| Currently,the commonly used synthetic antioxidants in food,such as tert-butylhydroquinone(TBHQ),butylated hydroxyanisol(BHA),and butylated hydroxytoluene(BHT),are reported with potential toxicity,carcinogenicity and teratogenicity to human.With people's increased awareness of food safety issues,it will be a trend to substitute synthetic antioxidants with natural or modified antioxidants.Compared with water-soluble antioxidants,natural or modified lipid-soluble antioxidants are less and cannot meet the demand of the market.Tea polyphenol palmitate is a novel and safe lipid-soluble antioxidant.Based on the demands of the market and food industry,this research aims to study the molecular modification of epigallocatechin gallate(EGCG),the main bioactive ingredient of tea polyphenols,and then apply it to the molecular modification of tea polyphenols.The main contents of this thesis are as follows:The first chapter gave an overview of tea polyphenols and EGCG,including the stability,bioavailability,biotransformation and various bioactivities of EGCG.Then,the difficulties of EGCG/tea polyphenols in practical use,and the technical indexes as well as technical barriers of tea polyphenol palmitate were introduced.Subsequently,the research status of molecular modification of EGCG and the application of modified EGCG were described.In addition,the solubility study of substances was briefly introduced.Finally,the research significance and contents of this thesis were expounded.In the second chapter,by conducting single-factor experiments,the optimal reaction condition was established.The optimized condition was reaction at 40? for 6 h,with sodium acetate as base(acid-binding agent),acetone as solvent,and molar ratio of EGCG/palmitoyl chloride/sodium acetate was 1/2/2.Under this reaction condition,the conversion of EGCG was 99%,and the yield was as high as 90.6%,which was significantly higher than that of the enzymatic methods and other chemical methods.HPLC-MS analysis confirmed the presence of EGCG palmitate monoester.In addition,the crude product was isolated and purified by column chromatography,and identified as EGCG 4'-palmitate by MS and NMR.Therefore,in the presence of sodium acetate,the acylation occurs at the site 4' on the B ring of EGCG molecule.Chapter three included the inspection of the technical indexes of EGCG palmitate and the study of the antioxidant activities.It was found that product obtained under the optimal reaction condition met the requirements of the technical indexes.In addition,products obtained under different reaction conditions showed significantly elevated solubility in edible oil,which was 96-144 times than that of EGCG.The cytotoxicity experiment and solvent residue test of EGCG palmitate proved that it was safe and reliable.DPPH and ABTS·+ free radical scavenging assays were used to give a preliminary evaluation of the antioxidant activity of EGCG palmitate.Finally,the accelerated stability tests of edible oils confirmed that EGCG palmitate exhibited potent and comparable antioxidant capacity to TBHQ.Moreover,the synthesis and purification of EGCG palmitate were amplified to hundreds of grams scale,and the yield was considerable(87%).The product met the requirements of the technical indexes.This technology is expected to apply to the industrial production.In chapter four,the established acylation reaction condition of EGCG was applied to the acylation reaction of tea polyphenols.The synthesis conditions of tea polyphenol palmitate were studied.The technical indexes of two tea polyphenol palmitate products were checked to see if they meet the requirements.The research results can offer help for the development of the production technology of tea polyphenol palmitate.The fifth chapter firstly studied the stabilities of EGCG palmitate under alkaline,long-term and thermal conditions.It was found that EGCG palmitate was significantly more stable than EGCG under these conditions.In addition,EGCG palmitate exhibited potent inhibition of a-amylase and ?-glucosidase,which was comparable to the antidiabetic drug acarbose,and superior to EGCG.Molecular docking experiments simulated the binding modes of inhibitors to the enzymes,and well explained the results of in vitro experiments.The results suggest that EGCG palmitate has the potential to be developed into an antidiabetic drug.The sixth chapter delineated the study of the solubility of EGCG peracetate,a prodrug of EGCG.First of all,an economical,facile and green synthesis of EGCG peracetate was developed,and by crystallization,high purity of the EGCG peracetate was obtained.Then,solubility of EGCG peracetate in 12 organic solvents at temperatures from 278.15 to 318.15 K was determined,and was correlated with several thermodynamic models.Among these,the Van't Hoff equation and the Apelblat equation gave the best fitting results.Moreover,thermodynamic properties of the dissolution process of EGCG peracetate were studied.The solid morphology of EGCG peracetate in different solvents was analyzed by scanning electron microscope(SEM).Based on the solubility data and SEM analysis,the optimum solvents for recrystallization were selected out.The solubility of EGCG peracetate studied in this paper has not been reported in literatures,therefore,these studies enrich the solubility database,and provide important guidance for the synthesis and purification process of EGCG peracetate.Chapter seven summarized all the work,and gave the future direction of the follow-up research. |
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