Effect of genetic polymorphism of milk proteins on rheology of chymosin-induced milk gels

Individual milk samples from 121 cows in mid lactation of the Swedish Red and Swedish Holstein breeds with known protein genotypes of β- and κ-casein and β-lactoglobulin were analysed. Chromatographically pure chymosin was added to skim milk and rheological properties of the gels were measured using a Bohlin VOR Rheometer. Coagulation time (CT) and curd firmness after 25 min (G′25) were registered for each sample. The B allele of κ-casein was associated with improved coagulating properties of milk, whereas the E allele showed a negative effect on these traits. The β-casein A2A2 genotype was associated with inferior milk coagulation characteristics. Total protein concentration of milk was positively associated with curd firmness, but showed no association with milk coagulation time.