Factors influencing degree of glycosylation and phosphorylation of caseins in individual cow milk samples

Abstract

The aim of this study was to examine variations in posttranslational modifications (PTM) of caseins (CN) in milk from individual cows and determine how these differ between breeds, across lactation, and between variants. Furthermore, we examined the variation of casein PTM in relation to rennet coagulation properties of milk. In total, detailed protein composition of milk from 892 Danish Holstein and Jersey cows was determined by liquid chromatography/electrospray ionization-mass spectrometry. The method measured relative contents of the main milk proteins as well as several variants and PTM. The results showed that the 2 breeds had distinct milk protein composition. Milk from Danish Holstein cows was mainly characterized by higher relative contents of β-CN, α-lactalbumin (α-LA), and β-lactoglobulin, and a higher fraction of glycosylated κ-CN (G κ-CN), whereas milk from Danish Jersey cows was characterized by higher relative contents of κ-CN, αS2-CN, and the less phosphorylated forms of αS1-CN and αS2-CN. Univariate linear models including days in milk and parity as class effects showed variation in the detailed protein profile across and between lactations; in particular, changes in the degree of glycosylation of κ-CN were pronounced, but changes in αS1-CN 8P to total αS1-CN and αS2-CN 11P to αS2-CN were also observed over lactation for both breeds. The phosphorylated forms of αS1-CN and αS2-CN were, to some extent, correlated. Further, the κ-CN BB genotype was associated with higher relative contents of both unglycosylated κ-CN (UG κ-CN) and G κ-CN compared with κ-CN AA; κ-CN AB showed intermediate results in both breeds. The influence of protein composition on rennet coagulation properties was explored based on 4 classes for curd firming rate: noncoagulation, and poor, average, and good coagulation. The results revealed breed differences: Holstein milk, higher relative content of κ-CN to total protein, and higher content of G κ-CN were associated with improved milk coagulation. In contrast, relative content of α-LA was the main component associated with milk coagulation properties in Danish Jerseys and it was shown to affect milk coagulation properties negatively. In addition, variation in phosphorylation degrees of αS1-CN also played a role. This study demonstrates that although the genetic influence of glycosylation seems to be the same in both breeds, nongenetic variation differs, which is further reflected in different associations with milk coagulation properties.

Comparison of milk protein composition and rennet coagulation properties in native Swedish dairy cow breeds and high-yielding Swedish Red cows

“…A positive influence of increased relative concentrations of κ-CN on milk coagulation properties is well documented (Wedholm et al, 2006;Jensen et al, 2012). This could be a consequence of the underlying κ-CN genotypes, where κ-CN B is related to higher relative content of κ-CN and a higher GD (Poulsen et al, 2016). Here, a higher frequency of κ-CN variant B was found in the WC group, but this was not reflected in significantly higher content of κ-CN in WC milk.…”

“…This was not confirmed in the current study. In Danish Jersey cows, a higher relative fraction of α-LA was associated with NC and poorly coagulating milk (Poulsen et al, 2016). Increasing the relative concentration of α-LA may affect the casein-to-whey ratio, as the relative concentrations of α-LA and β-LG were positively correlated; thus, increasing relative contents of the whey proteins would lower the casein-to-whey ratio, which may in turn affect milk coagulation properties negatively.…”

A Novel SNPs in Alpha-Lactalbumin Gene Effects on Lactation Traits in Chinese Holstein Dairy Cows

“…Polymorphism and milk quality studies have been widely used in the optimization of dairy population, and the link between milk composition and genetic variation in milk production has a profound impact on dairy production [2,3,24,25]. Recently, Poulsen et al found that α-LA is a major component, which has negative effect on milk coagulation in Danish Jersey [26]. GWAS data also showed that SLC37A1 gene might be associated with α-LA phenotypes in multiple breed, and might affect milk yield [4].…”

Quantification of bovine milk protein composition and coagulation properties using infrared spectroscopy and chemometrics: A result of collinearity among reference variables

“…Descriptive statistics (in quantities per unit milk) are presented in Table 1. Further descriptive statistics (in quantities per unit protein), including breed differences, for protein composition and milk coagulation properties of the samples have been described by Poulsen et al (2013) and Poulsen et al (2016).…”

“…Combined, the 4 caseins (α S1 -CN, α S2 -CN, β-CN, and κ-CN) and 2 whey proteins (α-LA and β-LG) comprise approximately 90% of the bovine protein fraction (wt/ wt; Walstra, 1999). Heterogeneity in the major milk proteins is related to underlying genetic polymorphism (Heck et al, 2009), and it is also affected by DIM and parity (Poulsen et al, 2016). Posttranslational modification of the proteins also adds to their isoform complexity and has been shown to affect the technological properties of milk, including milk coagulation (Frederiksen et al, 2011;Jensen et al, 2012).…”