Department of Food Science, University of Wisconsin-Madison, Madison 53706.
Center for Dairy Research, University of Wisconsin-Madison, Madison 53706.
J Dairy Sci. 2021 Dec;104(12):12249-12262. doi: 10.3168/jds.2021-20563. Epub 2021 Sep 16.
Dairy-derived lipids such as phospholipids (PL) have been gaining interest due to their functional and nutritional properties. Our research goal was to develop a separation process (nonsolvent based) to produce an enriched dairy lipid fraction from whey protein phospholipid concentrate (WPPC). Various chemical pretreatments (i.e., adjustment of pH, calcium, or temperature) were applied to rehydrated commercial WPPC solutions. These treatments were done on a bench-top scale to aid in the precipitation of proteins or PL. The chemically treated solutions were centrifuged and fractionated into the following 3 layers: (1) top fat layer, (2) supernatant in the middle zone, and (3) sediment at the bottom of the centrifuge tubes. The thickness and size of the layers varied with the treatment parameters. Compositional analysis of each layer showed that the proteins, fat, and PL always appeared to fractionate in similar proportions. The proteins in each layer were characterized using sodium dodecyl sulfate-PAGE under reducing and nonreducing conditions. Different proteins including whey proteins, caseins, and milk fat globule membrane proteins and lipoproteins were identified, and no specific type of protein had an affinity for either the top or bottom layer. All types of proteins were present in each of the layers after centrifugation, and there were no major differences in fractionation of the proteins between layers with respect to the chemical treatment applied. The microstructure of protein and fat in WPPC was investigated using confocal laser scanning microscopy. Dual staining of the rehydrated WPPC solution with Fast Green FCF (proteins) and Nile Red (lipids) showed the presence of very large protein aggregates that varied in size from 20 to 150 μm, with fat trapped within these aggregates. The confocal laser scanning microscopy images of liquid WPPC revealed fine strands of a weak protein network surrounding the fat globules. This indicated that there were specific interactions between the proteins, as well as between the fat and proteins in WPPC. Sodium dodecyl sulfate treatment was performed to understand the nature of the interactions between protein and fat. We found that about 35% of the fat present in WPPC was in the form of free fat, which was only physically entrapped within the protein aggregates. The remaining fat had some form of association with the proteins in WPPC. Other fractionation techniques would be needed to obtain an enriched dairy lipid fraction.
乳制品衍生的脂质，如磷脂（PL），由于其功能和营养特性而受到关注。我们的研究目标是开发一种分离工艺（非溶剂型），从乳清蛋白磷脂浓缩物（WPPC）中生产富含乳制品的脂质级分。对再水合的商业 WPPC 溶液应用了各种化学预处理（即 pH、钙或温度的调节）。这些处理在台式规模上进行，以帮助蛋白质或 PL 的沉淀。经化学处理的溶液经离心分离成以下 3 层：（1）顶层脂肪层，（2）中间区的上清液，和（3）离心管底部的沉淀物。层的厚度和大小随处理参数而变化。对各层的成分分析表明，蛋白质、脂肪和 PL 似乎总是以相似的比例分馏。使用还原和非还原条件下的十二烷基硫酸钠-PAGE 对各层中的蛋白质进行了表征。鉴定了不同的蛋白质，包括乳清蛋白、酪蛋白和乳脂肪球膜蛋白和脂蛋白，并且没有特定类型的蛋白质对顶层或底层有亲和力。离心后，每种蛋白质都存在于各层中，并且在所应用的化学处理方面，蛋白质在各层之间的分馏没有明显差异。使用共焦激光扫描显微镜研究 WPPC 中蛋白质和脂肪的微观结构。用 Fast Green FCF（蛋白质）和 Nile Red（脂质）对再水合的 WPPC 溶液进行双重染色，显示存在大小从 20 到 150μm 不等的非常大的蛋白质聚集体，脂肪被困在这些聚集体中。WPPC 的共焦激光扫描显微镜图像显示，脂肪球周围存在弱蛋白质网络的细纤维。这表明在 WPPC 中的蛋白质之间以及脂肪和蛋白质之间存在特定的相互作用。进行十二烷基硫酸钠处理以了解蛋白质和脂肪之间相互作用的性质。我们发现，WPPC 中约 35%的脂肪以游离脂肪的形式存在，仅物理地被困在蛋白质聚集体中。其余的脂肪与 WPPC 中的蛋白质有某种形式的关联。需要其他分离技术才能获得富含乳制品的脂质级分。
