The Research Of Conformation And Gel Properties Of Alkylated Pectin

Pectin is a kind of natural macromolecule polysaccharide extracted from the cell wall of plant.Its structure is complex,which is based onα-1,4-D-galacturonic acid units.The chain has many hydroxyl and carboxyl groups,which provides unlimited possibilities for the modification of pectin.In recent years,more attention was paid to the modification of pectin to overcome some inherent drawbacks.In this study,we successfully prepared alkylated pectin.On the one hand,we determined the conformation of alkylated pectin,on the other hand,we studied the effects of sugar content,p H,calcium concentration on gel properties of alkylated pectin.Furthermore,we evaluated the cytotoxicity of alkylated pectin.The main conclusion was as followed:1.Higher temperature can significantly increase the degree of substitution（DS）of alkylated pectin.The DS was determined by GC.Alkylated pectin with the same chain length(PC₆S^1.35,PC₆S^2.90 and PC₆S^4.53)and alkylated pectin with the same DS(PC₆S^2.90,PC₁₂S^2.90 and PC₁₈S^2.90)were obtained.The molecular weight was measured by high performance size exclusion chromatography with multi-angle laser light scattering and refractive index detector（HPSEC-MALLS-RI）and static laser light scattering（SLS）.We observed that the M_w of P_ctrl and alkylated pectin with the lowest DS and the shortest chain length were lower than original pectin,while M_w of alkylated pectin with higher DS and longer chain length were higher.The M_w of alkylated pectin was affected by degradation,alkylation and aggregation.2.The conformation of pectin after alkyl modification was changed.The conformation parameterα（obtained from R_g vs M_w）andρ（R_g/R_h）both indicated that original pectin,P_ctrl and alkylated pectin with the lowest DS and the shortest alkyl chain had random coil conformation,while alkylated pectin with the greater DS and longer chain had sphere conformation.3.The intrinsic viscosity of alkylated pectin was significantly lower than that of the original pectin and decreased with the increase of DS and alkyl chain.Combined with the M_w and conformation results,the decrease of the intrinsic viscosity of P_ctrl and alkylated pectin with the lowest DS were related to the degradation,while that of alkylated pectin with high DS and chain length could be attributed to the more compact conformation.4.The gel strength of original pectin and alkylated pectin increased with the decrease of p H,the increase of sugar content and calcium concentration.Increasing the DS,the carbon chain length of the substituents and the calcium ion concentration can improve the gel stability of alkylated pectin.In addition,the results of FT-IR,CD,and relative viscosities indicated the formation of a complex between calcium and ionized carboxylate groups during gelation.5.The gel strength of alkylated pectin was enhanced with the increase of DS and chain length.The gel strength of alkylated pectins with higher DS and longer chain length was higher than that of original pectin,while alkylated pectin with the lowest DS was lower.The enhanced gel strength of alkylated pectin may be significantly positively correlated with the higher M_w values.6.The original pectin and alkylated pectin had good biocompatibility.The biocompatibility of C₁₂-and C₁₈-alkylated pectin was better.