Influence de trois haplotypes des caséines αsl, β et Κ fréquents en race bovine Normande sur la composition du lait et l'aptitude à la fabrication fromagère

Summary - Effect of the three most frequent casein haplotypes occurring in the Norman breed used for cheesemaking. In the Norman cow breed, the influence of three casein haplotypes, us1-Cn B, Il-Cn B et K-Cn B (BBB), us1-Cn B, Il-Cn A2 et K-Cn A (BA2A) and us1-Cn C, Il-Cn A2 et K-Cn B (CA 2B), was compared on the composition of milk and its aptitude for cheese production. The physico-chemical composition of 89 samples (40 BBB, 30 BA 2A et 19 CA 2B) selected on the basis of genotype, filiation and lactation stage, as weil as their behaviour during coagulation with rennet were determined. The same samples were used to make Saint-Paulin type cheese from 6 kg of milk (one milking). The x-casein proportion was greater in BBB and CA2B milks than in BA2A milk. The micelle size varied conversely with the proportion of x-casein in total casein and was mu ch greater for milk BA2A (15% more as compared to CA2B milk) than for milk BBB and CA2B. The coagulation ability was higher for milk CA2B than for milk BA2A. The homozygote variant B of x-casein had a higher coagulation ability than variant A. In manufacture ofmicro-cheeses with individual milk of same composition, the association K-Cn Band Il-Cn B variants led to an increase in the cheese yield mainly due to a better retention of the amount of fat in the curd of chee se BBB. The microstructure of BBB curd was doser than these of curd BA2A. At the end of the ripening period (45 days), BBB cheeses were firmer, less elastic and more breakable th an the other two haplotypes. Neither the chee se composition, nor the degree of proteolysis, nor the pH of the ripened cheeses appeared to be responsible for these texture differences which existed since the coagulation stage.