Linking variation in the casein fraction and salt composition to casein micelle size in milk of Dutch dairy goats

The casein (CN) composition, salt composition and micelle size varies largely between milk samples of individual animals. In goats, the link between those casein characteristics are unknown and could provide useful insights into goat casein micelle structure. In this study, the casein- and salt composition of 42 individual Dutch goats from 17 farms was studied and linked to casein micelle size. Micelle size, proportions of individual caseins, and protein content were associated with each other. Milk with smaller casein micelles was higher in protein content, salt content, and proportion of αs1-CN, but lower in αs2-CN and β-CN. The higher salt content in milk with small casein micelles was mainly attributed to a higher protein content, but changes in casein composition might additionally contribute to differences in mineralization. The non-sedimentable casein content in goat milk correlated with non-sedimentable fractions of β-CN and κ-CN and was independent of micelle size. Between large and small casein micelles, goat casein micelles showed more differences in casein and salt composition than bovine micelles, indicating differences in internal structure. Nevertheless, the casein mineralization in goat milk was similar to casein mineralization in bovine milk, indicating that mineralization of casein micelles follows a general principle. These results can help to better understand how composition and micelle structure in goat milk are related to each other, which may be useful to improve processing and product properties of goat milk in the future.