挤压法处理高直链淀粉的消化特性与分子链结构和构象的变化及其相互关系

The research that starch was modified by many methods is of great interest because it can form slowly digestible starch and resistant starch which show beneficial functions such as decreasing glycemic index after meal. In our previous work, it was found that the digestion properties of high amylose starch were significantly changed by extrusion modification. However, the relationship between digestion properties and molecule structure or conformtion need to be further investigated. Therefore, the jackfruit seed starch with high amylose was chosen as material, extrusion modification is used as a treatment method, the extrusion modification effect on digestion properties and molecule or conformtion will be investigated, including detecting and comparing the differentiation of digestion properties; expressing and analyzing molecule structure (microscopic structure, molecule weight and distribution of molecule weight, particle size, crystal type and degree of crystallization, double helix molecular order. The conformtion structure was analyzed by static and dynamic light scattering, circular dichroism spectrum and atomic force microscope including intertangling, radius of gyration and hydrodynamic radius. After that, molecular construction and conformational simulation are performed based on the selected characteristic structure parameters. The relationship will be established between digestion properties and molecule or conformation structure on the level of molecule, which can be used to interpret the relationship between digestion properties and molecule or conformation structure based on different extrusion modification conditions. Those studies can provide the mechanism of extrusion modification on the digestion properties of starch.

淀粉改性会形成具有维持餐后血糖功能的缓慢消化淀粉和抗性淀粉而成为国内外研究的热点。前期研究发现挤压改性会改变高直链淀粉的消化特性，然而淀粉分子结构、构象与其消化特性变化的关系还有待深入研究，由此，本项目以高直链淀粉含量的菠萝蜜种子淀粉为对象，以挤压技术为手段研究其消化特性与分子链结构和构象变化的影响，测定和比较处理前后消化特性变化的差异性；表征和分析淀粉分子结构（形貌、分子量及分布、粒径、结晶类型、结晶度、分子序列、双螺旋）和官能团（甲基、还原末端和双键）的变化，推断淀粉糖链断裂形式；采用动静态光散射仪、圆二色谱和原子力显微镜等考察分子链构象（卷曲、回转半径、水动力学半径）的影响，根据分子结构特征用软件进行分子构象模拟。对淀粉消化特性与分子链结构和构象进行分析和总结，找出其显著性因素和各因素之间的相关性，揭示淀粉消化特性与分子链结构和构象间的关系，为解析淀粉消化特性的影响机理提供理论参考。

前期研究发现挤压改性会改变高直链淀粉的消化特性，本项目以高直链淀粉含量的菠萝蜜种子淀粉（JFSS）为对象，以挤压技术为手段研究其消化特性与分子结构变化的影响。研究发现JFSS快速消化淀粉、慢消化淀粉和抗性淀粉含量分别为3.93%、18.47%和77.60%。挤压改性后JFSS消化性增加：RDS和SDS增加，RS减少。挤压改性后JFSS颗粒表面有孔洞，颗粒尺寸显著增加，淀粉分子量变低，A链和B1链的比例变高，B2链和B3+链比例变小，结晶结构由A型变为V型，直链淀粉含量变化不显著。在挤压改性处理过程中JFSS的支链淀粉α-1,4-糖苷键被降解产生了更多支链支链淀粉片段引起一系列分子结构变化导致其消化率显著提高。.天然和挤压SDS+RS组分和RS组分均表现出较高的凝胶化温度、Rc和短程分子有序性、较低糊化焓（ΔH）。与天然JFSS相比，经挤压处理后的JFSS的ΔH值、Rc和分子有序性明显降低。经过挤压处理样品的分子结构，包括支链淀粉的分子尺寸更小，支链淀粉含量更低，这些样品呈现直链淀粉峰，但没有明显的支链淀粉峰，说明支链淀粉比直链淀粉更容易剪切降解成直链淀粉。与天然的SDS+RS和RS组分相比，挤压处理后的SDS+RS和RS组分短支链淀粉的比例更高。挤压后的JFSS样品具有更疏松、多孔的结构，容易被酶攻击。与原JFSS样品相比，支链淀粉经挤压处理后的降解不能形成完美的结晶，更容易水解。.随着物料所含水分含量增加，挤压菠萝蜜种子淀粉RDS含量显著降低、SDS，RS含量升高、消化性降低。挤压JFSS的双螺旋结构数量、长、短程分子有序性显著增加，表明支链淀粉结晶被破坏，形成直链淀粉，而高水分含量的物料吸水膨胀，导致直链淀粉分子溢出更易于发生重结晶，形成更多更有序的结晶。挤压SDS+RS和挤压RS组分的双螺旋结构数量长短程分子有序性显著增加的趋势，表明水分作为增塑剂使淀粉分子在挤压机内停留时间变短，原有的致密结晶未被完全剪切降解导致挤压SDS+RS和RS的结晶结构有序性增加。随着水分含量增加，挤压处理的JFSS呈现有更少的孔洞和更光滑的表面，降低淀粉颗粒对酶的敏感性，使之消化性降低。