MFGM与乳蛋白相互作用介导的脂肪球结构特性及对脂肪消化的影响研究

Currently, the problem of the "insufficient utilization of fat" in infant formula  affects the development and health of infants. The low digestion ratio of fat is the key reason for limiting its absorption and metabolism in infant. We found that the difference of structure and composition between fat globule membrane (MFGM) in infant formula and breast milk is the key factor affecting lipolysis. Adding bovine MFGM can improve the lipolysis rate of infant formula, but its mechanism is still unclear. In this project we bulid emulsion model useing OPO human milk fat substitute as the oil phase to mimic infant formula and lecithin was selected as the key compound in bovine MFGM influencing the interface properties of fat globule. Firstly, the interaction mechanism between lecithin and protein is comprehensively analyzed by studying the interaction between lecithin and milk protein in bulk and at the globule interface, and investigating the influence mechanism of milk powder processing parameters on the interaction. Secondly, study the self-assembly mechanism of fat globules induced by interaction of lecithin and proteins were also studied by characterizing the structure and interface properties of fat globules. Then, study the relationship of structure and properties milk fat globule with lipolysis. Finnally, the regulation mechanism of liposylsis is systematically investigated through correlation analysis of the interaction between lecithin and protein-the structural properties of fat globules indeced by interaction of lecithin and protein –structure and activity relationship between fat globules and lipolysis. The implementation of this project will provide theoretical support for the research and development of MFGM infant formula in China.

婴儿配方奶粉所存在的“脂肪利用不足”问题影响婴儿的发育和健康，其中脂肪消化慢是限制其吸收代谢的瓶颈。我们发现奶粉和母乳的脂肪球膜（MFGM）结构组成的差异是影响奶粉脂肪消化慢的关键原因。牛乳MFGM能改善奶粉脂肪消化速率，但机理不清晰。本项目拟以OPO型母乳替代脂为油相构建奶粉乳液模型，选以磷脂为牛乳MFGM中影响脂肪球界面性质的关键组分，通过研究磷脂与乳蛋白在体相中和脂肪球界面上的相互作用关系，考查奶粉加工参数对二者相互作用的影响机制，全面解析磷脂与蛋白的相互作用机理；通过表征脂肪球结构、界面性质差异，解析磷脂与蛋白互作效应介导的脂肪球自组装机制；研究不同自组装脂肪球结构与脂肪消化的构效关系，探明脂肪消化的调控机制；通过关联分析磷脂与蛋白相互作用关系—二者互作介导的脂肪球结构性质—脂肪球结构调控乳脂消化的构效关系，系统阐明牛乳MFGM中磷脂对奶粉脂肪消化的调控机理。本项目项目的实施将为我国MFGM婴儿奶粉的研发提供理论支撑。

通过调整奶粉乳液制备的不同工艺参数，初步得到脂肪球膜(MFGM)与乳蛋白在体相及界面上的相互作用关系，直接表现为影响乳液的粒径、界面电位和乳液的流变性、稳定性和围观结构等，证明可以通过调整MFGM的添加量或加入顺序来调控乳蛋白与MFGM之间的吸附/竞争/取代机制。研究发现以剪切速率为12000rpm，均质压力为300bar，5%的MFGM浓度所制备的奶粉乳液界面主要为MFGM，MFGM也可以更好的抑制乳蛋白的聚集、提高奶粉乳液的脂质消化率。但是鉴于我国MFGM原料依赖进口因此研究发现也以通过添加5%的卵磷脂来替代MFGM制备奶粉乳液或婴儿奶粉。. 为解析MFGM与乳蛋白在分子层面的相互作用关系，选取磷脂酰胆碱(PC)为单一与乳蛋白相互作用，以乳清蛋白(WPI)与PC的作用为例，二者可自发性的与WPI 发生相互作用，通过静态猝灭机制引起荧光猝灭现象，形成WPI-PC复合物；WPI和PC存在一个结合位点，复合物在较高温度下不稳定。PC主要通过疏水相互作用、氢键和范德华力与α-La的表面残基，β-Lg 中α-螺旋和β-桶之间凹槽中的表面疏水袋和BSA 的IIA 亚域结合，结合能分别为-5.59、-6.71和-7.85 kcal/mol，使得WPI微环境的疏水性改变，从而导致蛋白质二级结构的构象变化。. 磷脂与乳蛋白的相互作用也影响乳液的稳定性、也可适当抑制乳蛋白在消化过程中的聚集并提高脂质的消化速率。由于WPI与PC在乳液界面的共吸附作用，中等浓度PC(0.3%)与WPI在界面形成较强的分子间网络，具有最小的粒径和ζ-电位，可以有效稳定乳液，从而防止油脂氧化，导致乳液的乳化性能、氧化稳定性与其他浓度相比较好。高浓度PC(0.7%、0.9%)在界面与WPI竞争性吸附，导致发生一定程度的“造山取代”效应，形成PC结构域。除不含PC的乳液以外，其余所有乳液均具有良好的储藏稳定性和中性、碱性稳定性，但易于酸性条件下聚集；盐离子的添加导致乳液ζ-电位绝对值逐渐降低。中等浓度PC(0.3%)的乳液胃消化过程中无定型聚集相对较小，形成很多中小型颗粒，在肠消化结束后，其絮凝程度最低，蛋白质和脂肪消化率最高，分别为82.45%和27.64%。. 本项目的研究为婴儿配方奶的研就和开发提供一定的支撑。