Properties Of Emulsions Stabilized With Soy Protein Nanoparticles And Their Oleogels

Recently, food-grade Pickering emulsion stabilizers have shown great application prospect in food, medicine and cosmetic industries with their perfect compatibility, microencapsulation properties and ability against coalescence. In this thesis, we prepared soy protein nanoparticles(SPNs) by heating of soy protein isolates, and characterized their physical and chemical properties. We studied the adsorption kinetics of the SPNs at the oil/water interface and measured mechanical strength of the interfacial membrane formed. Then we prepared the Pickering emulsions stabilized by SPNs, investigated the effects of different conditions on their properties including microstructure, macroscopic stability and rheology, and evaluated the relationship between the interfacial properties of SPNs and the bulk rheological properties of their stabilized emulsions. Finally, we prepared oleogels templated with SPNs emulsions, and studied their rheological property. The main contents are as follows:(1) The aggregation behavior of SPNs in aqueous phase has been evaluated. We prepared SPNs by heating SPI at 95℃ and investigated the effects of different pH(5.9 and 7.0) and ionic strength(0, 100 and 400 mM NaCl) on the aggregation behavior of the SPNs. We characterized their particle size, Zeta potential, surface hydrophobicity and rheological behavior. As the results shown, SPNs can aggregate more easily at pH 5.9. The aggregation degree of SPNs first increases and then decreases with increasing ionic strength. A salting-out effect on the SPNs with the largest aggregates is found at 100 m M NaCl, while a salting-in effect on SPNs at 400 mM NaCl.(2) The adsorption and self-assembly behavior of SPNs at the oil/water interface have been investigated. We studied the effects of ionic strength(0, 100 and 400 mM NaCl) on dynamic interfacial tension and interfacial rheological property of the SPNs at pH 5.9 and p H 7.0, and obtained the effective diffusion coefficients using a mathematical model. The results show that, with increasing ionic strength, the dynamic interfacial tension of the SPNs decreases, their effective diffusion coefficients first decrease and then increase, and the interfacial elastic modulus first increase and then decrease.(3) The Pickering emulsions were prepared using SPNs, and the effects of pH, ionic strength, protein concentration and oil volume fraction on the emulsion microstructure, droplet size, creaming index and rheological properties have been investigated. The results show that all the emulsions exhibit shear-thinning behavior, reflecting the flocculation state of emulsion droplets. In the dynamic oscillation experiments elasticity modulus are always higher than viscous modulus, indicating the formation of elastic gel-like emulsions. The SPNs have higher emulsifying ability at the salting-out conditions(100 m M NaCl) compared to the salting-in conditions(400 mM NaCl), and their stabilized emulsions have higher shear viscosity and elastic modulus, with higher resistance against creaming and coalescence. The emulsions at pH 5.9 have larger shear viscosity and elastic modulus, smaller creaming index, and higher polydispersity index than at pH 7.0. With increasing SPN concentration, the emulsion droplet size decreases, but the creaming index keeps almost constant. With increasing oil volume fraction, the creaming index decreases significantly and the shear viscosity and elastic modulus increase. In order to get the relationship between interfacial properties of SPNs and the bulk rheological properties of their stabilized emulsions, on the basis of above research, we obtained critical oil volume fraction(φc) of emulsions under different ionic strengths, and correlated the interfacial elastic modulus(Gi’) with the bulk elastic modulus(G0’) at different oil volume fractions. It shows that G0’ is not only related to Laplace pressure and oil volume fraction, but also to Gi’.(4) Using the SPNs emulsions as the template, oleogels have been prepared through constant temperature drying. Xanthan gum(XG) is added into the emulsions templates to improve oleogels stability, and its role is evaluated in the emulsion templates and oleogels, respectively. The results show that XG prevents the emulsions from creaming and decreases their droplets size and elastic modulus, and improves the oleogels stability by increasing the shear viscosity and elastic modulus.