| Tea,originated in China and made from the leaves and buds of Camellia sinensis(L.)O.Kuntze,has a long history of over 5,000 years in traditional health drinks especially in Asian countries such as China,Japan,India,and Thailand.Nowadays,tea becomes more and more popular due to its unique flavor and alleged health-promoting effects.Next only to water,tea has been one of the most popular functional beverages consumed in the world.The chemical constituents of tea mainly includes polysaccharides,polyphenols,alkaloids,amino acids,etc.An increasing number of studies showed that tea has antioxidant,antibacterial,immunomodulatory,anti-inflammatory,lipid-lowering reducing weight,prevention of cardiovascular disease,anti-cancer activities.The recent studies show that the most of the polyphenols and polysaccharides in tea could pass through the digestive system without being broken down and absorbed,then reach the large intestine where it could interact with the gut microbiota,thereby modulating the gut microbiota and improving the human health level.Taipinghoukui,one of the ten most famous traditional Chinese teas,is produced in Xinming Township,Huangshan District,Huangshan City,Anhui Province.However,the study on Taipinghoukui polysaccharides(TPS)is still limited.In this study,Taipinghoukui was chosen as raw material.The extraction optimization,physicochemical properties of TPS were systematically studied,moreover in vitro digestion of TPS in simulated saliva,gastric and small intestinal conditions and the effect of TPS on gut microbiota were also investigated.The study has important significance to provide the theoretical basis and technical support for the development of TPS as functional foods.The main research contents and results are as follows:1.The extraction optimization and preliminary characterization of TPSThe single-factor tests were used to evaluate the effects of extraction temperature,extraction time,ratio of water to raw material,and extraction cycles on the yield of TPS.On the basis of the single-factor tests,extraction temperature,extraction time,ratio of water to raw material and and central experimental point were selected.A three-level,three-variable Box-Behnken design(BBD)was carried out to evaluate the optimal levels of extraction variables for the extraction of TPS.The data was statistically analyzed by Design-Experts 8.0.6 software.The results showed that the optimal extraction process was obtained as follows:extraction temperature 89?,extraction time 3 h,the ratio of water to raw material 26 mL/g.Under these conditions,the yield of TPS was 4.75±0.40%.At the same time,the preliminary characterization of TPS was carried out.The results showed that TPS consisted of 42.4±0.7%natural carbohydrate,2.5±0.4%proteins,4.8±0.3 mg GA/100 mg and 46.8±3.2%uronic acid.TPS was typical acidic heteropolysaccharides mainly composed of GalA,Gal,Ara with little molar contents of Man,Rib,Rha and Glc in the molar ratio of 42.6:20.6:19.4:3.5:2.6:4.4:6.9.The molecular weight of TPS was 782 kD.2.The digestion properties of TPS in vitroThe digestion properties of TPS under saliva,gastric and small intestinal conditions were investigated by in vitro simulated digestion system.Furthermore,the TPS digestion was evaluated by measuring the molecular weights of TPS,reducing sugars and free monosaccharides in the digestive solution before and after digestion.The results showed that no significant change for molecular weight of TPS in both retention time and response value was observed before and after saliva,gastric and small intestinal digestion.Moreover,there was no change for the reducing sugar(CR)values of TPS solutions,indicated that TPS could not be broken down in simulated saliva,gastric and small intestinal conditions.In general,TPS could pass through the saliva,gastric and small intestinal system without being broken down and reach the large intestine safely.3.The fermentation of TPS and the effect of TPS on gut microbiota in vitroIn this study,the effect of TPS on gut microbiota and the effect of gut microbiota on TPS metabolism were investigated by the anaerobic fermentation model in vitro.It was obvious that the response of TPS in HPLC significantly decreased with the increase of fermentation time.Furthermore,the polysaccharides contents in fermentation solution were also significantly gradually reduced.After 24 h of fermentation,the polysaccharides contents in fermentation solution remained 36.1±2.9%,suggested indigestible TPS could be broken down and utilized by gut microbiota in large intestine.At the same time,high throughput sequencing technology was used to evaluate the effect of TPS on the gut microbiota.The principal coordinate analysis(PCoA)and partial least squares discriminant(PLS-DA)showed that TPS could significantly modulate the structure and composition of gut microbiota.Furthermore,TPS could significantly reduce the ratio of Firmicutes/Bacteroidetes.Thereinto,the TPS could significantly enhanced the relative abundance of Bacteroides in genus level.In general,TPS has the potential to modulate the gut microbiota. |
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