Search Results (33)

Obesity is a heterogeneous chronic disease for which safe, scalable adjuncts to lifestyle and clinical care remain needed. Tea derived from Camellia sinensis contains catechins, caffeine, theaflavins, thearubigins, theabrownins, polysaccharides, and other constituents whose abundance is shaped by withering, fixation, partial oxidation, full oxidation, and post-fermentation. This review integrates processing-dependent composition with molecular mechanisms, gut–liver signaling, human evidence, safety, and real-world preparation. Evidence is strongest for modest effects of green-tea catechin–caffeine preparations on energy metabolism and selected anthropometric or lipid outcomes, whereas inhibition of adipogenesis, activation of AMP-activated protein kinase, browning of white adipose tissue, and many appetite-related pathways remain supported mainly by cell and rodent studies. A recent meta-analysis in women with overweight or obesity estimated mean reductions of −1.23 kg in body weight and −3.46 cm in waist circumference, with intervention durations across the included trials typically ranging from 4 to 24 weeks, though most of the evidence derives from short- to medium-term interventions (generally ≤12 weeks); heterogeneity was moderate to high and the average weight effect remained below conventional clinical thresholds. Partially oxidized oolong tea and fully oxidized or post-fermented teas provide distinct profiles of caffeine, oxidized polyphenols, and microbial metabolites; their metabolic effects are promising but are less consistently tested in adequately powered human trials. Across tea types, convergent mechanisms include reduced digestive-enzyme activity, increased fatty-acid oxidation, modulation of thermogenesis, reinforcement of the intestinal barrier, and microbiota-dependent production of short-chain fatty acids and bile-acid signals. Translation is constrained by low systemic polyphenol exposure (i.e., limited bioavailability of intact catechins and their metabolites in circulation due to poor intestinal absorption, extensive phase-II metabolism, and rapid clearance), non-standardized doses and products, short intervention periods, interindividual variability, and limited direct comparisons among tea types. Available clinical data do not support tea as a primary treatment for obesity; rather, unsweetened tea or standardized preparations may serve as adjuncts to evidence-based dietary, physical activity, behavioral, and medical management. Priority areas include physiologically relevant dosing, standardized reporting of brewed-tea composition, long-term trials, and microbiome-informed personalization. Full article

Liquid- and solid-state fermentation are both used to produce Eurotium cristatum-fermented Fu tea, but their final soluble products have rarely been compared directly. We compared a liquid-state fermented tea infusion (LFt-D7) with an aqueous extract of solid-state fermented Fu tea (SFt-D7), using an unfermented sterilized tea extract (SHt-D0) as the reference group. LFt-D7 developed a darker reddish-brown appearance and had higher theaflavin and theabrownin contents, lower thearubigin content, and larger Commission Internationale de l’Éclairage L*a*b* (CIELAB) color differences than SHt-D0 and SFt-D7. Liquid chromatography–tandem mass spectrometry (LC–MS/MS) profiling separated the three endpoint groups; 221, 180, and 203 Level 2 annotations met the variable importance in projection (VIP > 1) and nominal p < 0.05 screening criteria in LFt-D7 versus SHt-D0, SFt-D7 versus SHt-D0, and LFt-D7 versus SFt-D7, respectively. Targeted analyses showed substantially lower free amino acid levels in SFt-D7. LFt-D7 retained a larger soluble free-amino-acid pool, had the highest total quantified flavonoid content with a stronger flavanol contribution, and showed higher relative peak-intensity signals for selected alkaloid- and phenolic acid-related metabolites. Mantel analysis showed covariation between metabolite modules and pigment indices, CIELAB parameters, total free amino acid (FAA) content, and total quantified flavonoid content. Together, these results show that the two complete preparation routes produce different soluble chemical profiles. Full article

This study introduced freeze-withering to resolve the conflict in traditional Taiping Kuihong black tea processing, where rolling enhances flavor but damages the integrity of the leaf shape. Using sensory evaluation, high-performance liquid chromatography, and gas chromatography–mass spectrometry, the effects of three freezing treatments (−20 °C, −80 °C, and liquid nitrogen at −196 °C) were analyzed and compared with traditional withering (CK). The results demonstrated that low-temperature treatments better preserved the morphological integrity of ‘two leaves and one bud.’ Compared to the CK group, the −20 °C low-temperature treatment group had a significantly higher proportion of esters among the volatile compounds in Taiping Kuihong black tea. Key floral fragrance components were abundant, while grassy undertones were greatly decreased. Concurrently, this group had the highest levels of theaflavins and TF/TR ratios. The −80 °C treatment was highly effective in preserving thearubigins; however, it resulted in a less complex fragrance profile with a reduced theaflavin level. Liquid nitrogen treatment caused aberrant accumulation of theabrownins, poor aroma harmony, and the lowest theaflavin level. This study indicates that −20 °C freezing withering is the best method for harmonizing the appearance and internal quality of Taiping Kuihong, giving critical evidence for targeted processing of unique black teas. Full article

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 C_max by 61.76% and total exposure (AUC_0–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 T_max from 18 to 30 min and reduced C_max by 35.38% (p < 0.05). TPS (250 mg/kg) decreased C_max by 51.72% and AUC_0–t by 24.38% (p < 0.05). Ca and Al (800–3200 µg/kg) reduced C_max 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. Full article

Black tea quality is fundamentally determined by its biochemical composition, providing essential baseline data for producers, traders, and consumers. This study comprehensively evaluates key biochemical quality components of 32 black tea samples from Upper Assam and North Bank regions of Assam, India, produced by both orthodox and CTC methods, using standardized International Organization for Standardization (ISO) analytical protocols for total polyphenols (TP), theaflavins, catechins, water extract (WE), caffeine, thearubigins (TR), theanine, crude fibre (CF), and ash characteristics. The results reveal substantial variation in TP (83.54–184.52 mg g⁻¹, avg. 134.07 mg g⁻¹), theaflavins (4.88–15.54 mg g⁻¹, avg. 8.61 mg g⁻¹), caffeine (15.51–39.24 mg g⁻¹, avg. 30.09 mg g⁻¹), and theanine (2.47–8.16 mg g⁻¹, avg. 5.53 mg g⁻¹), demonstrating substantial biochemical variation reflecting differences in cultivation practices, leaf maturity, processing conditions and agroclimatic conditions. The orthodox and CTC methods yielded comparable WE (avg. 404.34 vs. avg. 407.91 mg g⁻¹) and theanine levels (avg. 5.65 vs. avg. 5.35 mg g⁻¹) indicating that both processing types successfully retain key quality components. All analyzed biochemical attributes with established minimum or maximum limits set by the ISO and Food Safety and Standards Authority of India (FSSAI) demonstrated compliance with national and international quality standards. These findings establish contemporary benchmarks for key quality indicators in Assam black teas and confirm the consistency of quality across diverse processing methodologies and cultivation practices. Full article

Rolling is a critical step in the processing of black tea, marking the beginning of fermentation. At this stage, the formation of tea pigments causes significant changes in the color of the processed leaves, laying the essential groundwork for the development of color and flavor quality components in subsequent fermentation processes. However, the rapid and non-destructive sensing of tea pigments during black tea rolling remains challenging. This study focused on black tea products undergoing rolling as its research subject, utilizing electrical characteristic detection technology to collect time-series electrical parameters of rolling leaves at various testing frequencies. The original electrical parameters were preprocessed using multiplicative scatter correction (MSC), min-max normalization (Min-Max), and smoothing (Smooth). Various selection methods, including the competitive adaptive reweighting algorithm (CARS), uninformative variable elimination (UVE), and the variable combination population analysis and iterative retained information variable algorithm (VCPA-IRIV), were employed to identify electrical parameters relevant to the targeted attributes. Quantitative prediction models for the content of tea pigments were established using partial least squares regression (PLSR) and support vector machine regression (SVR). The results demonstrated that the Smooth-VCPA-IRIV-SVR model exhibited superior performance in predicting the contents of theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs). Correlation coefficients of prediction (R_p) all exceeded 0.99, and Relative prediction deviation (RPD) values were all above 6.5, indicating that the model enables rapid and non-destructive detection of tea pigment content during black tea rolling. These findings provide preliminary technical support and reference for the digital production of black tea. Full article

Black tea is one of the most widely consumed beverages in the world, second only to water. Its properties are primarily due to the presence of polyphenols, which are associated with various effects, including antioxidant, anticancer, antiviral, and anti-inflammatory activities. These compounds include, among others, theaflavins (TFs) and thearubigins (TRs). The available literature provides numerous reports confirming the positive properties of these compounds. However, it is important to highlight their potential protective effects against oxidative stress induced by heavy metals. This is an important topic, given the ongoing exposure to such pollutants—resulting mainly from industrial development, among other factors. This manuscript provides a summary of the current knowledge on the properties of TFs and TRs and their effect against oxidative stress caused by heavy metals in in vitro studies. The limited amount of research in this area shows that this is still a poorly researched topic. Comparing the results obtained for epigallocatechin gallate (EGCG) from green tea, which has a similar structure to TFs and TRs suggests that they may exhibit similar or even enhanced antioxidant properties. Considering that black tea is consumed much more frequently than green tea worldwide, it is understandable that the antioxidant potential of these two compounds on cells needs to be investigated. Full article

Efficient and convenient intelligent online detection methods can provide important technical support for the standardization of processing flow in the tea industry. Hence, this study focuses on the key chemical indicators—tea pigments in the rolling process of black tea as the research object, and uses multi-source information fusion methods to predict the changes of tea pigments content. Firstly, the tea pigments content of the samples under different rolling time series of black tea is determined by system analysis methods. Secondly, the spectra and images of the corresponding samples under different rolling time series are simultaneously obtained through the portable near-infrared spectrometer and the machine vision system. Then, by extracting the principal components of the image feature information and screening characteristic wavelengths from the spectral information, low-level and middle-level data fusion strategies are chosen to effectively integrate sensor data from different sources. At last, the linear (PLSR) and nonlinear (SVR and LSSVR) models are established respectively based on the different characteristic data information. The research results show that the LSSVR based on middle-level data fusion strategy have the best effect. In the prediction results of theaflavins, thearubigins, and theabrownins, the correlation coefficients of the testing sets are all greater than 0.98, and the relative percentage deviations are all greater than 5. The complementary fusion of the spectrum and image information effectively compensates for the problems of information redundancy and feature missing in the quantitative analysis of tea pigments content using the single-modal data information. Full article

Black tea is widely consumed worldwide, and its characteristic taste and color result from fermentation, where polyphenols are enzymatically oxidized to generate major pigments, including theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs). This study investigated the effects of increased oxygen treatment during fermentation on the flavor attributes and chemical properties of Congou black tea. Fresh tea leaves (variety “Fuyun 6”) were subjected to four oxygen treatments: 0 h (CK), 1 h (TY-1h), 2 h (TY-2h), and 3 h (TY-3h), with oxygen supplied at 8.0 L/min. Sensory evaluation revealed that oxygen-treated samples exhibited tighter and deeper-colored leaves, a redder liquor, fuller taste, and a sweeter fragrance compared with CK. Chromatic analysis showed significant increases in redness (a*) and luminance (L*), alongside reduced yellowness (b*), indicating enhanced liquor color. Chemical analyses demonstrated elevated levels of TFs, TRs, and TBs in oxygen treatments, with TRs showing the most pronounced increase. Non-targeted metabolomics identified 2318 non-volatile and 761 volatile metabolites, highlighting upregulated flavonoids, phenolic acids, and lipids, and downregulated catechins and tannins, which collectively contributed to improved taste and aroma. Optimal results were achieved with 2–3 h of oxygen treatment, balancing pigment formation and sensory quality. These findings can provide a scientific basis for optimizing oxygen conditions in black tea fermentation to improve product quality. Full article

Background/Objectives: Ultraviolet B (UVB) radiation contributes significantly to skin aging and skin disorders by promoting oxidative stress, inflammation, and collagen degradation. Natural antioxidants such as theaflavins and thearubigins from Camellia sinensis L. (black tea) have shown photoprotective effects. This study aimed to optimize the extraction of theaflavins and thearubigins from black tea leaves and evaluate the efficacy of the extract against UVB-induced damage using a transfersome-based topical formulation. Methods: Extraction of theaflavins and thearubigins was optimized via response surface methodology (Box-Behnken Design), yielding an extract rich in active polyphenols. This extract was incorporated into transfersomes that were characterized for size, polydispersity, zeta potential, storage stability, and entrapment efficiency. Human dermal fibroblasts (NHDF) were used to assess cytotoxicity, protection against UVB-induced viability loss, collagen degradation, and expression of inflammatory (IL6, COX2, iNOS) and matrix-degrading (MMP1) markers. Cellular uptake of the extract’s bioactive marker compounds was measured via LC-MS/MS. Results: The transfersomes (~60 nm) showed a good stability and a high entrapment efficiency (>85%). The transfersomes significantly protected NHDF cells from UVB-induced cytotoxicity, restored collagen production, and reduced gene expression of MMP1, IL6, COX2, and iNOS. Cellular uptake of key extract’s polyphenols was markedly enhanced by the nanoformulation compared to the free extract. Conclusions: Black tea extract transfersomes effectively prevented UVB-induced oxidative and inflammatory damage in skin fibroblasts. This delivery system enhanced bioavailability of the extract and cellular protection, supporting the use of the optimized extract in cosmeceutical formulations targeting photoaging and UV-induced skin disorders. Full article

At present, the heavy bitter taste, poor flavor quality and low functional activity of summer and autumn tea are the bottleneck problems restricting the low utilization rate of summer and autumn tea resources. The research and development of new products of fruit-flavored black tea is conducive to expanding the utilization of summer and autumn tea resources. Different kinds of fruit juice were added during the fermentation and processing of classic black tea, such as bananas, apples, fragrant pear and Sydney pear, in this study. The effects of fruit juice on the flavor quality and amylase inhibitory activity of fruity black tea were researched. The sensory quality, flavor chemicals and α-amylase inhibitory activity were evaluated. The results showed that the sensory evaluation scores of black tea treated with fruit juice were significantly higher than those of black tea treated without fruit juice, especially the crown pear juice. The amylase inhibition rate of black tea treated with fruit juice was significantly higher than the control treated without fruit juice (p < 0.05). The sensory evaluation scores, polyphenol oxidase activity, water extract content, soluble sugar content, free amino acid content, theaflavin content, thearubigin content and inhibition rate of amylase activity of black tea treated with pear juice were significantly higher than those of the apple and banana juices (p < 0.05), especially crown pear juice. Tea polyphenol content and theaflavin content of black tea treated with added pear juice were significantly lower (p < 0.05) than the black tea control treated with added apple juice and banana juice, especially crown pear juice. The fruity black tea treated with crown pear juice had a redder broth, more pronounced sweet fruit aroma, sweet and mellow taste and reduced astringency. Therefore, the black tea treated with crown pear juice was preferred. The research hopes to provide a theoretical basis for the research of black tea quality control and the research of summer and autumn tea resources utilization technology. Full article

Background: Black tea processing conditions significantly affect the final taste and flavor profiles, so researchers are now focusing on developing equipment and improving the appropriate processing conditions of major black tea varieties. Methods: Here, we tested the effect of four different initial drying temperatures, i.e., R65 (65 °C), R85 (85 °C), R105 (105 °C), and R125 (125 °C), on the sensory and biochemical profiles and volatilome of the black tea variety “Lishui wild” (LWV). Results: Our results indicate that both 85 and 105 °C are better than 65 and 125 °C for initial drying for 20 min. R105 had the highest sensory evaluation scores due to better shape, aroma, taste, leaf base, thearubigins, theanine, caffeine, and ratio of theaflavins + thearubigins to theaflavins. Both R85 and R105 had higher catechins than R65 and R125. The LWV volatilome consisted of esters (19.89%), terpenoids (18.95%), ketones (11.3%), heterocyclic compounds (9.99%), and alcohols (8.59%). In general, acids, aldehydes, amines, aromatics, ethers, hydrocarbons, phenols, sulfur compounds, and terpenoids accumulated in higher amounts in R85 and R105. The highly accumulated compounds in R105 were associated with green, fruity, sweet, woody, floral, hawthorn, mild, nutty, powdery, rose, and rosy flavors. The main pathways affected are secondary metabolites, sesquiterpenoid and triterpenoid biosynthesis, glycerolipid metabolism, zeatin biosynthesis, phenylpropanoid biosynthesis, ABC transport, glutathione metabolism, etc. Therefore, R105 can be used to achieve the optimal taste, flavor, and aroma of LWV. Conclusions: Overall, the presented data can be used by the tea industry for processing black tea with the most optimum volatile substances, catechins, theanine, amino acids, and other compounds. Full article

As a crucial stage in the processing of black tea, rolling plays a significant role in both the color transformation and the quality development of the tea. In this process, the production of theaflavins, thearubigins, and theabrownins is a primary factor contributing to the alteration in color of rolled leaves. Herein, tea pigments are selected as the key quality indicators during rolling of black tea, aiming to establish rapid detection methods for them. A machine vision system is employed to extract nine color feature variables from the images of samples subjected to varying rolling times. Then, the tea pigment content in the corresponding samples is determined using a UV-visible spectrophotometer. In the meantime, the correlation between color variables and tea pigments is discussed. Additionally, Z-score and PCA are used to eliminate the magnitude difference and redundant information in original data. Finally, the quantitative prediction models of tea pigments based on the images’ color features are established by using PLSR, SVR, and ELM. The data show that the Z-score–PCA–ELM model has the best prediction effect for tea pigments. The Rp values for the model prediction sets are all over 0.96, and the RPD values are all greater than 3.50. In this study, rapid determination methods for tea pigments during rolling of black tea are established. These methods offer significant technical support for the digital production of black tea. Full article

To explore the effects of different withering methods on the quality of Congou black tea, this study focused on five different withering methods: natural withering, warm-air withering, sun–natural combined withering, sun withering, and shaking withering. Gas chromatography‒mass spectrometry (GC‒MS), high-performance liquid chromatography (HPLC), and ion-exchange chromatography techniques were used to analyze the nonvolatile and volatile components and composition of the tea. The results revealed significant differences (p < 0.05) in the contents of nonvolatile constituents including caffeine, polyphenols, soluble sugars, free amino acids and their components, theaflavins, thearubigins, and catechins among the five different withering methods, with varying degrees of correlation between these components. A total of 227 aroma compounds were detected, and significant differences in the contents of alcohols, aldehydes, and ketones were observed. A relative odor activity value (ROVA) analysis of the aroma compounds revealed that 19 compounds had an ROVA > 1. Among them, benzylaldehyde, trans-2-decenal, decanal, benzaldehyde, nonanal, hexanal, trans-linalool, and geraniol from the shaking withering method had significantly higher ROVA values than those from the other withering methods, which may be the reason for the prominent floral and fruity aroma of shaking withering. This study revealed the impact of different withering methods on the quality of Congou black tea, providing a scientific basis for the development of Congou black tea with different flavors and the improvement of Congou black tea processing techniques. Full article

This study investigated the effects of various characteristic components of tea—theaflavins, catechins, thearubigins, theasinensins, theanine, catechin (C), catechin gallate (CG), epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), epigallocatechin gallate (EGCG), gallocatechin (GC), and gallocatechin gallate (GCG)—on acrylamide formation. The results revealed that most of tea’s characteristic components could significantly eliminate acrylamide, ranked from highest to lowest as follows: GC (55.73%) > EC (46.31%) > theaflavins (44.91%) > CG (40.73%) > thearubigins (37.36%) > ECG (37.03%) > EGCG (27.37%) > theabrownine (22.54%) > GCG (16.21%) > catechins (10.14%) > C (7.48%). Synergistic elimination effects were observed with thearubigins + EC + GC + CG, thearubigins + EC + CG, thearubigins + EC + GC, theaflavins + GC + CG, and thearubigins + theaflavins, with the reduction rates being 73.99%, 72.67%, 67.62%, 71.03%, and 65.74%, respectively. Tea’s components reduced the numbers of persistent free radicals to prevent acrylamide formation in the model system. The results provide a theoretical basis for the development of low-acrylamide foods and the application of tea resources in the food industry. Full article