Rheological Properties Of Thermal-shear Induced Protein/Starch Blends

The relationship between shear rate and viscosity was called rheological properties, which could reflect the deformation degree of material under different shear stress. The essence of rheological properties was the change of the molecular structure and conformation, which could be affected by the heating and shearing history. Thermo-shear history in extrusion promoted the protein aggregation or depolymerization, the geletination of starch and the interaction between them, which could influence the rheological properties and the product properties.The variation degree of protein molecule structure under different thermo-shear treatment, could be characterized by rheological properties.Clarify the rheological properties of different material under various treatments makes for understanding the molecule structure change under thermo-shear and providing the guide of the textured protein production.Soybean protein isolates, wheat gluten and corn starches were blended at 16 ratios. The rheological properties of 16 mixtures under 80℃,80℃-shear and 145℃-shear were analysed with a capillary rheometer(RHEOGRAPH 25) and extruded with the Germany Brabender DSE-25 Twin Screw Extruder. The effect of thermal-shear treatment on the process parameters(specific mechanical energy, torque, and pressure), viscosity properties, product density(thermal properties, thermal decomposition temperature) and phase distribution were analysed. The difference between the actual value and theoretical value was used to characterize the protein aggregation degree, the starch gelatinition degree and the interaction between them.The actual viscosity value of protein or starch under different temperature was calculated through Arrhenius equation and the value of different ratio blends was calculated by building non-interaction ideal model.The main conclusions are as follows:(1)The consistency index K of SPI, WG and CS increased when the treated condition varied from 80℃ to 80℃-shear or 145℃-shear.The protein aggregation and starch gelatinization were promoted when heating from 80℃ to 145℃.(2)With the CS increasing, the consistency index K of SPI induced by 80℃ was decreased, and the K of SPI induced by 80℃-shear was firstly increased and then decreased, while the K of SPI induced by 145℃-shear was increased.The protein aggregation was promoted and the interaction between phases was broken under heating(from 80℃ to 145℃).The degree of mixing was increased and thus enhanced the interaction under shearing.(3)The consistency index K of WG/CS blends induced by 80℃-shear was increased with the CS increasing.The gluten aggragation was promoted and the interation in blends was broken when heating to 145℃.(4)The consistency index K of SPI/WG/CS blends was increased when heating from 80℃ to 145℃,and the K of blends was decreased under shearing.When the ratio of WG/CS was 1/3, the mixture showed the similar behavior with the dough. The heating increased the interaction among phases and shearing broken it.(5) When heating below the denature temperature, the protein maintained the native structure, and at this time the degree of mixing was increased and the well-distributed system was formed under shear treatment.When heating above the denature temperature, the protein aggragation was increased and the interaction with starch was weaken, even the phase separation occurred.