Zein-Tannic Acid Complex Particles And Their Regulations On Interface-Dominated Food Systems

Complex molecular interactions between food components underlie the structure formation during food processing and manufacturing,which eventually determines the physicochemical stability,sensory perception,and nutritional properties of foods.In this study,we prepared the food-grade complex colloidal particles(zein/tannic acid complex colloidal particle,ZTP)with tunable size,hydrophobicity,and functionality,via controlling the noncovalent interactions between macromolecule(zein)and small molecule(tannic acid,TA).The potential of ZTP as natural and efficient emulsifier and forming agents were then evaluated and investigated.The relationships between particle properties,interface behaviors,and macroscopic functional properties were also analyzed.These findings would develop the theoretical and technical supports for the development of novel natural ingredients in food industry.The main conclusions are as follows:1.A novel ZTP based on the noncolvent interaction between zein and TA was prepared by using a simple antisolvent approach.Pickering emulsion gels with 50%(v/v)oil were successfully fabricated via one-step homogenization.The spectroscopy studies showed that the interaction between zein and TA was mainly hydrogen-bonding interaction.The resultant ZTP had lower wettability and enhanced interfacial reactivity,which allowed ZTP to stabilize the oil droplets and further triggered cross-linking to form a continuous network among and around the oil droplets and protein particles,leading to the formation of stable Pickering emulsion gels.2.The particle-particle and particle-interface interactions that govern the assembly of particles adsorbed at fluid interfaces determine the rheology and microstructure of particle laden interface.For bare zein particle(ZP),the rapid adsorption and high interparticle forces led to the low coverage and formation of large ZP aggregates at the interface.The hydrogen-bonding of TA weakened the particle hydrophobicity and thus interparticle forces at fluid interfaces.Therefore,the adsorption process and assembly rate of ZTP at the interface obviously reduced,which also provided enough time for ZTP to rearrange into orderly interfacial networks.Furthermore,the Lissajous plots of surface pressure versus deformation were used to understand the interface rheological response to large mechanical deformation in terms of interfacial microstructure.The rheological response of interface stabilized by ZTP showed strain hardening during extension and strain softening during compression.These findings indicate that the adsorb behavior,self-assemble behavior,nonlinear rheology behavior,and microstructure of zein particle-laden interface can be tuned by changing the TA content.3.A detailed investigation into the behavior of foams stabilized by the mixtures of ZTP with a conventional anion surfactant(sodium dodecyl sulfate,SDS)has been made.ZTP can be induced to form fractal clusters in the presence of surfactant.In mixed particle-surfactant systems,a synergism occurred with respect to foam properties,since the large fractal clusters could be used as building blocks to form stable foams with orderly interfacial architecture.The formability of ZTP-SDS mixtures increased with an increase of the SDS concentration.However,the foam stability increased to a maximum at 0.6 m M SDS followed by a decrease at higher SDS concentrations.4.A detailed investigation into the structure formation and large deformation rheological properties of ZTP-stabilized Pickering emulsion gels.ZTPs provided stabilization at the droplet interfaces,and that excess ZTPs provided a particle network in the continuous phase to give a solid-like structure to the ZTPs-stabilized emulsion gels.The low frequency dependency of storage modulus(G')and low values for loss factor(tan ?)imply that these emulsion gels have highly elastic networks.The G' of emulsion gels increases in a power-law manner with increasing particle concentration(cp)and oil content(?),which can be scaled as G' ~ cp n and G' ~ ?m,respectively.The exponent n decreased with an increase of oil content,and m decreased with an increase of particle concentration.This indicates that the structure of the network depends on both the particle concentration and the oil content.The difference in network structures was also seen in the critical strain ?co,since three regimes were observed: for ? ? 20%,?co decreased with an increase in the particle concentration;for 30% ? ? ? 50%,?co increased with increasing the particle concentration;and for ? = 60%,?co was almost independent on the particle concentration.5.The influence of hydrophobicity of ZTP on the rheological behavior of ZTP-stabilized emulsion gels was described.An increase in TA content decreased the hydrophobicity of ZTP,while retaining a similar particle size.The resulting ZTPs with varying hydrophobicity were successfully used to form emulsion gels with similar oil droplet size.With a decrease in the hydrophobicity of ZTPs,the storage modulus(G')of emulsion gels increased,while tan ? and the frequency dependence decreased,indicating the formation of a stronger gel network.The crossover strain,?co,increased with a decrease in the hydrophobicity of ZTPs,indicating the gel network becomes more resistance against breakdown.In all cases,G' increased in a power-law manner with an increase in protein concentration(G' ~ cp n)and oil content(G' ~ ?m).The exponent n and m decreased with decreasing particle hydrophobicity,indicating that hydrophobic interactions between particles within the particle network in the continuous phase and the oil droplets provide a relatively larger contribution to the gel strength for emulsion gels stabilized by ZTPs with higher hydrophobicity.Increasing the oil polarity provided a lower gel strength for emulsions stabilized by particles with high hydrophobicity,while it increased the gel strength for particles with low hydrophobicity.6.The influence of particle size(68 nm,ZTP1;108 nm,ZTP2)and charge density(+38,+20,and +1 m V)on the structure formation and rheological property of ZTP-stabilized high internal phase emulsion(HIPE)was studied.Extensive centrifugation of the ZTP-stabilized emulsions with a particle concentration of 1%(w/v)and an oil volume fraction of 50% resulted in stable HIPE with a particle concentration of 0.7-1.4%(w/w)and an oil content ranging between 72-87%(w/w).A decrease in the particle size resulted in an increase in the particle concentration in HIPE,on the contrary,an increase in the particle size led to an increase in the oil content in HIPE.In all cases,the value of the storage modulus showed a similar range,indicating oil content was not the limited factor for the gel strength of HIPE.It is assumed that the particle network in the continuous phase plays a more important role for the gel strength compared to the interfacial particle network.