Variation in casein distribution and mineralisation in the milk from Holstein-Friesian cows

In this study, protein and salt distributions in the milk of 48 Holstein-Friesian cows were studied. Gross composition of milk samples and variation between individual cows was in line with expectation. However, the mineralisation of the casein fraction, expressed in mmol protein-associated calcium per 10 g casein, differed >2-fold between the milk samples. Reasons for this variation are unknown and could not be correlated to casein composition and/or genetic variants of caseins. Furthermore, notable differences (>5-fold) in non-sedimentable (100,000×g for 60 min) casein were observed. Percentages of non-sedimentable caseins differed for κ-casein genetic variants (BB > AB > AA) and increased with increasing degree of glycosylation. Higher levels of non-sedimentable caseins with increasing degree of glycosylated κ-casein could be attributable to increased repulsion between the micelles, leading to the formation of a less cohesive sediment on centrifugation.