Effects of milk proteins and posttranslational modifications on noncoagulating milk from Swedish Red dairy cattle

摘要

Milk that does not coagulate after rennet addition,also called noncoagulating (NC) milk, is unwanted incheese production due to prolonged processing time.Amounts of whey and casein proteins, genetic variants,as well as posttranslational modifications (PTM) ofproteins are all contributing factors in rennet-inducedcoagulation of milk. In this study, we conducted a wideranginginvestigation of milk proteins in milk samplesfrom 616 Swedish Red dairy cattle using liquid chromatography-high resolution mass spectrometry. Relativeconcentration of proteins, genetic variants, and PTMwere compared between NC milk and coagulating milk.The PTM investigated were phosphorylation of caseinsand glycosylation of κ-casein. Several genetic variantsand PTM were found, including rare phosphorylationvariants of the αS-caseins. Genetic variants were foundto effect the expressed amount of different proteins.Further, the effect of protein amounts and PTM ona binary NC milk trait was modeled using a generalizedlinear model. The model showed that NC milksignificantly correlated with higher relative concentrationsof α-lactalbumin and β-casein and lower relativeconcentrations of β-lactoglobulin and κ-casein. RegardingPTM of caseins, an effect on NC milk from a lowerrelative concentration of αS1-casein with 8 phosphategroups were found, even though an effect from totalrelative concentration of αS1-casein was not found. Thisstudy has provided insights into protein variants andPTM important for NC milk to improve this undesirableproperty.