Nanoparticles Prepared In Water Phase Based On Zein-EGCG Complexes And Their Application

Zein is capable of self-assembly to form nanoparticles for carrying functional ingredients.However,single zein nanoparticles have poor stability under neutral conditions,poor redispersibility after freeze-drying,and low antioxidant activity,which limits the application of zein in nanoparticle delivery systems.The covalent complexes formed by zein and polyphenols can play a synergistic effect of different components,improve the stability of nanoparticles,and inhibit the oxidation of oil in the emulsion system.In this research,covalent zein-EGCG complex was prepared in water phase with zein as the research object,and the formation mechanism of the complex was studied.On this basis,Na Cas was added to prepare ternary composite nanoparticles during a pH cycle,and the effects of covalent zein-EGCG complex and Na Cas on the stability of composite nanoparticles were studied.The composite nanoparticles were further applied to preparation of Pickering emulsion to study its effect on oil oxidation.This research not only introduces the interaction between zein and polyphenols into a new reaction environment,but also improves the application value of zein in nanosystems and emulsion systems.The main results are shown as follows:First,covalent zein-EGCG complex was prepared in water phase by the alkaline induction method,its formation mechanism was discussed,and its physical and chemical properties were studied.After covalent modification,free amino group of zein was reduced by 53.37 nmol/mg protein,binding amount with polyphenols was 105.31 nmol/mg protein.The non-covalent bond was broken by reduction electrophoresis,the result showed that the relative molecular weight of the covalent complex increased,indicating that a covalent bond was formed.The FTIR of the covalent complex has a red shift of about 3 cm^-1 at the peak of the amide A band,and the fluorescence spectrum has fluorescence quenching,which indicated that the free amino group of zein interacts with EGCG.The results of circular dichroism showed that the?-helical and?-turn in the secondary structure of zein covalently modified by EGCG were reduced by 0.9%and 1.8%,but the random coil increased by 3.4%,indicating that after covalently binding with EGCG,the internal structure of zein has been changed.The physical and chemical experimental results of the covalent zein-EGCG complex showed that the covalent modification of EGCG improved the thermal degradation and antioxidant properties of zein.Secondly,zein-EGCG-Na Cas composite nanoparticles were prepared in water phase by pH cycle,and the effects of covalent zein-EGCG complex and Na Cas on nanosystems were studied.The optimal preparation conditions for composite nanoparticles are:zein-EGCG/Na Cas mass ratio is 5:1,the total protein concentration is 8 mg/m L,and dynamic light scattering is used to determine its particle size of about 249 nm,PDI is less than 0.3,electron microscopy observations showed that the covalent composite nanoparticles were spherical.FTIR results showed that the amide I band peak of the composite nanoparticles had a red shift of about 21 cm^-1,indicating that the covalent zein-EGCG complex and Na Cas formed nanoparticles through electrostatic interaction.The decrease in fluorescence intensity of composite nanoparticles indicated that the interaction between the covalent complex and Na Cas made the microenvironment of the protein in the nanoparticles more polar and hydrophilic,and the two had a hydrophobic interaction in this process.The circular dichroism result showed that the addition of Na Cas can increase the?-helix and?-turn of the protein secondary structure in the composite nanoparticles by 2.8%and 5.1%,and reduce the random coils by 5.2%,indicating that the protein structure has been changed.Under different environmental conditions(pH,temperature,Na Cl,freeze-drying),the particle size and PDI measurement results of the composite nanoparticles showed that the covalent composite nanoparticles have good dispersibility and stability.Finally,in order to broaden the application of the covalent zein-EGCG complex in the emulsion system,Pickering emulsion was prepared with covalent composite nanoparticles as a stabilizer,and its effect on the oxidation of oils was discussed.Laser confocal microscopy observations showed that the Pickering emulsion stabilized by covalent composite nanoparticles is uniformly distributed.In the accelerated oxidation experiment,the concentration of hydroperoxide produced by the Pickering emulsion stabilized by the covalent composite nanoparticles was 8.4?g/g lower than that of the control emulsion,indicating that the covalent composite nanoparticles can inhibit the oxidation of oil in the emulsion.