【作者】 黄祖强；

【导师】 童张法；

【作者基本信息】 广西大学 ， 化学工艺， 2006， 博士

【摘要】 淀粉是一种多晶高聚物，其颗粒中一部分分子排列成疏松的非晶区，另一部分分子则排列成高度有序的结晶区，结晶结构主要是由淀粉分子通过氢键连接，结晶区约占颗粒的25％～50％。淀粉分子的这种结构特点，限制了淀粉的使用范围，如淀粉结晶区分子排列紧密，水及化学试剂等不易触及结晶区内的分子，导致淀粉的糊化温度高、化学反应活性低等；淀粉的相对分子量大及众多的羟基彼此以氢键缔合成紧密的网络结构，导致淀粉糊粘度过大、流动性差。因此，研究如何改变淀粉颗粒结构、结晶区超分子结构以及减少淀粉结晶区的方法来改善淀粉的物理化学性质、提高淀粉的反应活性已成为一项极其重要的研究课题。本文采用自制的搅拌磨对淀粉进行机械活化。主要进行了如下几方面的研究：（1）采用X-射线衍射仪（XRD）、差示扫描量热仪（DSC）、扫描电子显微镜（SEM）、粒度分析仪及红外光谱（FTIR）对活化淀粉进行表征分析，用化学分析方法测定活化淀粉的直链淀粉含量，分别研究木薯、玉米淀粉在机械活化过程中其结晶结构、热特性、颗粒形貌、粒度分布、分子基团及直链淀粉含量变化的特征及规律，并根据测试结果对淀粉的机械活化过程机理进行分析讨论。（2）通过考察机械活化对木薯、玉米淀粉的冷水溶解度、流变特性、透明度及冻融稳定性的影响来研究机械活化对淀粉理化性质的影响。（3）以抗性淀粉含量为评价指标，通过考察活化时间、储存时间、淀粉糊浓度、糊化温度及储存温度对抗性淀粉形成的影响来研究机械活化对淀粉分子重结晶能力的影响。（4）采用不同活化时间的淀粉为原料、醋酸酐为乙酰化试剂、甲磺酸为催化剂、醋酸为反应介质制备乙酰化淀粉，并以其取代度为评价指标，通过研究机械活化对乙酰化反应取代度及活化能的影响规律来探讨机械活化对淀粉化学反应活性的影响。用红外光谱对产物的结构进行表征。（5）以不同活化时间的淀粉为原料、α-淀粉酶为液化试剂，以液化水解产物的葡萄糖值（Dextrose Equivalent，DE）为评价指标，通过研究机械活化时间、糊化温度、反应时间、反应温度、淀粉糊浓度、淀粉酶用量、pH值对DE值的影响规律来探讨机械活化对淀粉酶解反应活性的影响。通过上述的研究，根据实验结果和理论分析，得到如下主要结论：（1）在机械活化过程中木薯与玉米淀粉的结晶结构受到破坏，结晶度降低，最终由多晶态转变成非晶态；淀粉的颗粒形貌从不规整的大颗粒结构向片状细小颗粒结构演变，得到由众多细小颗粒团聚而成的聚集体，粉体界面模糊；两种淀粉的糊化温度、糊化吸热焓随活化时间的增加而逐渐降低，最终糊化相变吸热峰消失；直链淀粉含量随着活化时间的延长而增加；红外光谱分析表明淀粉在活化过程中并没有新的基团产生。（2）机械活化能显著提高木薯与玉米淀粉的冷水溶解度和淀粉糊的透明度，降低淀粉糊的冻融稳定性；木薯和玉米原淀粉及其活化淀粉糊均呈现假塑性流体特征，符合幂定律。活化时间越长，淀粉糊的表观粘度就越低，越趋近牛顿流体，具有很好的流动性，并能显著地降低两种淀粉糊的剪切稀化现象和触变性；由于和木薯淀粉相比，玉米淀粉的颗粒小、内部结构排列紧密，直链淀粉含量高，氢键作用力强，其结晶结构不易崩溃，因此活化玉米淀粉的冷水溶解度、淀粉糊的透明度及冻融稳定性均比相应的活化木薯淀粉低。（3）淀粉经机械活化后由于其分子链发生断裂，分子量变小，聚合度降低，粘度下降，直链淀粉含量提高，从而加强了淀粉分子重结晶的能力，抗性淀粉含量增加；但过度的降解会使直链淀粉的聚合度过低，淀粉链太短，淀粉分子易于扩散而不利于老化结晶。在相同条件下，由活化玉米淀粉所制备的抗性淀粉含量比活化木薯淀粉的高，说明直链淀粉含量对抗性淀粉的形成有很大的影响。其它的影响因素如淀粉糊浓度、糊化温度、储存温度等对抗性淀粉的形成也有较大的影响，但它们对淀粉糊重结晶能力的影响程度受到机械活化时间的制约，活化时间越长，对它们的依赖性越低。抗性淀粉的XRD分析表明，抗性淀粉的晶型结构不同于原淀粉，属于B型结构。（4）在实验条件下，木薯原淀粉及活化0.25、1.0h淀粉乙酰化反应的表观活化能分别为60.95、48.03、22.98 kJ·mol^-1，玉米原淀粉及活化0.25、1.0h淀粉乙酰化反应的表观活化能分别为66.21、51.92、25.06 kJ·mol^-1，表明机械活化对木薯、玉米淀粉的乙酰化反应有显著的强化作用，反应活性提高，乙酰化反应对反应温度的依赖性降低。虽然其它的影响因素如催化剂用量、醋酸酐用量对淀粉的乙酰化反应也有较大的影响，但它们的影响规律受到活化时间的制约，活化时间越长，酯化反应对它们的依赖性越低。红外光谱分析表明，乙酰化淀粉和原淀粉及活化淀粉的结构差异随着取代度的增加而增大；乙酰化反应过程也能破坏淀粉的结晶结构，降低淀粉的结晶度。（5）机械活化能显著提高淀粉的酶解反应活性，酶解反应速度加快。虽然其它的影响因素如糊化温度、反应温度、底物浓度、淀粉酶用量等对淀粉的酶解反应也有较大的影响，但它们的影响规律受到活化时间的制约，活化时间越长，酶解反应对它们的依赖性越低。更多还原

【Abstract】 Starch is a morphologically complex polymer substance, consisting of loose amorphousregions that are interspersed with highly regular crystalline regions, resulting from the formationof hydrogen bonds between the starch molecules. The crystalline composition consists of around25～50% of the starch granules. The scope of starch application is both enhanced and limited byits unique molecular structure. For instance, the compact arrangements of molecules in thecrystalline regions inhibit water or chemical reagents from making contact with the molecules inthe crystalline region. As a result, the gelatinization temperature is higher and chemical reactivityof starch is decreased. Meanwhile, the relative large molecular weight and the extensive networkformed by hydrogen bonds lead to high gelatinization temperature and lower fluidity. For manypurposes, the market prefers starch with less extensive crystalline regions, resulting in improvedphysico-chemical properties and increased reactivity for planned applications. Therefore, there isgreat interest in methods to modify the structure in the crystalline region, or decrease the size ofcrystalline regions. In this thesis, cassava and maize starch were mechanically activated with acustomized stirring-type ball mill. The key researchful contents are as follows:（1）The effects of mechanical activation on crystal structure, thermal properties, functionalgroups, granular morphology, size distribution and amylose content of cassava and maize starchwere investigated respectively by using granularity analysis, scanning electron microscopy,X-ray diffractometry, Fourier transform infrared spectroscopy and differential scanningcalorimetry, the amylose content were mensurated with chemical method. The mechanism ofmodification process of starch by mechanical activation was also discussed.（2）The mechanical activation effects on physicochemical properties of cassava and maizestarch were investigated by analyzing the influence of mechanical activation on cold-watersolubility, rheological characteristics, transparency and freeze-thaw stabilization. （3） Using the resistant starch （RS） content as an evaluating parameter, the mechanicalactivation effects on recrystallization of cassava and maize starch were investigated by analyzingthe influence of activation time, storage time, starch paste concentration, gelatinization andstorage temperature on the RS formation.（4） Using acetic anhydride as esterification reagent, methanesulfonic acid （MSA） as catalystand acetic acid as reaction medium, acetylated starch was synthesized from starch with differentactivation time. Moreover, using the degree of substitution （DS） as an evaluating parameter, themechanical activation effects on chemical reaction activity of starch were investigated byanalyzing the influence of mechanical activation on DS and apparent activation energy （E_a）. Thestructures of acetylated starch with different DS were further characterized by using FTIR.（5） Using starch with different activation time as crude materials,α-amylase asliquefaction reagent, and dextrose equivalent （DE） as an evaluating parameter, the mechanicalactivation effects on enzymolysis reactivity of starch were investigated by analyzing theinfluence of activation time, gelatinization temperature, reaction time, reaction temperature,substrate concentration, amylase amount and pH value on DE.The following main conclusions can be drawn on the basis of the experimental results andtheoretical analysis.（1） The crystal structure of cassava and maize starch could be destroyed by mechanicalactivation, the crystallinity decreased from polycrystalline to amorphous. When subjected tomechanical activation, the starch granules shape were fractured, and agglomerating into largermore amorphous particles, congregates consisting of tiny granules, structural change fromirregular agglomerates to layered grains. The gelatinization temperature decreased withincreasing of activation time and the phase transition peak disappeared gradually. The amylosecontent increased with increasing of activation time. FTIR showed no new functional groupsproduced during the mechanical activation process.（2） The mechanical activation was evidenced to cause change of physicochemical propertiesof cassava and maize starch: cold-water solubility and transparency increased, freeze-thawstabilization reduced. All activated starch samples with pseudoplastic characteristics in accordingto the power law, starch solution in a tendency to Newton fluid. The apparent viscosity,thixotropy and shear-thinning nature of the starch pastes decreased with increasing of activation time. The cassava starch showed greater cold-water solubility, transparency and freeze-thawstabilization than maize starch under similar activation treatments, the different might beattributed to differences of size, amylose content and fragility of granules, the cassava starch aresize larger, amylose content lower and more fragile than maize starch.（3） Mechanical activation could cause degradation of starch molecules, the degree ofpolymerization （DP） and viscosity decreased and amylose content increased. As a result, mildmechanical activation treatment was proved to be in favor of the recrystallization of starchmolecule and the RS content increased evidently. RS content from activated maize starch werehigher than activated cassava starch under same experimental conditions, showed amylosecontent was one of important factors that affect yields of RS. Moreover, it was also found thatother affecting factors, such as starch paste concentration, gelatinization and storage temperaturehad a certain influence on RS formation and were closely related to activation time. XRDshowed that the structure of RS is B pattern.（4） Under the experimental conditions, the Ea of esterification from 60.95 and 66.21kJ·mol^-1 for non-activated cassava and maize starch to 48.03 and 51.92 kJ·mol^-1 （activation time0.25h）, 22.98 and 25.06 kJ·mol^-1 （activation time 1.0h） for activated cassava and maize starch,respectively. The results showed that the mechanical activation pretreatment obviously enhancedenzymolysis reactivity of starch, and the dependence of esterification on reaction temperature,catalyst and acetic anhydride concentration decreased with increasing of activation time. FTIRshowed that the structural difference of between acetylated starch, native starch and activatedstarch increased with increasing of DS. The crystal structure of starch could be also destroyedduring acetylation process.（5） Mechanical activation obviously enhanced the enzymolysis reactivity of starch. Otheraffecting factors, such as gelatinization temperature, reaction temperature, substrateconcentration and amylase amount had a certain influence on enzymolysis and were closelyrelated to activation time. Moreover, the dependence of enzymolysis on these affecting factorsdecreased with increasing of activation time.更多还原