| As a new type of functional food and drug delivery carrier, soybean protein cold-set gel has been paid more attention. It is very important to study the gelling mechanism and microstructure of the soybean protein cold-set gel. Rheology is the best tool to study the soft solid gel. With the analysis of electron microscopy and fractal dimension, it can provide a reliable theoretical basis for this kind of food. The main research results are as follows:The rheological properties of acid-induced soybean protein gels were tested by the small deformation oscillatory rheology. The effects of GDL concentration, soybean protein concentration and temperature on SPI cold-set gels’storage modulus and loss modulus were researched. At the same time we use luminance fluctuation to characterize the gel process. Results indicate that while increasing the GDL concentration, the pH value of 8% soluble aggregates decreased rapidly, the storage modulus (G’) and loss modulus (G") increased sharply, the strength of the gel increased gradually at room temperature(25℃). The damping factor tan delta was about 0.2, forming a weak gel system. Protein concentration (1%-7%) and cooling processes (95℃～25℃) significantly affect the gel strength. The higher the concentration of the protein, the formation of the gels’ G’ values were greater, indicating higher strength. Forming in the cooling process of the hydrogen bonds and Van der Waals’ forces further enhance the gel strength. The turbidity increased during gel process. We use the colorimeter to measure luminance value changing exactly. From the Angle of optical analysis, we studied the dynamic behavior of acid- induced gel.The rheological properties and scaling behavior of cold-set soy protein gels induced by different coagulants (GDL, MgSO4, CaCl2, 1%-4%, w/v) has been studied. The results show that:After adding coagulant, all the samples show obvious gelling behavior with the passage of time. The strength of cold gel increased with the increasing of coagulant concentration. Frequency curve of cold-set gel can be highly fit power-law model (R2>0.938). Characteristic value n’ and n" indicates that cold-set gel system is weak gel system. Compared to salt-induced gel, acid-induced gel is higher thermal stability. After heating, the structure of cold-set gel destructed seriously. The creep-recovery rate of salt-induced gel is higher than acid-induced gel. Salt bridges played a decisive role. According to the fractal model, acid-induced gel and salt-induced gel have different microstructures. According to fractal dimension calculated by the Shih model, the Df value of GDL-induced gel is 2.73-2.76, MgSO4-induced gel is 2.57-2.59, CaCl2-induced gel is 2.5-2.69.The fractal dimension calculated by Wu&Morbidelli model is smaller than Shih model. The dynamic storage modulus and gel fractal structure are significantly affected by the type and concentration of the coagulant.The protein aggregates of 7S, 11S and 7S&11S mixed globulin were prepared by heating. After analysis of turbidity, average particle size, intrinsic viscosity and apparent viscosity, the results showed that the aggregation of 11S globulin was stronger than 7S. The aggregates are a regular crystal structure, and the structure of this crystal is much larger than a single crystal structure. The crystal structure of 7S is small and the distribution is uniform, and the crystal structure of 11S is not very regular. Rheological analysis showed that the gel strength of 11S gel was larger, and the content of 7S was increased, and the Df value of Shih model was about 2.7, and the Dfvalue of 11S was about 2.68. |
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