Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.
Department of Food Science, CiFOOD Center for Innovative Food Research, Aarhus University, Agro Food Park 48, 8200 Aarhus N, Denmark.
Soft Matter. 2022 Nov 23;18(45):8613-8625. doi: 10.1039/d2sm00724j.
Casein micelles extracted from milk are 100-400 nm-sized particles, made up of proteins and calcium phosphates, with the latter as colloidal calcium phosphate particles (CCPs) in a size range of 2-4 nm embedded in a protein network. The hierarchical structures give rise to a variation of scattering intensity over many orders of magnitude, which can be measured by small-angle X-ray scattering and static light scattering. Expressions for the scattering intensity of a general simple model for composite particles with polydispersities of overall size and subparticles are derived, and some approximations are checked by generating scattering data for systems generated by Monte Carlo simulations. Based on the simpler models, a new model has been developed for casein micelles, where the scattering is expressed on an absolute scale and where the concentrations of, respectively, protein and CCPs are used as constraints, providing a consistent model. The CCPs are modelled as oblate ellipsoids and the protein as star structures. Correlations between the substructures of CCPs and protein structures are taken into account in terms of partial structure factors. The overall structure as well as some heterogeneities at intermediate length scale are modelled as polydisperse spheres. The model fits the data very well on all length scales and demonstrates that both the scattering from CCPs and protein is important. Thus, the model provides a detailed description of the casein structure, which is consistent with the information available in the literature.
从牛奶中提取的酪蛋白胶束是 100-400nm 大小的颗粒，由蛋白质和磷酸钙组成，后者是尺寸在 2-4nm 之间的胶体磷酸钙颗粒（CCP）嵌入在蛋白质网络中。这种层次结构导致在许多数量级上散射强度的变化，这可以通过小角 X 射线散射和静态光散射来测量。推导了具有整体尺寸和亚颗粒多分散性的复合粒子通用简单模型的散射强度表达式，并通过为通过蒙特卡罗模拟生成的系统生成散射数据来检查一些近似值。基于更简单的模型，为酪蛋白胶束开发了一种新模型，其中散射在绝对标度上表示，并且分别使用蛋白质和 CCP 的浓度作为约束条件，提供了一致的模型。CCP 被建模为扁长椭球体，蛋白质被建模为星型结构。在部分结构因子方面考虑了 CCP 和蛋白质结构的亚结构之间的相关性。将整体结构以及中间长度尺度上的一些非均相性建模为多分散球体。该模型在所有长度尺度上都非常好地拟合数据，并表明 CCP 和蛋白质的散射都很重要。因此，该模型提供了酪蛋白结构的详细描述，与文献中提供的信息一致。
