Casein polymorphism heterogeneity influences casein micelle size in milk of individual cows

Abstract

Milk samples from individual cows producing small (148-155 nm) or large (177-222 nm) casein micelles were selected to investigate the relationship between the individual casein proteins, specifically κ- and β-casein phenotypes, and casein micelle size. Only κ-casein AA and β-casein A1A1, A1A2 and A2A2 phenotypes were found in the large casein micelle group. Among the small micelle group, both κ-casein and β-casein phenotypes were more diverse. κ-Casein AB was the dominant phenotype, and 3 combinations (AA, AB, and BB) were present in the small casein micelle group. A considerable mix of β-casein phenotypes was found, including B and I variants, which were only found in the small casein micelle group. The relative amount of κ-casein to total casein was significantly higher in the small micelle group, and the nonglycosylated and glycosylated κ-casein contents were higher in the milks with small casein micelles (primarily with κ-casein AB and BB variants) compared with the large micelle group. The ratio of glycosylated to nonglycosylated κ-casein was higher in the milks with small casein micelles compared with the milks with large casein micelles. This suggests that although the amount of κ-casein (both glycosylated and nonglycosylated) is associated with micelle size, an increased proportion of glycosylated κ-casein could be a more important and favorable factor for small micelle size. This suggests that the increased spatial requirement due to addition of the glycosyl group with increasing extent of glycosylation of κ-casein is one mechanism that controls casein micelle assembly and growth. In addition, increased electrostatic repulsion due to the sialyl residues on the glycosyl group could be a contributory factor.

Current and future prospects for nanotechnology in animal production

“…Casein micelles are naturally occurring nanoparticles in milk, where casein phosphoproteins make up approximately 80% of the protein profile in cow’s milk [20, 21]. Some casein isoforms assemble themselves around calcium, proteins, and other nutrients to allow for transport from mother to young.…”

Changes in Milk Protein Interactions and Associated Molecular Modification Resulting from Thermal Treatments and Storage

“…The protein compositions of the micelle and serum phases were determined by RP-HPLC, according to the method described by Day, Williams, Otter, and Augustin (2015) and Nguyen, Schwendel, Harland, and Day (2018). The sample (1 mL) was mixed with 1 mL of buffer solution.…”

Caseins as Regulators of Hematopoiesis

“…Bovine milk caseins are composed mainly of equal amounts of β-casein and αS1casein [11] also contains κ-caseins [18], whereas human milk contains β-and κ-casein and a low concentration of α-casein. The whey/casein ratio in the formula is similar to that of mature human milk (60/40), but the formula contains all bovine milk caseins.…”