Construction And Properties Of Zein-based Nanoparticles And Pickering Emulsion Delivery Systems

Many hydrophobic functional factors in plants,such as lycopene,resveratrol and curcumin,play an active role in anti-oxidation,anti-inflammatory and cardiovascular disease prevention.However,these functional factors have some problems such as poor water solubility,easy degradation against light and heat,and low bioavailability,which seriously limits their application in food and other fields.A large number of studies have shown that,it is an effective way to solve above problems for designing and constructing appropriate delivery systems using food grade raw materials for functional factor,such as nanoparticles,emulsions,microcapsules and liposomes.Among them,nanoparticles and oil in water emulsions are widely used as carrier systems for encapsulation and delivering hydrophobic functional factors.Compared with the traditional emulsions stabilized by surfactants,Pickering emulsions stabilized by solid particles have better stability through steric hindrance and electrostatic repulsion provided by particles.In this study,zein was chosen as the main carrier material,and zein composite nanoparticles with different structures and Pickering emulsions stabilized by these nanoparticles were prepared.The properties of different delivery systems and the encapsulation and protection effects of curcumin were studied.The main contents and results of this study are as follows:（1）Epigallocatechin gallate（EGCG）modified zein-sodium caseinate（NaCas）composite nanoparticles loaded with curcumin were prepared by antisolvent precipitation method,the interaction between the ingredients of composite nanoparticles was investigated;the effect of the addition of EGCG on the encapsulation efficiency of curcumin was analyzed;the dispersibility and antioxidant activity of different composite nanoparticles,bioaccessibility of curcumin were compared.The results showed that the core-shell nanoparticles with average diameter of 100～200 nm were obtained by adjusting the ratio of curcumin to zein;the interaction between curcumin and proteins is mainly hydrogen bond and hydrophobic interaction;the encapsulation efficiency of curcumin in the composite nanoparticles increased from 77.9%to 96.2%,and the dispersibility and DPPH radical scavenging ability of curcumin composite nanoparticles were improved with the addition of EGCG;the simulated gastrointestinal experiments in vitro showed that curcumin had high bioaccessibility in the optimized core-shell nanoparticles.（2）The different NaCas-EGCG covalent complexes were prepared by alkaline and enzymatic treatment respectively,and their structures and physicochemical properties were characterized;and the effects of different NaCas-EGCG complexes on emulsifying property of zein and the potential of ternary composite nanoparticles（zein-NaCas-EGCG）as Pickering particles stabilizer were also investigated.The results showed that,compared with NaCas-EGCG non-covalent complex,more EGCG could be grafted onto sodium caseinate in the covalent complexes,and the covalent binding of EGCG turned theα-helix structure of sodium caseinate toβ-sheet structure,changing secondary structure of sodium caseinate,and giving the covalent complexes better thermal stability and emulsification;the emulsifying properties of zein composite nanoparticles were significantly improved after interaction with NaCas-EGCG covalent complex,and the stable high internal phase Pickering emulsions with polygonal droplets were formed at very low particle concentration（0.3%,w/v）.（3）The hollow zein nanoparticles were constructed by combining the antisolvent precipitation method and the Na₂CO₃ template method（solid zein nanoparticles as the control group）,then the ternary composite nanoparticles with hollow structure were formed with NaCas-EGCG covalent complexes;the emulsifying properties of zein composite nanoparticles with different structures（hollow and solid）were investigated;and the influence of loading positions of curcumin on the stability of high internal phase Pickering emulsion and the bioaccessibility of curcumin were analyzed.The results showed that hollow zein nanoparticles with average diameter of less than 100 nm were obtained by adjusting the ratios of zein to Na₂CO₃ and the mixture to pure water（antisolvent）;the encapsulation rate of curcumin in hollow zein nanoparticles increased from 51.2%to 83.5%,and the emulsification also significantly improved,compared with solid zein nanoparticles;the loading position of curcumin had little effect on the environmental stability of the high phase Pickering emulsions,however,curcumin had higher bioaccessibility in the emulsions stabilized by composite nanoparticles loaded with curcumin,instead of curcumin loaded in oil phase.In this study,different types of delivery systems for curcumin were constructed based on covalent and non-covalent interactions between protein and polyphenols,improving the bioaccessibility of curcumin.To a certain extent,it will provide scientific basis for the design and development of nutrition fortified health food.