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

作者：Liao Yalin; Weber Darren; Xu Wei; Durbin Johnson Blythe P; Phinney Brett S; Lonnerdal Bo^*

来源：Journal of Proteome Research, 2017, 16(11): 4113-4121.

DOI：10.1021/acs.jproteome.7b00486

• human milk
• alpha-casein
• beta-casein
• kappa-casein
• total protein
• whey/casein ratio
• label-free LC-MS/MS
• amino acid analysis
• iBAQ

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 alpha-casein, beta-casein, and kappa-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 (alpha-), 0.04 to 4.42 g/L (beta-), and 0.10 to 1.72 g/L (alpha-), 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 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.

• 出版日期2017-11