Study On Mixing Characteristics In Neutralization Process Of High-concentration Soybean Protein Curd

Many domestic and overseas scholars have studied production process of soybean protein isolate(SPI) and mainly focused on the optimization of extraction technology and modification of soybean protein. The neutralization of soybean protein curd is an important process of producing SPI with alkali-solution and acid-isolation method. There are mixing process and chemical reaction during the neutralization. The neutralization needs to be conducted under high concentrated soybean protein curd in order to reduce the energy consumption of spray drying and develop new soybean protein products. The paramount significance of this study is that it can upgrade the technology of manufacturing SPI.Firstly, this paper studied the effect of p H and concentration of soybean protein curd on the rheological characteristic during the neutralization. The result was that soybean protein curd showed the characteristic of shear thinning during neutralization. With increase of p H and concentration, consistency index K increased and flow-behavior index n reduced, i.e., the apparent viscosity increased and pseudoplastic enhanced.A new stirrer needed to be designed since the common stirrer can’t meet the requirement of stirring under high concentration. Given that determine the p H and add alkali solution, several holes needed to be set on the top and side wall of the reaction vessel. In order to make the impeller rotate steadily, the connection between the motor and mixing shaft used flexible joint, which can minimize the wear and were easy to clean.The effect of feeding position and concentration of alkali solution on the mixing time was studied during the neutralization. The comparison on mixing time of different feeding position showed that middle paddle of feeding alkali solution had the longest total mixing time, upper paddle is less and the superficial position has the shortest total mixing time. Taking the power consumption into consideration, it was found that adding alkali solution at the middle paddle had the highest mixing efficiency. In the study of effect of alkali solution concentration on the mixing time, it was found that 2mol/L showed less total mixing time than 3mol/L.The effect of feeding velocity and concentration on mixing characteristic was studied with a three-layer pitched blade turbine impeller, which was a kind of axial impeller. It was found that different feeding velocity influenced the total mixing time and 20 m L/min had the longest total mixing time, followed by 4m L/min and 8m L/min under protein concentration of 18%. But after finishing feeding alkali solution, the effect of feeding velocity on the net mixing time had the opposite result. It was found that the faster feeding velocity was, the shorter total mixing time was, under protein concentration of 12% and 14%. The Result also showed that the higher protein concentration was, the longer mixing time was. The power consumption of three-layer pitched blade turbine was also studied in this paper. Result showed that power consumption increased with the increase of rotational speed; the higher protein concentration was, the higher power consumption was.The mixing characteristic of the combined impellers of four-blade disk turbine impeller(DT), which was a radial impeller, and double pitched blade turbine impeller(PBT) were studied in this paper, which can be a support for optimizing copmbined impeller type. It was found that the combined impeller PBT-PBT-DT had the highest power consumption, followed by PBT-DT-PBT, which is approximately equal to DT-PBT-PBT, and PBT-PBT-PBT had the lowest power consumption. That was to say the addition of DT impeller can increase the power consumption of combined impeller and different position of DT impeller showed different power consumption. PBT-PBT-DT had the minimum energy consumption per volume, which means it had the highest mixing efficiency. As mixing efficiency is often used to measure the mixing characteristic of stirrer in the industrial process, PBT-PBT-DT can be considered the best combined impeller in this paper, which can provide theoretical evidence for choosing combined impeller in the neutralization process of soybean protein curd.