The Investigation On The Antidiabetic Components From Tea (Camellia Sinensis L.)

In recent years,natural products have attracted increasing attentions in the fields of nutrition,health,cosmetics,feed and drug.Tea?Camellia sinensis?is the second most consumed beverage in the world.It has been widely used for a long history especially in Asia including China and Japan.Tea polysaccharides?TPS?and tea polyphenols are the two main components of tea which play critical roles in the bioactivities including antioxidant,anticancer,immunomodulatory and antidiabetic activities,etc.The study aimed at providing a reference for the full utilization of tea resources,with tea polysaccharides and epigallocatechin gallate?EGCG?as the research objects.The changes of physicochemical properties and the inhibitory activity on?-amylase of tea polysaccharides after simulated digestion in vitro were studied.The hypoglycemic mechanisms of EGCG were elucidated from multiple perspectives.And BSA-EGCG-TPS-2 nanoparticles were prepared to prevent the oxidation of EGCG and improve its bioavailability,as well as provide a theoretical basis for the application of plant active polysaccharide in the drug delivery system,and provide references for the development of related functional food and clinical drugs.The results of this study were as follows:1.In the present study,TPS was extracted and purified by polyamide chromatography according to our previous study.The physicochemical properties were determined.By using the in vitro digestion model,TPS was simulated digested and the physicochemical properties TPS after digestion were characterized by UV-Vis,FT-IR,scanning electron microscope?SEM?,high performance gel permeation chromatography?HPGPC?and gas chromatography?GC?.In addition,the?-amylase inhibitory effects of TPS before and after digestion were detected by DNS method.The results showed that there was no obvious change of TPS in the oral phase.After simulated gastric digestion,parts of peptide bonds were broken down while the polysaccharides still kept the skeleton of polysaccharides.However,the TPS was digested after simulated gastric and intestinal digestion.The morphological properties of TPS were changed with increasing small pieces,rugged surface,more cavities and crack.The molecular weight was significantly decreased and the reducing sugar content was remarkably increased by breaking the glycosidic bonds.In addition,molar ratio of monosaccharide was changed throughout the whole digestion process in different degrees.And the?-amylase inhibitory rate was significantly increased after gastrointestinal digestion.2.In order to elucidate the hypoglycemic mechanism of EGCG from multi-perspectives,the interaction between EGCG and?-glucosidase was investigated by kinetics analysis,fluorescence spectra,FT-IR,and molecular docking methods.The effect of EGCG on glucose uptake and the effect on lipid accumulation were investigated by using L6 cell line model.The results showed that EGCG was an effective inhibitor against?-glucosidase with the IC₅₀ value of 19?M.The kinetic analysis showed that EGCG was a non-competitive reverse inhibitor.EGCG quenched the fluorescence of?-glucosidase due to the complex formation of EGCG and?-glucosidase.Hydrogen bonds played a critical role in the complex.The results showed that the microenvironment and the secondary structure of?-glucosidase were affected by EGCG.And the results of molecular docking indicated that the binding sites on?-glucosidase for EGCG were close to the active site pocket of the enzyme.In addition,EGCG could enhance the glucose uptake in L6 cells and significantly ameliorate the lipid accumulation induced by free fatty acid.These results suggested that EGCG exhibited strong hypoglycemic and hypolipidemic effects.3.In order to broaden the application of tea polysaccharides,overcome the setbacks of EGCG,develop the combination of tea polysaccharides and tea polyphenols,and provide information about application of polysaccharides-protein complex in the drug delivery system,a biodegradable and non-toxic BSA-EGCG-TPS-2 novel nanoparticles?BETN?were prepared and characterized.The characteristics were analyzed by?potential,dynamic light scattering?DLS?,SEM,FT-IR and differential scanning calorimeter?DSC?methods.The in vitro release and in vitro antioxidant activities were studied.The results showed that the loading capacity and loading efficiency were 45.14%and 47.54%,respectively.The nanoparticles had a spherical surface with the average particle size was 272 nm.EGCG presented an amorphous,disordered crystalline or solid solution state rather that the crystalline form in the nanoparticles.The interactions among BSA,EGCG and TPS-2 included hydrogen bonds and electrostatic interaction.In addition,EGCG could display a noticeable sustained in vitro release.The results improved that the preparation of BSA-EGCG-TPS-2 nanoparticles was feasible.And this work provided information about the polysaccharides-protein complex which has good potential for the application in the nanoparticles.