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In this study, gas chromatography–mass spectrometry (GC–MS) and gas chromatography–olfactometry (GC–O) analysis was performed to figure out the characteristic aroma compounds of high-latitude black teas and select the suitable cultivar for producing high-aroma black tea. Sensory evaluation revealed that Jinxuan presented an obviously floral aroma and got the highest score, followed by Longjing Changye, Zhongcha 302, Yingshuang, Baihaozao and Huangshan Quntizhong. Furthermore, a total of 135 volatiles were identified in all black teas and 12 components can be used to distinguish different latitude black teas by principal component analysis (PCA). Cluster analysis (CA) showed six samples were divided into two clusters and Jinxuan was classified separately of cluster B. Based on GC–O analysis, 41 volatile organic compounds (VOCs) were found to promote the aroma of high-latitude black teas. Among them, phenylethyl alcohol, geraniol, linalool, α-ionone, cis-3-hexenyl hexanoate and methyl salicylate were the major contributors to the floral fragrance of black tea and accounted for a relative high proportion in Jinxuan, Longjing Changye and Baihaozao. In summary, Jinxuan and Longjing Changye were suitable for producing high-quality black tea in high-latitude area.

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.

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.

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 objective of the present study was to evaluate the effect of steeping temperature on the biological activities of green tea, including the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging capacity, α-glucosidase and α-amylase inhibitory activities, and glucose uptake inhibitory activity in Caco-2 cells. Results showed that, with increasing extraction temperature, the polyphenol content increased, which contributed to enhance antioxidant activity and inhibitory effects on α-glucosidase and α-amylase. Green tea steeped at 100°C showed the highest DPPH radical-scavenging activity and inhibitory effects on α-glucosidase and α-amylase activities with EC50 or IC50 values of 6.15μg/mL, 0.09mg/mL, and 6.31mg/mL, respectively. However, the inhibitory potential on glucose uptake did not show an upward trend with increasing extraction temperature. Green tea steeped at 60°C had significantly stronger glucose uptake inhibitory activity (p

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.