Comparative Study On The Regulation Of Intestinal Flora And Alleviating Excessive Deposition Of Liver Fat By Black Tea

Black tea is a kind of tea with the largest output and consumption in the world.It has a wide range of health effects and can better prevent chronic diseases such as cardiovascular diseases,obesity and type 2 diabetes.There are many kinds of black tea,due to the different varieties,producing areas and processing techniques of tea trees,their chemical compositions are quite different,and their corresponding health effects are also significantly different.However,there is no clear conclusion in the reports on the types of black tea and its biological activity,and there is no systematic study on the relationship between the material basis and its activity.In this study,two typical black teas in China,Keemun black tea(KBT)and Dianhong black tea(DBT,raw materials of fresh leaves are one bud and two leaves),were selected as the research objects.Chemical compositions of two typical categories of tea were analyzed by HPLC and UPLC-Q-TOF-MS/MS.The effects of black tea on regulating intestinal flora and relieving excessive deposition of fat in the liver of obese animals were evaluated by using the anaerobic fermentation model outside intestinal flora and the obesity mouse model induced by high fat.The main experimental results are as follows:1.There are great differences in chemical composition between the two kinds of black tea.Theanine,TF-3-G and TFDG contents in KBT are significantly higher than those in DBT,while catechins,alkaloids,TF and TF-3’-G contents in DBT are significantly higher than those in KBT.The key difference compounds between the two kinds of black tea mainly belong to phenolic acids and contraction phenolic acids,β hydroxy acids and their derivatives,catechins,flavonoids,amino acids and their derivatives and hydrolysable tannins.2.Adding 1% black tea powder to anaerobic fermentation system in vitro can significantly increase the production of acetic acid,propionic acid,n-butyric acid and total short chain fatty acids.Specifically,the two kinds of black tea promoted the yield of acetic acid,propionic acid and n-butyric acid at a similar ratio,and increased the abundance of Bacteroides and Roseburia,while the positive control group fructooligosaccharides mainly promoted the yield of acetic acid and increased the abundance of Bifidobacterium.Black tea can be used as a new prebiotic to regulate human intestinal flora,and its mechanism is different from fructooligosaccharides.3.The experimental results of obesity induced by high fat showed that adding 2%DBT in the diet could significantly reduce the body weight,the weight of perirenal fat and the serum ALT level of mice.Compared with the high-fat control group,the total lipid content,triglyceride(TG)and total cholesterol(TC)in the liver of mice treated with DBT decreased by 53%,26% and 26% respectively.The total lipid content and triglyceride(TG)level in feces increased by 67% and 52% respectively.However,the same dose of KBT has no obvious effect on reducing the weight gain of animals fed with high fat diet and relieving excessive fat deposition in mice liver.Gene expression analysis showed that DBT treatment significantly increased the expression of lipid oxidation related genes(PPARα,ATGL and Cpt1α)and inhibited the expression of cholesterol synthesis gene(HMGR).At the same time,it promoted the expression of cholesterol efflux(ABCG5)and lipolysis gene(ATGL)in small intestine,but the expression of genes related to intestinal fat absorption and transportation did not change significantly.At the same time,the composition and proportion of intestinal flora in obese mice were not significantly changed by the two categories of black tea treatments.In summary,as two typical black teas in China,the chemical compositions of KBT and DBT are quite different.The content of crude protein,theanine and two theaflavin monomers TF-3-G and TFDG in KBT is higher than that in DBT,while the content of total phenol,crude fiber,tea polysaccharide,catechin,alkaloid,theaflavin monomer TF and TF-3’-G in DBT is higher than that in KBT.The main difference compounds between the two black teas belong to phenolic acids,catechins and flavonoids.The data of intestinal flora in vitro showed that both kinds of black tea can be used as a new prebiotic to regulate human intestinal flora.Adding 2% DBT to the feed can alleviate the weight gain and excessive liver fat deposition induced by long-term high-fat diet in mice.The mechanism mainly involves the promotion of liver fat decomposition,the inhibition of liver cholesterol synthesis and intestinal lipid absorption by tea leaves.The regulating effect of KBT was significantly lower than that of DBT.The possible reason is that the content of total phenol and tea polysaccharide in KBT is lower than that in DBT,which leads to the difference of health efficacy.Whether the key difference compounds of the other two black tea cause differences in their health effects needs deeper verification.