挤压处理下杨梅叶原花色素-大米淀粉复合体形成机制及其消化特性研究

In addition to inhibiting the enzymes actives, polyphenols (particularly proanthocyanidin) could bind with starch through intermolecular forces, and therefore reduce the digestibility. However, the lower binding quantity and stability as well as the unclear understanding of the binding mechanism limit the application of polyphenols on the reduction of starch digestion. In previous study, we have found that Chinese bayberry leaves proanthocyanidins (CBLPs) could bind with rice starch with high efficiency and stability during extrusion,, and the complexes showed a lower digestion. However, the binding mechanism and digestive characteristics have not been clearly stated. In the present proposal, the mixtures of CBLPs and rice starch will be extruded to form CBLPs-starch complexes; the binding quantity will be measured by HPLC/MS, and the binding mechanism of the complexes as well as the structural characteristics will be investigated by NMR, SAXS, Micro-CT and other technologies. Finally, the digestibility of the complexes will be analyzed by auto-docking, in vitro and in vivo models, and the relationship among intermolecular forces, structures and the digestibility of complexes will be preliminary clarified. This project will provide a basic scientific theory on the formation of polyphenol-starch foods as well as some new insights on the utilization of plant polyphenols.

以原花色素为代表的多酚类物质除直接抑制消化酶活性外，也可与淀粉通过分子间作用力形成复合体，从而延缓淀粉消化。但常规温和条件下多酚与淀粉存在结合量低、结合不稳定、分子间作用力不明确等问题。前期研究发现在适度挤压下杨梅叶原花色素（CBLPs）可与淀粉高量、稳定地结合成缓慢消化的复合体，但挤压下复合体的形成机制及消化特性还未阐明。本项目拟以CBLPs、大米淀粉为研究对象，在挤压构建CBLPs-大米淀粉复合体的基础上，采用HPLC-MS探究挤压过程中CBLPs与大米淀粉结合量的变化规律；运用核磁共振、同步辐射小角X光散射、微计算机断层扫描等表征复合体分子间作用力特点及不同尺度结构特征；通过分子对接、体外/内消化模型等探究复合体的消化特性，明确复合体分子间作用力及不同尺度结构差异对其消化速率的影响。结果不仅为后续构建可控的多酚-淀粉缓慢消化食品提供科学理论依据，也为植物多酚的利用提供创新思路。

如何降低/延缓淀粉的消化速率，是食品科学领域亟待解决的关键科学问题之一，通过适度挤压对淀粉进行物理改性，从而制备具有一定慢消化功能的淀粉产品，以其性质稳定、品质优良、无外源化学成分添加等优点而倍受关注，但其消化速率仍不能满足特定消费者的需求。多酚被认为可通过调控淀粉消化酶活性，改变淀粉理化性质，调控葡萄糖转运等诸多途径来调控因摄入淀粉后所带来的血糖波动。本研究创新性的选择来源于杨梅叶的原花色素（CBLPs），通过对适度挤压下CBLPs可与淀粉高量、稳定地结合成缓慢消化的复合体这一现象进行了相关机制的探索。首先阐明了CBLPs与大米淀粉在挤压条件下的结合规律，发现在不同的挤压处理条件下CBLPs与淀粉的结合量最高可达30.52 mg/g，结合效率高达86.52%。在此基础上，对CBLPs与大米淀粉的结合机制进行了探究，发现CBLPs与大米淀粉通过挤压处理后，并未形成共价键，暗示着二者是通过非共价键进行结合，粉末晶体衍射结果表明CBLPs与大米淀粉结合后形成了V型结晶结构。通过对结合后的复合体的理化特性分析表明，明添加一定量的CBLPs可以显著的影响大米淀粉的糊化特性。在加热过程中，CBLPs不断释放出来，与水竞争性的结合，从而降低了淀粉的溶胀，延迟了糊化过程，最终表现为复合体较低的峰值黏度、最终黏度及更高的糊化温度。与原淀粉相比，复合体的ΔH从12.52 J/g 降到1.57 J/g，这可能与复合体在制备过程中加热导致的淀粉结构破坏有关。最后还对复合体的消化特性进行了系统探究，发现在CBLPs-大米淀粉复合体中，随着CBLPs含量的上升，复合体中抗性淀粉的含量由13.29%上升至36.29%。表明CBLPs与淀粉结合后，显著的降低了淀粉的消化速率，这可能与CBLPs与淀粉分子结合后，阻碍了酶分子对淀粉的水解及游离态的CBLPs降低了淀粉消化酶的活性有关。研究的开展不仅为后续构建可控的多酚-淀粉缓慢消化食品提供科学理论依据，也为植物多酚的利用提供创新思路。