【作者】 康立宁；

【导师】 魏益民；

【作者基本信息】 西北农林科技大学 ， 食品科学， 2007， 博士

【摘要】 挤压法是适于工业化、连续化大生产,高效、节能的植物蛋白质质构重组核心技术。由挤压法生产的组织化大豆蛋白是现代大豆蛋白工业的重要组成部分。高水分湿法挤压组织化是国际上新兴的植物蛋白重组技术。产品具有组织化化程度高、质地均匀、富有弹性和韧性、营养成分和生理活性成分损失少等优点。本文对大豆蛋白高水分挤压组织化技术和机理进行了研究,研究内容包括:首先采用系统分析法,研究了大豆蛋白高水分挤压过程中,挤压机操作参数(螺杆转速、物料水分、喂料速度和机筒温度)对系统参数(系统压力、扭矩、单位机械能等)、目标参数(组织化度、色泽、硬度、弹性、咀嚼性、吸水率、产量等)的影响规律,建立了各因变参数的统计模型;采用因子分析法对产品进行了综合评价,并对高水分挤压组织化工艺进行了优化;其次,研究了大豆蛋白高水分挤压中的停留时间分布以及大豆异黄酮的损失动力学;最后,研究了大豆蛋白组织化过程中化学键、微观结构和蛋白质二级结构的变化规律,提出了大豆蛋白高水分挤压组织化的机理假设。主要结论如下:响应面分析结果表明,系统参数一般随物料水分和机筒温度的升高而降低;压力和扭矩随喂料速度的提高而增加,单位机械能随喂料速度的提高而减小;螺杆转速对压力和扭矩影响较小,对单位机械能影响显著。依据逐步回归分析法建立了双螺杆挤压机系统参数的数学统计模型,预测精度较高,可用于挤压过程的控制和挤压结果的预测。相关分析表明,挤压机系统参数间存在极显著相关性。不同的产品品质指标符合不同的回归模式,物料水分对产品的组织化度、弹性、色泽、水分含量和产量起正向效应,而对产品的硬度、咀嚼性起负向效应;机筒温度对产品的组织化度、硬度、色泽、粘结性起正向效应,而对产品水分含量起负向效应;螺杆转速主要对产品的粘结性起正向效应;喂料速度对产品的弹性、咀嚼性、色泽、水分含量和产量起正向效应,而对产品的组织化度、粘结性起负向效应。其中物料水分和机筒温度是影响各目标参数的最重要工艺参数。相关分析表明,系统参数与目标参数也存在着密切联系。系统参数一般与产品的组织化度、L*值、产品水分含量呈显著或极显著负相关,而与硬度、咀嚼度、和△E*呈显著或极显著正相关。应用因子分析方法,采用4个公因子来表征目标参数的12个原始指标,公因子间无相关性,而同一公因子所控制的原始指标间显著相关。根据各样本的因子得分对样本进行了综合评价,构建了综合评分的回归方程,采用频数分析法对高水分挤压组织化工艺进行了优化。优化的工艺参数为:物料水分为52.5%～53.5%,机筒温度为144～148℃,螺杆转速为113～127rpm,喂料速度为28.3～32.4g/min。大豆蛋白高水分挤压的最小停留时间在70.7～163.3s之间,平均停留时间在108.2～255.4s之间,彼克列准数值(Pe)在16.3～277.0之间。操作参数对停留时间分布的各表征参数具有显著的影响。影响最小停留时间的操作参数按作用强弱依次为:喂料速度>螺杆转速>物料水分>机筒温度,最小停留时间均随前三者的提高而减小,机筒温度对其影响不显著。影响平均停留时间的操作参数依次为:喂料速度>机筒温度>螺杆转速>物料水分,平均停留时间均随前三者的增加而减小,物料水分对其影响不显著。影响彼克列准数的操作参数依次为:机筒温度>物料水分>喂料速度>螺杆转速,机筒温度对其为正效应,物料水分和喂料速度对其为负效应,螺杆转速对其影响不显著。Wolf-Rescnick模型和Yeh-Jaw模型均能较好的描述大豆蛋白高水分挤压中物料的流动状态。根据Yeh-Jaw模型,表示活塞流体积分数的p值范围为0.55～0.83,均值为0.69;保留体积分数和叉流体积分数所占比例很小,两者之和为1%左右。p值随着螺杆转速和物料水分的增加而降低,随着机筒温度的升高而增加。大豆蛋白高水分挤压后异黄酮总含量和组分分布发生了明显改变,总异黄酮损失率在0%～47.6%之间。4个操作参数对异黄酮总含量和组分均有显著影响,以机筒温度影响最大,随机筒温度的增加总异黄酮和丙二酰基异黄酮含量明显减少,异黄酮糖苷含量略有增加;喂料速度和物料水分对异黄酮含量均起正效应,随着喂料速度和物料水分的增加,总异黄酮损失和丙二酰基异黄酮的降解减少;螺杆转速的影响最小,主要起负效应,螺杆转速增加,丙二酰基异黄酮降解速率加快。丙二酰基染料木苷(MG)损失的速率常数在0.00043～0.01034s-1之间,平均为0.0040 s-1,活化能为85.21 kJ/mol;丙二酰基大豆苷(MD)损失的速率常数在0.000006～0.01072 s-1之间,平均为0.00383 s-1,活化能为96.58 kJ/mol;总异黄酮损失的速率常数在0.00002～0.00420 s-1之间,平均为0.00193 s-1。组织化后的大豆蛋白的氮溶解指数一般在6.4%～9.2%之间。操作参数对氮溶解指数有一定的影响。挤压加工并没有造成新的蛋白质亚基的形成。蛋白质的不溶性主要是由疏水作用和二硫键共同导致的。根据对高水分组织化过程的系统分析和产品扫面电镜结果判断,提出了挤压机理的“膜状气腔理论”假设。高水分挤压组织化并没有完全破坏蛋白质的二级结构,仍保留着一定的β-折叠和转角结构。机筒温度、物料水分含量、喂料速度和螺杆转速等操作参数对大豆蛋白二级结构具有显著的影响。较低温度时(温度<140℃,只发生蛋白质的热变性而不发生组织化),二级结构的变化主要表现为α螺旋向转角的转变;较高温度时(温度>140℃,蛋白质开始发生组织化),二级结构的变化主要表现为β-折叠向无规则卷曲的转变。较高的水分对组织化起促进作用,水分促进了α螺旋向转角的转变,以及β-折叠向无规则卷曲的变化过程。喂料速度太低时大豆蛋白二级结构向无规则卷曲发展;当喂料速度增至一定程度,对大豆蛋白二级结构的影响较小。随螺杆转速的加快,β-折叠逐渐降低,而转角的比例逐渐升高。更多还原

【Abstract】 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.更多还原