不同卷曲构象的魔芋葡甘聚糖对淀粉老化的影响及机制

Despite of abundant research on starch retrogradation regulated by various polysaccharides, detailed effects and in-depth mechanisms of starch retrogradation affected by the same polysaccharides with different conformations have been lacking. Based on advantages of konjac glucomannan (KGM) conformation that is variability, large amplitude, and precisely controlled, this project intends to explore the effects and mechanisms of different conformation parameters of KGM on starch retrogradation, which is obtained from dilute solution (self-coiling) and sub-concentration solution (intermolecular coiling). A combination of experimental methods and molecular dynamics simulation technology will be utilized. Firstly, KGM conformations with diverse molecular weights and deacetylation degrees will be characterized to acquire conformation metrics, such as mean square rotation radius, undisturbed size, and steric resistance parameter. Secondly, the impact of above samples in dilute and sub-concentrated solution on the thermodynamic properties, crystallinity, moisture migration and retrogradation process of starch will be discussed. Finally, phase compositions and microstructures in a typical KGM-starch system will be deeply explored, and correlations between conformation metrics, retrogradation process and interaction will be constructed. Thereby, the influence of KGM with different coiled conformations on starch retrogradation and its mechanism will be revealed. From a new perspective of different coiled conformations, this project can enrich the theoretical understanding of starch retrogradation interfered by polysaccharides, clarify the regulation of starch retrogradation by the same polysaccharides with different conformations, and provide a theoretical reference for food processing involving starch retrogradation.

不同种类多糖调控淀粉老化的研究众多，但同种多糖的不同构象对淀粉老化的细节影响及深入机制缺乏探究。基于魔芋葡甘聚糖（KGM）构象易变、大变幅、可精准调控的优势，本项目拟探讨KGM在稀溶液（自卷曲）及亚浓溶液（分子间卷曲）中不同的构象参数对淀粉老化的影响及机制。采用实验手段结合分子动力学模拟方法，首先对不同分子量、不同脱乙酰度KGM构象进行表征，获得均方根旋转半径、无扰尺寸、空间位阻参数等系列构象度量值；进而研究上述试样分别在稀及亚浓溶液范围内，对淀粉热力学性质、结晶性、水分迁移及老化进程的影响；最后利用典型KGM-淀粉体系，深入探究其相组分及微结构，构建构象度量值、老化进程及相互作用三者的相关关系，揭示不同卷曲构象KGM对淀粉老化的影响及机制。本项目从不同卷曲构象这一新的视角，可丰富多糖调控淀粉老化的理论认识，明确不同构象的同种多糖对淀粉老化的影响规律，为涉及淀粉老化的食品加工提供理论参考。

利用亲水胶体调控淀粉老化是食品领域的研究热点。本项目以魔芋葡甘聚糖KGM为研究对象，通过改变KGM的分子量和脱乙酰程度，制备具有构象差异的KGM。通过在不同浓度条件下，具有典型构象的KGM与淀粉的相互作用，探究其对淀粉老化性质的影响。针对不同分子量KGM的研究发现：在溶液条件下，稀溶液至浓溶液的浓度范围，对体系凝聚态结构表征发现：与中高分子量KGM相比，小分子量KGM会增大体系的构象参数，如缠结浓度、回转半径和分形指数。在更高浓度的凝胶状态下，利用色度、流变、质构、低场核磁、X射线衍射等表征淀粉的老化程度。结果显示：随着KGM分子量减小，淀粉凝胶的明度、凝胶强度，水分自由度和结晶度呈现增大趋势。小分子量KGM由于分子链段小，移动速度快，更易与淀粉分子形成氢键作用，发生分子间的缠结与交联，在一定程度上促进淀粉老化。中高分子量KGM则会降低淀粉体系的凝胶强度、水分自由度、结晶度等，对淀粉的长期回生发挥抑制作用，且KGM分子量越大，抑制效果越明显。针对不同脱乙酰度KGM研究发现：在低浓度条件下，体系处于溶液状态时，与单一的淀粉体系相比，脱乙酰KGM降低体系的缠结浓度、回转半径和分形指数。在高浓度条件下，当体系处于凝胶状态时，脱乙酰KGM贡献了淀粉体系更高的弹性模量，且凝胶强度随着KGM脱乙酰程度增大而上升。然而，经过低温储藏后，体系的凝胶强度、结晶度并未随着KGM脱乙酰度程度加剧出现明显的变化规律。但与天然KGM对淀粉体系的影响相比，KGM部分或全部脱除乙酰基后，导致淀粉凝胶水分析出严重，以及结晶度下降。脱乙酰KGM由于分子自卷曲作用，对淀粉老化起到一定的抑制作用。该研究可丰富多糖的分子构象对淀粉老化的影响规律，为涉及淀粉类食品加工提供理论参考和数据支撑。