Texturization Technology And Mechanism Of Soy Protein By High Moisture Extrusion

Extrusion cooking is an important textural reorganization technology of vegetable protein in food industry, which has the advantages such as low energy cost, high efficiency, and continuous process. The texturization soy protein produced by extrusion is an important part of modern soy protein industry. Texturization processes via high moisture extrusion is a new development area in extrusion cooking, which can make products that imitate the texture, taste, and appearance of meat with high texturized degree, springiness, and nutritional value.In this paper, texturization technology and mechanism of soy protein by high moisture extrusion, the study includes: First, using system analysis method, the relationships of extruder operation parameters (screw speed, mass moisture content, feed rate, and barrel temperature) on the system parameters (pressure, torque, specific mechanical energy, etc.), and objective parameters (texturized degree, color, hardness, springiness, chewing, water absorption, yield, etc.) were investigated in the high moisture soy protein extrusion process, and the statistical models of system and objective parameters were built, using the step-by-step regression analysis; A comprehensive evaluation of the products, and the process optimization of high moisture extrusion were obtained,using factor analysis; Secondly, residence time distribution and soy isoflavones losses kinetics were studied in the high moisture extrusion; Finally, chemical bonding process, the micro-structure and protein secondary structure changes were investigated in the texturization of soy protein, then the mechanism assumptions of texturization soy protein by moisture extrusion were proposed.Response surface analysis results showed that with the barrel temperature and moisture content increase, the system parameters were dropped; With feed rate increase, torque and pressure increased, but the specific mechanical energy (SME) decreased; screw speed was significantly affected on SME, but a relatively small impact on the pressure and torque. According to the stepwise regression analysis, the models of system parameters with high prediction precision was obtained, which can be used to control the process, and forecast the outcome of extrusion. Correlation analysis shows that there were very significant correlations between the system parameters.Stepwise regression analysis showed that with the increase of mass moisture content, the texturized degree, springiness, color, moisture content and yield of products increased, and the hardness and chewiness of products reduced; With the increase in barrel temperature, the texturized degree, hardness, color, and adherence of products increased, and moisture content of products decreased. With the increase in feed rate, the springiness, Chewiness, color, moisture content, and yield of extrudates increased, and the texturized degree reduced. With the increase of Screw speed, the extrudates'adhesiveness increased, but little effect on other products'properties. the models of objective parameters with high prediction precision was obtained, which can be used to control the process, and forecast the properties of extrudates. Correlation analysis shows that there were very significant correlations between the system parameters and objective parameters.With factor analysis method, four common factors were used to substitute the 12 objective parameters in order to simplify and reduce the number of dimensional space. According to the factor score of samples, a comprehensive evaluation of samples was carried out, and the regression equation of the comprehensive evaluation score was constructed. A frequency analysis was used to optimize the high moisture extrusion process. Optimization of process parameters were: moisture content 52.5%~53.5%, barrel temperature 144~148℃, screw speed 113~127rpm, feed rate 28.3~32.4g/min.In high moisture extrusion of soy protein, the minimum residence time was between 70.7~163.3s, average residence time was between 108.2~255.4s, and the Peclet numer (Pe) was between 16.3~277.0. The operating parameters had significant effects on characterization parameters of the residence time distribution. The effect of Operating parameters to the minimum residence time, was followed by feed rate> screw speed> moisture content. The minimum residence time was decreased with the increase of the three operating parameters, and was effected little by barrel temperature. The effect of Operating parameters to the mean residence time, was followed by feed rate> barrel temperature > screw speed> moisture content. The mean residence time was decreased with the increase of the three anterior operating parameters, and was effected little by moisture content. The effect of Operating parameters to the Pe, was followed by barrel temperature > moisture content> feed rate> screw speed. The Pe was increased with the increase of barrel temperature, and decreased with the increase of the moisture content and feed rate, and was effected little by screw speed.Wolf-Rescnick model and Yeh-Jaw model all described the flow modality of blend in extruder suitably. According to the Yeh-Jaw model, the p value, which represent the volume fraction of piston flow, was 0.55~0.83, and the mean was 0.69; the volume fraction of dead space and crossing flow had a very small percent, the sum of the two fractions was about 1%. P value was decreased with the increase of screw speed and moisture content, and increased with the increase of barrel temperature.The profile and total isoflavones were changed obviously after the extrusion texturization, and the losing percent of total isoflavones was between 0%~47.6%. The four operating parameters had markedly effect on the profile and total isoflavones. With the increase of barrel temperature, the total and malonyl isoflavones were decreased remarkably, and the conjugates (daizin and genistin) were increased slightly. With the increase of feed rate and moisture content, the decomposed speed decreased. With the screw speed increase, the decomposed speed increased.The degradation rate constant of malonylgenistin (MG) was between 0.00043 ~ 0.01034 s-1, with an average of 0.0040 s-1, and the activation energy was 85.21 kJ/mol; the degradation rate constant of malonyldaidzin (MD) was between 0.000006 ~ 0.01072 s-1, with an average of 0.00383 s-1, and the activation energy was 96.58 kJ/mol; The degradation rate constant of total isoflavones was between 0.00002 ~ 0.00420 s-1, with an average of 0.00193 s-1.The nitrogen solubility index of extrudates ranged from 6.4%～9.2%, which was influenced by operating parameter. New protein subunit was not formed after high moisture extrusion. The insoluble of protein was caused by the hydrophobic interaction and disulfide bond. The microstructure of the extrudates was studied on three profiles by scanning electron microscopy (SME), and then the"membranous air cavity"hypothesis of soy protein texturization by extrusion was present.The protein secondary structure was not damaged completely, and theβ-sheet andβ-turn structure was preserve at some degree. The protein secondary structure was affected by the temperature remarkably, and at the lower temperature (T<140℃), the secondary structure changed fromα-helix to turn; but at the higher temperature (T>140℃) , changed fromβ-sheet to random coil. High moisture accelerated the secondary structure changed which was beneficial to texturization, because water was advantageous to the second structure transformation fromα-helix to turn andβ-sheet to random coil. With the lower feeding rate, more random coil was became; but with the higher feeding rate, the soy protein secondary structure was affected little. With the screw speed increase, theβ-sheet decreased, and turn segment increased.