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Tea plant (Camellia sinensis L.) is capable of accumulating a large amount of fluorine (F) in leaves without showing toxicity symptoms and thus offers a good model for exploring F tolerance mechanisms. Here, gas chromatography time-of-flight mass spectrometry (GC-TOF–MS) was used to investigate metabolic changes in leaves of tea seedlings under control (0 mM), low F (0.2 mM) and high F (0.8 mM) conditions. Differentially changed metabolites such as galacturonic acid, lactose, fructose, malic acid, alanine were identified by the comparison among the three F treatment groups. A pathway map depicted based on the KEGG database reflected the involvement of pectin biosynthesis metabolism in F stress response. The gene expression and enzyme activity of key enzymes involved in pectin biosynthesis pathway and the content of pectic polysaccharides were increased by exogenous F treatments, indicating the promotion effect of F on the pectin biosynthesis. Pectin was also immunochemically stained in vivo using monoclonal antibody (2F4), which confirmed the increment. The increased pectin might contribute to combining the exogenous F in tea leaves. This research provided some novel insights into further research on F detoxification of plants.

This study aimed to clarify the bioavailability mechanism of theaflavins by using the Caco-2 monolayer in vitro model. Prior to the transport of theaflavin (TF), theaflavin-3-gallate (TF3G), theaflavin-3’-gallate (TF3’G), and theaflavin-3, 3’-digallate (TFDG), we found the cytotoxicity of theaflavins was in the order of TF3’G > TFDG > TF3G > TF, suggesting the galloyl moiety enhances the cytotoxicity of theaflavins. Meantime, the galloyl moiety made theaflavins unstable, with the stability in the order of TF > TFDG > TF3G/TF3’G. Four theaflavins showed poor bioavailability with the Papp values ranging from 0.44 × 10−7 to 3.64 × 10−7 cm/s in the absorptive transport. All the theaflavins showed an efflux ratio of over 1.24. And it is further confirmed that P-glycoprotein (P-gp), multidrug resistance associated proteins (MRPs) and breast cancer resistance protein (BCRP) were all shown to contribute to the efflux transport of four theaflavins, with P-gp playing the most important role, followed by MRPs and BCRP. Moreover, theaflavins increased the expression of P-gp, MRP1, MPR3, and BCRP while decreased the expression of MRP2 at the transcription and translation levels. Additionally, the gallated theaflavins were degraded into simple theaflavins and gallic acids when transported through Caco-2 monolayers. Overall, the structural instability, efflux transporters, and cell metabolism were all responsible for the low bioavailability of four theaflavins in Caco-2 monolayers.

The freshness and color quality of postharvest tea leaves can be markedly prolonged and retained by proper preservation measures. Here, we investigated the dynamic changes of chlorophyll and its derivatives in postharvest tea leaves under different low-temperature treatments using natural withering as a control. Chlorophyll decomposition was found closely related with chlorophyllide, pheophorbide, and pheophytin. Low-temperature withering could slow chlorophyll degradation in postharvest tea leaves via significant inhibition on the enzyme activity and gene expression of Mg-dechelatase, chlorophyllase, and pheophorbide a oxygenase. At the initial stage of withering, a significant increase was observed in the chlorophyll content, expression of chlorophyll-synthesis-related enzymes (such as glutamyl-tRNA synthetase, etc.), and chlorophyll synthase activity in newly picked tea leaves. Moreover, an obvious decrease was found in the content of l-glutamate as the foremost precursor substance of chlorophyll synthesis. Hence, our findings revealed that the chlorophyll synthesis reaction was induced by the light-dehydration-stress in the initial withering of tea leaves. This study provides a theoretical basis for exploring preservation technology in actual green tea production.

Tea is one of the most popular beverages in the world and is believed to be beneficial for health. The main components in tea change greatly depending on different processes, and thus, the effects of different teas on human health may differ. In this study, we compared the effect of green, oolong, black, and dark tea extracts on sucrase-isomaltase (SI) activity and glucose transport, which are two intervention options for postprandial blood glucose control, using Caco-2 cells as a model. Theaflavin-rich black tea extracts showed the highest inhibition of SI activity and retardation of the hydrolysis of sucrose, maltose, and isomaltose, with IC50 values of 8.34 μg/mL, 16.10 μg/mL, and 21.63 μg/mL, respectively. All four kinds of tea extracts caused a dose-dependent inhibition of glucose transport, which were closely related to the catechin content. Green tea extracts showed the highest inhibition of glucose transport and was more effective against sodium-dependent glucose cotransporter 1 (SGLT1) than glucose transporter 2 (GLUT2) in the management of glucose transport. Black tea extracts also inhibited glucose transport despite low level of catechins. The reason could partly lie in the suppression of Na+/K+-ATPase, which reduced the energy needed for SGLT1 to actively transport glucose. Furthermore, the mRNA level of SI, SGLT1, GLUT2, and Na+/K+-ATPase in Caco-2 cells were significantly reduced after treatment with tea extracts for 2 h. These in vitro studies suggested that tea could be used as a functional food in the diet to modulate postprandial hyperglycaemia for diabetic patients.

Citrus blend black teas are popular worldwide, due to its unique flavor and remarkable health benefits. However, the aroma characteristics, aroma profiles and key odorants of it remain to be distinguished and cognized. In this study, the aroma profiles of 12 representative samples with three different cultivars including citrus (Citrus reticulata), bergamot (Citrus bergamia), and lemon (Citrus limon) were determined by a novel approach combined head space-solid phase microextraction (HS-SPME) with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC&times, GC-TOFMS). A total of 348 volatile compounds, among which comprised esters (60), alkenes (55), aldehydes (45), ketones (45), alcohols (37), aromatic hydrocarbons (20), and some others were ultimately identified. The further partial least squares discrimination analysis (PLS-DA) certified obvious differences existed among the three groups with a screening result of 30 significant differential key volatile compounds. A total of 61 aroma-active compounds that mostly presented green, fresh, fruity, and sweet odors were determined in three groups with gas chromatography-olfactometry/mass spectrometry (GC-O/MS) assisted analysis. Heptanal, limonene, linalool, and trans-&beta, ionone were considered the fundamental odorants associated with the flavors of these teas. Comprehensive analysis showed that limonene, ethyl octanoate, copaene, ethyl butyrate (citrus), benzyl acetate, nerol (bergamot) and furfural (lemon) were determined as the characterized odorants for each type.

Tea plant (Camellia sinensis) may hyperaccumulate fluorine (F) in its leaves, which may cause fluorosis in tea consumers. Recent studies have implied that exogenous calcium (Ca) may reduce F in tea leaves, although our mechanistic understanding of this phenomenon remains limited. Here, the effects of exogenous Ca on the physiological, biochemical and ionic homeostasis of tea leaves were investigated in the presence and absence of F. Elevated levels of malondialdehyde (MDA) and impaired cellular ultrastructure indicated that exogenous F induced stress in tea plants subjected to deficient Ca (0.01, 0.05 mM) and extremely excessive Ca (10 mM) treatments. Additionally, more F were accumulated in leaves compared to the control when tea plants were treated with 0.5 mM Ca. The lowest levels of MDA and F were observed at an optimal level of 5 mM Ca. F increased the levels of caffeine, polyphenols, and catechins, but decreased the content of soluble sugars and gallic acid when the level of Ca was within 5 mM. Moreover, based on a multivariate analysis on ionic composition, the Ca-regulated disorder in the homeostasis of B, Al, Cu, and Zn was strongly correlated with the accumulation of F. Our results demonstrate that within a range of concentrations, exogenous Ca was able to reduce F content and enhance F tolerance in tea leaves. These effects of exogenous Ca on F tolerance may be related to ionic homeostasis.

Red-light withering (RLW) was shown to improve the aroma of summer-autumn black tea, probably due to the increase in the content of main floral aroma components. Analysis of the dynamic changes of volatile components during withering showed that RLW mainly played a role in the late withering period. Non-target metabolomics and transcriptomics were used to analyze the main biosynthetic pathways of volatile components. RLW was shown to significantly up-regulate the expression of terpene synthesis-related genes (LIS, FAS, etc.) in the late withering stage and further promote the synthesis of volatile terpenoids (linalool and α-farnesene). Meanwhile, RLW leaves could release more leaf alcohol in the late withering period, due to the high expression of enzyme genes (LOX, ADH). Additionally, RLW could significantly increase the content of phenylethyl alcohol in the early withering stage. Moreover, the relative content of volatile bound glycosides (GBVs) did not change significantly among the three treatments (0 h, RLW9h and CK9h) after withering, suggesting that the hydrolysis of GBVs contributed little to aroma content during withering. Overall, RLW can significantly increase the activity of glycosidase in the later withering stage, thus improving the aroma quality of black tea in the subsequent processing.

Fungal community and non-volatile metabolites changes during the pile-fermentation are key factors to organoleptic qualities of dark green tea. However, the correlation between fungal succession and non-volatile compounds has never been satisfactorily explained. The purpose of the present study was to investigate fungal succession and its correlation with flavor compounds by multi-omics. Illumina Miseq sequencing of ITS1 region was conducted to analyze the fungal succession, a total of 78 OTUs which consisted of one phyla, nine classes, 15 orders, 26 families, 37 genera were identified, with Ascomycota as dominant phyla. Cluster analysis and non-metric multidimensional scaling of samples demonstrated the distribution of OTUs in multi-dimensional space, the pile-fermentation process of dark green tea can be divided into four periods according to the generated trajectory of fungal population, S0, S1-S3, S4-S5, and S6. Aspergillus is the dominant genus. Penicillium, Cyberlindnera, Debaryomyces, Candida, Thermomyces, Rasamsonia, Thermoascus, and Byssochlamys appear in different periods. three alkaloids, seven catechins, nine amino acids, five organic acids, five flavones and flavonoid glycosides were identified by UPLC-QTOF-MS/MS, and the contents were all decreasing. Caffeine, EGC, EGCG, L-theanine, kaempferitrin, L-phenylalanine, gallic acid, and myricetin-3-O-galactoside are important ingredients which contribute to the flavor of dark green tea. This study demonstrated the fungal succession, non-volatile flavor compounds and their relationships during pile-fermentation of dark green tea, and provides new insights into evaluating pivotal role of fungal succession in the manufacturing process of dark green tea.

The aim of the present study was to determine whether curculigoside protects against myocardial ischemia-reperfusion injury (MIRI) and to investigate the underlying mechanisms. An in vitro model of hypoxia/reoxygenation (H/R) was established by culturing H9c2 cells under hypoxic conditions for 12 h, followed by reoxygenation for 1 h. Cell Counting kit-8 and lactate dehydrogenase (LDH) assays were subsequently used to examine cell viability and the degree of cell injury. In addition, isolated rat hearts were subjected to 30 min of ischemia followed by 1 h of reperfusion to establish a MIRI model. Triphenyltetrazolium chloride (TTC) staining was performed to measure the infarct size. Furthermore, TUNEL staining and flow cytometry were employed to evaluate cell apoptosis. The opening of the mitochondrial permeability transition pore (MPTP) and changes in the mitochondrial membrane potential (ΔΨm) were assessed. Reverse transcription-quantitative PCR and western blot analysis were performed to investigate the expression levels of mitochondrial apoptosis-related proteins. Curculigoside pre-treatment significantly improved cell viability, decreased cell apoptosis and LDH activity, and reduced the infarct size and myocardial apoptosis in vitro and ex vivo, respectively. Moreover, curculigoside markedly inhibited MPTP opening and preserved the ΔΨm. In addition, curculigoside significantly decreased the expression of cytochrome c, apoptotic protease activating factor-1, cleaved caspase-9 and cleaved caspase-3. Notably, atractyloside, a known MPTP opener, abrogated the protective effects of curculigoside. On the whole, the present study demonstrated that curculigoside protected against MIRI, potentially by decreasing the levels of mitochondria-mediated apoptosis via the inhibition of MPTP opening. Therefore, the results obtained in the present study may provide the theoretical basis for the future clinical application of curculigoside.

This study investigated the influence mechanism of red-light withering on the taste quality of black tea. Compared with natural withering (control), red-light withering (RLW) can significantly improve the taste quality of the summer-autumn black tea by reducing its bitterness and astringency. Specifically, RLW was shown to have a greater impact on the amino acids and theaflavins of tea, with an increase of 10.6% and 25.6% in their content after RLW, respectively. The increase in amino acid content is mainly attributed to the content increase of the protein-amino acids induced by the up-regulated expression of phenylalanine and tryptophan synthesis genes as well as the activity of peptidases. Additionally, RLW can inhibit the down-regulation of key genes in catechin synthesis to increase the content of partial catechins (EGC and GCG). Meanwhile, RLW can also significantly increase the enzyme activity of polyphenol oxidase and peroxidase and promote the formation of theaflavins in the fermentation stage. This study provides a theoretical basis for improving black tea withering technology and withering equipment.

Volatile compounds are important contributors to dark tea quality. However, the aroma formation during the key processing pile-fermentation remains unclear. Herein, a total of 46 compounds including 17 alcohols, nine ketones, eight alkenes, five aldehydes, four esters, one heterocyclic oxygen, one alkane, and one pyranoid were identified by GC-MS. At the end of pile-fermentation, alcohols and aldehydes decreased by 21.2% and 12.9% respectively, while ketones and alkenes increased by 40.3% and 11.5% respectively, esters doubled compared to the initial period. PLS-DA analysis demonstrated that the characteristic aroma components were mainly ionone, linalool and its oxides (floral, citrus-like, fruity), safranal (woody, herbal and spice), β-cyclocitral, β-terpinene, limonene (fruity), trans-2-hexenyl hexanoate (fragrance) and roses oxide (rose). Importantly, Pearson correlation analysis demonstrated microbial communities and volatile compounds were highly correlated (|r|>0.7, p

Tea plant is capable of hyper-accumulating fluoride (F) in leaves, suggesting drinking tea may cause excessive F intake in our body and threaten the health. This study investigated the changes in the structure, composition, and F content in the leaf cell wall of the tea (Camellia sinensis) under different F conditions to demonstrate the role of cell wall in F enrichment in tea plants. The cell wall was shown as the main part for F accumulation (67%-92%), with most of F distributed in the pectin fraction (56%-71%). With increasing F concentration, a significant increase (p 0.05) was observed in the F content of cell wall and its components, the level of cell wall metal ions (i.e. Cu, Mg, Zn, Al, Ca, Ba, Mn), as well as the content of total cell wall materials, cellulose, and pectin. Meanwhile, the level of Cu, Mg, Zn, pectin, and cellulose was significantly positively correlated with the F content in the leaf cell wall. F addition was shown to increase the fluorescence intensity of LM19 and 2F4 antibody-labeled low-methylesterified homogalacturonans (HGs), while decrease LM20-labeled high-methylesterified HGs, coupled with an increase in the activity and gene expression of pectin methyl esterases (PMEs) in tea leaves. All these results suggest that F addition can increase pectin content and demethylesterification, leading to increased absorption of metal cations and chelation of F in the cell wall through the action of metal ions.

Sulforaphane (SFN) exhibits chemopreventive effects through various mechanisms. However, few studies have focused on the bioactivities of its metabolites. Here, three metabolites derived from SFN were studied, known as sulforaphane glutathione, sulforaphane cysteine and sulforaphane-N-acetylcysteine. Their effects on cell viability, DNA damage, tumorigenicity, cell migration and adhesion were measured in human hepatoma HepG2 cells, and their anti-angiogenetic effects were determined in a 3D co-culture model of human umbilical vein endothelial cells (HUVECs) and pericytes. Results indicated that these metabolites at high doses decreased cancer cell viability, induced DNA damage and inhibited motility, and impaired endothelial cell migration and tube formation. Additionally, pre-treatment with low doses of SFN metabolites protected against H₂O₂ challenge. The activation of the nuclear factor E2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway and the induction of intracellular glutathione (GSH) played an important role in the cytoprotective effects of SFN metabolites. In conclusion, SFN metabolites exhibited similar cytotoxic and cytoprotective effects to SFN, which proves the necessity to study the mechanisms of action of not only SFN but also of its metabolites. Based on the different tissue distribution profiles of these metabolites, the most relevant chemical forms can be selected for targeted chemoprevention.

Tea plant, Camellia sinensis, can accumulate high levels of fluoride (F); however, it is unclear how F influences secondary metabolism in tea plants. In this study, two tea cultivars seedlings, Fuyunliuhao (FY) and Wuniuzao (WNZ), were cultivated in nutrient solutions containing different concentrations of F for 4 weeks to investigate the effects of F on the content of catechins, the activity of related biosynthetic enzymes in the leaves. The content of tea polyphenols reached to the top at 2 mg L−1 (FY) or 4 mg L−1 (WNZ) and then decreased dose-dependently with the F concentration increasing; the content of catechins increased between 2 and 8 mg L−1 and decreased at 16 mg L−1 significantly comparing with the control; the activity of PAL, C4H, CHI and DFRm in WNZ, DFRm and DFRq in FY increased significantly at 4 mg L−1 F concentration comparing to the control and the activity of ANR in WNZ, C4H in FY decreased dose-dependently with the increasing F concentration, while the activity of PAL, CHI in FY changed little with the F concentration between 0 and 16 mg L−1. These results suggested that F concentrations lower than 4 mg L−1 promote the biosynthesis of catechins in tea plants by up-regulating the activity of related biosynthetic enzymes, whereas F concentrations more than 8 mg L−1 restrain tea plant growth and the synthesis of catechins. The pathways of catechins biosynthesis are tremendously complicated, and further research is required to determine whether F regulates the metabolism of tea catechins by altering other pathways and enzymes in addition to those analyzed in this study.

This study aimed to figure out the optimum fermentation temperature by analyzing the major chemical constituents of black tea and its antioxidant activities, inhibitory activities against α-amylase, α-glucosidase and glucose uptake. Sensory evaluation revealed 28°C-fermented black tea showed best sensory quality with highest scores for aroma (6.5) and taste (29.8). With increasing fermentation temperature, polyphenols, polysaccharides, (−)-epigallocatechin, (+)-catechin, theaflavins and thearubigins decreased significantly, while amino acids, soluble sugars and volatiles increased when temperature increased up to 31 °C. Furthermore, black tea fermented at 28 °C showed strongest DPPH radical scavenging ability, anti-lipid peroxidation and inhibitory effect on α-glucosidase activity with IC50 value of 17.72 μg/mL, 1.49 mg/mL and 21.69 μg/mL respectively. While 25°C-fermented black tea showed highest inhibition rate of glucose uptake in Caco-2 cells. The results demonstrate that appropriately lowering fermentation temperature could improve both sensory quality and bioactivity of black tea.

SCOPE Na+ /K+ -ATPase is an important membrane-bound enzyme and high levels of Na+ /K+ -ATPase activity in intestine result in increased monosaccharide absorption and aggravated undesirable postprandial hyperglycemia in diabetic. The aim is to characterize the effects of green and black tea extracts on the intestinal Na+ /K+ -ATPase. METHODS AND RESULTS The STZ-induced type 1 diabetic mice model and high-fat diet combined with low-dose STZ-induced type 2 diabetic mice model are used in this study and the data indicate that both green and black tea extracts show significant hypoglycemic effect. The Na+ /K+ -ATPase activities in intestine associated with glucose absorption are increased in type 1 diabetic mice, while those are even normal in type 2 diabetic mice. Green and black tea extracts can attenuate type 1 diabetes-induced intestinal Na+ /K+ -ATPase disturbance to control postprandial hyperglycemia. Black tea is more effective than green tea in reducing of Na+ /K+ -ATPase activity and protein expression. Theaflavins are the major functional components of black tea and theaflavine-3,3'-digallate presents the strongest inhibitory effect exhibiting anticompetition with ATP and mixed inhibition with Na+ and K+ . CONCLUSION Tea, especially black tea, can be considered a potential therapeutic agent against type 1 diabetes-induced intestinal Na+ /K+ -ATPase disturbance to control postprandial hyperglycemia.

The transcellular transport and metabolism of eight green tea catechins (GTCs) were studied in Caco-2 monolayers, with the aim of investigating the effect of cis&ndash, trans isomerism on the membrane permeability and biotransformation of GTCs. The results showed that the catechin stereochemistry significantly affects the efflux transport rather than the absorption transport in the Caco-2 monolayers. The trans catechins showed a better transcellular permeability than their corresponding cis (epi) catechins in the efflux transport, as the efflux amount of trans catechins were all significantly higher than that of the cis (epi) catechins at each concentration and each time point tested. Moreover, the relative contents of the (+)-catechin (C)-O-sulfate, (+)-gallocatechin (GC)-O-sulfate, (&minus, )-catechin gallate (CG)-O-sulfate, and (&minus, )-gallocatechin gallate (GCG)-O-sulfate in the efflux transport were 2.67, 16.08, 50.48, and 31.54 times higher than that of the (&minus, )-epicatechin (EC)-O-sulfate, (&minus, )-epigallocatechin (EGC)-O-sulfate, (&minus, )-epicatechin gallate (ECG)-O-sulfate, and (&minus, )-epigallocatechin gallate (EGCG)-O-sulfate, respectively. It indicated that more metabolites were observed after the transcellular efflux of trans catechins. Furthermore, after two hours of incubation, the GTCs could significantly increase the expression of multidrug resistance-associated protein 2 (MRP2) and breast cancer-resistance protein (BCRP), and decrease the expression of P-glycoprotein in the Caco-2 cells. The regulation of GTCs on P-glycoprotein, MRP2, and BCRP could also be significantly influenced by the chemical and dimensional structure. In a conclusion, catechin stereochemistry significantly affects the transport and metabolism of GTCs when refluxed in the Caco-2 monolayers.

Six Green tea powders (GTPs) were prepared from green tea with superfine grinding process. Their main quality components were determined by chemical methods and the scavenging effects of GTPs on ·OH and O2.− in vitro were evaluated by using deoxyribose assay and xanthine oxidase method, respectively. The results indicated that tea polyphenols and catechins contents decreased, while the contents of water-soluble carbohydrates in GTPs increased markedly, and no significant difference in amino acids and caffein with the decrease in particle size during superfine grinding, which benefited to reduce bitterness and preserve briskness of GTPs. Meanwhile, superfine grinding increased extraction of TPS markedly, which could lead to more potent scavenging capacity of GTPEs on ·OH. Based on the above analysis, it suggested that superfine grinding time should be controlled within 30–50 min, with ideal parameters of GTP: X: 4.93–4.75%, d50: 20.3–13.5 μm, ρbulk: 0.323–0.297 kg/m3, ρtapped: 0.666–0.614 kg/m3. Under this condition, we could prepare GTP with green and bright color, narrower and more uniform particle size distribution, as well as possessing more food processing property.

A pre-column derivatization high-performance liquid chromatography (HPLC) method was developed and optimized to characterize and quantify the monosaccharides present in tea polysaccharides (TPS) isolated from Yingshuang green tea. TPS sample was hydrolyzed with trifluoroacetic acid, subjected to pre-column derivatization using 1-phenyl-3-methyl-5-pyrazolone (PMP), and separated on an Agilent TC-C18column (4.6 mm × 250 mm, 5 μm) with UV detection at 250 nm. A mixture of ten PMP derivatives of standard monosaccharides (mannose, ribose, rhamnose, glucuronic acid, galacturonic acid, glucose, xylose, galactose, arabinose, and fucose) could be baseline separated within 20 min. Moreover, quantitative analysis of the component monosaccharides in Yingshuang green tea TPS was achieved, indicating the TPS consisted of mannose, ribose, rhamnose, glucuronic acid, galacturonic acid, glucose, xylose, galactose, and arabinose in the molar contents of 0.72, 0.78, 0.89, 0.13, 0.15, 0.36, 0.39, 0.36, 0.36, and 0.38 μM, respectively. Recovery efficiency for component monosaccharides from TPS ranged from 93.6 to 102.4% with RSD values lower than 2.5%. In conclusion, pre-column derivatization HPLC provides a rapid, reproducible, accurate, and quantitative method for analysis of the monosaccharide composition and contents in TPS, which may help to further explore the relationship between TPS monosaccharides isolated from different tea varieties and their biological activity.

In the present work, Qingzhuan tea, a unique dark tea produced by post-fermentation technology, was selected to investigate its antioxidant and pancreatic α-amylase inhibiting activities. Water extract of Qingzhuan tea was successively isolated by solvent partitioning procedures to obtain chloroform, ethyl acetate, n-butanol, sediment and residual aqua fractions. Of different fractions, the ethyl acetate fraction (QEF) had the highest total polyphenols and catechins contents, demonstrated the strongest DPPH radical scavenging activity and exhibited the greatest inhibitory effect on porcine pancreatic α-amylase activity in vitro. Further separation of QEF by a Sephadex LH-20 column generated eight subfractions (QEF1–QEF8), with QEF8 being the most active subfraction based on the assays above mentioned. The major active components in QEF8 were identified as catechins EGCG and ECG by LC-MS analysis, with contents of 22.29 % and 11.11 % respectively. Inhibitory effects of catechin standards EGCG and ECG on porcine pancreatic α-amylase activity were also observed. In conclusion, Qingzhuan tea or its water extract could be potentially used as complementary therapy ingredients for diabetes treatment through lowering postprandial blood glucose, and catechins EGCG and ECG may be the most efficient components in the water extract.

The present study investigated effects of solvents, temperature, and duration on extracting efficiency of catechins from green tea by an orthogonal test. The results suggested that extraction of epigallocatechin gallate (EGCG) was highly dependent on these factors, whereas that of epigallocatechin (EGC) was significantly affected by duration and solvent (P0.05). Effects of these factors on epicatechin (EC), catechin (C), and epicatechin gallate (ECG) were not significant. A two-step preparation was adopted to produce green tea extract enriched in EGC (GTE-EGC) and green tea extract enriched in EGCG (GTE-EGCG). The optimum conditions for GTE-EGC were that green tea was brewed in 75% ethanol at 30 degrees C for 10 min, whereas for GTE-EGCG the same tea was brewed in 35% ethanol at 90 degrees C for 60 min. Compared with GTE-EGC, GTE-EGCG had EGCG increased by 110.42%, whereas EGC decreased by 40.38% with EC and ECG being unchanged. Most importantly, GTE-EGCG possessed greater antioxidant activity (in vitro) than GTE-EGC.

Natural products have being used as potential inhibitors against carbohydrate-hydrolyzing enzymes to treat diabetes mellitus. Chinese dark tea has various interesting bioactivities. In this study, the active compounds from Qingzhuan dark tea were separated and their anti-diabetic activity was examined using an in vitro enzymatic model. The chloroform, ethyl acetate, n-butanol, sediment and residual aqua fractions of a Chinese dark tea (Qingzhuan tea) were prepared by successively isolating the water extract with different solvents and their in vitro inhibitory activities against α-glucosidase were assessed. The fraction with the highest inhibitory activity was further characterized to obtain the main active components of Qingzhuan tea. The ethyl acetate fraction had the greatest inhibitory effect on α-glucosidase, followed by n-butanol, sediment and residual aqua fractions (with the IC50 values of 0.26 mg/mL, 2.94 mg/mL, 3.02 mg/mL, and 5.24 mg/mL, respectively), mainly due to the high content of polyphenols. Among the eight subfractions (QEF1-8) isolated from the ethyl acetate fraction, QEF8 fraction showed the highest α-glucosidase inhibitory potential in a competitive inhibitory manner (the K i value of 77.10 μg/mL). HPLC-MS analysis revealed that (−)-epigallocatechin gallate (EGCG) and (−)-epicatechin gallate (ECG) were the predominant active components in QEF8. These results indicated that Qingzhuan tea extracts exerted potent inhibitory effects against α-glucosidase, EGCG and ECG were likely responsible for the inhibitory activity in Qingzhuan tea. Qingzhuan tea may be recommended as an oral antidiabetic diet.