Research On The Fractionation And Characteriation Of Soy Protein-Dextran Conjugates

Conjugates of β-conglycinin and Dextran were prepared by heating in solution under macromolecular crowding environment(Macromolecular crowding environment,MC) and dry-heating methods(Dry-heating,DH), and then fractionated by solubility at p H 4.8 and p H 6.5( MC48, MC65, DH48 and DH65) and characterized. The protein structure, microstructure of the conjugates, molecular inter-atomic forces, self-assembly properties and emulsification properties was investigated. The physicochemical properties of different groups were also compared. The results of our study desire to guide the employment of the conjugations prepared by different methods and treatments. The results are as follows:(1) The covalent attachment of Dextran to soy β-conglycinin was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE). The results of SDS-PAGE indicated that several β-conglycinin of MC48 was dissociated into lower molecular weight proteinaceous compound after heating in the liquid environment. And the glycation degree of MC48、MC65、DH48 and DH65 were 46.02%,21.58%,18.03% and l.93%. Corresponding to the results of gel permeation chromatography(GPC), the glycation degree of conjugates carried out by macromolecular crowding system(MC48 and MC65) were all higher than the conjugates of dry-heating system(DH48 and DH65). In addition, the glycation degree of group 4.8 was higher than the group 6.5.(2) The difference of the secondary structure of proteins caused by conjugates with different system was studied by far-UV spectra. Compared with the dry-heating system, the liquid system has greater impact on the structure of protein than the solid system. There were a remarkable difference between MC48 and MC65. As for the macromolecular crowding environment, there are more highly ordered structure(α-helix and β-sheet) turn to random structures for MC48 than MC65. In the dry-heating system, there were no remarkable changes among various glycated samples than the 7S. Surface hydrophobicity(H0) is an important indication of the tertiary structure of protein. Compared to the 7S(H0=3346.6), there are a greater change of H0 among the MC48 and MC65, the H0 of MC48 has dropped to 166.42 and MC65 has increased to 6533.65 dramatically. As for the dry-heating system, the change between DH48 and DH65 are less than the macromolecular crowding system, the H0 of DH48 and DH65 are 2793.85 and 3761.80 respectively.(3) With the analysis of sulfhydryl group content of β-conglycinin after glycation with Dextran and treating in different p H value, the sulfhydryl group content of group 4.8(MC48 and DH48) have dropped from 0.51μmol/g(7S) to 0.29μmol/g and 0.62μmol/g respectively.(4) This work aimed at preparing emulsion(O/W) from the fractionation of soy protein isolate(SPI) –Dextran conjugates carried out by macromolecular crowding system. The mean size, zeta-potential and stability of the resulted nanoparticles, as well as the storage stabilization were studied at different p H values, heating temperatures, ironic strengthes. The emulsions stabilized by MC45 show more stable on the mean size, zeta-potential and creaming in Dex than the others controls with the changing p H values, heating temperatures, ironic strength. But the creaming phenomenon of the emulsions stabilized by MC45 are more remarkable than the other controls after storing for two months, indicating the worse storage stability. As for the emulsions stabilized by MC65, the changing p H values, heating temperatures, ironic strength have greater impact on the mean size, zeta-potential and stability than the emulsions stabilized by MC45, which show similar changing trend with SPI.(5) Curcumin-loaded nanoparticles were prepared from the fractionation of β-conglycinin-Dextran conjugates and other controls by desolvation method. The solubility of the curcumin has been greatly improved. The order of the loading amount(LA) were MC65>CON>MC45>SPI. The molecule of curcumin combines with protein through the hydrophobic interaction. The surface hydrophobicity of MC65 are higher than other controls, indicating the stronger combination with the curcumin molecule, so the LA of MC65 are higher than MC45.