| Pickering emulsions prepared by protein nanoparticles alone were not stable,which are difficult to be applied in food systems.The intermolecular interaction between proteins and polysaccharides can control the characteristics of particles,and the composite particles after combination between individual proteins and polysaccharides can enhance the stability of Pickering emulsions through the synergistic effect of components.Zein was reported to be soluble in aqueous ethanol solution and aqueous alkaline solution.According to the unique soluble property of zein,in this research,the anti-solvent co-precipitation(ASCP)method and a pH-cycle method were developed to prepare zein-based binary and ternary composite colloidal particles.The interaction between different components,properties and structures of composite colloidal particles were explored to reveal the formation mechanism of composite colloidal particles.Composite colloidal particles were introduced as stabilizers to prepare the high interphase Pickering emulsions.This study not only introduced a new model system for the interaction between proteins and polysaccharides,but also constructed a new method for the preparation of composite colloidal particles,and provided a new idea for the design of the emulsion-based carrier to deliver fat-soluble bioactive compounds with a high loading capacity.The main results are shown as follows:(1)Most polysaccharides were not able to dissolve in the aqueous ethanol solution because they were prepared by the method of alcohol precipitation.However,propylene glycol alginate(PGA)was found to show a great solubility in the aqueous ethanol solution even with a high ethanol concentration(70%,v/v).At pH 4.0,zein and PGA were combined due to the non-covalent interaction forces,mainly including attractive electrostatic interaction,hydrogen bonds and hydrophobic effects.A potential two-process mechanism was proposed to explain the formation of zein-PGA binary composite colloidal particles,including the formation of large aggregates at low concentrations of PGA addition(zein to PGA mass ratios of 20:1,10:1 and 5:1),and the generation of small binary complex particles at high levels of PGA incorporation(zein to PGA mass ratios of 2:1 and 1:1).(2)A synergistic effect was found between zein and PGA on improving the entrapment efficiency and loading capacity of Quercetagetin(Q).A solid sponge-like entity was formed after lyophilization of Q-loaded zein-PGA composite colloidal dispersion.A fruit tree-like microstructure was observed for zein-PGA-Q ternary composite colloidal particles:zein particles were typically spherical,PGA exhibited a fine filamentous network structure,while zein-PGA-Q ternary composite colloidal particles showed a rough branch-like pattern,its "branches" were closely adsorbed by zein particles,Q was mostly filled in the trunk and branches,and a few of Q may be entrapped into zein particles.(3)The incorporation of Ca2+ resulted in the formation of aggregates with a large dimension between zein particles,led to obvious conformational,secondary and tertiary structural changes of zein due to the particle-particle collision for zein particles,and caused the disappearance of crystalline structure of zein.PGA became much thicker and stronger in the presence of Ca2+ due to the chain-chain association for PGA molecules.The presence of Q promoted the affinity and binding capacity of Ca2+ to zein and PGA.An interwoven network structure with enhanced firmness and density was observed in Q-loaded zein-PGA composite particles due to simultaneous cross-linking coupled with aggregating,leading to the improved thermal stability.(4)Lyophilized zein-PGA composite colloidal particles exhibited a slower release rate of Q after digestion in simulated gastric fluids(SGF),and a high cumulative release amount in simulated intestinal fluids(SIF);Q in zein-PGA composite colloidal dispersions showed a burst release after digestion in SGF,and a low cumulative release amount in SIF.The most distinguished difference between liquid and solid samples occurred in the digestion stage of SGF,(5)Compared with the HCl acidification method,zein nanoparticles prepared by a pH-cycle method with D-glucono-delta-lactone(GDL)acidification had a smaller mean hydrodynamic diameter(64.3 vs.134.8 nm)and a narrower distribution,and exhibited the excellent storage stability.The added sodium caseinate(NaCas)was interacted with zein through hydrophobic forces,also possibly hydrogen bonds to form binary nanocomplexes with the improved physical stability.(6)A pH-cycle method based on partially alkaline hydrolysis of propylene glycol alginate(PGA)to prepare zein-NaCas-PGA ternary nanocomplexes was developed in the present work.Properties of composite colloidal particles were dependent on incorporating sequences of PGA and different mass ratios of zein to PGA.Zein-NaCas-PGA nanocomplex with equal mass ratio of zein to NaCas was proved to be an excellent interfacial stabilizer for Pickering emulsions,showed a synergistic improvement in coalescence stability of particularly high interphase Pickering emulsions(O/W)with an oil fraction of 80%(v/v).Such Pickering emulsions exhibited a gel-like structure. |
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