Qianlin cha (QLC), a traditional Taoist herbal tea derived from Camellia cuspidata, is prized for its health benefits, but its bitter taste is obvious and has a herbal flavor. In order to reduce the bitterness in QLC, enhance the fragrance of florals, and develop new products. The purpose of this study is to reduce the bitterness and astringency of QLC and improve the fragrance of florals through the application of yellowing process. Comprehensive assessments, including sensory evaluation, color analysis, partial least squares discriminant analysis (PLS-DA) of physicochemical parameters, headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), and gas chromatography-olfactometry (GC-O), were employed to identify key determinants of QLC's sensory appeal. The yellowing-treated QLC (QLC-Y) exhibited significantly improved sensory scores, marked color transformation toward desirable yellow hues with reduced a and b values, and enhanced levels of amino acids and soluble sugars (P < 0.05), contributing to a sweeter taste profile. In contrast, bitter and astringent ester catechins decreased notably, indicating superior physicochemical characteristics. Aroma analysis indicated the elevated aroma indices (P < 0.05), leading to the identification of four aroma-active compounds by GC-O: linalool, nonanal, sulcatone, and (E,E)-2,4-heptadienal. These results indicated that the yellowing treatment alters the sensory profile of QLC from herbaceous and bitter notes to a sweeter, more floral character by modifying its volatile compounds. This study provides preliminary mechanistic evidence suggesting that yellowing treatment associated with improvements in Camellia cuspidata tea quality, which could offer a scientific basis for premium herbal tea production.

This study systematically investigates the regulatory role of processing technology in the aroma differentiation of Fuding Dabai tea (Camellia sinensis). Using an integrated sensomics approach combining quantitative descriptive analysis and GC × GC-TOF-MS, we deciphered aroma formation in green (GT), white (WT), black (BT), and dark (DT) teas. Among 187 volatiles detected, WT exhibited the highest VOC content (2349.42 μg/L) and the most key odorants (30 of 36). Multivariate statistical modeling identified fermentation degree as the primary factor driving aroma divergence, clearly discriminating fermented (BT/DT) from non/light-fermented (GT/WT) teas. OPLS-DA selected 12 marker compounds (VIP > 1), predominantly alcohols and aldehydes. Sweet aroma exhibited strong correlations with benzeneacetaldehyde (r = 0.91) and (E)-2-hexenal (r = 0.92), while aged aroma correlated strongly with (E,E)-2,4-heptadienal (r = 0.92) (all p < 0.001). We demonstrate that processing reconfigures aroma profiles through enzymatic inhibition, oxidative conversion, and microbial fermentation pathways. These results provide a biochemical basis for aroma-oriented optimization in tea processing and establish the superior suitability of Fuding Dabai for white tea production.

Floral aroma is a key indicator of high-quality black tea. Response surface methodology (RSM) was applied to systematically optimize the processing technology of floral-flavored black tea from Ziyang population fresh leaves, with the timing of shaking (leaf moisture), rolling time and fermentation time as independent variables and sensory aroma score as the response value. The optimal floral quality was obtained when shaking started at 71.84% moisture content, with 45.22 min rolling and 3.06 h fermentation. Gas chromatography-olfactometry (GC-O), odor activity value (OAV) and aroma recombination experiments revealed that benzeneacetaldehyde, linalool, geraniol, phenylethyl alcohol and β-damascenone were key floral aroma compounds. The enrichment analysis of floral aroma active compounds during processing indicated that appropriate the timing of shaking (70%−72% moisture), rolling (45−55 min) and fermentation (3−3.5 h) promote their accumulation in black tea. This study provides new insights into the precise regulation and improvement of floral aroma substances in black tea.

To investigate the effects of different drying methods on the quality of Tanyang Gongfu black tea, five drying processes were employed in this study: Vacuum-freeze drying (FD), hot-air drying (HD), hot-air-vacuum-freeze combined drying (HFD), vacuum-freeze-hot-air combined drying (FHD), and microwave drying (MD). The five dried tea samples were compared by combining sensory evaluation, physicochemical component determination, aroma compound detection, and chemometric analysis. The results indicated that the Tanyang Gongfu black tea was characterized mainly by sweet floral aroma and sweet mellow taste. Among them, the FHD sample was characterized by a pure, sweet, refreshing taste and a pronounced sweet floral aroma, achieving the highest sensory score (90.90 points). Significant differences were observed in the quality components of the tea samples subjected to different drying methods. FD treatment was found to be conducive to increasing the thearubigins content (3.08%). The free amino acid (6.69%) and tea polyphenol (12.28%) contents in the FHD sample were significantly higher than those in the other groups (P<0.05). The highest water extract content (38.23%) was found in the HFD sample. Soluble sugars (44.34 mg/g) in the HD sample were found to contribute to its sweet mellow taste characteristic. Flavonoids were maximally retained (24.61 mg/g) in the MD sample. A total of 99 aroma compounds were detected in the five tea samples, mainly including aldehydes, esters, and alcohols. The FD sample possessed unique grassy and floral characteristics, mainly contributed by hexanal (OAV=33.51), linalool (OAV=75.45), and geraniol (OAV=239.77). The sweet and honey-like aroma characteristics of the HD sample were associated with the enrichment of isovaleraldehyde (OAV=254.73) and phenylacetaldehyde (OAV=41.44). Geraniol (OAV=210.22) was identified as the characteristic aroma compound for the FHD treatment. Geraniol (OAV=130.04) and isovaleraldehyde (OAV=122.23) were determined to be the main aroma-contributing components for HFD. Nonanal (OAV=71.89) was identified as the key aroma component for MD treatment. This study systematically elucidated the influence of different drying processes on the quality of Tanyang Gongfu black tea, providing a theoretical basis for optimizing black tea processing technology.

Background: Roasting conditions significantly influence the sensory profile of Hubei strip-shaped green tea (HSSGT). Methods: This study examined the effects of roast processing on the sensory attributes, color qualities, physicochemical properties, and key aroma compounds of HSSGT. Sensory evaluation, color qualities determination, principal component analysis of physicochemical components (PCA), HS-SPME (headspace solid-phase microextraction) coupled with GC-MS (gas chromatography–mass spectrometry), relative odor activity value (ROAV), gas chromatography–olfactometry (GC-O), and absolute quantification analysis were employed to identify the critical difference in compounds that influence HSSGT desirability. Results: The results indicated that HSSGT roasted at 110 °C for 14 min achieved the highest sensory scores, superior physicochemical qualities, and an enhanced aroma index, which was attributed to shifting the proportion of chestnut to floral volatile compounds. Additionally, sensory-guided ROAV, GC-O, and absolute quantification revealed that linalool, octanal, nonanal, and hexanal were the most significant volatile compounds. The variations in these four critical compounds throughout the roasting process were further elucidated, showing that the ideal roasting conditions heightened floral aromas while diminishing the presence of less desirable green odors. These findings offer technical guidance and theoretical support for producing HSSGT with a more desirable balance of chestnut and floral aroma characteristics.

Astringency is crucial in determining the taste quality of matcha, primarily influenced by flavonoids. However, the specific impact of cultivars and processing techniques on flavonoid composition remains unclear. This study employs quantitative descriptive analysis, multivariate statistical analysis, dose over threshold (Dot) values, and sensory verification to comprehensively analyze changes in flavonoid profiles during the processing of two cultivars (Longjing 43 and Zhongcha 108) and their effects on matcha's astringency. 679 flavonoid metabolites were identified, predominantly comprising flavones and flavonols. Longjing 43 fresh leaves predominantly contain glycosylated flavonoids, whereas Zhongcha 108 has a higher proportion of O-methylated modifications. Drying is a critical process, significantly boosting flavonoid glycoside content. Cultivar emerges as the primary and most influential factor determining matcha astringency, with processing techniques exerting a lesser impact. Furthermore, by utilizing Dot values and sensory verification, it was determined that quercetin-3-O-glucoside, kaempferol-3-O-rutinoside, (-)-epigallocatechin gallate, and kaempferol-3-O-glucoside are pivotal components of matcha's astringency.

γ-Aminobutyric acid (GABA), a four-carbon non-protein amino acid functions as a key signaling molecule in plants. As a signature bioactive compound in tea, GABA plays a crucial role in determining both flavor profile and health-promoting properties. Despite its importance, the molecular regulation of GABA accumulation in tea plants-especially its metabolic crosstalk with key quality determinants like flavonoids-remains elusive. While amino acid transporters are known to mediate source-sink allocation in plants, the functional characterization of GABA transporters in Camellia sinensis has been lacking. In this study, we identified and functionally characterized the bidirectional amino acid transporter CsBAT in tea plants. Through a comprehensive multiplatform validation system encompassing yeast heterologous expression, Arabidopsis genetic transformation, and tea transgenic system, we revealed that CsBAT shows vascular-specific expression and facilitates directional amino acid transport from source (mature leaves) to sink (young shoots), thereby significantly boosting GABA accumulation in buds and young leaves. Importantly, we discovered that CsBAT functionally interacts with key flavonoid biosynthetic enzymes (LAR, 4CL, C4H) within secondary metabolic networks. Our findings provide the first mechanistic link between CsBAT-mediated amino acid transport and tea quality formation, establishing both theoretical frameworks and practical tools for molecular breeding of premium tea cultivars.

With the steady rise in tea production, the need for effective tea quality monitoring has become increasingly pressing. Traditional sensory evaluation and wet chemical detection methods are insufficient for real-time tea quality monitoring. As an emerging technology, near infrared spectroscopy (NIRS) offers numerous advantages, such as preserving sample integrity, generating objective results, and enabling rapid, straightforward assessments. These features make it an ideal choice for real-time tea quality testing. This paper systematically reviews the principles of NIRS, spectral preprocessing methods, statistical modeling techniques, and commonly used machine learning approaches. Furthermore, it provides an in-depth discussion of the research progress of NIRS in areas such as fresh tea leaf quality evaluation, rapid detection of tea-specific components, tea quality assessment and species identification, geographic traceability, development of NIRS equipment, and standardization. Future research directions in the tea field are also proposed. This review serves as a valuable resource for researchers aiming to understand the application and development of NIRS technology in the tea field. It offers insights to facilitate real-time tea quality monitoring and ultimately achieve intelligent quality control.

This study systematically investigates lipid dynamics and their role in aroma formation during Qingzhuan tea (QZT) processing. Using UHPLC-MRM-MS/MS and GC-MS, we analyzed fatty acids (FAs) and oxidized fatty acids (OFAs) across seven processing stages, identifying 31 FAs and 55 OFAs. Polyunsaturated fatty acids (PUFAs), particularly α-linolenic acid (C18:3) and linoleic acid (C18:2), dominated the lipid profiles (43.7 %-60.1 %), exhibiting biphasic dynamics: a 5.3-fold increase during pile fermentation and natural aging (RT → A12) followed by oxidative degradation (30.0 % reduction in QZT). Multivariate analysis revealed 76 differential lipids correlating with 22 key volatiles, including (E,E)-2,4-heptadienal and (E)-2-octenal. Metabolic pathway analysis mapped lipoxygenase/cyclooxygenase (LOX/COX)-mediated oxidation of C18:3/C18:2 to hydroperoxides, which were then cleaved by lyases into aldehydes. Isotope labeling confirmed cross-pathway interactions between linoleic and arachidonic acid metabolism, while modeling experiments validated enzymatic generation of C6-C9 aldehydes from lipid precursors. This work elucidates the biochemical basis of QZT's aged aroma, providing actionable insights for flavor modulation in fermented teas.

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BackgroundQingzhuan tea (QZT) is classified as compressed dark tea and has been an essential daily commodity for ethnic minority communities in China's border areas. It boasts unique flavor characteristics and health benefits, captivating the attention of consumers both domestically and internationally. However, the QZT industry's historical closed nature and lengthy processing cycle have impeded a comprehensive scientific understanding and evaluation of this tea, as well as hindered the overall healthy development of the industry.Scope and approachThis article provides a comprehensive overview of the research progress on QZT, covering defluoridation techniques, processing technology, flavor characteristics, chemical composition, microbial communities, health benefits, and their underlying mechanisms.Key findings and conclusionsA technology system aimed at reducing fluoride levels in tea, known as “appropriate fertilization-selection of low-fluorine tea tree varieties-control of raw material tenderness and growing period,” has been proposed. Through the implementation of specific processing techniques, QZT exhibiting an orange-red infusion color, a mellow taste, and an aged aroma. During the key pile fermentation process, microorganisms release extracellular enzymes that initiate enzymatic and moist heat reactions, resulting in oxidation, hydrolysis, polymerization, and secondary metabolic conversions. These reactions serve as the underlying foundation for the distinctive sensory attributes of QZT. The regulation of microorganisms plays a vital role in attaining the desired flavor of QZT. Moreover, QZT encompasses a diverse array of bioactive constituents, which offer numerous health advantages such as antioxidative properties, anti-obesity and anti-diabetes effects, modulation of the intestinal microbiota, and alleviation of non-alcoholic fatty liver.

To determine the effects of microbial proteins on Qingzhuan tea sensory quality during tea pile fermentation, tea leaf metabolomic and microorganism proteomic analyses were performed. In total, 1835 differential metabolites and 443 differentially expressed proteins of the microorganisms were identified. Correlation analysis between metabolomics and proteomics data revealed that the levels of microbial proteins EG II and CBH I cellulase may play important roles in cell wall construction and permeability, which were crucial for the interaction between tea leaves and microorganisms. Microbial proteins heat shock proteins (HSP), alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and CuAO related to detoxification and stress responses showed a positive correlation with tea theanine, glutamine, gamma-aminobutyric acid, glutamic acid, catechin, (-)-gallocatechin gallate, and (-)-catechin gallate, suggesting their effects on tea characteristic compound accumulation, thus affecting Qingzhuan tea sensory quality.

Lettuce, a globally consumed nutritious vegetable, is often linked to concerns regarding pesticide residues. To address this issue, we conducted field trials and utilized dynamiCROP modeling to examine the uptake, distribution, translocation, and dissipation of five pesticides (lambda-cyhalothrin, difenoconazole, acetamiprid, dimethomorph, and beta-cypermethrin) commonly detected in lettuce. At harvest, pesticides residues were below the maximum residue limits (MRLs) at 0.05, 0.39, 0.047, 0.72, and 0.072 mg kg- 1, respectively. Simulation results elucidated distinct behaviors of the pesticides following application to lettuce foliage across various compartments. However, all pesticides exhibited a common dissipation trend, initially stabilizing or increasing before gradually declining. For all five pesticides, the largest contribution of residues on lettuce leaves came from the leaf surface during the early period after application, and from the soil in the long term. Health risk assessments indicated negligible risks associated with consuming lettuce containing these pesticides, both in the short and long term.

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Volatile constituents are critical to the flavor of tea, but the changes in Enshi Yulu tea during the processing have not been clearly understood. Using headspace solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME/GC-MS) techniques, we analyze the aroma components of Enshi Yulu tea and changes in them during the processing stages. In total, 242 volatile compounds were identified. From fresh leaves to the shaping process in tea production, there are significant decreases in overall aroma substances, followed by increases after drying. Linalool is the dominant aroma component in Enshi Yulu tea, with a proportion of 12.35%, followed by compounds such as geraniol (7.41%), 2,6-dimethyl-5-heptene (6.93%), phenylmethanol (5.98%), isobutyl acetate (4.16%), hexan-1-ol (3.95%), 2-phenylacetaldehyde (3.80%), and oct-1-ene-3-ol (3.34%). The number of differential volatile components varied by production stage, with 20 up- and 139 down-regulated after steaming, 24 down-regulated after rolling, 60 up- and 51 down-regulated after shaping, and 68 up- and 13 down-regulated after drying. Most variation in expression occurred because of steaming, and the least during the rolling stage. PLS-DA analysis revealed significant differences in aroma components throughout processing and the identification of 100 compounds with higher relative contents, with five distinct change trends. Phenylmethanol, phenylacetaldehyde, (2E)-non-2-enal, oct-1-ene-3-ol, and cis-3-hexenyl hexanoate could exert a profound influence on the overall aroma quality of Enshi Yulu tea during processing. The results offer a scientific foundation and valuable insights for understanding the volatile composition of Enshi Yulu tea and its changes during the processing.

This paper applies near-infrared spectroscopy (NIRS) and multiple chemometrics to efficiently distinguish the origins of fresh tea leaves. The key components were obtained using the partial least squares discriminant analysis (PLS-DA) method. PLS, synergy interval PLS (siPLS), principal component analysis (PCA), genetic algorithm (GA), and their combination methods were used to establish NIRS non-destructive discrimination models. Then, the practical application was examined using external samples. The study identified nine key components (variable importance for the projection (VIP) > 1): epigallocatechin, epicatechin, total sugar, water extracts, total catechins, gallocatechin gallate, tea polyphenols, gallocatechin, and epigallocatechin gallate. Of the six NIRS models, the siPLS-GA model that used 37 spectral data points produced the best results (Rp2 = 0.9706, RMSEP = 0.0772, RPD = 6.59). This model had a prediction accuracy of 96.67% for the prediction set samples and 93.33% for the external samples. It offers a rapid, precise, and non-invasive approach to monitor and regulate the illicit trade of fresh tea leaves, thereby guaranteeing the authenticity of Enshi Yulu products from the processing source and fostering the long-term prosperity and stability of the Enshi Yulu tea industry.

Steamed green tea has unique characteristics that differ from other green teas. However, the alteration patterns of non-volatile metabolites during steamed green tea processing are not fully understood. In this study, a widely targeted metabolomic method was employed to explore the changes in non-volatile metabolites during steamed green tea processing. A total of 735 non-volatile compounds were identified, covering 14 subclasses. Of these, 256 compounds showed significant changes in at least one processing step. Most amino acids, main catechins, caffeine, and main sugars were excluded from the analysis. The most significant alterations were observed during steaming, followed by shaping and drying. Steaming resulted in significant increases in the levels of most amino acids and their peptides, most phenolic acids, most organic acids, and most nucleotides and their derivates, as well as some flavonoids. Steaming also resulted in significant decreases in the levels of most lipids and some flavonoids. Shaping and drying caused significant increases in the levels of some flavonoids, phenolic acids, and lipids, and significant decreases in the levels of some amino acids and their peptides, some flavonoids, and some other compounds. Our study provides a comprehensive characterization of the dynamic alterations in non-volatile metabolites during steamed green tea manufacturing.

Changes in key odorants and aroma profiles of three types of green tea during storage and after baking treatment were determined using headspace solid-phase microextraction–gas chromatography–mass spectrometry/olfactometry, odor activity value (OAV) and orthogonal partial least-squares discriminant analysis. As the stale odor developed during storage, the content of aldehydes decreased, whereas the contents of ketones and heterocycles (furans, pyrroles, etc.) increased. Key odorants, including (E,E)-2,4-heptadienal, α-terpineol, (E,E)-2,4-nonadienal and (E,E)-2,4-decadienal, appeared to be mainly responsible for the stale odor. After baking treatment, the stale odor was significantly improved, the contents of aldehydes and heterocycles were significantly increased and the content of alcohols was significantly decreased. Of these, 2-pentylfuran, hexanal, nonanal and limonene, which increased after baking, contribute the green, fruity and roasted aromas of green tea, because of their high OAVs, aroma intensities and variable importance in projection values. This study has improved understanding of the chemical changes resulting in stale odor development in green tea during storage and improvements arising from baking treatment, as well as providing a theoretical basis for the improvement of storage conditions and green tea flavor.

Fresh leaves of Echa 1 were fixed by roller, steam/hot air and light-wave, and the effects of the three fixation methods on the chemical characteristics of straight-shaped green teas (GTs) were studied by widely targeted metabolomic analysis. 1001 non-volatile substances was identified, from which 97 differential metabolites were selected by the criteria of variable importance in projection (VIP) > 1, p < 0.05, and |log2(fold change)| > 1. Correlation analysis indicated that 14 taste-active metabolites were the major contributors to the taste differences between differently processed GTs. High-temperature fixation induces protein oxidation or degradation, γ-glutamyl peptide transpeptidation, degradation of flavonoid glycosides and epimerization of cis-catechins, resulting in the accumulation of amino acids, peptides, flavonoids and trans-catechins, which have flavor characteristics such as umami, sweetness, kokumi, bitterness and astringency, thereby affecting the overall taste of GTs. These findings provided a scientific basis for the directional processing technology of high-quality green tea.

In order to analyze the changes in the microbial community structure during the pile fermentation of Qingzhuan tea and their correlation with the formation of quality compounds in Qingzhuan tea, this study carried out metagenomic and metabolomic analyses of tea samples during the fermentation process of Qingzhuan tea. The changes in the expression and abundance of microorganisms during the pile fermentation were investigated through metagenomic assays. During the processing of Qingzhuan tea, there is a transition from a bacterial dominated ecosystem to an ecosystem enriched with fungi. The correlation analyses of metagenomics and metabolomics showed that amino acids and polyphenol metabolites with relatively simple structures exhibited a significant negative correlation with target microorganisms, while the structurally complicated B-ring dihydroxy puerin, B-ring trihydroxy galloyl puerlin, and other compounds showed a significant positive correlation with target microorganisms. Aspergillus niger, Aspergillus glaucus, Penicillium in the Aspergillaceae family, and Talaromyces and Rasamsonia emersonii in Trichocomaceae were the key microorganisms involved in the formation of the characteristic qualities of Qingzhuan tea.