Relationships Between The Thermal Properties Of Raw Materials And The Textural Properties Of Extruded Texturized Soybean Protein

Raw materials are the foundation of the extruded textured protein. Different materials show different physicochemical properties, thus have different denaturation and aggregation degrees under the treatments of barrel temperature, pressure and shear, and have a significant effect on the extrusion system parameters and product properties. Clarify the relationship between the thermal properties of raw materials and the system parameters and the products properties makes for the raw materials selecting of extruded textured protein.Soybean protein isolates and9different commercial starches including wheat starch, corn starch, potato starch, sweet potato starch, cassava starch, mung bean starch, pea starch, amylose and amylopectin were analysed with a differential scanning calorimetry and extruded with the Germany Brabender DSE-25Twin Screw Extruder. Different starches and mixtures with different ratios show different thermal properties. The effect of thermal properties of raw materials on the process parameters (specific mechanical energy, torque, pressure and viscosity online) and product properties (thermal properties, textural properties and fibrous degree) were analysed. The main conclusions are as follows:(1) The contents of water, soybean protein isolates, wheat starch and wheat gluten had a significant on the fibrous degree of the extruded products. Under the laboratory condition, the optimal ratio of soybean protein isolates, wheat starch and wheat gluten was65:20:15, the moisture content of the raw materials was50%.(2) The denature temperature of soybean protein isolates decreased and the rate of the thermal denaturation increased with the moisture content increasing. There was only partial transition of corn starch when the moisture content was low. Soybean protein isolates and corn starch are independent during heating. The transition temperature of the corn starch increased due to the migration of water from the corn starch to the soybean protein isolates. The presence of corn starch protected the soybean protein isolates from denaturation. When the content of wheat gluten increased, the enthalpy change and denaturation rate of the soybean protein isolates decreased, the trasition temperature of the corn starch increased. When the ratio of soybean protein isolates was over60%in the mixtures of soybean protein isolates, corn starch and wheat gluten, only the transition of soybean protein isolates was observed. The changing of the mixtures with moisture content change was the similar with the single component.(3) The peak viscosity, final viscosity, breakdown viscosity and setback viscosity were positively correlated with each other, and were positivily correlated with the total starch content. Ptemp was positively correlated with To, To and PTemp Were negatively correlated with the granule size. The hardness of the starch gels was positively correlated with the granule size. Whereas, the peak viscosity and the breakdown viscosity were positively correlated with the mean volume size. To, final viscosity, breakdown viscosity and PTemp were negatively correlated with theâ–³H. (4) The specific mechanical energy, viscosity, hardness, springiness, tensile strength, chewiness and shear forces were the lowest, the fibrous degree was the largest when amylopectin was in the raw material. Amylopectin from corn contributes to the formation of high fibrous structure of the extrudates. During the extrusion, the lower the starch pasts, the higher the fibrous strcture of the extrudates.