【作者】 陈卫江；

【导师】 阮榕生；

【作者基本信息】 南昌大学 ， 粮食油脂及植物蛋白工程， 2007， 硕士

【摘要】 大多数食品和生物体系在许多方面都是高度不均匀的，包括结构、化学组成、热力学性能，温度分布等。从热力学角度讲，我们说这种体系具有低熵，低无序性或高自由性，且处于高能量水平和不稳定状态。它们很易“活动”而达到低能级和热平衡态。另一方面，我们认为许多食品和生物体系都是多相的，它们由许多重复单元构成。一些单元具有相同的物理化学性质，因而聚集成一个大基团或具有独特物理化学性能的多仓。如果体系中有几个这样的基团，那么对各基团来说水分子的性能是唯一的。核磁共振及其成像是一种用来研究物体内部结构的技术。对于食品科学的研究，核磁共振成像可以把核磁共振波谱信号在样品中定位，直观地显示食品中水分等物质的迁移运动状态。它在研究水分活度及其分布状况方面具有明显优势，通过核磁共振技术可从分子热力学及分子动力学的角度探索食品变质的机理，从而可以建立可靠的食品货架期预测的数学模型，为开发含低、中等水分的食品，以及在保证其品质的前提下延长它们的货架期提供科学的理论依据，大大缩短新产品研究开发的周期。整篇论文借助开发核磁共振及其成像技术研究淀粉回生机理，通过研究不同淀粉在加工和储藏过程中核磁共振弛豫参数的变化特性，解释不同组分对淀粉加工的影响，并探讨了不同淀粉的回生机理，以及一些常用添加剂对淀粉回生的影响。论文的第一部分研究了不同类淀粉在加工过程中的核磁共振弛豫参数的变化趋势，结果表明：淀粉在糊化时可分成三个阶段，加热开始，淀粉继续加大水分的溶解，当吸收足够的水分后淀粉溶液发生相变，随着加热的持续，淀粉开始糊化直到完成。淀粉糊化过程中，自由水发生了相变转为多层水，T12大大降低，但是质子密度显著升高，T11升高，大分子体系的活度增加。淀粉糊化的难易主要受淀粉的直链淀粉和支链淀粉组成影响，直链淀粉含量越高淀粉越难糊化。糊化的顺序按：糯米淀粉、木薯淀粉、小麦淀粉、玉米淀粉和绿豆淀粉，木薯淀粉的特有性质有利于糊化的进行。不同水分含量的淀粉糊化难易度不同，水分含量的降低延缓了淀粉的糊化过程。论文的第二部分主要研究了不同淀粉以及不同水分含量的小麦淀粉在储藏期内各部分水分的变化情况。研究结果表明淀粉储藏过程中T11的变化主要受短期回生的影响。而长期回生主要表现在质子密度的迁移变化，在储藏后期糊化淀粉的T12质子密度下降向单层水的T11组分迁移。淀粉短期回生的速率主要受直链淀粉含量的影响，糯米淀粉最慢，而绿豆淀粉最快，但木薯淀粉的突出的持水特性以及低凝聚性，使其回生过程不受直链淀粉含量主导，回生速率较慢。淀粉的长期回生受水分的影响显著。回生过程中质子密度发生了明显迁移，结合紧密的单层水增多，而多层水明显下降，在储藏过程中木薯糊化淀粉具有很好的持水性和稳定性，在储藏过程中糯米淀粉和木薯淀粉最稳定，虽然淀粉的长期回生与支链淀粉有关，但是支链淀粉的含量并不主导淀粉回生的速率，糯米淀粉支链淀粉为100％，但却有较好的长期储藏特性。不同糊化度的淀粉对淀粉的长期回生影响显著，50％糊化度的淀粉显著促进了淀粉的回生，而75％和100％的糊化淀粉的储藏特性相似，在加工过程中淀粉的糊化度不宜过低，但可以适当降低淀粉食品的糊化度。论文的第三部分主要研究了一些常用的食品添加剂对淀粉的加工糊化以及储藏的影响，论文中主要研究了糖类和一些乳化剂和持水性物质。研究发现不同糖类对淀粉溶液体系的影响并不相同，蔗糖、麦芽糖和海藻糖同属于二聚糖，但由于其单糖的组成以及结合点的不同而表现出不同的性质。蔗糖提高了体系的T11值，增加了大分子的流动性，而麦芽糖和海藻糖降低了T11值，没有表现出好的流动性。三种糖对T12都有明显的降低，一方面糖作为溶剂改变了自由水的结构，降低了水分子的流动性。另一方面，糖在淀粉液体系中有均一化的作用，改善了体系的分布，降低了淀粉在糊化过程中水分的大量迁移，缓和了糊化过程。添加糖的淀粉液体系T12质子密度在糊化后期显著提高，糖的作用加强了大分子在淀粉糊化后期的持水性。结果还发现糖对淀粉的短期回生有明显的影响，糖阻碍了大分子的运动和接触，尤其是直链淀粉的有序化迁移。海藻糖的强持水性抑制了淀粉长期回生过程支链淀粉结晶所必需的水分。因此有效的延缓了淀粉的长期回生。CMC、大豆蛋白、单甘酯和大豆纤维具有较好的持水性，能改善样品的分布状态，有利于样品的均一组成，但大豆纤维持水性与样品中其它组分形成了竞争性。乳化剂、稳定剂和持水性并具有好的相容性物质可以延缓淀粉在储藏过程中的变化。但持水性好的纤维，由于其相容性差，相反促进了淀粉在储藏过程中的变化。第四部分主要利用NMR状态图研究了不同食品添加剂对糊化淀粉性质的影响。实验中发现，糖类对糊化淀粉的NMR状态图有明显的改善，海藻糖对样品的影响最大，其次是蔗糖和麦芽糖。蔗糖和海藻糖对糊化淀粉温度状态度的影响机制完全不同。海藻糖具有较好的持水性，蔗糖虽然能加快分子的流动性，但具有更好的相容性，增加了样品的分子量，提高了糊化淀粉的Tg。更多还原

【Abstract】 Most of foods and biomass are not uniform in many interior aspects, for example structure, components, calorific property, temperature distribution and so on. As far as thermodynamics, we have been thinking this system take on some characters of low entropy, few out of order or freedom and this state is high energy and unsteady which is easy to move to low energy and thermo-equilibrium. On the other hand we acknowledge food and biomass system are multiphase which is composed by many repeated units and some of them have the same physical and chemical characters, we character them together as a special compartment. Usually, a system has several compartments which only can be defined individually by the character of moisture. If all units are distributed we can describe them through the method of spectrum.NMR and MRI technique are good way to research inner-structure of objects. Especially for food science, NMR imaging technique can locate NMR spectrum signal in samples which can indicate the movement of moisture and other components. NMR/MRI techniques have great advantage to research moisture activity and distribution that are redound to explore the principle of food deterioration from the basis of molecule thermodynamics and kinetics, consequently to build up credible mathematic model for pre-indicating food shelf life, develop low and moderate moisture food and provide theoretic principle for extending shelf life on the basis of ensuring product quality, so that will greatly cut the period of new product exploration.The overall objective of my thesis was to develop Nuclear Magnetic Resonance (NMR) relaxometry and Magnetic Resonance Imaging (MRI) based techniques to study starch retrogradation. In thesis, we have explained the effect of different starch in the process and storage, through the research NMR parameters, and also have discussed the principle and effect of retrogradation in different starch.The first specific research aim of present work was to study the changes of NMR parameters in the process of different starch gelling, the state of water was measured using spin-spin relaxation time, in this study we got two components of T1, T11 and T12 respectively. Result showed the gelling of starch can be divided into three parts, at the beginning, the more moisture dissolve in starch, then the starch system happen to phase change when accept enough water. With heating continued, the starch system began to be gelled until gelling complete. In the process of gelling, T12 dropped quickly and T11 raised that means T11 component or large-molecule component increased its activity and bulky water transfer to multi-water. Result showed that the gelling time mainly decided by the proportion of amylose and amylopectin in starch, generally the more amylose and harder gelling, in this research gelling time raised as the sequence of sticky rice, tapioca, wheat, corn and green soybean. Tapioca displayed a quick gelling time because of its speciality and low moisture content of starch increased gelling time significantly.The second specific research aim of present work was to study moisture changes of gelling-starch system during storage, result showed that the changes of T11 affected chiefly by short-term retrogradation and long-term retrogradation mainly displayed on thechanges of proton density, during long storage, the proton density of T11 descended and transferred to T11 that reflect bulky water turn to combined water. The velocity of starch short-term retrogradation mainly decided by the content of amylose, research found stick rice starch changed lowest and green soybean fastest during storage, but tapioca starch which get special capability of moisture maintained and low agglomerate that make tapioca starch change lower but not decided by its amylose content. Long-term retrogradation mainly affected by moisture concentration, during retrogradation, the proton density transferred obviously, combined water increased and bulk water dropped significantly, sticky rice and tapioca starch were more stability than others. Research showed that amylopectin content in starch can not decide the velocity of retrogradation absolutely although amylopectin related with retrogradaion. Amylopectin is 100 percent in Sticky rice starch but has a good storage. The long-term storage speciality is Different with different extent of gelling starch, 50 percent grade of gelling sample promoted starch retrogradation but samples of 75 and 100 percent had similar storage speciality. This can instruct real production, we should better strengthen the gelling grade in the process of starch-food, but sometimes we need to weaken it at certain grade for reducing cost and increasing special tasty.The third specific research aim of present work was to study the effect of some general additives for the produce and storage of gelling-starch, in research some sugars and emulsions and moisture-maintained reagents were used. Results showed different sugar have their own function, although sucrose, maltose and fucose all belong to dimeric-sugar that because of their different compose and structure. In research we found sucrose boosted T11 and increased the fluidity of large molecular in gelling system but three sugars a11 reduced T12 value, one hand sugar as solvent changes the structure of single-water that contribute to low down the fluidity. On the other hand, sugars in system attribute to improve the distribution of components and increase the uniformity of starch-system so that prevented the movement of vast moisture during gelling and delayed the process of gelling. In starch solution, sugar promoted T12 proton density amplitude during the gelling last time which means sugar enhanced water-maintained capability. Result also showed that sugar had an improved effect to starch short-term retrogradation, sugar can interdict the movement and reduce the chance of interaction among different molecules especially prevent the sequenced movement of amylose. Research found fucose could restrain long-term retrogradation by its great water-maintained ability to reduce the necessary water for the crystalline of amylopectin. Other additives for example CMC, soybean protein, glycerol monostearate and soybean fiber all have good water retentivity which improve the component’s distribution that good at uniform structure in system and this compatibility and water retentivity will avail to long storage. But soybean fiber displayed a different effect for its incompatibility with other components, so that its water absorbability attribute to compete with others in system and destroy a normal structure distribution and promote the change of gelling starch during storage if it add more enough.The forth specific research aim of present work was to study the effect of different additives to NMR state diagram. Results showed that sugars have improved NMR state diagram greatly, the effect sequence as fucose, sucrose and maltose decreased gradually. In research, we found that the effecting mechanism was wholly different between sucrose and fucose. Fucose has a good water retentivity and sucrose can boost the fluidity of molecule, but sucrose also has a better compatibility that will augment molecular weight and boost the Tg in gelling-starch system.更多还原