Rheological Studies Of Soy Protein At The Air-Water And Oil-Water Interfaces

The formation and stability of protein food dispersed systems (emulsions and foams) are considered to be primarily dependent on the interfacial properties of proteins, which can be described by interfacial rhelogy of proteins. The study for interfacial rheology of food proteins is crucial for understanding the the formation and controlling the physico-chemical stabilities of food dispersed systems.Soy proteins as macromolecular emulsifiers and foaming agents are being using increasingly for the formation and stabilization of food emulsions and foams. Therefore, in order to further understand the formation and stabilization of soy protein food dispersion, interfacial rheological properties of soy protein at the air-water and oil-water interfaces were studied. The aim of this study was to obtain the interfacial rheological information related to the formation and stability of soy protein food emulsions and foams.Changes of interfacial pressure (Ï€) and interfacial dilatational characteristic parameters (i.e. interfacial dilatational modulus, E ; interfacial dilatational elasticity, E_d; interfacial dilatational elasticity, E_v; and phase angle, θ) with adsorption time were measured using dynamic drop shape analysis, for adsorption of glycinin, P-conglycinin, soy protein isolates (SPI) and acylated SPI at the air-water and oil-water interfaces as a function of the initial bulk protein concentration (1%-0.001%, w/w) and pH value (7.0, 5.0 and 3.0). The adsorption kinetics of glycinin and β-conglycinin and dilatational rheological characteristics of adsorption films at the air-water and oil-water interfaces were investigated. Effect of modification on interfacial rheological properties of SPI was discussed. Main results are as follows:1. The research of adsorption dkinetics showed that Ï€ increased with adsorption time extended, indicating the adsorption of protein molecules at the interfaces, Ï€-t plots may be divided into three regimes roughly: induction, sharp increase and gradual increase regime. After an induction period, Ï€ began to rise. At low surface pressures, a good fit of the experimental data to the Wardand-Tordai equation (Ï€(t) = 2C₀KT(Dt/3.14)^1/2) was found, and plots of Ï€-t^1/2 were linear. Thus, diffusion controlled the adsorption kinetics. While at higher surface pressures, a good fit of the experimental data to the (1n[(Ï€₁₈₀ -Ï€_t)/(Ï€₁₈₀-Ï€)0)] = -k_jt) was...