Fabrication And Characterization Of Stimuli-responsive Food Delivery System Driven By Microenvironment

Food delivery systems refer to the delivery systems that encapsulates specific functional compounds through food-grade polymer or colloid systems to achieve specific purposes,including nanoparticles,liposomes,hydrogels,emulsions,etc.,which could improve the stability,control the release process and enhance the bioavailability of embedded substances through designing structure and tailoring the component.These delivery systems are of great significance for improving the absorption of active ingredients or nutrients and promoting human health.However,traditional food delivery systems are prone to be changed in physicochemical and structural properties under external environmental pressures,which affects the corresponding stability and the functional properties of embedded components.Environmental responsive delivery system refers to a delivery system that is responsive to external stimuli based on structural designment,component distribution,and external pressure regulation,which has attracted extensive attention in recent years due to the ability of regulating of inherent structural characteristics precisely and achieving responsive release of the embedded components by controlling or reversibly changing microstructure and physicochemical properties according to the changes of specific stimuli.Until now,there are few researches about the raw material selection,construction methods,structural characterization and functional properties of environmental responsive food delivery systems.Therefore,in this research,different biomacromolecules were used as raw materials to fabricate nanoparticle-protein amyloid fibril-stabilized hydrogel,nanocrystal-whey protein isolate amyloid fibril stabilized fibril emulsion,gliadin nanoparticle-stabilized Pickering emulsion,gliadin nanoparticle-whey protein isolate stabilized Pickering emulsion gel,glycyrrhizic acid fibril-whey protein isolate amyloid fibril stabilized high internal phase emulsion by altering microenvironment driven and component distribution.Overall,we achieved the comprehensive construction from oil-free(hydrogel)delivery system to high oil content delivery system(high internal phase emulsion),and investigated the effects of microenvironment driven(p H,salt,heat)and component distribution on the physicochemical stability,structural properties,microstructures and potential of loading bioactives of the delivery system.Primary results are as follows.(1)Hydrogel was fabricated from gliadin nanoparticles and whey protein isolate amyloid fibrils.It was found that the fractal structure of the protein(solution molecular,native fibril and partial-degraded fibril)exhibited different impacts on the formation and strength of hydrogels.Whey protein isolate unfolded(p H 2.0)to form a rigid fibrous structure,sequentially the fibers undergo partial degradation at p H 4.0 and then exposed internal groups,which could capture gliadin nanoparticles to form hydrogels.The presence of salt ions and heat treatment could significantly enhance the strength of the hydrogel.Curcumin was selected as a model drug to evaluate the loading performance and protective effect of the hydrogel.The results indicated that the hydrogel showed a high encapsulation efficiency for curcumin(p H 2.0,EE=89.76%),and significantly improved thermal stability and photodegradation of curcumin.,the structural properties of the hydrogel can be regulated to achieve different protective effects on curcumin according to the different p H values.(2)Gliadin nanoparticle-stabilized Pickering emulsion was developed.Nanoparticles with small and uniform particle size distribution were prepared by anti-solvent precipitation method combined with dynamic high pressure microfluidic,which were sensitive to environmental pressures(p H,Na Cl concentration).Therefore,Pickering emulsions with different flow states and gel strengths can be prepared by adjusting p H values,Na Cl concentrations and component ratios of the system due to the changes in the electrostatic interactions between emulsion droplets.Laser confocal images indicated that gliadin nanoparticles could adsorb at the surface of oil droplets and then form a dense rigid film structure,suggesting that the emulsion was formed by Pickering stabilization mechanism.The size of the emulsion droplets can be adjusted by shear speed and different oil phase volume.A gel network structure of Pickering emulsion could be formed with 70% oil content,which can effectively improve the creaming phenomenon.(3)Cellulose nanocrystal-whey protein isolate amyloid fibril-stabilized fibril diluted emulsion was prepared.The effect of CNC-C on the stability of the dilute emulsion and the stability mechanism were investigated with the oil content fixed at 20%.The results suggested that stable fibril emulsion can be prepared by adjusting the concentration of CNC-C in the system,and different amounts of CNC-C will lead to different stabilization mechanisms.When the CNC-C concentration is 0.18%-0.30%,CNC-C acts as a depletion factor to promote the adsorption of WPF at the oil-water interface and reduce the interfacial tension of the oil-water interface,thereby improving the stability of the emulsion;when the CNC-C concentration is higher than 0.3%,the stabilization mechanism of CNC-C is changed,where CNC-C tends to interact with WPF in the continuous phase,thereby improving the stability of the emulsion by enhancing the viscosity and gel strength of the emulsion which suppressed the movement and aggregation of oil droplets.Confocal laser microscopy and cryo-scanning electron microscopy indicated that different concentrations of CNC-C could significantly change the adsorption and interface structure of WPF on the surface of oil droplets,confirming that CNC-C could significantly improve the stability of dilute emulsions through depletion interaction.(4)Pickering emulsion gel stabilized by gliadin nanoparticles(GNP)and whey protein isolate(WPI)was fabricated.The possibility of constructing Pickering emulsion gel through the synergistic effect of complex proteins was investigated with the oil content fixed at 30%.The results suggested that Pickering emulsion gel with controllable gel strength could be prepared by adding whey protein isolate solution(WPI)to the gliadin nanoparticle-stabilized Pickering emulsion and adjusting the microenvironment(p H value,ionic strength,temperature)of the system.The electrostatic interaction between GNP and WPI can be regulated by altering the p H value and Na Cl concentration of the system.Thermal treatment can promote the unfolding of WPI to expose the internal hydrophobic groups and strengthen the hydrophobic interaction with GNP,thereby enhancing the gel strength of the emulsion.Furthermore,the freeze-thaw stability of Pickering emulsion-gel was investigated.The freeze-thaw stability of emulsion could be improved by high concentrations of Na Cl(200 m M,500 m M)combined with thermal treatment at 85 °C for 30 min,which can effectively enhance the gel strength of Pickering emulsion gels by adjusting the electrostatic and hydrophobic interactions between droplets,and inhibiting creaming and oiling off phenomenon during repeated freeze-thaw cycles,thereby improving the freeze-thaw stability of Pickering emulsion gel.(5)Finally,thermosensitive high internal phase emulsion stabilized by glycyrrhizic acid fiber(GA)-whey protein isolate amyloid fibril(WPF)was developed.Results showed that the electrostatic interaction and hydrophobic interaction between GA and WPF can be changed by adjusting the ratio of GA and WPF,so that high internal phase emulsion systems with different gel strengths and stabilities can be developed.On the other hand,the presence of GA could enhance the viscosity of the system and promote the formation of the aqueous gel network,thus enhance the stability of the emulsion.Thermosensitive high internal phase emulsion can be used as ideal delivery system for the volatile component allicin,which exhibited high encapsulation efficiency and good stability at room temperature.The retention rate of allicin in stable WPF-GA emulsion was about 94% after 8 h storage,while high temperature treatment(85 °C)can promote the release of allicin and the retention rate of allicin after 8 h is 68%,which can be attributed to the states of GA changing from solid to liquid at high temperature,therefore weakened the strength of emulsion gel and caused the release of allicin.Our study confirmed that the temperature-sensitive WPF-GA high internal phase emulsion has great potential as excellent delivery system for volatile component.