高压均质诱导果胶的分子结构、构象行为和功能性质的变化及其相互关系

Pectin has been widely used in food, pharmaceutical and cosmetic industries. However, some processing such as heating, acid or enzymatic hydrolysis, and mechanical forces always lead to pectin degradation and decrease of functional properties. Our previous study has pointed out that pectin was significantly degraded by high pressure homogenization and the mechanism of degradation was investigated, but the change of pectin structure, conformation, functional properties and their relationships keep unknown. In this work, pectin is treated by dynamic high pressure microfluidization, which is an emerging high pressure homogenization technology. The factors that influencing the degradation of pectin are evaluated by characterizing the change of functional properties (gelling properties, apparent viscosity, emulsion stabilizing properties and clarity) treated at different conditions. Though seperating and characterizing the degraded pectin, the model of chain scission and the connection of sugar residues are also proposed, and the molecular model of pectin is constructed. The change of functional properties is explained by analyzing the change of structure (methoxyl group, acetyl group, reducing sugar ends, unsaturated bond, molecular weight and particle size and their distribution) and especially by determining the change of conformation (circular dichroism, radius of gyration, hydrodynamic radius, flexibility). Then the relationship between structure, conformation and functional properties can be understand. This project provides theory evidence to explain the change of stucture and functional properties during pectin degradation, and offer an academic reference for analysis the fine structure of pectin.

果胶在食品、医药和化妆品行业应用广泛，然而加热、酸处理、酶解、机械作用等加工手段常引起果胶降解和功能性降低。前期研究发现高压均质对果胶有明显降解作用并探讨了其降解机制，但分子结构、构象行为和功能性质变化关系有待深入探讨。由此，本项目以动态高压微射流为高压均质手段，通过测定不同降解条件下果胶功能性质(凝胶性、表观粘度、乳化稳定性、持水性、澄清度)的变化，分析高压均质降解果胶的影响因素；通过对果胶降解组分的分级和糖链结构鉴定，推导果胶链断裂形式和果胶链的连接关系，构建果胶的分子模型；通过分子结构（甲氧基、乙酰基、还原末端及双键含量、分子量和粒径及其分布等），特别是构象行为(圆二性、回旋半径、水动力学半径、分子柔韧性等）的变化来探讨果胶功能性质改变的原因，揭示果胶分子结构、构象行为和功能性质间的相互关系，为解释果胶降解过程中结构与性质发生改变提供理论依据，为果胶大分子精细结构的解析提供理论参考。

果胶在食品、医药和化妆品行业应用广泛，然而加热、酸处理、酶解、机械作用等加工手段常引起果胶降解和功能性降低。关于动态高压微射流处理对果胶分子结构、构象行为和功能性质变化关系有待深入探讨。由此，本项目以动态高压微射流(DHPM)为高压均质手段，通过测定不同降解条件下果胶功能性质的变化，分析高压均质降解果胶的影响因素，表明随着DHPM处理压力和次数的增加，果胶浊度、凝胶强度、硬度、咀嚼性、胶着性逐渐降低，粘着性则逐渐增加；流变性研究表明处理后果胶呈典型凝胶状（G’＞G’’），且随着处理强度的增加果胶的储藏模量和损失模量降低，果胶形成凝胶需要更低的温度。通过超滤对果胶降解组分进行分级和糖链结构鉴定，推导果胶链断裂形式和果胶链的连接关系，构建了果胶的分子模型和微射流降解模型，在天然的状态下，果胶可被机械力作用和氢离子攻击的位点是有限的，而在微射流处理过程中，果胶链可能被机械力打开和伸展，伸展的果胶链不仅更加容易受到机械力的作用，也更容易受到H+的攻击造成表观粘度，分子量以及粒径降低，还原糖含量升高，表观形貌从片状向多孔碎片转变。分子量的降低和还原糖含量升高间存在线性关系，表明果胶的降解发生在糖苷键。动态高压微射流处理过程中，酸水解扮演了重要的角色，使得微射流降解果胶行为类似于酸降解，中性糖间的糖苷键比半乳糖醛酸间的糖苷键更加容易断裂；通过分子结构，特别是构象行为的变化来探讨果胶功能性质改变的原因，揭示果胶分子结构、构象行为和功能性质间的相互关系，表明动态高压微射流处理过程中分子量、粒径的降低，表观形貌从片状向多孔碎片转变，还原糖含量升高，从而造成果胶功能特性诸如浊度、凝胶强度、硬度、粘度的改变等，而果胶分子构象的聚集或卷曲，减弱DHPM对果胶的降解，本项目为解释果胶降解过程中结构与性质发生改变提供理论依据，为果胶大分子精细结构的解析提供理论参考。