Fabrication And Characterization Of Protein-Polysaccharide Core-Shell Nanogels Via Maillard Reaction And Self-Assembly Approach

With small-size eddect,surface effect and lipophilic binding capability,protein-based nanogels have provided a possibility for target delivery of drugs and hydrophobic bioactives.The goal of this research was to fabricate novel,green and core-shell protein-polysaccharide nanogels by modifying protein and adjusting pH,temperature,concentration and heating time,which is based on the synthesis technique of nanomaterials.The morphology,structure and other properties of nanogels have been characterized.Furthermore,the mechanism of nanogels formation has been proposed basing on the theory that the steric hindrance of polysaccharide can play as a role to prevent the aggregation of nanogels.Finally,curcumin was selected as a hydrophobic nutraceutical model to evaluate the loading behavior of nanogels.This study aims to develop novel food functional ingredients,and to provide theoretical and technical basis for the research and application of protein-based nutraceutical delivery system.The results are as follows: 1.The soy ?-conglycinin-dextran nanogels were fabricated through a combination of Maillard dry-heating reaction and self-assembly method.The covalent attachment of dextran to soy ?-conglycinin was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE)and glycation degree analysis.Dynamic light scattering was used to study the optimum condition of nanogels preparation,and the uniform nanogels can be prepared by heating the soy ?-conglycinin-dextran conjugates(1 mg/mL)at pH 4.8 and 95 ? for 50 min.The morphology observation indicated that nanogels were of spherical shape with core-shell structures,and the zeta-potential study further verified that soy ?-conglycinin was covered with nonionic dextran.The circular dichroism spectra and surface hydrophobicity investigation displayed that more ?-sheet structures were formed and the hydrophobic groups of soy ?-conglycinin were exposed to the surface of protein to form several hydrophobic compartments.The nanogels were pretty stable against pH change,ionic strength change,dilution and lyophilization followed by rehydration.2.The soy protein isolate-soluble soy polysaccharide nanogels were fabricated through a combination of Maillard wet-heating reaction in macromolecular crowding condition and self-assembly method.The covalent attachment of dextran to soy ?-conglycinin was confirmed by SDS-PAGE and intrinsic fluorescence spectroscopy;the glycation degree of conjugates was 34.8%,indicating the hydrophilicity of protein was improved.Two kinds of uniform nanogels(NG38 and NG45)were obtained by self-assembling at pH 3.8 and 4.5,respectively.NG38 was prepared by heating the conjugates(0.5 mg/mL)at pH 3.8 and 90 ? for 60 min;NG45 was prepared by heating the conjugates(0.5 mg/m L)at pH 4.5 and 80 ? for 45 min.The morphology observation indicated that both kinds of nanogels were of spherical shape with core-shell structures,and NG38 were well-seperated but NG45 were more compact.Furthermore,the cores of NG38 were composed of soy protein isolate and some polysaccharide chains,while the cores of NG45 were composed of soy protein isolate.The zeta-potential study further verified that soluble soy polysaccharide located at the shells of nanogels.The circular dichroism spectra and surface hydrophobicity investigation showed that the secondary structures of protein in nanogels were change,more random coil structures were formed and the hydrophobic groups of protein were exposed to the surface of protein to form several hydrophobic compartments.The nanogels were pretty stable against pH change,long-term storage,dilution and lyophilization followed by rehydration.3.Curcumin was selected as a nutraceutical model to be loaded directly by NG38 and NG45 through hydrophobic interaction.The more compact NG45 showed better loading behavior than the looser NG38: the encapsulation efficiency of NG38 and NG45 was 23.58% and 51.41%,respectively;the loading amount of NG38 and NG45 was 6.59 ?g/mg and 8.74 ?g/mg,respectively.Dynamic light scattering and morphology analysis indicate that the size and structures of NG38 did not change after loading curcumin,while the size of NG45 was smaller and the structures of NG45 were more spherical-like after encapsulating curcumin.4.Two kinds of curcumin-soy ?-conglycinin-soluble soy polysaccharide nanogels(denote as dry-haeting nanogels and wet-heating nanogels)were fabricated via Maillard reaction(either dry heating or wet heating in macromolecular crowding condition)and co-assembly method.The effects of pH,conjugate concentrations and curcumin concentrations on the preparation of nanogels were studied.When the dry-heating nanogels were prepared at pH 4 using 10 mg/m L conjugates and 1 mg/m L curcumin,the size,encapsulation efficiency and loading amount of them were 165.82±2.58 nm,92.3±0.23% and 46.15±0.12%,respectively.When the wet-heating nanogels were prepared at pH 4.8 using 10 mg/m L conjugates and 0.8 mg/mL curcumin,the size,encapsulation efficiency and loading amount of them were 136.68±1.32 nm,95.97±1.23% and 47.99±0.62%,respectively.Both kinds on nanogels were ideal nutraceutical carriers,but wet-heating nanogels showed better loading behavior than dry-heating nanogels.The in vitro controlled-release experiment indicates that both kinds of nanogels had the ability to control the release of curcumin.But dry-heating nanogels showed better controlled-release behavior than wet-heating nanogels: the percentage of cumulative released curcumin of dry-heating nanogels was 33% while that of wet-heating nanogels was 68%.However,both kinds of nanogels can act as curcumin carriers with well loading and unloading behaviors.