基于酪蛋白胶束表面重构的浓缩乳蛋白热诱导失稳机理与控制

The concentrated dispersion of high-protein-containing milk protein concentrate is susceptible to destabilization such as sedimentation and gelation during heat processing and subsequent storage. This is mainly caused by aggregation of casein micelle, and the suggested contributors include heat-induced acidification and active calcium bridging, while both theories have limitations. Based on previous research, we propose a hypothesis based on micelle surface reorganization, and divide the MPC destabilization mechanism into two processes: micelle surface κ-casein dissociates and the micelle swells, resulting in a decreased inter-micellar energy barrier as well as an exposure of micelle’s internal calcium sensitive site and hydrophobic microdomain; the surface-reorganized micelle reaches a critical inter-micellar distance driven by Brownian motion, and then aggregates via calcium bridging and hydrophobic interaction. Based on micelle’s stress factors encountered during MPC production and application as well as from the perspective of thermo-kinetics and updated micelle structure model, this project will investigate key factors inducing the micelle surface reorganization behavior and their effects on micelle aggregation behavior as well as the MPC destabilization mechanism. Moreover, from the perspective of colloidal and interface science, this project will explore strategies regulating the micelle surface reorganization behavior induced by sensitive factors based on micelle surface decoration in terms of covalent cross-link, steric hindrance and charge density, and the corresponding mechanism on improving MPC heat stability will be investigated. This project will refine the MPC destabilization mechanism, and establish strategies to improve the heat stability of MPC while maintaining its unique features such as the intact micelle structure and high colloidal calcium content.

高蛋白含量浓缩乳蛋白（MPC）的液态浓缩体系在热加工及随后贮藏中易产生沉淀、胶凝等失稳现象，这主要是由酪蛋白胶束聚集导致，相关机理假说有热诱导酸化和活性钙离子桥连，两者都有局限性。结合前期研究，我们提出胶束表面重构假说，将MPC失稳机理分为两步：胶束表面κ-酪蛋白解聚，胶束溶胀，导致胶束间能垒降低、及内部钙敏感位点和疏水微区暴露；表面重构的胶束在布朗运动驱使下相互靠近到临界距离，通过钙桥和疏水作用聚集。项目针对MPC生产应用中胶束所受胁迫，从热动力学和胶束结构学角度，揭示导致胶束表面重构行为的关键因素及其对胶束聚集行为的影响规律，解析MPC失稳机理；进而从胶体和界面学角度，探究基于表面共价交联修饰、表面空间位阻修饰、表面电荷密度修饰的敏感影响因素下胶束表面重构行为调控策略，解析其对MPC的增稳机理。项目将完善MPC热诱导失稳机理，建立能保持完整胶束结构、高胶束钙含量等MPC特性的增稳策略。

浓缩乳蛋白（MPC）的液态浓缩体系在热加工及随后贮藏中易失稳，针对该应用缺陷，我们根据既定计划开展了以下两方面的研究：探究热处理温度、pH、离子强度、钙含量等关键因素对牛羊乳胶束、MPC体系在热处理过程中胶束表面重构行为和胶束聚集行为的影响，解析MPC失稳机理；进而探究如何通过胶束表面修饰、胶束适度脱钙等策略来提高MPC在热处理过程中的稳定性，解析其增稳机理。..研究结果表明：在MPC液态浓缩体系的高温热处理过程中，温度、pH、离子强度、钙含量、乳清蛋白的存在等关键因素都显著影响胶束表面κ-酪蛋白的解离，pH、离子强度、钙含量等关键因素都显著影响钙离子的活度，进而影响胶束的聚集行为，而胶束内部结构受热处理影响较小，羊乳MPC热稳定性比牛乳MPC更低，主要归因于前者更高程度的κ-酪蛋白解离、更高的钙离子活度，升高pH、添加柠檬酸盐、添加一定量氯化钠都能提高MPC的热稳定性；相比于谷氨酰胺转移酶交联、葡聚糖接枝、磷脂添加等胶束表面修饰策略，离子交换脱钙策略对MPC热稳定性的改善效果更优，当脱钙率为28%时，MPC热稳定性得到显著改善，且胶束结构仍保持较好；离子交换、添加柠檬酸盐等适度脱钙的增稳策略还能显著改善胶束在婴儿、成年、老年人群胃肠道中的絮凝行为和消化性。本研究结果将为今后提高MPC液态浓缩体系的热稳定性提供进一步的理论依据，同时对推动MPC在高蛋白乳饮料等功能性液态食品中的应用具有重要意义。..项目执行期间，邀请了乳品领域专家荷兰瓦赫宁根大学Thom Huppertz教授、美国康奈尔大学Joe M. Regenstein教授、深圳大学Hemar Yacine教授，以线上方式展开合作并联合指导学生，先后共培养了4名研究生，与Thom Huppertz教授共同申获了科技部2022-2023年高端外国专家引进计划。目前，所取得的与本项目相关的研究成果如下：发表SCI论文5篇，参编英文专著1章节，申请专利5项。