Preparation And Properties Of Nano Starch-based Pickering Emulsions

Pickering emulsions refer to the emulsions that are stabilized by using solid colloidal particles as emulsifiers to work at oil/water interface of emulsions.Compared with traditional emulsions stabilized by molecular emulsifiers,Pickering emulsions have advantages of less particle dosage,excellent stability,no chemical pollution,easy subsequent separation and environmental friendliness.Starch,as a kind of primary agricultural product,has a wide source,lower price,easy to modify,and good biocompatibility and processing adaptability.In this paper,maize starch was used as raw material with modification to prepare nano-starch-based particle emulsifiers.The properties of the nano-starch-based particle emulsifiers prepared by various means were studied and their influences on physical stability and oxidative stability of the Pickering emulsions were investigated.Finally,the food-grade Pickering emulsion delivery vehicles were fabricated through regulating the nano-starch-based particle emulsifiers.(1)Preparation of Pickering emulsions stabilized by starch nanoparticles modifying with octenyl succinic anhydride(OSA).Starch nanoparticles(SNPs)prepared through ethanol precipitation were esterified by OSA to make OSA modified starch nanoparticles(OSA-SNPs).Characteristics of nano-starch-based particle emulsifiers and their stabilized oil-in-water(O/W)Pickering emulsions were determined by various means including morphology,particle size distributions,spectroscopy and so on.The results showed that the absolute value of surface Zeta potentials of the SNPs increased after OSA esterification.In addition,water contact angle of the OSA-SNPs raised,indicating their enhanced hydrophobicity.The stability of the Pickering emulsions stabilized by the OSA-SNPs was influenced by particle mass concentrations,p H and ionic strength.Adjusting p H to the acidic or alkaline,or adding KCl to improve the ionic strength of emulsions could induce the increase of emulsion droplet mean size and decrease of emulsified index(EI),thus leading to the instability of the emulsions for oil/water phase separation.The emulsion droplet size decreased with the increasing concentration of the OSA-SNPs under neutral p H and without KCl in emulsions.While EI of emulsions increased under that of conditions.Fluorescence microscopy showed that OSA-SNPs of 2%(w/v)could absorb at oil/water interface of the Pickering emulsions to form a physical barrier which inhibited the coalescence of dispersed oil droplets,thus keeping physical stability of the Pickering emulsions.(2)Sodium caseinate(SC),as traditional emulsifier,can adsorb at the oil/water interface of the emulsions.The interactions between traditional emulsifier(SC)and particle emulsifier(OSA-SNPs)and their influences on the properties of Pickering emulsions were studied by adding a small number of the OSA-SNPs into SC dispersions.The results showed that hydrodynamic diameters of the mixture increased with the increase of OSA-SNPs concentrations.Moreover,the absolute values of surface Zeta potential of the mixture decreased as the increasing the OSA-SNPs contents,and also the oil contact angles and interfacial tension of the mixture.Concentrations of interfacial protein,fat partial coalescence rate and mean particle size of the emulsions stabilized by the mixture of the SC and the OSA-SNPs increased firstly and then decreased with the increasing concentrations of the OSA-SNPs.It was proved that the OSA-SNPs of 0.04 g/100 m L could promote the adsorption of SC at the oil/water interface,which was in favor of the stability of the Pickering emulsions.(3)The nano-starch-based particle emulsifiers with antioxidant capacity and their stabilized food-grade Pickering emulsions were fabricated.Natural antioxidant tea polyphenol(TPs)and waxy maize starch(WMS)were combined to prepare WMS/TP nanoparticles through ethanol precipitation.Effect of TP additions on the physicochemical properties and emulsifying capacity of the WMS/TP nanoparticles were investigated.The physical stability and oxidation stability of the Pickering emulsions stabilized by the WMS/TP nanoparticles with different additions of TPs and with various particle concentrations were analyzed.The results showed that morphology and size of the WMS/TP nanoparticles changed obviously as increasing the additions of TPs in the WMS nanoparticles from 5% to 15%.Morphologies of the WMS/TP nanoparticles transformed from spherical to the mixture of rod-like and stretched strips,indicating the bridge functions of TPs among starch molecular chains.The hydrogen bond interactions between TPs and starches were proved by Fourier transform infrared spectroscopy(FT-IR).Compared with the WMS nanoparticles,the water contact angles of the WMS/TP nanoparticles increased and the oil contact angles decreased,suggesting that the addition of TPs enhanced the hydrophobicity of the WMS nanoparticles.Laser confocal fluorescence microscopy(CLSM)showed that the WMS/TP nanoparticles with different TP additions can adsorb to the oil/water interface of the emulsions,and the droplet mean sizes of emulsions decreased with the increasing concentrations of the WMS/TP nanoparticles.Moreover,the viscoelasticity and EI values of Pickering emulsions stabilized by the WMS/TP nanoparticles increased when increased the added TPs.Emulsions stabilized by the WMS/TP nanoparticles could keep the physical stability during 15 d of storage.Accelerated oxidation test showed that compared with the emulsions stabilized by the WMS nanoparticles,the primary oxidative products(POV)and secondary oxidative products(TBARS)of the emulsions stabilized by the WMS/TP nanoparticles decreased significantly during storage,indicating the oxidative stability of emulsions was enhanced.(4)Based on the interfacial property of the OSA esterified starch(OSS)and its interactions with TPs,OSS/TP nanoparticles with antioxidant function were prepared through ethanol precipitation to fabricate Pickering emulsion delivery system for bioactive substances.The results showed that the mean particle size of the OSS/TP nanoparticles increased with increasing the addition of TPs(from 5% to 20%),and the absolute values of surface Zeta potential and water contact angles of the OSS/TP nanoparticles decreased,suggesting their reduced emulsifying capacity.Mean droplet size of emulsions decreased with the increasing concentration of the OSS/TP nanoparticles.Interfacial structure with oil droplets close-packed was formed in the Pickering emulsions stabilized by the OSS/TP nanoparticles with TP additions of 10%,which could inhibit the migration of emulsion droplets and keep the stability of the Pickering emulsions.Compared with other emulsion samples,the POV of the Pickering emulsions stabilized by the OSS/TP nanoparticles decreased after 15 d of storage.In addition,the stability of resveratrol encapsulated in Pickering emulsions improved obviously.In vitro digestion model showed that encapsulated in Pickering emulsions stabilized by the OSS/TP nanoparticles,the resveratrol was not eroded in digestive environment,so it delaying the release of the resveratrol.These facts indicated that the Pickering emulsions stabilized by the OSS/TP nanoparticles can be used as a delivery carrier to improve the stability and bioavailability of bioactive substances.