Effect of milk β-casein variants on cheese making traits

Caseins are a heterogeneous class of milk proteins and, on average, they represent 82% of total protein content of bovine milk. They are the main protein component of cheese and are responsible of milk coagulation process, forming a reticulum in response to acidification and specific enzymatic proteolysis. Caseins family mainly includes four different fractions: αs1, αs2, β and κ. In particular, β-casein represents approximately 45% of total casein content. Specific β-casein variants, presenting a histidine at the amino acid position 67, have been largely studied for the supposed adverse role on the digestive process of milk. Moreover, β-casein variants are known to affect milk technological traits. Specifically, milk of cows with A1 and B alleles has better coagulation properties than milk of cows with the A2 allele. This study aimed to quantitatively investigate the effect of β-casein variants A1, A2 and B on quality and coagulation traits of bulk milk. A total of 132 commercial herds located in northern and central Italy were visited and bulk milk was collected after morning milking. Traditional milk quality traits (fat, protein, casein, lactose, somatic cell count and urea nitrogen), major minerals content and coagulation properties were assessed. Major minerals were determined by inductively coupled plasma optical emission spectrometry, and milk protein composition and the genetic variants of β-casein were determined using high pressure liquid chromatography. Effects of β-casein variants on milk quality and coagulation traits were estimated fitting a mixed model, with the concentrations of β-casein variants as covariates, and the day of analysis and herd as random effects. Results indicated that β-casein variants differently affected milk quality, major minerals content and milk coagulation properties. In particular, greater amounts of variants A1 and B had positive effects on rennet coagulation time and curd firmness, and were linked to greater Ca and P content compared with A2 variant.