甘薯淀粉回生过程中直、支链淀粉超分子相互作用机理研究

Sweet potato retrograded starch is a kind of crystallization formed from amylose and (or) amylopectin in starch paste，with the abilities to improve bowel function, lower blood sugar, and enhance disease resistance and other functions. Macromolecules Interaction between amylose and amylopectin plays a fundamental role in their retrogradation rate. The amylose and amylopectin with relatively narrow molecular weight distribution will be isolated via many methods. Crystals will be obtained by retrogradation of amylose, amylopectin and their mixtures labeled with isotope, and then the possible type, location and numbers of connection bonds between amylose and amylopectin in crystals will be inferred by means of analyzing the crystals data among them such as NMR, infrared, MS, X-ray diffraction, AFM images -and so on. Connection bonds between amylose and amylopectin in crystals will be confirmed by their dynamic and thermodynamic parameters related to retrogradation process according to Avrami equation and solid-liquid equilibrium theory, finally the connection bonds among them will be identified by single molecule force spectroscopy technology. The mechanism of interaction between sweet potato amylose and amylopectin in retrograded starch will be further deduced based on the above results, the law of interaction of both and the effects of environmental conditions on such interaction will be further explored. Achievements concerning this research subject will enrich the academic crystallization theory of long-chain organic, provide theoretical support for exploring preparation process of high retrogradation rate, and are also significant from the practical points for understanding internal boundaries of retrogradation of sweet potato starch superamolecular and controlling its retrogradation.

甘薯回生淀粉是淀粉糊化后冷却过程中部分直、支链分子形成的结晶，具有改善肠道功能、降血糖、增强疾病抵抗力等功效，回生过程中甘薯直、支链淀粉超分子相互作用对淀粉回生率有重要影响。本项目采用多种方法制备出分子量分布范围极窄的甘薯直、支链淀粉；用同位素标记直、支链淀粉后，再次回生结晶，比对直、支链淀粉混合前后晶体核磁、红外、质谱、X-射线衍射、原子力图像等，推测其相互作用键的可能类型、连接位置和数量；采用Avrami方程和固液平衡理论研究甘薯直、支链淀粉混合前后的回生动力学、热力学数据的差异，缩小二者相互作用的可能方式的范围，最后采用单分子力谱技术锁定二者相互作用的方式，推测二者相互作用的机理,探索二者相互作用规律及其环境条件对相互作用的影响。项目研究成果将丰富长链高分子结晶理论，为探寻甘薯淀粉高回生率制备工艺提供理论指导，对了解甘薯淀粉超分子回生的内界过程和控制淀粉回生方法的探索也有现实意义。

项目通过溶胀甘薯淀粉球释放其中直支链淀粉，蛋白酶和脂肪酶酶解分解与淀粉连接的蛋白和脂肪，水洗纯化后得到纯的甘薯直支链淀粉。利用回生法制备分子量分布范围窄的甘薯直支链淀粉，以分子量分布范围窄的甘薯直支链淀粉为原料培养回生淀粉晶体，制备出衍射峰尖锐的回生淀粉晶体。通过比对混合前后晶体特征确定了二者结合的可能位置和连接键类型。X射线动力学研究发现仅有直链淀粉回生符合Avrami方程，而且结晶率计算要采用衍射角17°附近峰面积与总面积的比值作为结晶率。差热法可更为准确反映回生动力学。在室温（7~28℃）、4℃、25℃、70℃条件下，甘薯直链淀粉Avrami方程指数n均小于1，成核方式为一次成核；甘薯支链淀粉在4℃和25℃温度下n均大于1，成核方式为多次成核；甘薯直、支链混合淀粉仅在4℃出现多次成核。70℃条件下甘薯直、支链淀粉混合后回生速度明显加快。甘薯淀粉回生过程核生长方式为一维生长，所得回生晶体为针状晶体。热力学研究发现在4-70℃温度范围内甘薯支链淀粉溶解度最大，其次为甘薯直链淀粉，二者混合淀粉的溶解度最低，24h内三种淀粉凝聚基本达到恒定值。原子力显微镜观察显示，甘薯直链回生淀粉、支链回生淀粉和混合回生淀粉层状结构高度最高分别为5200, 180 和 200 nm，贮藏期间直链和支链淀粉的高度减低，而混合淀粉的高度保持不变。从晶体特征、回生动力学和回生热力学等研究可以确定得出结论：甘薯直、支链淀粉超分子在回生过程相互作用并加速回生速度、提高回生淀粉结晶度。