Effect of subclinical intramammary infection on milk quality in dairy sheep: II. Matured-pressed cheese (Manchego) produced from milk of uninfected and infected glands and from their blends

Manchego is a high-fat, long ripened hard cheese, which is produced by enzymatic coagulation of sheep milk. Manchego produced in the La Mancha region in Spain and has Protected Designation of Origin (PDO) status. The objective of the study was to evaluate the effects of intramammary infection (IMI) in Manchega and Lacaune dairy sheep with various coagulase negative staphylococci bacteria (CNS) on milk coagulation properties and cheese whey syneresis. The effect of the length of milk storage before processing on cheese yield and its quality was also evaluated. The study included 20 Manchega and 16 Lacaune dairy ewes. The half-udder model was applied: each of the selected animals had one gland free of infection, while the contra-lateral gland was infected with various CNS species. Pasteurized milk (10L) from uninfected glands, and 50:50 and 75:25 milk blends from uninfected:CNS-infected glands was used for cheese production. Overall, 23 batches of cheese were made and ripened for 63d. Cheeses were analyzed for organic components, physical and mechanical structure. The taste and sensual qualities of the cheese were evaluated by experts and consumers in two separate panels.Milk yield in the glands infected with CNS was significantly lower than in control glands. The milk of infected glands had higher somatic cell count and poorer coagulation properties in comparison to controls. Cheese made from infected milk had a significant effect on % fat, total fat, fat loss, total protein, protein loss and dry matter in both breeds. However, cheeses made of blends of 25% or 50% milk from infected glands had only minor losses of fat and protein content, which were not associated with noticeable changes in the final weight of the cheese; though, as discussed herein, further research in this line is warrant. The cheeses made of milk stored under refrigerated conditions were clearly perceived as different from the other cheeses because it had more intense attributes related with tangy taste (i.e., bitter, sharp, intense taste, acid) and soft texture (i.e., soft, pasty, not tough).