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Microbial fermentation, especially the microbes involved, plays a crucial role in the quality formation of dark tea. Over the last decade, numerous microbes have been isolated from dark tea and in turn, applied to dark tea manufacture through pure-strain, mixed-strain, and enhanced fermentation. This article systematically summarizes the specific metabolic function and quality contribution of tea-derived microbes, with special attention paid to their safety risk. Aspergillus niger converts catechins via hydrolysis, addition, oxidative polymerization, and B-ring fission, contributing greatly to the reddish-brown color and mellow taste of dark tea. Aspergillus sydowii and Penicillium simplicissimum are caffeine-degrading microbes, degrading caffeine mainly into theophylline. However, under adverse conditions, Aspergillus, Penicillium, and Fusarium species potentially produce aflatoxins, ochratoxin A, and citrinin, the mycotoxins occurring in dark tea. The in-depth knowledge of tea-derived microbes is important for improving the quality and safety of dark tea, providing a theoretical basis for its industrial modernization., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Dark tea with a unique aroma is a particular type of tea. Post-fermentation is the key manufacturing process that forms a unique aroma, distinguishing dark tea from other types of tea. Different post-fermentation conditions may be the reason for forming unique aromas in various dark teas. Microbial community and composition during post-fermentation are the main contributors to the formation of characteristic aroma in various dark teas. In this paper, we illustrated the differences in fermentation length, pile temperature and water content of ripened Pu-erh tea, Liupao tea and Tibetan tea during post-fermentation, and only six dominant microorganisms and six key aroma-active compounds were found to be consistent among the three dark teas. Furthermore, we elaborated on the correlations between key aroma-active compounds and core functional microorganisms during post-fermentation. Exploring these interrelationships during post-fermentation is crucial and worthwhile to maintain the stability of the aroma quality of the three dark teas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Pu-erh tea is post-fermented sun-dried tea leaves of Camellia sinensis (Linn.) var. assamica (Masters) Kitamura plant, native to Yunnan, China. Pu-erh tea is a highly prized commodity with unique aroma and taste and multiple health effects. This review overviews the chemical constituents, tentative bioactive compounds and their mechanisms responsible for bioactivities of Pu-erh tea. The bioactivities include antioxidative, antimutagenic, antimicrobial, laxative and neuroprotective activities, and controlling or preventing hypercholesterolemia, hyperglycemia, obesity, diabetes, osteoporosis and Alzheimer's disease. Limited human trials hardly convince the claimed therapeutic efficiency of Pu-erh tea. Raw and ripened Pu-erh tea possess their respective sensory characteristics, chemical and microbial diversities. Chemical and biological differences between Pu-erh and other tea types could be explained by different extents of their respective processing-induced compound transformations. Undesirable heavy metals, mycotoxins and other biocontaminants detected in Pu-erh tea relate to growing conditions of tea plantations, processing and storage conditions. Chemistry- and nutrition-derived mechanisms for tea pricing are lacking. Decontamination strategies and future studies for quality improvement of Pu-erh tea are recommended., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Background: Dark tea, comprising one of the six major teas, has many biological activities, which originate from their active substrates, such as polyphenols, polysaccharides, and so on. The hypoglycemic effect is one of its most prominent activities, although less is known about their evaluation and potential role in the hypoglycemic mechanism., Results: In the present study, we separately analyzed the phytochemical composition, glycosidase inhibition and free radical scavenging activities, and hypoglycemic activity in type 2 diabetes mellitus mice, as well as the alleviation of insulin resistance in HepG2 cells of four dark tea aqueous extracts. The results showed that the phytochemical composition of dark tea aqueous extracts was significantly different, and they all had good glycosidase inhibition and free radical scavenging activities, in vivo hypoglycemic activity and alleviation of insulin resistance, and could also activate the phosphatidylinositol 3-kinase-Akt-perixisome proliferation-activated receptor cascade signaling pathway to regulate glucose and lipid metabolism, change the key enzyme activities related to glucose metabolism and antioxidant activity, and reduce oxidative stress and inflammatory factor levels. Among them, Liubao brick tea (LBT) and Pu-erh tea (PET) possessed better glycosidase inhibitory activity, in vivo hypoglycemic activity and improved insulin resistance activity, whereas Qingzhuan brick tea and Fuzhuan brick tea had better free radical scavenging activity, which may be explained by their distinct phytochemical compositions, such as tea proteins, polysaccharides, polyphenols, catechins, and tea pigments and some elements., Conclusion: Dark tea is a highly attractive candidate for developing antidiabetic food, LBT and PET may be good natural sources of agricultural products with anti-diabetic effects. © 2021 Society of Chemical Industry., (© 2021 Society of Chemical Industry.)

Dark tea, a unique tea fermented primarily in China, has numerous potential beneficial effects. However, harmful substances present in dark tea have provoked significant concern. To conduct a quantitative benefit-risk assessment of dark tea for Chinese residents and provide guidance on rational consumption, a framework of Benefit-Risk Analysis for Foods (BRAFO) and meta-analysis was applied to construct a disability-adjusted life year (DALY). Based on the BRAFO-tiered approach, a reference scenario (no intake) and an alternative scenario (intake of 3 cups/day) were determined. The overall health impacts of dark tea were simulated by comparing the risks of fluoride and AF with benefits of reduced-risk to coronary heart disease (CHD) and diabetes in different scenarios. Three cups of fermented tea consumed per day decreased risks of CHD and diabetes by 8.16% and 12.77% respectively. After quantitative integration of information, the ultimate net health effect was found to be -1958.827 illustrating that the benefits of drinking three cups of dark tea per day outweigh the risks. However, considering the uncertainties in the process, decision-makers should proceed with caution, consulting additional well-conducted studies and further managing harmful substances in dark tea., (Copyright © 2021. Published by Elsevier Ltd.)

The present study aims to explore the glucose-lowering effects of the previously characterised dark tea (Camellia sinensis L.) protein extract (DTPE) from Heimaojian on the spleen-brain axis of diabetic mice. DTPE was orally administrated (50-100 mg/kg) to alloxan-induced mice for 21 d; a biochemical assay and transcriptome profiling (RNA sequencing (RNA-Seq)) were performed. The results showed that DTPE can improve glucose tolerance. Compared with the model group, at day 21, the fasting blood glucose values were significantly (P < 0·05) decreased by 44·9 % (13·8 v. 7·6 mmol/l) and 51·4 % (13·8 v. 6·7 mmol/l) for high dose of DTPE (100 mg/kg) and drug metformin (125 mg/kg) groups, respectively. Subsequently, transcriptome profiling (RNA-Seq) was performed on the spleen and brain of diabetic mice. Totally, fifty-two spleen-derived and forty-seven brain-derived differentially expressed genes related to the synthesis, transport and metabolism of glucose were identified. The regulatory network analysis indicated that DTPE may exert glucose-lowering effects through a thirty-seven-gene sub-network related to metabolism, Parkinson's disease, oxidative phosphorylation and immunity. In summary, for the first time, the present data revealed that dark tea-derived DTPE could exert a potential anti-hyperglycaemic effect by modulating the spleen-brain axis.

In the present study, we produced Pu-erh, Liubao, Qingzhuan, and Fuzhuan teas using a single raw tea material and applied widely targeted metabolomics to study the impact of various microbial-fermented methods on the chemical profile of dark tea. The contents of catechins and free amino acids decreased drastically, whereas the contents of gallic acid and theabrownins increased significantly during microbial fermentation. Pu-erh tea had the highest content of theabrownins (11.82 ± 0.49%). Moreover, MS-based metabolomics analysis revealed that the different types of dark teas were significantly different from their raw material. A total of 85 differential metabolites were screened among 569 metabolites identified referring to self-compiled database. Glycosylated, hydroxylated, methylated, and condensed and oxidated products originating from microbial bioconversion of their corresponding primitive forms were significantly increased in dark teas. These results suggest that various microbial-fermented methods greatly affect the metabolic profile of dark tea, which can provide useful information for dark tea biochemistry research.

Green and dark tea extract (GTE/DTE) ameliorate chemical-induced colitis in mice; however, the role of gut microbiota in the anticolitis effects of green and dark tea in mice remains unclear. This study aims to explore the role of modulations in gut microbes mediated by green and dark tea in colitis mice by fecal microbiota transplantation (FMT). Our results indicated that GTE and DTE (5 mg/kg bodyweight/day for 4 weeks) exhibited prebiotic effects on the donor mice. Moreover, the FMT treatments (transferring the microbiota daily from the 1 g/kg bodyweight fecal sample to each recipient) indicated that, compared with the fecal microbiota from the normal diet-treated donor mice, the fecal microbiota from the GTE- and DTE-treated donor mice significantly ameliorate colitis-related symptoms (e.g., loss of bodyweight, colonic inflammation, loss of barrier integrity, and gut microbiota dysbiosis) and downregulated the TLR4/MyD88/NF-κB pathway. Collectively, GTE and DTE ameliorate chemical-induced colitis by modulating gut microbiota.

Objective: Eurotium sp. are the sexual states of the genus Aspergillus, and their ascospore is a spherical closed capsule with a golden colour. The growth of Eurotium sp. during tea production is a key step in achieving the unique quality of dark tea. This study aimed to evaluate the relationship between Eurotium sp. amount and Liupao tea quality., Methods and Results: The amounts of Eurotium sp. in 26 differently aged Liupao tea samples from several factories were studied. Indicators related to the quality of Liupao tea were investigated. The amounts of Eurotium sp. were divided into 0, 10 5 and 10 6 levels, and quantitative real-time polymerase chain reaction (qPCR) was performed. Using ultrahigh-performance liquid chromatography and high-performance liquid chromatography, the amounts of emodin and physcion were determined to be closely related to the amount of Eurotium sp. Emodin was not found or occurred in minimal amounts in all raw Liupao tea samples. By contrast, physcion was found in Liupao tea at the 10 6 level of Eurotium sp. Liupao tea samples with varying levels of Eurotium sp. also exhibited evident differences in aroma and chromaticity. Result of the Pearson correlation test showed that the amount of Eurotium sp. plays a key role in creating the unique quality of Liupao tea., Conclusion: The amount of Eurotium sp. in dark tea detected via qPCR can be used as a quantitative quality indicator for evaluating dark tea., Significance and Impact of the Study: The present study provides an efficient method for identifying the different qualities of dark tea and addressing quality control issues in fermenting dark tea., (© 2020 The Society for Applied Microbiology.)

Dark tea is a unique fermented tea produced by solid-state fermentation of tea leaves (Camellia sinensis). It includes ripe Pu-erh tea, Fu brick tea, Liupao tea, and other teas. Microbial fermentation is considered to be the key factor controlling the quality of dark tea. It involves a series of reactions that modify the chemical constituents of tea leaves. These chemical conversions during microbial fermentation of dark tea are associated with a variety of functional core microorganisms. Further, Multi-omics approaches have been used to reveal the microbial impact on the conversion of the chemical components in dark tea. In the present review, we provide an overview of the most recent advances in the knowledge of the microbial bioconversion of the chemical components in dark tea, including the chemical composition of dark tea, microbial community composition and dynamics during the fermentation process, and the role of microorganisms in biotransformation of chemical constituents., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Liupao tea, a popular dark tea, exhibited anti-diabetic activity in Chinese tea culture. However, the bioavailability of the main active components is low. Therefore, the relationship between the anti-diabetic activity and the modulation of gut microbiota was investigated in this study for the first time. Liupao tea extract (LTE) could significantly alleviate hyperglycemia, insulin-resistance, and plasma lipid profiles. The hypoglycemic effect of high-dose LTE was comparable to that of metformin. Importantly, LTE exhibited beneficial effect on modulating the diabetic-induced disorder of gut microbiota, such as increasing Bacteroidetes/Firmicutes ratio and up-regulating putative short-chain fatty acid (SCFA)-producing bacteria, including Prevotella and Bacteroides. Moreover, 29 key phylotypes were significantly correlated with at least one diabetic index. In conclusion, LTE could be developed into an anti-diabetic functional beverage and its beneficial effects is likely to be associated with the prebiotic effects for increasing the level of SCFAs and the relative abundance of SCFA-producing bacteria., (Copyright © 2019 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Dark teas are rich in secondary metabolites, such as phenolics and flavonoids, which have been suggested to be associated with their health benefits. In this study, the concentrations of tea polyphenols, tea pigments, catechins, flavonoids, alkaloid, and volatile components in 44 dark tea samples, including Pu-erh, Fuzhuan and Liubao teas, were systematically examined. Among the samples tested, Pu-erh tea contained the highest total flavonoid content (5.24±0.05%), followed by Liubao (4.45±0.61%) and Fuzhuan teas (3.33±0.23%). The tea polyphenols levels in the dark teas were approximately 10%, and no statistically significant differences (p>0.05) were found among the different types. Hexadecanoic acid was the most abundant aroma component in the dark teas, accounting for 15-20% of the total volatile oils. Moreover, the antioxidant activities of these dark teas were analyzed using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) assay, ferric reducing antioxidant power (FRAP) assay, and cellular antioxidant activity (CAA) assay (HepG2 cells). The fat metabolism modulation activities (FMMA) of the dark teas were tested using a high-throughput screening method (SMMC-7221 cells). The results indicated that the different dark teas had diverse antioxidant activities, and the variation in the activities was significant. Correlation analysis showed that there was a significant positive correlation between the levels of EGCG and antioxidant activities measured using the ABTS (r=0.916) and FRAP (r=0.853) assays, and the levels of total flavonoids and theabrownins correlated well with the values determined using the CAA (r=0.845 and 0.865, respectively) assay., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Non-alcoholic fatty liver disease (NAFLD) has emerged as a leading public health challenge and is closely associated with metabolic syndromes, such as obesity. Intestinal microbiota dysbiosis could play a vital role in the pathogenesis and progression of NAFLD. Tea is the second most popular health drink in the world behind water, and exhibits many health-promoting effects. In this study, the protective effects of different black and dark teas on NAFLD induced by long-term high-fat diet (HFD) exposure and their regulation of gut microbiota were evaluated and explored. The results indicated that supplementation with different black and dark tea extracts could significantly suppress the energy intake, alleviate abnormal accumulation of visceral fat, and prevent obesity, hepatic abnormal lipid deposition and liver steatosis in HFD-fed mice at varying degrees. In addition, Dianhong tea and Liupao tea interventions could significantly decrease the ratio of Firmicutes to Bacteroidetes, and selenium-enriched black tea and selenium-enriched dark rea supplementation could remarkably reduce the relative abundance of Actinobacteria compared to the model group. Moreover, these teas could partly shift the relative abundances of Allobaculum, Roseburia and Dubosiella. Taken together, black teas and dark teas could prevent HFD-induced features of obesity and NAFLD, which might partly be due to the modulation of gut microbiota. [ABSTRACT FROM AUTHOR]

Non-alcoholic fatty liver disease (NAFLD) has emerged as a leading public health challenge and is closely associated with metabolic syndromes, such as obesity. Intestinal microbiota dysbiosis could play a vital role in the pathogenesis and progression of NAFLD. Tea is the second most popular health drink in the world behind water, and exhibits many health-promoting effects. In this study, the protective effects of different black and dark teas on NAFLD induced by long-term high-fat diet (HFD) exposure and their regulation of gut microbiota were evaluated and explored. The results indicated that supplementation with different black and dark tea extracts could significantly suppress the energy intake, alleviate abnormal accumulation of visceral fat, and prevent obesity, hepatic abnormal lipid deposition and liver steatosis in HFD-fed mice at varying degrees. In addition, Dianhong tea and Liupao tea interventions could significantly decrease the ratio of Firmicutes to Bacteroidetes, and selenium-enriched black tea and selenium-enriched dark rea supplementation could remarkably reduce the relative abundance of Actinobacteria compared to the model group. Moreover, these teas could partly shift the relative abundances of Allobaculum, Roseburia and Dubosiella. Taken together, black teas and dark teas could prevent HFD-induced features of obesity and NAFLD, which might partly be due to the modulation of gut microbiota.

In order to supply genetic information of Camellia sinensis cultivar Anhua, characterization of the complete chloroplast genome sequence was reported based on high-throughput sequencing data. The complete cp genome of C. sinensis cultivar Anhua is shorter than other C. sinensis cultivars with 157,025 bp in length, comprising a large single copy (LSC) region of 86,585 bp and a small single copy (SSC) region of 18,276 bp, separated by two inverted repeat regions (IRs) of 26,082 bp. The overall G + C content is 37.30%. The genome contained total of 135 genes, including 90 protein coding genes, 37 tRNA genes, and 8 rRNA genes. Phylogenetic analysis showed all the cultivars were clustered into a group except C. sinensis var. pubilimba.

Background: 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. Methods: 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. Results: 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 Ki 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. Conclusion: 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. [ABSTRACT FROM AUTHOR]

• Analysis of volatiles changes during pile fermentation of dark tea. • Basic volatiles analysis of Yinghong No. 9 dark tea at an industrial scale. • On day 20 of pile fermentation, fresh, clean and chest-nutty smell disappeared. • On day 40 of pile fermentation, stale, fungus and aged fragrance began to present. • β-Myrcene, acetophenone, and terpinen-4-ol may be the key aged aroma compounds. Each type of tea has a unique volatile profile due to its variety, processing technologies and origin. Using HS-SPME and GC/MS, we analyzed the changes of volatile components in cultivar Yinghong No. 9 during pile-fermentation every 10 days. A total of 94 compounds showed significant differences during a total of 60 days mainly including alkanes, ketones, esters, terpenes, aromatics and heterocyclic compounds. Interestingly, 13 metabolites were progressively reduced during the first 20 days and remained unchanged in subsequent procedures, while 17 metabolites remained unchanged in the early stage and progressively increased during the last 20 days of pile fermentation, indicating that they are characteristic volatile compounds of raw material sun-dried green tea and dark tea, respectively. β-ionone, phenylethyl alcohol, and a-ionone could be the top three contributed aroma compounds in the final dark tea. Our study provides a theoretical basis for process and quality improvement of Yinghong No. 9. [ABSTRACT FROM AUTHOR]

In order to supply genetic information of Camellia sinensis cultivar Anhua, characterization of the complete chloroplast genome sequence was reported based on high-throughput sequencing data. The complete cp genome of C. sinensis cultivar Anhua is shorter than other C. sinensis cultivars with 157,025 bp in length, comprising a large single copy (LSC) region of 86,585 bp and a small single copy (SSC) region of 18,276 bp, separated by two inverted repeat regions (IRs) of 26,082 bp. The overall G + C content is 37.30%. The genome contained total of 135 genes, including 90 protein coding genes, 37 tRNA genes, and 8 rRNA genes. Phylogenetic analysis showed all the cultivars were clustered into a group except C. sinensis var. pubilimba. [ABSTRACT FROM AUTHOR]