Pectin Degree Of Esterification Determination And The Relationship Between Gel Rheological Properties And Molecular Structure Research

To investigate the the method of Fourier transform infrared spectrum(FTIR)and high performance anion exchange chromatography(HPAEC)for rapid pectin degree of esterification(DE)determination.At first,research demethylation kinetics,thermodynamics and demethylation mechanism of pectin in alkaline condition to make a series of demethylation pectin.Then,the difference of FTIR calibration line which with different pretreatment and the difference of DE determination of the FTIR and titration were compared,optimize DE determination.According to the retention time of pectin characteristic peaks which with different DE by HPAEC built the linear relationship of DE and retention time.Besides,to research the relationship of pectin gel rheological properties and molecular structure,the gel rheological properties,sensibility with calcium,HPAEC performance of three commodity orange pectins were measured.Pectins were purify with DEAE and the hightly purify compoents of their infrared structure,molecular weight and charge were analysised.The main researches of this paper are as follow.? Both temperature and p H had remarkable effects on demethylation process.The influence of p H is greater than temperature and the interaction effect between them is significant.Pectin alkaline demethylation followed first-order kinetic reaction model.Demethylation reaction rate constants(k)and p H showed exponent sign relationship.At p H 10.7,11.0 and 11.3,the activation energy(Ea)were 136.97?122.37 k J/mol and 104.20 k J/mol,the activation enthalpy(?H)were 134.52?119.92 k J/mol and 101.75 k J/mol,the activation entropy(?S)were 141.86,100.28 J/(mol·K)and 44.81 J/(mol·K)and the free energy of activiation(?G)were 92.76?90.40 k J/mol and 88.56 k J/mol,respectively.The reaction belongs to similar single molecule reaction mechanism.? The result of optimistic FTIR to determine pectin DE is accurate and feasible.The measurement conditions are as follow: Adjusting p H of pectin to 6,then freezing drying and finaly transimissing scan directly can optimize FTIR to determine DE of pectin.The linear relation of DE and ester pectin peak area percentage(I)can be expressed as: DE=120.15I+9.7617(R2=0.995 3).Standard mixed to make different DE of pectins and there is big difference between the theory calculate value and FTIR optimistic method determination value when the DE of the mixture pectin above 75%.? The performance of HPAEC can characterize DE of demethylation pectin.The linear relation of DE and HPAEC characterize peak retention time(t)is good and can be expressed as DE=-13.811t+175.95(R2=0.9964).? Orange pectins with similar DE,but have big difference of gel,rheology and sensitivity with calcium charactersic.Analysis pectins ion chromatographic behavior with HPAEC,purify pectin with DEAE and three components can be obtained.Combined FTIR structure,molecular weight and quantity of electric charge of the components with the differences of gel rheological properties and we can concluded that compoents two and component three influence the gel rheological properties.The bigger of the molecular weight and quantity of electric charge of component three is,the stronger of gel rheological properties will be and component two just play as supporting role.Natural sugure have little influence on pectin gel rheological properties.