【作者】 赵雷；

【导师】 李琳；

【作者基本信息】 华南理工大学 ， 制糖工程， 2012， 博士

【摘要】 小麦面制品的品质主要由面筋蛋白所决定的，本论文以面筋蛋白为研究对象，通过研究不同冻藏的模式（恒温冻藏和冻融冻藏）和时间对面筋蛋白分子量大小与分布、面筋蛋白分子链结构（分形维数、链构象、链尺寸和形貌）、聚集态的结构、热特性及面团的流变与质构性能的影响，分别从分子水平、微观水平和宏观水平深入探讨了冻藏处理对面筋蛋白微观构造和宏观性能变化的机理，建立了冻藏处理后面筋蛋白结构的变化与面团品质之间的关系，为扩大面团的深加工方向建立科学的理论基础。主要研究内容如下：一、冻藏处理对面筋蛋白分子量及其分布的影响采用SAXS、SEC MALLS、SDS PAGE和分光光度法分别研究冻藏模式处理后的面筋蛋白分子量及亚基大小与分布、自由氨基和自由巯基的变化。结果表明，乙酸为溶解面筋蛋白的良溶液，在面筋蛋白的稀乙酸溶液中（8mg/mL），可以忽略乙酸溶剂对面筋蛋白分子链的影响；研究发现冻藏处理后面筋蛋白的平均分子量与重均分子量都发生下降；从SEC紫外图谱上可以看出面筋蛋白洗脱峰的保留时间会随着冻藏时间的增加而延迟，峰面积下降，当洗脱时间为12.0min时出现新的吸收峰，且新吸收峰的峰面积随着冻藏时间增加而增加，面筋蛋白的高分子聚合物发生了解聚；自由氨基含量分析发现，在冻藏过程中面筋蛋白的自由氨基含量没有发生变化；SDS PAGE电泳研究发现，冻藏对面筋蛋白的亚组分麦谷蛋白和醇溶蛋白的亚基分子量的大小和分布没有影响；但是，自由巯基的含量会随着冻藏时间的增加而增加。冻藏过程中面筋蛋白二硫键断裂是导致高聚物发生解聚，分子量的大小与分布发生下降的主要原因。二、冻藏处理对面筋蛋白分子链结构（分形维数、链构象、链尺寸和形貌）的影响采用SAXS、SEC MALLS和AFM方法分别研究面筋蛋白链结构的变化。研究发现，面筋蛋白的链构形为相互交联的纤维状网络结构；经过冻藏处理后会导致网络状结构的弱化及分形维数的下降；分子链在乙酸溶液呈现一种类似于扁椭圆球体的构象，但是，无法判断冻藏处理对面筋蛋白分子链构象的影响；面筋蛋白的流体力学半径（Rg）大小与分布随着冻藏时间的增加呈现下降的趋势，与分形维数（Dm）的变化呈正相关。分子链的断裂是导致分子尺寸Rg下降的原因之一。三、面筋蛋白Mark Houwink Sakurada（MHS）方程的建立及冻藏对分子链构象的影响在25°C，建立了未经冻藏处理的面筋蛋白在1%SDS缓冲液中易溶和难溶两部分的MHS方程如下：[η]=1.7459×102M0.6933v=1.7375×102q0.6933=×20.6933MHSMw1.667710Mw(SDS S G)[η]=7.5682×103M0.7372=7.56×30.737230.7372v8210qMHSM=7.2079×10wMw(SDS IS G)它们的特征因子α分别为0.6933和0.7372，易溶部分呈现半柔顺链，难溶部分呈现半刚性链的构象。建立冻藏处理后面筋蛋白的MHS方程，结果发现在恒温冻藏过程中，易溶部分的分子链都呈现半柔顺性，并且，其柔顺性随着冻藏时间的增加而增加；难溶部分的分子链仍呈现半刚性，随着冻藏时间的增加构象没有明显变化。在冻融冻藏过程中，易溶部分分子链的柔顺性增加；难溶部分分子链还呈现半刚性链，随着冻藏时间达到90d时，链构象由半刚性链转变为半柔顺性链。冻藏导致面筋蛋白分子链柔顺性增加，分子链构象的变化也是Rg下降的原因之一。四、冻藏处理对面筋蛋白聚集态结构与热特性质的影响以湿面筋蛋白、脱水后面筋蛋白和麦谷蛋白为研究对象，冻藏过程中由于水分的迁移使面筋蛋白显微网络结构明显弱化，随着冻藏时间的增加出现了不规则孔洞；湿面筋蛋白的二级结构没有发生明显变化，但将水分除去后发现，随着冻藏时间的增加，面筋蛋白高分子解聚后产生的小分子物质发生聚集导致部分β转角结构转化为β折叠结构；而面筋蛋白和麦谷蛋白的热稳定性下降，其裂解温度的下降趋势与三维网络结构弱化的趋势相一致。五、冻藏后面筋蛋白对面团流变与质构性能的影响选择中筋粉作为研究对象，根据掺粉实验结果表明，随着添加的面筋蛋白冻藏时间的增加，其面团的流变学与质构特性呈现下降的趋势。添加面筋蛋白分子量的大小和面团的硬度呈正相关。面筋蛋白分子量及分子链结构的变化是冻藏后面团品质变化的重要原因。更多还原

【Abstract】 With the increasing market for frozen foods, the gluten quality during frozen storage hasattracted attention in food industry. In this dissertation, Wheat gluten was used as modelmaterials. The mechanism of induced by frozen storage was elucidated by exploring theeffects of frozen mode (frozen and freeze thaw cycles) and storage time on molecular weightsize and distribution, molecular chain structure (fractal dimensions, conformation, size andtopography), aggregated structure and thermodynamic behavior of wheat gluten andrheological properties of dough under different frozen mode and storage time on. We will usethose basic data to explore the relationship between the microstructure of gluten with differentsize scale (chain structure and aggregated structure) structure and properties changes duringfrozen storage, and further study quality of the product was developed during the frozenstorage which has great commercial benefits as it will provide a useful practical guideline tomanufacture dough products. The main research and results are as follows:1. Effect of frozen mode and storage time on molecular weight size and its distribution ofwheat glutenWheat gluten and its subunits were affects by different frozen mode and storage time onmolecular weight size, distribution, free amino groups content and free sulfhydryl groupscontent analyzed by SAXS, SEC MALLS, SDS PAGE and spectrophotometrically. Theresults indicated that the dilute acetic acid solution (8mg/mL) is a good solution, so avoidingthe influence of the solvent on the characterization of the solute. The mean molecular weightand weight average molecular weight of the gluten decreased with increasing frozen time. Inthe elution pattern of SEC, as the frozen storage time increasing, the retention time of thegluten is negatively delayed and the areas also decreased, compared with that of the controlgluten. There is a new absorption peak in the frozen stored samples, the area of the peakincreased with frozen storage time. It was clearly seen that no remarkable difference andrelative mobilities of band could be observed for wheat gluten subunits with or without frozenstorage. The free amino groups content changed few and the free sulfhydryl group content ofthe gluten increased with the frozen storage time, indicating that the depolymerization of thegluten during frozen storage was attributed to the breakage of disulfide bonds. 2. Effect of frozen mode and storage time on molecular chain structure (fractaldimensions, conformation, size and topography)The effects of frozen mode and storage time on gluten molecular chain structureexplored by SAXS, SEC MALLS and AFM. It was found that the gluten chain forming afibril like network. But the network was weakened and the fractal dimensions decreasedduring the frozen storage. The radius of gyration (Rg) was positively related to fractaldimensions of the gluten, indicating that the breakage of the gluten chain is one reason of thedecrease of Rg. The results also showed that the gluten dissolved in the50mM acetic acidappeared to be similar to quasi spherical of the chain conformation, but the change of thestructure did not show an obvious relationship with the storage time.3. Estimation of Mark-Houwink-Sakurada (MHS) equation parameters for gluten andeffect of the frozen mode and storage time on conformation of the chainFractional separation of gluten using the fast protein liquid chromatography (FPLC) anda numerical method for determination of MHS equation were studied. With1%SDS buffer assolvent, MHS equations for SDS soluble gluten (SDS S G) and SDS insoluble gluten(SDS IS G) proteins were established as:[η]=1.7459×102M0.6933=×2qM0.6933=×2M0.6933v1.737510MHSw1.667710w(SDS S G)[η]=7.5682×103M0.737230.737230.7372v=7.5682×10qMHSMw=7.2079×10Mw(SDS IS G)The value of α (0.6933and0.7372) suggested that in this solvent the gluten behaved like asemiflexible and a semistiff chain for the SDS S G and SDS IS G respectively. Establish theMHS equation for the frozen stored gluten. The results indicated that the conformation of theSDS S G was a semiflexible chain and more flexibility with the storage time, but theconformation of the SDS IS G changed few during the constant temperature frozen storage.In the freeze thaw cycles, the conformation of the SDS S G and the SDS IS G became moreflexibility with the storage time. The decrease of the Rgalso attribute to the change of thechain conformation. 4. Effect of frozen mode and storage time on aggregated structure and thermodynamicbehaviorThe hydration gluten, dry gluten and glutenin using the SEM, FIRT and TGA, and theeffects of frozen mode and storage time on aggregated structure and thermodynamic behaviorexplored. Microstructure of the frozen stored gluten had great change based on SEMobservation. In secondary structure, the hydration gluten had no change, but modification ledto increase in β sheet for the dry gluten. The decomposition temperature decreased during thefrozen storage led to the thermostability deteriorated, which was positively related to theweakened tendency of gluten network.5. Effect of frozen mode and storage time on rheological properties of doughThe gluten and AP flour using a Micro dough farinograph and TPA, and the effects offrozen mode and storage time on rheological and textural properties explored. The resultsindicated that the rheological and textural properties of the dough deteriorated with add thefrozen stored gluten. The hardness of the dough had positively related to the molecular weightof the additive of the gluten. This suggested that the molecular weight and the molecularchain were the decisive influencing the quality of the dough for frozen storage.更多还原