水分子的原位冻结影响淀粉类食品品质的机理研究

Upon the principle of water dynamics, the fusion, crystallization temperature and enthalpy change of water molecules under different states are investigated comparatively, ascertaining the mechanism of water molecules in situ freezing. The measurement of water in situ freezing is to be realized by transformation of hexamethylene crystals. 13C-CP/MAS-NMR and FT Raman are employed to probe the amorphous and crystalline regions of starch granules after annealing to understand the correlation between the structure modification and the characteristics of thermostability, shear stability and anti-retrogradation. The incubation temperature and time facilitate the infusion of water into the amorphous and reversible, limited granules swelling. When crystalline regions are in the molten state, chains are in a dynamic manner, and the entanglement points are excluded from the crystalline domains and become concentrated in the interlamellar amorphous regions after annealing. Hence, the mechanisms of such transformations and how they are related to the resulting morphology, structure, physicomechanical properties and product qualities are of great theoretical and practical importance in food science. Since the relaxation parameters reflect the mobility of hydrogen nuclear, the information of water molecules in situ freezing obtained will be taken into considerations, and the changes of relaxation time of water is used to reflect the properties of water distribution and migration. According to the time-temperature equivalence rule of the macromolecule dynamics, the correlation between the retrogradation dynamic parameters of starch molecule recrystallization and orientation to squeeze out water could be established by employing the Arrhenius equation combined with the calculation of cohesive energy density, together with the texture analysis and magnetic resonance imaging(MRI) to reveal the relationship between the quality deteriorating rate and the storage temperature. By means of realization of water molecules in situ freezing, the quality and shelf life of starchy foods will be ensured.

依据水分子动力学原理，对不同状态水分子的熔融、结晶温度及焓变等进行比较，探明冻结水和非冻结水形成机理及特点。通过晶-晶转变温度校准和绘制相图，实现原位冻结水的准确测定。13C-CP/MAS-NMR、FT Raman等研究经过热历史的淀粉分子结构，其热稳定性、剪切稳定性、抗老化性改善机理。LF-NMR研究反映水分子流动性的弛豫参数，得到水分子原位冻结状态信息。AFM观察糊化淀粉分子的凝聚态结构、回生淀粉分子重结晶"挤出"水分子的取向态结构，通过控制条件及添加NaCl和小分子糖等改变分子链段之间的作用力，控制取向速度。从物性学的角度印证水质子密度成像学关于水分子原位冻结对品质影响的相关性。运用Arrhenius方程拟合在品质发生劣变进程中反应速度与储藏温度的依赖关系，结合内聚能密度计算结果，揭示水分迁移变化息影响品质变化的机理，尽可能实现水分子在体系中的原位冻结，为保证品质稳定性提供理论依据。

本项目针对大米、高直连玉米和小麦等以淀粉为主的原料进行研究，已发表论文23篇，其中SCI论文9篇，已授权发明专利2件。具体研究内容如下：.低温储藏使水分子更易进入籼米颗粒，易糊化。蒸煮后淀粉颗粒间空隙增大，水分子更易进入。高温储藏使淀粉晶体更完善，水分子难以进入，难糊化，但蒸煮后淀粉颗粒之间空隙也增大，水分子更易进入。高温使淀粉晶体更完善，但颗粒会出现更多裂纹，水分子通过缝隙进入内部，淀粉更易糊化。MRI图像的明亮处是散乱分布的，加热过程中，T21时间与其质子密度变化较小。T23的峰高随蒸煮时间延长而增大，与质子密度成正比。高温储藏的籼米蒸煮时T23峰高值增长速率大于新米T23值增长速率，表明水分子进入新鲜籼米的速度小于进入高温储藏籼米的速度。.利用激光共聚焦配合扫描电子显微镜和差示扫描量热仪、X-衍射仪从不同角度研究了高直链玉米淀粉的形态结构和糊化特性。高直链玉米淀粉颗粒呈现明显的偏光十字，起始糊化温度较高，在115.3℃开始糊化，而在125.7℃糊化明显，在130.7℃糊化完成，糊化温度明显高于普通玉米淀粉和其它种质淀粉的糊化温度。高直链玉米淀粉在17.3°，20.0°，22.0°有衍射峰，属于典型的B-型结晶。.LF-NMR表明，小麦胚芽粉的加入使新鲜馒头的流动性增大，对馒头的老化起延缓水分迁移的作用，可以延长货架期。添加胚芽促进结合水向弱结合水转化，表现为紧密结合水下降、弱结合水明显提升，这归因于体系中蛋白、淀粉等含量降低，与之紧密结合的单层水部分被释放以及胚芽中的油脂在淀粉表面形成油膜，使水分更不容易被固定。紧密结合水在释放过程中被胚芽中的有效物质捕获，形成胚芽与水复合体系，使弱结合水含量上升。当胚芽添加比例为6%时，T21和T22值均较低，水分相对稳定，老化馒头弱结合水含量高于新鲜馒头，说明馒头老化过程中紧密结合水的释放速度低于被胚芽捕获并形成的弱结合水的速度。