Estimation of variation in concentration, phosphorylation and genetic polymorphism of milk proteins using capillary zone electrophoresis

Capillary zone electrophoresis (CZE) was tested for reproducibility and was shown to be a suitable method for estimating the relative concentration of α-lactalbumin, β-lactoglobulin, αS2-casein (αS2-CN), αS1-CN, κ-CN, and β-CN in milk. This study showed how the method can also be used to determine the relative concentration of two different phosphorylation states of αS1-CN (αS1-CN-8P and αS1-CN-9P) and three of αS2-CN (αS2-CN-10P, αS2-CN-11P and αS2-CN-12P). Furthermore, with CZE it was possible to determine most common genetic variants including the κ-CN E variant that has not been identified by CZE before. Analyses of milk samples of 1948 Dutch Holstein-Friesian cows showed large variation in both the relative protein concentration and the relative concentration of different phosphorylation states for all milk proteins studied. Correlations between different phosphorylation states of αS1- and αS2-CN indicated that the relative concentration of specific phosphorylation states of αS1- and αS2-CN were related to each other.