Liquid chromatography-mass spectrometry-based identification of casein variants in Dutch goat milk and their effect on casein composition, protein content, and micelle size

Casein polymorphism can be related to compositional differences in milk. The objective of this study was to identify CN variants in the Dutch goat population and to investigate their relation to CN composition, protein content, and CN micelle size. In this study, the CN variants were identified for 234 goats based on the intact protein mass determined by liquid chromatography (LC)-MS. The highest number of protein variants was detected for κ-CN and α_S1-CN. The effect of CN variants was studied using a mixed linear model accounting for family relations among goats. The results indicate that CN composition, protein content, and micelle size are heritable traits. External goat-related factors (e.g., parity, lactation stage) were less relevant for the studied traits. The results show that variants of α_S1-CN affect protein content in goat milk. The relative CN composition and CN micelle size were mainly affected by variants of α_S1-CN and α_S2-CN. Variants affecting the CN composition also affected CN micelle size. This study highlights the importance of considering all CN fractions when determining the effects of CN variants on milk traits in goat milk. The Dutch goat population differed in certain aspects from other dairy goat breeds, mainly in variants of α_S1-CN and α_S2-CN, which may also explain differences in overall CN composition.