Absolute Quantification of Human Milk Caseins and the Whey/Casein Ratio during the First Year of Lactation

• DOI: 10.1021/acs.jproteome.7b00486
• Publication Date: 2017-09-19T10:11:11Z
• Authors: Yalin Liao; Darren Weber; Wei Xu; Blythe P. Durbin-...; Brett S. Phinney; Bo Lönnerdal
• Keywords: 2. Zero hunger; 0303 health sciences; 03 medical and health sciences; Whey Proteins; Milk, Human; Whey; Caseins; Humans; Lactation; Milk Proteins; 3. Good health

Whey proteins and caseins in breast milk provide bioactivities and also have different amino acid composition. Accurate determination of these two major protein classes provides a better understanding of human milk composition and function, and further aids 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 α-casein, β-casein, and κ-casein in human milk samples (n = 88) collected between day 1 and day 360 postpartum. 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 (α-), 0.04 to 4.42 g/L (β-), and 0.10 to 1.72 g/L (α-), with β-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, β-casein, κ-casein, total casein, and a 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.