乳脂球膜组成对乳脂结构的影响及机理研究

The membrane of breast milk fat globules (MFGM) has abundant polar lipids and functional membrane proteins which are considered to be vital for the early development of infants. However, most of the infant formulas so far either do not contain the natural component of MFGM, or the ingredients used for supplying the MFGM has a multi-component composition. The lipid composition and structure of infant formulas will be greatly influenced by both the composition of the ingredients and processing conditions. Therefore, various complex-emulsifiers will be designed based on the differences between the composition of diverse MFGM-ingredients and breast milk to form a biomimetic milk fat globule model system. The formation and stability of the emulsions against gravity separation, aggregation, flocculation and coalescence of oil droplets as well as Ostwald ripening will be explored. The rheological properties of the emulsions will be measured to investigate the interactions between droplets and droplets under different conditions (multi-composition of complex emulsifiers, amplitude and frequency of deformation, volume of oil fraction, temperature, pH, concentration of salts and lactose). Subsequently, the dilatational surface rheology will be applied to study the adsorption behavior of multi-surfactants as well as the composition and structure of the oil/water interface stabilized with various complex-emulsifiers. The correlation between the mutual interactions of multi-surfactants and the composition of the bulk phase will be analyzed. The mechanism on the effect of the complex composition of MFGM-ingredients on lipid structure will be elucidated at different length scales from macro to micro, which could shed light on the improvement of lipid composition and structure of infant formulas.

母乳乳脂球膜含多种极性脂和膜蛋白，对婴儿生长发育具有重要生理功能。目前婴儿配方奶粉存在天然乳脂球膜丢失或乳脂球膜配料组成复杂多样的问题。乳脂球膜配料组成直接影响婴儿配方奶粉中乳脂的组成和结构。本课题拟根据乳脂球膜配料之间及其与母乳乳脂之间的组成差异，设计乳脂球膜复配乳化剂体系变量组合；以仿母乳脂滴为模型，研究复配乳化剂组成对乳液形成和稳定性（重力分离、脂肪球聚集、絮凝、破碎和奥斯特瓦尔德成熟）的影响。研究乳液的剪切流变性质，揭示脂滴之间的相互作用及影响因素（复配乳化剂组成、剪切速率和幅度、油脂体积、温度、pH、盐度和乳糖浓度）；利用界面扩张流变学方法研究乳脂球膜复配乳化剂在油水界面的吸附行为和界面组成结构，揭示油水界面上不同分子间相互作用及其与体相组成的关系，从宏观到微观不同尺度研究乳脂球膜复配乳化剂对乳脂结构的影响机制，为改善婴儿配方奶粉的乳脂组成和结构提供理论依据和技术支撑。

乳脂球膜对婴儿的大脑发育、免疫成熟和机体代谢有重要生理功能，补充乳脂球膜形成的乳脂体系备受关注。乳脂球膜配料含乳蛋白、乳磷脂和膜蛋白等多种天然乳化剂，复合乳化剂组成对乳脂结构的影响不明，而乳脂的组成和结构会显著影响乳脂消化。.本文对比了不同乳脂体系的稳定性，物化性质和油水界面性质，即由乳蛋白（乳清分离蛋白），磷脂（乳磷脂和鸡蛋卵磷脂）和天然生物膜片段（MFGM分散系）稳定的乳脂体系。在低乳化剂浓度下，MFGM-乳液极易发生聚结，提高浓度可减少聚结和上浮，其它乳化剂形成的乳脂体系无明显聚结。乳化剂的电荷性质和组成比例显著影响仿生乳脂球在酸性条件下的静电性质、微观形貌和失稳机制（聚结、絮凝或相转）。对于乳清蛋白/磷脂混合体系，乳清蛋白主导复合油水界面的扩张流变性质。不同乳化剂稳定的油水界面线性和非线性界面流变性质差异显著，暗示界面结构不同：乳清蛋白稳定的油水界面具有2D-固相行为；而磷脂稳定的界面流动性较强；与蛋白或磷脂稳定的界面相比，MFGM分散系稳定的界面粘性较低，在低幅度扩张形变下显示出类似磷脂的油水界面行为，而在高幅度扩张形变下，压缩过程中突然呈现较强应变硬化，暗示MFGM分散系稳定的油水界面具有由MFGM膜片段及少量磷脂分子和蛋白共同稳定的复合结构。由于MFGM膜片段的特殊组成和结构，MFGM形成的仿生乳脂与简单蛋白/磷脂混合体系形成的乳脂结构显著不同。综上，乳化剂的组成和结构（例如MFGM膜片段）显著影响乳脂的组成和结构。本文阐释了乳脂球膜组成对乳脂结构的影响机制，能够为实际生产中调控仿生乳脂和其他乳基功能乳液的稳定性、物化性质和微观结构提供数据支撑。此外，本文中的MFGM膜片段经超声处理，形成不规则、类似脂质体的球形颗粒，可作为天然乳脂球膜的模型，用于今后的研究。