Department of Nutrition, University of California, Davis 95616.
Genome Center, University of California, Davis 95616.
J Dairy Sci. 2020 Apr;103(4):3002-3016. doi: 10.3168/jds.2019-17179. Epub 2020 Feb 7.
Milk fat globule membrane (MFGM) is a glycosylated, protein-embedded, phospholipid fraction that surrounds triglycerides in milk. Commercial bovine sources have recently come to the market as a novel food ingredient and have been added to various products, including infant formula. Considering that MFGM is a heterogeneous mixture of fat, protein, and carbohydrate, it can be expected that variations among MFGM products exist. For this reason, our aim was to characterize the composition of commercial MFGM samples through a combination of proteomic and lipidomic analyses. Six bovine milk fractions, represented as MFGM fractions or phospholipid fractions, were obtained from various commercial sources. Additionally, the MFGM samples were compared with 2 infant formulas, a standard formula as well as a premium formula containing MFGM. For proteomic analysis, bottom-up data-dependent liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed on each MFGM fraction, and nearly a thousand proteins were identified across all samples, with 364 of them having different abundance across the samples tested. One hundred twelve proteins differed by a fold-change of 10 or greater, 14 by a fold-change of 50, and 2 by a fold-change of 100 in at least 1 pair, suggesting large differences in the proteins present in these fractions. Even though the classical MFGM proteins were enriched in the MFGM fractions, the relative protein composition varied considerably, and all contain an abundance of milk (casein and whey) proteins. Lipidomic analysis identified a total of 393 lipid species across both positive and negative ionization modes, with the major classes detected being triglycerides, sphingomyelins, and several phospholipids. Across all samples, triglycerides comprised at least 50% of total lipids, with phosphatidylcholine and sphingomyelin being the second and third most abundant lipid classes, respectively. These findings demonstrate the heterogeneous nature of various bovine commercial MFGM fractions. This variation must be considered when evaluating and describing potential functional benefits of these products shown in clinical trials.
牛奶脂肪球膜（MFGM）是一种糖基化的、蛋白嵌入的、磷脂部分，围绕着牛奶中的甘油三酯。商业牛源最近作为一种新型食品成分进入市场，并已添加到各种产品中，包括婴儿配方奶粉。考虑到 MFGM 是一种脂肪、蛋白质和碳水化合物的不均匀混合物，可以预期 MFGM 产品之间存在差异。出于这个原因，我们的目标是通过蛋白质组学和脂质组学分析相结合来描述商业 MFGM 样品的组成。从各种商业来源获得了 6 种牛奶级分，分别表示为 MFGM 级分或磷脂级分。此外，还将 MFGM 样品与 2 种婴儿配方奶粉进行了比较，一种是标准配方奶粉，另一种是含有 MFGM 的优质配方奶粉。对于蛋白质组学分析，对每个 MFGM 级分进行了自上而下的数据依赖液相色谱-串联质谱（LC-MS/MS）分析，在所有样品中鉴定了近千种蛋白质，其中 364 种蛋白质在测试的样品中有不同的丰度。112 种蛋白质的变化倍数为 10 或更高，14 种蛋白质的变化倍数为 50，2 种蛋白质的变化倍数为 100，至少在 1 对样品中存在差异，表明这些级分中存在的蛋白质存在很大差异。尽管经典的 MFGM 蛋白在 MFGM 级分中富集，但相对蛋白质组成差异很大，并且都含有丰富的牛奶（酪蛋白和乳清）蛋白。脂质组学分析在正离子和负离子模式下共鉴定了 393 种脂质种类，主要检测到的类别是甘油三酯、神经鞘磷脂和几种磷脂。在所有样品中，甘油三酯至少占总脂质的 50%，其次是磷脂酰胆碱和神经鞘磷脂。这些发现表明各种商业牛源 MFGM 级分具有异质性。在评估和描述临床试验中这些产品的潜在功能益处时，必须考虑这种变化。
