Metabolome and Microbiome Analysis to Study the Flavor of Summer Black Tea Improved by Stuck Fermentation.

Tea is the most popular and widely consumed beverage worldwide, especially black tea. Summer tea has a bitter and astringent taste and low aroma compared to spring tea due to the higher content of polyphenols and lower content of amino acids. Microbial fermentation is routinely used to improve the flavor of various foods. This study analyzed the relationship between the quality of black tea, metabolic characteristics, and microbial communities after microbial stuck fermentation in summer black tea. Stuck fermentation decreased the bitterness, astringency sourness, and freshness, and increased the sweetness, mellowness, and smoothness of summer black tea. The aroma also changed from sweet and floral to fungal, with a significant improvement in overall quality. Metabolomics analysis revealed significant changes in 551 non-volatile and 345 volatile metabolites after fermentation. The contents of compounds with bitter and astringent taste were decreased. Sweet flavor saccharides and aromatic lipids, and acetophenone and isophorone that impart fungal aroma showed a marked increase. These changes are the result of microbial activities, especially the secretion of extracellular enzymes. Aspergillus, Pullululanibacillus, and Bacillus contribute to the reduction of bitterness and astringency in summer black teas after stuck fermentation, and Paenibacillus and Basidiomycota_gen_Incertae_sedis contribute positively to sweetness. In addition, Aspergillus was associated with the formation of fungal aroma. In summary, our research will provide a suitable method for the improvement of tea quality and utilization of summer tea, as well as provide a reference for innovation and improvement in the food industry.

Tea and its components reduce the production of uric acid by inhibiting xanthine oxidase.

Background: The health benefits of tea are as diverse including the reduction of uric acid levels. Xanthine oxidase is the most directly mediated enzyme in the production of uric acid. Objective: To explore the inhibitory effects of different teas and its main bioactive components on the production of uric acid. Design: Experimental study. The experiments were conducted in vitro using human immortalized normal liver cell line HL-7702 (L-02). Results: The inhibition of the xanthine oxidase activities and the expression level of xanthine dehydrogenase mRNA stimulated in the hyperuric hepatocyte cell model showed that the unfermented green tea and th1e lightly fermented yellow tea, white tea, and oolong tea significantly stronger than the highly fermented black tea and dark tea. The main bioactive compound, gallic acid, showed the strongest inhibitory effect on uric acid production, followed by tea polyphenols and theaflavins. Discussion: All teas exhibited significant inhibition of xanthine oxidase activities, and the degree of fermentation of tea may be inversely proportional to its ability to inhibit the production of uric acid. Compared with tea polyphenols rich in tea, gallic acid may be a more potential uric acid-lowering component. Conclusion: In this article, we first compared the effects of six traditional Chinese tea made from a single variety in stabilizing the synthesis of uric acid and found that the lighter the fermentation, the greater the potential for inhibiting the production of uric acid. Furthermore, we analyzed the inhibitory effects of its main biochemical active ingredients and found that the inhibitory effects of polyphenols rich in lightly fermented tea were significantly stronger than caffeine rich in highly fermented tea. Our findings will be helpful for people to choose a proper tea for alleviating hyperuricemia and provide a scientific basis for uric acid-lowering tea processing.

Chinese Tea Alleviates CCl4-Induced Liver Injury through the NF-κBorNrf2Signaling Pathway in C57BL-6J Mice.

Liver injury is a life-threatening condition that is usually caused by excessive alcohol consumption, improperdiet, and stressful lifestyle and can even progress to liver cancer. Tea is a popular beverage with proven health benefits and is known to exert a protective effect on the liver, intestines, and stomach. In this study, we analyzed the therapeutic effects of six kinds of tea on carbon tetrachloride (CCl4)-induced liver injury in a mouse model. The mice were injected with 10 mL/kg 5% CCl4 to induce liver injury and then given oral gavage of green tea, yellow tea, oolong tea, white tea, black tea, and dark tea, respectively. The serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured, and the expression levels of inflammation and oxidative stress-related proteins in the liver tissues were quantified. All six kinds of tea partly reduced the liver index, restored the size of the enlarged liver in the CCl4 model, and decreased the serum levels of ALT and AST. Furthermore, the highly fermented dark tea significantly reduced the expression levels of NF-κB and the downstream inflammatory factors, whereas the unfermented green tea inhibited oxidative stress by activating the antioxidant Nrf2 pathway. Taken together, tea can protect against liver inflammation, and unfermented tea can improve antioxidant levels. Further studies are needed on the bioactive components of tea to develop drugs against liver injury.

Six types of tea reduce high-fat-diet-induced fat accumulation in mice by increasing lipid metabolism and suppressing inflammation.

A high-fat diet results in obesity because of white fat accumulation. Although tea extracts alleviate lipid metabolism disorders and decrease white fat accumulation, the mechanisms underlying the therapeutic actions of different types of Chinese tea are unclear. We established a murine model of obesity by feeding mice with a high-fat diet (HFD) and treating them with atorvastatin (positive control) or water extracts (WEATs) of different tea types. The food and water intake, body weight gain, white fat accumulation, and triglyceride (TG) and total cholesterol (TC) levels were evaluated to assess the effects of the WEATs on obesity. The levels of the lipid metabolism enzymes p-AMPK, CPT-1A and FAS and the pro-inflammatory factors iNOS and IL-6 were determined. The WEATs not only reduced the body weight and white fat accumulation in the HFD-induced obese mice, but also relieved hepatic steatosis. Comparing the effects of the six kinds of tea showed that white tea has the best anti-obesity effect. Yellow tea and raw pu-erh tea significantly up-regulated p-AMPK, green tea, white tea and raw pu-erh tea markedly inhibited FAS, and white tea, yellow tea and oolong tea up-regulated CPT-1. Therefore, it is possible that white tea, yellow tea and oolong tea inhibit obesity by increasing energy expenditure and fatty acid oxidation, while green tea, white tea and raw pu-erh tea exert their effects by inhibiting fatty acid synthesis. In addition, the WEATs also significantly decreased the levels of IL-6, while green tea, yellow tea and oolong tea significantly inhibited iNOS. Different types of tea have specific chemical compositions and can regulate different lipid metabolism related proteins. In conclusion, despite variations in its composition and mechanism of action, tea is a potent anti-obesity agent.