Abstract Whey proteins and caseins in breast milk provide bioactivities and also have different amino acid composition. Accurate determination of these two major protein classes will therefore provide a better understanding of human milk composition and function, further aid in developing improved infant formulas based on bovine whey proteins and caseins. In this study, we implemented a LC-MS/MS quantitative analysis based on iBAQ label-free quantitation, to estimate absolute concentrations of alpha-casein, beta-casein and kappa-casein in human milk samples (n=88) collected between day 1 and day 360 post partum. Total protein concentration ranged from 2.03 to 17.52 with a mean of 9.37±3.65 g/L. Casein subunits ranged from 0.04 to 1.68 g/L (alpha-), 0.04 to 4.42 g/L (beta-), and 0.10 to 1.72 g/L (kappa-), with beta-casein having the highest average concentration among the three subunits. Calculated whey/casein ratio ranged from 45:55 to 97:3. Linear regression analyses show significant decreases in total protein, beta-casein, kappa-casein, total casein, and significant increase of whey/casein ratio during the course of lactation. Our study presents a novel and accurate quantitative analysis of human milk casein content, demonstrating a lower casein content than earlier believed, which has implications for improved infants formulas.

中文翻译：

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泌乳第一年中人乳酪蛋白的绝对定量和乳清/酪蛋白比率

摘要母乳中的乳清蛋白和酪蛋白具有生物活性，并具有不同的氨基酸组成。因此，这两种主要蛋白质类别的准确测定将提供对人乳成分和功能的更好理解，进一步帮助开发基于牛乳清蛋白和酪蛋白的改良婴儿配方食品。在这项研究中，我们基于无iBAQ标签的定量方法进行了LC-MS / MS定量分析，以估计一天之间收集的人乳样品（n = 88）中α-酪蛋白，β-酪蛋白和κ-酪蛋白的绝对浓度第1天和产后360天。总蛋白浓度范围为2.03至17.52，平均值为9.37±3.65 g / L。酪蛋白亚基的范围为0.04至1.68 g / L（α-），0.04至4.42 g / L（β-）和0.10至1.72 g / L（kappa-），β-酪蛋白在三个亚基中的平均浓度最高。计算的乳清/酪蛋白比率为45:55至97：3。线性回归分析显示，在泌乳过程中，总蛋白，β-酪蛋白，κ-酪蛋白，总酪蛋白显着减少，乳清/酪蛋白比率显着增加。我们的研究提出了一种新颖，准确的定量分析人乳中酪蛋白含量的方法，证明了酪蛋白含量比以前认为的更低，这对改善婴儿配方奶粉具有重要意义。