As a significant economic crop in China, the flavor quality of tea plays a crucial role in determining its economic value and serves as a key factor in the competitive advantage of the high-quality development of the tea industry. Tea plants inoculated with the endophyte Luteibacter sp. CsE7 can significantly improve their nitrogen fixation, flavor and quality of tea products, leading to increased utilization efficiency and economic value of summer-autumn tea products. This study examined the effects of endophyte CsE7 on the total nitrogen content, growth status, and quality-related compounds of tea plants. The nitrogen fixation and plant-growth-promoting (PGP) activities of CsE7 were assessed to determine its effectiveness as a bacterium that supports nitrogen fixation and enhances plant growth. Through genomic and transcriptomic analyses of CsE7, two key nitrogenase proteins, CsENifB1 and CsENifB2, were identified as primary contributors to its nitrogen-fixation capability. The investigation of PGP traits revealed that CsE7 enhances plant growth by producing phytohormones, aiding siderophore biosynthesis, and synthesizing 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Based on the evaluation results of tea shoots treated with CsE7 through irrigation inoculation, it was observed that CsE7 significantly increased the weight of hundred-bud samples, and enhanced axillary bud development, and stem elongation. Inoculation with CsE7 enhanced free amino acids and theanine levels in tea shoots, enriching the taste profile while maintaining the polyphenol-to-amino acid ratio. In conclusion, Luteibacter sp. CsE7 demonstrated notable nitrogen fixation and growth-promoting capabilities, thereby enhancing the quality of tea shoots. These findings highlight its potential significance for the summer-autumn tea industry and offer a novel perspective for enhancing tea flavor quality.

UV-B application enhances the aroma quality of oolong tea; however, the underlying regulatory mechanism remains unclear. This study investigates the regulatory role of UV-B in the biosynthesis of α-farnesene, an important floral and fruity characteristic aroma. UV-B treatment significantly improved the aroma quality of ‘Foshou’ and ‘Yuquan’ oolong teas, increasing α-farnesene levels by 1.8- and 1.4-fold, respectively. The α-farnesene synthase (CsAFS), ELONGATED HYPOCOTYL 5 (CsHY5), and myelocytomatosis protein 2 (CsMYC2) exhibited a highly correlated expression pattern closely associated with α-farnesene accumulation. Single-factor treatment revealed that CsAFS expression was induced by both UV-B and mechanical wounding, with CsHY5 predominantly responding to UV-B radiation, while CsMYC2 primarily responded to tumbling-induced mechanical wounding signal. Transient suppression of CsHY5 in tea leaves reduced the expression of both CsAFS and CsMYC2 whereas CsMYC2 suppression decreased CsAFS expression. G-box motifs were identified in promoters of CsMYC2 and CsAFS, and the dual-luciferase reporter assay (LUC) and electrophoretic mobility shift assays (EMSA) demonstrated direct binding functions of CsHY5 to CsAFS and CsMYC2 promoters, as well as CsMYC2 to the CsAFS promoter. Based on sensory evaluation, odourant quantification, gene expression, and molecular functional analysis, we propose that UV-B radiation and tumbling-induced wounding signals synergistically regulate α-farnesene biosynthesis through a coordinated interaction of CsHY5 and CsMYC2 during oolong tea processing. These findings improve our understanding of flavour formation during oolong tea production and also provide novel insights into artificial light application in tea manufacturing.

INTRODUCTION:The regulation of aroma quality during the postharvest processing of fresh tea leaves is a critical yet underexplored area. Green tea spreading, a key step that induces dehydration stress, significantly influences aroma formation but the underlying molecular mechanisms remain poorly understood. OBJECTIVES:This study aimed to identify the optimal spreading degree for the fresh aroma quality of Lu'an Guapian (LAGP) green tea and to elucidate the key volatile compounds, biosynthetic genes, and regulatory transcription factors responsible for this process. METHODS:We utilized an integrated multi-omics approach, combining gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry-mass spectrometry (GC-O-MS), and odor activity value (OAV) analysis to profile aroma compounds. Transcriptomics was used to identify associated gene expression changes. Key findings were validated through subcellular localization, in vitro enzyme assays, transient overexpression in tea plants, promoter cloning, yeast one-hybrid (Y1H) assays, luciferase (LUC) reporter assays, electrophoretic mobility shift assays (EMSA), and exogenous ethephon treatment. RESULTS:An optimal moisture range of 68%-71% was found to maximize the fresh aroma quality. (Z)-3-hexen-1-ol was identified as a critical contributor, and its biosynthetic gene, CsADH1, was strongly upregulated. In vitro assays confirmed CsADH1's cytoplasmic localization and its specific activity in converting (Z)-3-hexenal to (Z)-3-hexen-1-ol. Transient overexpression of CsADH1 in tea plants significantly increased (Z)-3-hexen-1-ol production. Furthermore, we discovered that the transcription factor CsERF105 directly binds to the CsADH1 promoter to activate its expression in response to dehydration stress and potential ethylene signal. CONCLUSION:Our results demonstrate that dehydration stress and potential ethylene signal during spreading triggers CsERF105-mediated activation of CsADH1, which in turn enhances the biosynthesis of the key fresh aroma compound (Z)-3-hexen-1-ol. This study successfully links a specific spreading processing condition to a molecular regulatory module, providing crucial insights and novel targets for improving aroma quality in tea processing.

Fluoride poisoning from consuming brick-tea, drinking water, and coal burning poses significant health risks, including dental and skeletal fluorosis. To address this, a novel colorimetric probe (probe R) for fluoride ion (F–) detection was designed and synthesized. Probe R exhibited a distinct UV-vis absorption response to F⁻, accompanied by visible color changes, with a detection limit of 1.91 μmol/L. Mechanistic studies using ¹H NMR confirmed hydrogen bonding as the driving force behind the interaction between probe R and F⁻. Leveraging this mechanism, a portable test strip was developed for F⁻ detection in organic and aqueous organic systems. Furthermore, probe R was successfully applied to detect F⁻ in Antarctic krill extraction solutions, demonstrating its practical utility. In conclusion, probe R demonstrates excellent optical performance and can be utilized for monitoring F– in aqueous organic systems and real food samples.

Tea with milk is a widely consumed beverage in which tea polyphenols usually interact with milk proteins through non-covalent interactions. Although researchers have reported heat-induced covalent conjugation between green tea polyphenols and beta-lactoglobulin, the nature of these interactions and their effects on protein properties remain poorly understood. Here, we investigated thermal processing-induced covalent conjugation between beta-lactoglobulin (beta-LG) and theaflavin (TF), a characteristic of black tea polyphenol, and evaluated its functional consequences. Heat treatment promoted beta-LG unfolding and TF incorporation, resulting in significantly enhanced radical scavenging activity compared with free TF, with the strongest effect observed at 90 degrees C (p < 0.05). Simulated gastrointestinal digestion showed that covalent conjugation accelerated gastric proteolysis and improved intestinal digestibility of beta-LG, reaching approximately 74% after 120 min. These results demonstrate that heat-driven beta-LG-TF conjugation modulates protein structure, antioxidant performance, and digestive behavior, providing mechanistic insight and a potential strategy for designing dairy-based matrices with improved phenolic stability and tailored digestion profiles.

Tea offers health benefits, but some teas accumulate high fluoride (F), posing fluorosis risks. However, the roles of individual tea components in regulating F bioavailability remain unclear. This study investigated the effects of major tea constituents on F metabolism in male rats (n = 5/group) administered F (40 mg/L) alone or with graded doses of epigallocatechin gallate (EGCG, 150-450 mg/kg); theaflavins, thearubigins, and theabrownin (TFs, TRs, TB, 200-800 mg/kg each); tea polysaccharides (TPSs, 25-250 mg/kg); and calcium and aluminum (Ca, Al, 800-3200 µg/kg each) via gavage. Pharmacokinetic analysis of plasma F (0-480 min) and fecal F excretion were assessed. The result showed that high-dose EGCG (450 mg/kg) reduced Cmax by 61.76% and total exposure (AUC0-t) by 37.48% compared to the control, while significantly increasing fecal F by 26.79% (p < 0.05). TB (800 mg/kg) delayed F absorption by prolonging Tmax from 18 to 30 min and reduced Cmax by 35.38% (p < 0.05). TPS (250 mg/kg) decreased Cmax by 51.72% and AUC0-t by 24.38% (p < 0.05). Ca and Al (800-3200 µg/kg) reduced Cmax by 39.19-69.62%, and low-dose aluminum (800 µg/kg) increased fecal F by 35.58% (p < 0.05). These findings elucidate distinct roles of tea constituents in mitigating F bioavailability, providing a scientific basis for tea safety assessment and dietary interventions against F overexposure.

BACKGROUND:Dysfunctional adipose tissue drives metabolic and immune dysregulation in obesity. Adaptive thermogenesis is a promising therapy, but its efficacy is limited by low brown adipose tissue (BAT) activity. Epigallocatechin gallate (EGCG) has anti-obesity effects, yet it remains unknown whether it can trigger BAT-independent thermogenesis and remodel the adipose immunometabolic environment. OBJECTIVE:This study investigated whether EGCG counteracts diet-induced obesity by remodeling the immunometabolic microenvironment and activating BAT-independent thermogenesis. METHODS:In this study, high-fat diet-induced obese C57BL/6 J mice received EGCG intervention via gavage (5 groups, n = 8-12 per group, intervention 8 weeks) and dietary administration (4 groups, n = 8 per group, intervention 12 weeks), along with cell experiments. We evaluated the effects of EGCG on metabolic parameters, energy expenditure, adipose browning, macrophage infiltration, oxidative stress, and mitochondrial biogenesis. In addition, correlation analysis, protein-protein interaction network analysis, and molecular docking were performed to identify key targets. RESULTS:This study demonstrates that EGCG counteracts diet-induced obesity through a dual mechanism. Firstly, EGCG alleviates adipose tissue inflammation by inhibiting macrophage infiltration and reduces oxidative stress and apoptosis, thereby remodeling the immune microenvironment. More critically, EGCG unlocks a BAT-independent thermogenic pathway. EGCG was found to increase systemic energy expenditure independently of BAT function, and beige adipogenesis in subcutaneous white adipose tissue (scWAT) was also induced in an in vivo model of BAT blockade. Meanwhile, in vitro studies further confirm that EGCG directly stimulates the thermogenic capacity of adipocytes derived from scWAT progenitor cells. CONCLUSION:This study demonstrates that EGCG ameliorates adipose tissue inflammation and activates a potent BAT-independent thermogenic program in scWAT. This BAT-independent mechanism highlights the multi-target potential of EGCG against metabolic dysfunction.

Theanine, a unique nonproteinogenic natural amino acid predominantly accumulated in tea plants (Camellia sinensis), is a key determinant of tea flavor and quality, with broad applications. Theanine synthase (CsTSI) is a key enzyme in theanine biosynthesis. However, the transcriptional regulation of CsTSI, particularly by bHLH transcription factors, remains largely unexplored. Through coexpression network screening and tissue-specific qPCR, we identified CsbHLH18 as a putative regulator of CsTSI. Yeast one-hybrid (Y1H) and dual-luciferase reporter assays confirmed the direct interaction between CsbHLH18 and the CsTSI promoter. An electrophoretic mobility shift assay (EMSA) further identified the specific binding motif of CsbHLH18 as "CAAATG". Transient overexpression and virus-induced gene silencing (VIGS) in tea plants demonstrated that CsbHLH18 positively regulates theanine biosynthesis by activating CsTSI transcription. These findings elucidate a previously uncharacterized molecular mechanism underlying theanine biosynthesis and provide theoretical insights into molecular breeding and cultivation of high-quality tea varieties.

Rapid screening of dithiocarbamate fungicide (DTC) residues in complex food matrices remains challenging. Herein, we developed a coordination-driven ratiometric fluorescent hydrogel sensor by co-immobilizing Cu2+ anchored hydrogen-bonded organic framework (PFC-1@Cu2+) and fluorine-doped carbon dots (F-CDs) within an agarose matrix. Among the tested dimethyldithiocarbamates (DMDTCs), thiram, ziram, and ferbam induced pronounced quenching of the green emission of PFC-1@Cu2+ by chelating Cu2+ active sites, while the red emission of F-CDs remained stable as an internal reference. The resulting dual-emission hydrogel patch enabled a distinct fluorescence transition from green to pink for naked-eye screening and smartphone-based quantification via RGB feature extraction. The platform achieved low detection limits of 3.45 ng mL(-1) for thiram, 3.91 ng mL(-1) for ziram, and 2.55 ng mL(-1) for ferbam. In spiked black tea and green tea samples, recoveries of 96.8 similar to 108.1% and 99.1 similar to 104.8% were obtained, respectively. A lightweight machine-learning workflow further supported concentration prediction and binary classification under the current small-sample framework, with K-nearest neighbors (KNN) achieving classification accuracies of 100.00% for black tea and 97.22% for green tea samples. Overall, this work presents a low-cost, portable, and intelligent ratiometric sensing strategy integrating coordination chemistry, hydrogen-bonded organic frameworks-based signal transduction, and data-driven smartphone readout, offering a promising platform for DMDTC residues screening in complex food samples.

INTRODUCTION:L-theanine, a nitrogen compound uniquely synthesized in tea plant roots, is a core determinant of tea flavor and a key carrier for nitrogen. Its metabolic dynamics are tightly linked to root development, yet whether auxin signaling participates in regulating theanine biosynthesis and the underlying molecular mechanisms remain unclear. OBJECTIVES:This study aims to elucidate the molecular pathways and key regulatory factors governing auxin signaling in the regulation of root-specific theanine biosynthesis in tea seedlings. METHODS:Changes in free amino acids (FAA), ethylamine, and endogenous hormone contents in roots, stems, and leaves of tea seedlings across five developmental stages (S1-S5) were detected by HPLC, GC-MS, and LC-MS, respectively. A theanine biosynthesis regulatory network was constructed by integrating time-series transcriptome and weighted gene co-expression network analysis (WGCNA). Additionally, exogenous indole-3-acetic acid (IAA) treatment, yeast one-hybrid assays, in vivo function validation, and DAP-seq were employed to screen and characterize key regulatory factors. RESULTS:During tea seedling radicle development, theanine content rapidly increase from 10% to over 80% of the total FAA. Multi-Omics correlation analysis revealed a feedback inhibition relationship between rapid theanine biosynthesis and auxin signaling levels. Exogenous IAA treatment and in vivo/in vitro assays confirmed that the CsZAT6/CsZAT12-CsAlaDC modules, which respond to auxin signaling, exert bidirectional regulation on theanine metabolism: CsZAT6 positively regulates theanine biosynthesis by activating the expression of CsAlaDC (the rate-limiting enzyme for ethylamine production), while CsZAT12 negatively regulates theanine biosynthesis by repressing CsAlaDC expression. CONCLUSION:This study uncovered that CsZAT6 and CsZAT12, as core response factors to auxin signaling, differentially regulate CsAlaDC expression to modulate theanine biosynthesis rate and nitrogen flux allocation during tea seedlings radicle development. These findings explore the feedback regulatory mechanism between auxin signaling and theanine metabolism, providing novel molecular insights into the unique nitrogen nutrition distribution system centered on theanine in tea plants.

Green tea is highly popular due to its richness in polyphenols exhibiting broad bioactivities. Tea polyphenols, primarily catechins and flavonoids, demonstrate health benefits following biotransformation by the gut microbiota to overcome limited bioavailability. However, metabolites and interaction between green tea polyphenol and the gut microbiota remains to be fully elucidated. This study investigates the biotransformation of metabolites and interaction between human gut microbiota (HGM) and green tea extract (GTE) through in vitro anaerobic fermentation. Temporal bioactivity assessments demonstrated that fermentation-enhanced antioxidant capacity and inhibition potential of α-glucosidase, α-amylase and pancreatic lipase peak at 6 h, showing strong correlations with polyphenol and flavonoid biotransformation kinetics. Using the untargeted metabolomics approach, 55 characteristic differential compounds during the fermentation process in GTE were characterized, including 15 catechins, 29 flavonoids, five organic acids and six other phytochemicals. Furthermore, nine microbial-transformed metabolites derived from GTE flavonoids were identified and the corresponding metabolic pathways were proposed simultaneously. Analysis of 16S rRNA gene sequencing revealed that GTE significantly enhanced gut microbiota diversity and induced structural reorganization, specifically enriching genera such as Bacteroides, Bifidobacterium, Lactococcus and Enterococcus, which are likely involved in flavonoid biotransformation of GTE. Thus, the findings provide new insights for elucidating microbiota-mediated metabolites of green tea polyphenol, and their bidirectional interactions in the human gut.

The “floral” aroma is highly valued in green tea quality and has attracted growing interest in green tea flavor research recently. However, comparative studies among them remain limited. In this study, three representative floral green teas from Anhui—Taiping Houkui (TPHK), Shucheng Xiaolanhua (SCXLH), and Lu’an Guapian (LAGP)—were analyzed using the sensomics approaches. Multi-criteria evaluation (OAV, PLS-DA, correlation) screened out five key odorants—linalool, geraniol, methyl epijasmonate, δ-valerolactone, and jasmone—as major contributors to floral differentiation. Jasmone consistently presented across all analytical dimensions, indicating its key role in both floral intensity and style. Correlation analysis based on lexicon frequency-weighted sensory attributes further revealed that floral style was shaped by not only floral-related odorants but also enhancing (e.g. lactones) and antagonistic (e.g. aldehydes, sulfur compounds) odorants. These findings provide molecular insights into the floral characteristics of Anhui green teas and offer a chemical basis for future efforts to optimize desirable floral profiles.

Abstract The albino leaves of cold-sensitive tea plants exhibited a marked reduction in chlorophyll content. However, the underlying regulatory mechanism remains elusive. In this study, we determined lower chlorophyll levels in tender leaves of cold-sensitive ‘Baiye 1’ compared to green leaves during the spring. Comparative transcriptome analyses identified the chlorophyll biosynthesis gene CsPORA, which was significantly downregulated in albino leaves. Functional assays confirmed that CsPORA positively regulates chlorophyll content. Electrophoretic mobility shift assay, yeast one-hybrid, dual-luciferase, and GUS staining results demonstrated that CsNAC87 binds to the promoter of CsPORA and suppresses its expression. Additionally, CsZAT12 physically interacts with CsNAC87 to enhance the repression. Overexpression of either CsZAT12 or CsNAC87 negatively regulated chlorophyll accumulation in tea plants and tobacco leaves, while co-transformation of CsZAT12 and CsNAC87 intensified the albino phenotype in tobacco leaves. Low temperature treatment of ‘Baiye 1’ triggered the marked upregulation of CsNAC87 and CsZAT12, leading to dramatical downregulation of CsPORA and leaf albinism. Collectively, our study reveals a novel cold-responsive CsZAT12-CsNAC87 module that negatively regulates chlorophyll synthesis by repressing CsPORA, providing new insights into chlorophyll metabolism in albino leaves of cold-sensitive tea cultivars.

Camellia sinensis cv. Baiye 1 is a temperature-sensitive albino tea cultivar. During early spring, the albino tender shoots exhibited a distinct temperature-dependent fluctuation in theanine content and chlorophyll levels, but the underlying regulatory mechanism remains unclear. This study elucidates a regulatory mechanism involving the transcription factor CsNAC73, which mediates cold signal transduction to regulate theanine biosynthesis during the seasonal greening process of 'Baiye 1'. Leaf albino phenotypes and metabolite determinations in field-grown plants revealed close but distinct correlation of both theanine and chlorophyll levels with the accumulated effective temperature. Gene expression-metabolite correlation analysis identified CsNAC73 as a positive regulator of both theanine accumulation and the expression of its biosynthetic gene, alanine decarboxylase (CsAlaDC), in response to temperature fluctuations. Controlled cold treatments demonstrated a significant increase in CsNAC73 expression under cold stress, which was accompanied by concomitant increases in CsAlaDC expression and theanine content. Furthermore, transient suppression of CsNAC73 in albino tender shoots resulted in a reduction of CsAlaDC transcripts and a corresponding decrease in theanine levels. Yeast-one-hybrid, electrophoretic mobility shift assays, and luciferase assays demonstrated that CsNAC73 directly binds to the CsAlaDC promoter, thus enhancing its transcription and subsequently increasing theanine biosynthesis during the seasonal greening of spring albino tender shoots. These findings establish CsNAC73 as a critical transcriptional activator of cold-induced theanine biosynthesis by enhancing CsAlaDC expression during the seasonal greening of 'Baiye 1'.

Authenticating the geographical origin of Anji Baicha, a premium China Geographical Indication (GI) tea, is critical for combating fraud in high-value markets. This study established a robust traceability system by integrating elemental fingerprinting with advanced chemometrics. Using inductively coupled plasma-mass spectrometry and inductively coupled plasma-optical emission spectrometry (ICP-MS/OES), we profiled mineral signatures in 365 tea samples (185 authentic Anji, 180 non-Anji). The support vector machine (SVM) model demonstrated exceptional classification performance, achieving 94.9 % accuracy in the training set and 92.7 % in the test set. Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) identified Mo, Cu and Rb as key discriminators of geographic origin. Substantiating the biogeochemical transfer paradigm, robust soil-tea correlation (R2 > 0.5) was mechanistically established for Rb, Mn, Pb, Mg, and K. This integrated mineral profiling strategy delivers a scientifically verifiable framework for protecting the GI integrity of premium agri-products, with immediate applicability to Anji Baicha authentication.

Fluoride (F) is a nonessential but potentially harmful element for plants, especially when present in excess. The tea plant is known for its ability to hyperaccumulate F from the soil and eventually accumulates in the leaves; however, how the tea plant transports F to the leaves remains unclear. Here, we found that Se can significantly decrease the transport efficiency of F from root to leaf. Therefore, RNA-Sequencing was performed on tea roots cotreated with selenite and fluoride, and then we isolated a plasma membrane-localized F transporter CsNPF2.3 from tea plant roots and examined its role in transport of F in tea plants. The results showed that CsNPF2.3 exhibited F transport activity when heterologously expressed in yeast. Expression pattern analysis revealed that CsNPF2.3 is expressed in epidermal cells, cortex cells, and xylem parenchyma cells in roots. Overexpression of CsNPF2.3 in tea roots significantly increased F content in the root, stem, and leaf, and enhanced the transport efficiency of F from root to leaf. Furthermore, in nine tea cultivars, CsNPF2.3 expression in the root was significantly positively correlated with F content in the leaf and root, and the transport efficiency of F from root to leaf. Altogether, these findings suggest that CsNPF2.3 was involved in uptake and transport of F in tea plants.

Cooked note is an undesired flavor in green tea, while the key odorants and inhibition mechanisms were unknown. Here, volatiles of four green tea samples and two thermal reaction models of methionine-glucose and methional were assessed using gas chromatography-sulfur chemiluminescence detector and two dimensional gas chromatography-time-of-flight mass spectrometry. Nonvolatiles of reaction models were determined using ultra performance liquid chromatography-Q-Exactive orbitrap mass spectrometry. Four cooked smelling sulfur- containing odorants including dimethyl trisulfide, dimethyl sulfide, diethyl disulfide, and methanethiol having odor activity values > 1 were characterized in tea samples. Aroma addition tests confirmed dimethyl trisulfide (> 0.4 mu g/L) as a reliable predictor of the cooked note. Seven sulfur-containing odorants were detected in reaction models. The addition of (-)-epigallocatechin gallate depleted glucose and interrupted the reaction, thus reduced sulfur-containing odorants' amounts. The study provides a novel insight on targeted strategic guidance for mitigating cooked off-flavor during the thermal processing of green tea production.

Brick tea is a type of post-fermented food that involves microorganisms. Long-term consumption of brick tea exposes consumers to high fluoride levels, which can adversely affect their health. This study explored the feasibility of selective defluorination of Qingzhuan brick tea through membrane separation technology, and pilot production was conducted to produce defluorinated instant brick tea. The concentration of tea polyphenols increased by more than 10 times after nanofiltration, demonstrating the high selectivity of nanofiltration membranes toward fluoride. Defluorination trends were studied at different initial material concentrations (0.5–4%) and operating pressures (0.1–0.5 MPa) under cyclic defluorination. Defluorinated instant brick tea products were also industrially prepared using 300- (DF-300) and 1000-Da (DF-1000) membranes, followed by vacuum freeze-drying. The DF-1000 and DF-300 products exhibited a defluorination rate of 51.46% and 67.96%, respectively. The products have excellent characteristics in terms of color, aroma, and flavor quality, as well as solubility. Gas chromatography–mass spectrometry indicated that the volatile components in the defluorinated instant brick tea were slightly different from those in the original tea, but the key aroma and flavor characteristics of the defluorinated brick tea remained unchanged. Membrane separation provides technical support for the large-scale production of low-fluoride post-fermented tea.

Tanyang Congou black tea, renowned for its distinctive floral and fruity aroma, is meticulously produced using the shaking technique. However, the specific aroma profile and the key odor-active compounds responsible for this characteristic fragrance have not been fully elucidated. This study integrated sensory evaluation with molecular sensory science approaches to identify and characterize the principal odorants contributing to the tea's aroma. Sensory analysis confirmed that the prepared black tea exhibited typical high-quality attributes, with a prominent floral and fruity aroma markedly reduced in lower-grade samples. A total of 70 volatile compounds were detected, among which 29 key aroma-active compounds were identified across all three quality grades using aroma extract dilution analysis (AEDA) and gas chromatography-olfactometry-mass spectrometry (GC-O-MS). Of these, 16 volatiles exhibited high flavor dilution (FD) factors (≥8), and 11 compounds showed relative odor activity values (ROAV) greater than 1. Notably, seven compounds—(E)-β-ionone, (E)-nerolidol, geraniol, citral, linalool, hexanal, and phenylacetaldehyde—were identified as the primary contributors to the characteristic floral-fruity aroma of Tanyang Congou black tea. These findings provide comprehensive insight into the aroma profile of Tanyang Congou black tea, offering a scientific basis for quality assessment and targeted aroma modulation in tea production.

Selenium (Se) biofortification plays a vital role in addressing dietary selenium deficiencies and enhancing the nutritional value of plant-based foods. This study aimed to elucidate the effects of foliar selenium biofortification on the structural and digestive properties of tea proteins. Result showed that Se incorporation significantly altered the secondary structure of tea proteins, characterized by increased proportions of α-helix and β-sheet and a reduced β-turn content. Amino acid profiling showed that selenium-enriched tea proteins (Se-TPs) exhibited a higher total content of essential amino acids. In vitro fermentation analysis demonstrated that Se-TPs promoted the production of lactic acid and short-chain fatty acids. Moreover, Se-TPs selectively enriched beneficial taxa such as Prevotella and Streptococcus salivarius, while significantly suppressing the intestinal pathogen Shigella. These findings provide novel insights into the structure-function-microbiota relationships of selenium-enriched tea proteins and highlight their potential as functional food ingredients for gut health promotion and selenium supplementation.