Research On Experiment And Numerical Simulation Of Soy Protein Extrusion Texturization

Food extrusion is a new subject-across high technology, and it is one of the developing directions in food industry and agriculture engineering in the 21th century. As a high temperature-short time processing method, extrusion can continually accomplish multi-process units, such as transporting, compressing, mixing, cooking, denaturing, dehydrating, sterilizing, swelling, and shaping. So, extrusion texturization is a very effective texturization method for plant proteins. The experimental and numerical simulation study on the extrusion texturization of soy proteins was carried out in this thesis. The main contents included the rheological properties of soy protein, the processing parameters in twin-screw extrusion texturization of soy proteins, the process of high moisture extrusion of soy protein/animal protein blends, and the numerical simulation of the three-dimensional transport in the melt conveying section of single-screw extrusion of defatted soy flour.The rheological properties of soy proteins were investigated respectively using a capillary rheometry and a Brabender torque rheometry. The results showed that soy protein was a typical pseudoplastic fluid in the normal processing ranges; and the apparent viscosity decreased with increasing shear rate, decreased with increasing moisture content, and decreased with increasing temperature before protein denaturation; while as temperature exceeded 120℃, the apparent viscosity increased. The viscosity model of soy protein dough was also presented.Effects of processing parameters on system parameters during extrusion texturization of soy proteins were studied using a twin-screw extruder. The experimental results indicated that increasing screw speed resulted in an increase in throughout, power consumption, swelling ratio, die pressure, specific mechanical energy, and dough temperature in the die, and a decrease in material resident time; increasing moisture content resulted in an increase in throughout and material resident time, and a decrease in power consumption, swelling ratio, die pressure, specific mechanical energy, and dough temperature in the die; increasing barrel temperature resulted in an increase in dough temperature in the die, and a decrease in specific mechanical energy. The detailed results were also described as response surfaces and regression equations.High moisture content protein-based blends composed of soy protein, lean pork meat, starch and other additives were extruded to form a meat analog by a twin-screw extruder. The effects of extrusion processing variables and the properties and composition of the material system on the extrusion and product texture were studied.The experimental results indicated that increasing protein content and nitrogen solution index promoted the product textural quality; the oil content can be added as high as above 10%; the suitable addition ratio of soy protein, meat and starch was 4: 1: 0.5; the suitable pH value of the materials was in the range of 6.5-7.5; increasing barrel temperature resulted in an increase in tensile strength of the extrudates; the effect of moisture content and screw speed on the textural characteristics of the extrudates was complex in nature, and screw speed must match moisture content; the optimum processing variables were as follows: screw speed in the range of 60 r/min~100 r/min; moisture content in the range of 37%~45% for defatted soy flour material system, and in the range of 60%~65% for soy isolated protein material system; the optimum temperature curve of the extruder was: 30#~45#~80#~100# ~130#~150#~100#.A quasi-three-dimensional finite-based computer model for a power-law fluid was used to describe the three-dimensional transport during the processing of defatted soy flour in the melt conveying section of a single-screw extruder. The velocity vector plots showed weak recirculation in the cross-sectional plane, and the down-channel velocity w variation with y showed that back flow occurred, and the velocity w increased with increasing moisture content; the dimensio...