Abstract Aggregation of casein micelles (CMs) was followed with single-particle tracking using fluorescence microscopy. Initial concentrations of up to a mass fraction of 3% (w/w) were studied. A small fraction of the CMs was labelled with Atto 488 fluorescent dye to achieve sufficient dilution to position single micelles, despite the diffraction limit of light and to allow particle tracking without overlapping tracks. In addition, a higher fraction of CMs was labelled with a second dye (Atto 647N) to visualise in parallel the resulting CM aggregates. Distributions of hydrodynamic radii obtained from up to 2000 individual tracks were log-normally distributed around a most frequent value of rh = 114 nm. The evaluation of the particle tracking experiments during the temperature-induced coagulation of para-casein micelles indicates that the aggregation proceeds in two phases. First, the formation and steady growth of aggregates occurs, which, after reaching a certain size, abruptly form a coherent gel.

中文翻译：

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单粒子追踪作为表征凝乳酶凝固过程的新工具

摘要酪蛋白胶束 (CMs) 的聚集使用荧光显微镜进行单粒子跟踪。研究了质量分数高达 3% (w/w) 的初始浓度。尽管存在光的衍射极限，一小部分 CM 用 Atto 488 荧光染料标记，以实现足够的稀释以定位单个胶束，并允许粒子跟踪而不重叠跟踪。此外，更高比例的 CM 用第二种染料 (Atto 647N) 标记，以平行观察所得 CM 聚集体。从多达 2000 个单独轨道获得的流体动力学半径的分布在最常见的 rh = 114 nm 值附近呈对数正态分布。在副酪蛋白胶束的温度诱导凝固过程中对粒子跟踪实验的评估表明聚集分两个阶段进行。首先，发生聚集体的形成和稳定增长，在达到一定尺寸后，突然形成凝聚的凝胶。