Starch-based Pickering Emulsion: Stabilizing Mechanism And Application In Lutein Delivery

Bioactive compounds,such as polyphenols and flavonoids,have poor solubility,rapid aggregated precipitation,and oxidative decomposition,resulting in their instability during food processing and storage environment,and relatively low bioavailability in the human body.In this study,we used native starch as raw material to systematically investigate the effect of hydrophobic modification degree(Degree of substitution,DS and contact angle),particle size and oil volume fraction(Φ)on the multi-scale characterization combined with gelling rules of Pickering emulsions;then “Green” hydrophobic modification was achieved by complex coacervation between starch molecule and zein to prepare starch-based Pickering emulsifier with novel hydrophobic and functional properties;finally lutein as hydrophobic bioactive model,through construction of starch-based Pickering emulsion system with various interfacial activity and emulsion architecture,the structure-function relationship between interfacial activity combined with emulsion architecture and bioactive delivery characteristics was explored.These results could theoretical guidance for the design and development of starchbased Pickering emulsifier,further enrich and promote the related theory on the multi-scale characterization combined with functional features of Pickering emulsions,which will provide potential application prospects in the food,medicine,and cosmetics areas.Starch spherulites(<5 μm),rice starch(5～10 μm),waxy maize starch(10～20 μm)and waxy potato starch(20～30 μm)with different average particle size were modified with octenylsuccinic anhydride(OSA).Results showed that octenylsuccinylation(OS)caused a significant increase in the contact angle,and there was a weak positive linear correlation with the emulsifying capacity of the starch granules.After OSA modification,smaller particles of OS starch granules exhibited better emulsifying properties with smaller droplet size and lower creaming index.Quinoa starch granule with average smaller particle size(1～3 μm)and lower cost was used as raw material to prepared OS quinoa starch through OSA modification,and the effects of DS(0.007-0.029)and Φ(10-90%)on the formation process and gelling mechanism of their stabilizing Pickering emulsions were investigated systematically.OSA modification did not change the morphology or the granule size of quinoa starch but significantly increased the contact angle from 36.2° to 68.7°.OS quinoa starch-stabilized emulsion gels were formed at a DS of 0.029 with Φ values ranging from 50-70%.At the Φ value of 70%,increasing DS progressively increased the apparent viscosity(η)and storage modulus(G’)of the emulsions as a result of the adsorption of more OS quinoa starch granules at the oil/water interface.Both η and G’ showed an increasing trend as a function of Φ(50-70%)at a DS value of 0.029,and this was closely related to the microstructure of the formed emulsion gels.The network of quinoa starch-based emulsion gels at high Φ values(e.g.,60% and 70%)was mainly composed of compact “aggregated” oil droplets,which was largely attributed to the inter-droplet interactions.Transiting from chemical hydrophobic modification to "green" hydrophobic modification,hydrophobic modified starch nanoparticles were fabricated through combined starch nanoprecipitation and complexation with zein.Starch/zein nanocomposites under optimum conditions with unimodal distribution of particle size at 147.9 nm,and contact angle of 83.0 ° were achieved.Fourier transform-infrared spectroscopy,X-ray diffraction(XRD),X-ray photoelectron spectroscopy and differential scanning calorimetry and confocal laser scanning microscopy(CLSM)evidenced that zein has been successfully complexed with starch molecules.Dissociation test further confirmed that electrostatic interaction and hydrogen bond were main driving forces for the formation and maintenance of starch/zein nanocomposites.Complexing with zein endowed starch nanoparticles with emulsion p H-response behavior,showing various emulsion stability under different environment p H values.In order to improve the complexing efficiency of starch/zein nanocomposites,zein was further complexed with starch spherulites(SS)during the recrystallization formation from debranched starch,and zein modified SS(ZSS)was obtained.At p H 10,zein content of ZSS was highest,which alleviated particle aggregation and increased the contact angle.FT-IR result confirmed that zein was successfully complexed with SS,and XRD evidenced that increasing zein content is beneficial for the formation of ZSS,leading to “A-type” crystallization structure.Electrostatic interaction and hydrogen bond were main driving forces for the formation and maintenance of ZSS.CLSM result showed that zein was evenly distributed in the ZSS,showing water-insoluble without gelling phenomenon.The best emulsification performance was achieved at the concentration of 4% and Φ of 50% for ZSS,possessing highest emulsification volume,lowest creaming volume,lowest mean particle size and most uniform droplet size distribution.Regarding for the application of bioactive delivery,OS starch was used as particular emulsifiers to construct the Pickering emulsions with various interfacial activity and emulsion architecture,which was further developed to delivery lutein,and the influence of different gel network on the storage stability of lutein was explored systematically.Increasing Φ progressively increased the droplet size,storage modulus,and apparent viscosity,resulting in the formation of gel-like structure.CLSM showed that OS starch formed a densely packed layer at the oil/water interface,the degree of aggregation between droplets increased,and the gel network enhanced through droplet flocculation with increasing Φ.After 31 d of storage,the retention index of lutein in the emulsion gel could reach 55.38%,and the corresponding halflife times increased from 12 to 41 d.