composition of black tea was investigated by human sensory evaluation, electronic tongue, colorimetric analysis, tea pigments quantification and liquid chromatography-mass spectrometry (LC-MS) based non-targeted metabolomics. With increasing rolling time, tea liquor color attributes a*, b*, C* and pigments theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs) were significantly increased. Fifty-two key differential metabolites were identified among four treatments. Catechins, dimeric/trimeric catechins, amino acids were significantly declined. The changes of flavonol/flavone glycosides depended on the linkage pattern. Flavonol O -glycosides such as myricetin 3- O -glucoside were decreased, whereas flavone C -glycosides such as vitexin were increased. These results suggested that different rolling times influenced the catechins oxidative polymerization, flavonol O -glycosides hydrolysis and amino acids oxidation. Black tea by 100-min rolling rendered optimal sensory quality, with highest umami and low bitter intensities in electronic tongue, and higher quality index (10 TFs + TRs)/TBs. Similar result was obtained in a validation batch in a different year. This study provides novel insights into the effect of rolling on black tea quality, which may serve as guidance for the manufacturing of high-quality congou black tea. [Display omitted] • The effect of rolling time on the black tea quality was studied by metabolomics. • Rolling time affected the taste, liquor color and chemical profile of black tea. • Catechins, dimeric/trimeric catechins, amino acids declined with longer rolling. • Flavonol O -glycosides declined but flavone C -glycosides increased in long-rolled tea. • An appropriate rolling duration is beneficial to black tea quality. [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]

Aroma is one of the key factors in evaluating tea quality. However, the dominant aroma components of black teas with different aroma characteristics are still unknown. In this study, the key aroma compounds in black teas with floral aroma, sweet aroma, and sweet & floral aroma were systematically characterized by the combination of gas chromatography electronic nose (GC-E-Nose), gas chromatography-ion mobility spectrometry (GC-IMS), and odor activity value (OAV) analysis. A satisfactory discrimination was obtained by using partial least squares-discriminant analysis, based on the volatile fingerprints from the GC-E-Nose and GC-IMS, with robustness model parameters (R2Y = 0.981, and Q2 = 0.967) and (R2Y = 0.893, and Q2 = 0.86), respectively. Among the 38 identified aroma compounds, 15 volatiles were simultaneously identified as important odorants with OAVs greater than 1 in three fragrant black teas, namely (E)-2-nonenal, linalool, nonanal, benzene acetaldehyde, octanal, benzaldehyde, oct-1-en-3-ol, heptanal, ethyl 2-methylpentanoate, (E)-2-hexen-1-ol, hexanal, 2-methylbutanal, 3-methylbutanal, (E)-3-penten-2-one, and butanal, with ethyl 2-methylpentanoate (176.44≤OAV≤1453.47), 3-methylbutanal (19.59≤OAV≤76.16), (E)-2-nonenal (37.43≤OAV≤56.46) and linalool (3.29≤OAV≤56.72) being the most notable. The results provide a theoretical support for flavor quality improvement and oriented processing of black tea. [Display omitted] • Four volatile biomarkers were identified based on VIP＞1.2 and p ＜0.05. • 15 volatiles with odor activity values＞1 were identified in three aroma black teas. • Linalool displayed a higher odor activity value in three fragrance black teas. • Ethyl-2-methylpentanoate was identified as the most important key odorant. [ABSTRACT FROM AUTHOR]

Rapid and accurate measurement of the moisture in black tea during withering is crucial for the digitalization of the processes in the black tea industry. Therefore, computational systems should be developed for the rapid detection of moisture in withered leaves. In this study, relying on miniaturized near-infrared spectroscopy (micro-NIRS) coupled with a smartphone, an Elman neural network (ENN)-based moisture-prediction model was developed. Specifically, the ENN-based moisture-prediction model incorporated principal component analysis (PCA) and was designed to perform rapid detection and analysis of the water content of withered leaves. The combination of an ENN and PCA can both embody spectral features and exhibit strong dynamic information-processing capabilities. The proposed approach improves the anti-interference ability and training efficiency of the model. Experimental results show that micro-NIRS is an effective and fast tool for evaluating the moisture content of withered leaves and that the proposed model is highly suited as a rapid-detection system, with a correlation coefficient of prediction of 0.99314 and a residual predictive deviation of 11.8108. Thus, this research provides a portable, accurate, fast, and non-destructive method for predicting the moisture content of withered leaves. • Smartphone-coupled micro-NIRS was used to detect withered leaf moisture. • Different data sets pre-processing and prediction model were compared. • A rapid quantitative prediction model for withered leaves moisture was established. • The SNV-PCA-ENN model provided the best withered leaf moisture prediction. [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 drying technology plays an important role in aroma quality. Herein, the dynamic change of volatile profiles of green tea under different temperature gradients and duration were analyzed by using gas phase electronic nose (GC-E-Nose) and gas chromatography-ion mobility spectrometry (GC-IMS) combined with multivariate statistical analysis. A total of 33 compounds were identified. Three drying stages could be clearly discriminated from the samples with different drying time, and 20-min-drying was a key transition point. 3-Methylbutanal, isopropyl alcohol, methyl benzoate, and heptanal were found to play an important role in discrimination of the above three stages, basing on variable importance in projection ＞1.2 and p ＜0.01. The volatile profiles changed dynamically with increasing drying temperature, and the significant change occurred under the temperature of 105 °C. In addition, the GC-E-Nose could quickly and effectively characterize the dynamic changes under different drying conditions, and verified and complemented the GC-IMS analysis results. This study provides comprehensive insight into variation in the volatile metabolite profile during the drying process of green tea. [Display omitted] • The volatile fingerprints of green tea were developed by GC-E-Nose and GC-IMS. • Four volatile biomarkers were identified based on VIP＞1.2 and p ＜0.01. • The most prominent alterations occurred at 20-min-drying. • The significant change of volatiles occurred under the temperature of 105 °C. [ABSTRACT FROM AUTHOR]

Aroma is one of the most important quality attributes of black tea infusions. In this study, the aroma quality of 44 Dianhong black tea (DBT) infusions were investigated by rapid gas phase electronic nose (GC-E-Nose) combined with multivariate statistical analysis for the first time. Among 61 volatile compounds identified, the most abundant ones were aldehydes. Both partial least squares discriminant analysis (PLS-DA) and Fisher discriminant analysis (FDA) could effectively classify the aroma quality of DBT infusions. The prediction accuracy of FDA (95.2%) was higher than that of PLS-DA (78.6%). Moreover, stepwise multiple linear regression was shown to accurately predict the quality score of DBT infusions, and the Rp value of the sensory score of the predicted model was 0.94. Furan, methyl acetate, 2,3-pentanedione, limonene, and linalool were found positively correlated with the aroma quality of DBT infusions, while 3-ethylpentane, 1-pentene, (E)-2-hexene, and methyl eugenol were negatively correlated with the aroma quality of DBT infusions. These results contribute to understand that rapid GC-E-Nose technology is a supplement to the objective sensory evaluation, and provide a new technical method for the quality evaluation and control of tea infusions. [Display omitted] • Aldehydes were the most abundant among 61 volatile compounds identified. • 7 key components in quality category were screened out based on VIP >1.5 & p < 0.05. • 2-Methylfuran and linalool played an important role in aroma quality score. [ABSTRACT FROM AUTHOR]

Theaflavins (TFs) are the main components responsible for the bright, orange-yellow color of liquor and fresh, brisk, and astringent taste of black tea. TFs are formed from the enzymatic oxidative condensation of catechins. In this study, we aimed to optimize the production of TFs from catechins in an in vitro liquid-state fermentation system. We examined (1) three different enzyme sources (2) two different times for the addition of catechins and (3) three different ratios (1:2, 1.5:1.5, and 2:1) of key catechins [(−)-epigallocatechin (EGC); (−)-epigallocatechin gallate (EGCG)]. The results indicated that the use of polyphenol oxidase (PPO) promoted a rapid and uniform consumption of catechins, resulting in a sustained high-level production of TFs. The batchwise addition of catechins was the best method for sustained and high-efficiency TFs formation. An EGC/EGCG ratio of 1:2 led to the formation of relatively higher amounts of theaflavin-3ʹ-gallate (TF-3ʹ-G) and TF-3,3ʹ-digallate (TF-D-G), which resulted in a significantly higher total TFs content. These results demonstrate that the batchwise addition of catechin substrates with a high EGCG content using PPO as an enzyme source can improve the formation of TFs. Our results provide a theoretical basis for understanding the mechanisms of TFs synthesis. • Mechanisms of theaflavin formation during liquid-state fermentation were elucidated. • Different enzyme, catechin addition times, and catechin ratios were studied firstly. • PPO promoted the uniform consumption of catechins and continuous production of TFs. • EGC and EGCG are key catechins substrates that affect theaflavin formation. • Batchwise addition of high EGCG-content catechins was optimal for theaflavin. [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]

Selection of appropriate tea (Camellia sinensis) cultivars, represents an essential prerequisite for tea manufacture. A detailed phytochemical comparison of different cultivars, and its influence on flavor quality of finished tea, remain to be explored. Herein, different Chinese tea cultivars which are suited for only green or black tea processing (GT, BT cultivars), or compatible for both tea types processing (BT&GT cultivars), were pre-selected and carefully collected. A nontargeted metabolomics using liquid chromatography coupled to mass spectrometry (LC-MS) was performed, combined with comprehensive pathway mapping. Meanwhile, all cultivars were subjected to parallel processing for sensory evaluation of finished black tea. BT cultivars showed most prominent differences, with significantly higher levels of catechins, condensed products and phenolic acids including gallotannins, whereas lower contents of flavone C -glycosides, free sugars and amino acids were found. Particularly, unique glycosylation patterns of flavonol glycosides were identified for the first time. O -rutinosylation and O -glucosylation were predominant in BT cultivars, whereas O -glucosyl/galactosyl-rutinosylation were predominant in GT and BT&GT cultivars. The flavor attributes of differential compounds could be well associated with corresponding processing suitability of studied cultivars. This study provides an in-depth elucidation of metabolic features associated with processing suitability of different tea cultivars. • Black tea processing-suited cultivars exhibited more metabolic variations. • Different tea cultivars show unique flavonol glycosylation patterns. • Flavone C -glycosides are lower in black tea processing-suited cultivars. • (Condensed-)catechins are higher in black tea processing-suited cultivars. • Phenolic acids including gallotannins are low in green tea processing-suited cultivars. [ABSTRACT FROM AUTHOR]