The Rheological Properties And Fractal Analysis Of Acid-induced Soy Protein Isolate Gel

Obtaining from the byproduct of soy oil industry-bean meal, soy protein isolate has been widely utilized in food industry due to its outstanding functional properties and nutritional components. Acid-induced soy protein isolate gel is one of ways that soy protein was applied in. This thesis focuses on the rheological properties, microstructural properties and fractal dimensions of acid-induced soy protein isolate gel and stresses on the influence of ionic strength, edible polysaccharide and homogenous process on the soy protein isolate gel as well as the mechanism of these influences. We explored the optimization condition and application prospect of acid-induced soy protein isolate gel, while revealing the effect law and basis of how external condition impact the physicochemical characteristics of acid-induced soy protein isolate gel.The viscoelastic property and scaling behavior of acid induced soy protein isolate gels were investigated at various ionic strengths and five protein concentrations. The ionic strength dependence of infinite storage modulus and the gelation start time, which indicate the progress of gelation process, was investigated. The storage modulus and critical strain were found to exhibit a power-law relationship with protein concentration. Rheological analysis and confocal laser scanning microscopy (CLSM) analysis were applied to estimate the fractal dimensions(Df) of the gels and the values were found to vary between2.319and2.729. The comparison of the rheological methods and the CLSM image analysis method showed that the Shih et al.(1990)’s model was better suited in estimating the Df value of acid-induced SPI gel system.The effect of the addition of locust bean gum on the rheological properties, microstructure and fractal dimension of glycono-8-lactone induced soy protein isolategels were studied. Both the small and large amplitude oscillatory shear measurements were carried out to characterize the rheological properties of SPI and SPI-LBG gels. Fourier transform rheology was used to analyze the higher harmonic signals from nonlinear stress waveform. Creep/recovery tests was applied to investigate the impact of addition of LBG on the creep recovery parameter and compliance of SPI-LBG gels. The image of the microstructure captured by confocal laser scanning microscopic (CLSM) was used to determine the fractal dimension. The protein network structure of SPI-LBG gels showed greatly bigger pore volume, better scale behavior than SPI gels, and the chaos and complexity of the protein aggregates in SPI-LBG gels were much less than that in SPI gel.High shear homogenization (HSH) process was used to homogenize soy protein isolate (SPI) dispersions. These dispersions were subsequently gelled by acidification. The rheological properties, creep-recovery behavior, gel microstructure, fractal characteristics of these SPI gels were studied. The results showed that the application of high shear homogenization significantly decreased the particle size and lowered the polydispersity index of the SPI dispersions. The SPI gels produced by using the homogenized dispersions significantly increased the gel strength, increased the frequency dependence of elastic modulus and weakened the order and increased the chaos/disorder in the network structure. The application of high shear homogenization during dispersion stage also reduced the voids/pores in SPI gel microstructure and increased the gel compactness.The non-linear viscoelastic properties of soy protein isolate (SPI) dispersions and acid-induced gels were investigated. The SPI dispersions showed Type Ⅲ (week strain overshoot) and Type IV (strong strain overshoot) networks when the strain amplitudes varied between0.01and1.00and1.00to100.00, respectively. In the case of acid induced SPI gels the rheological parameters showed the characteristics of Type Ⅰ (strain thinning) network. The medium amplitude oscillatory shear (MAOS) regime of SPI dispersion and gel was determined in this investigation.