Effect of somatic cell counts on ewes' milk protein profile and cheese-making properties in different sheep breeds reared in Spain

Bulk tank ewe's milks from Assaf, Castellana and Churra breeds categorized within three different Somatic Cell Count (SCC) groups (LSCC: <500,000; MSCC: 1,000,000 to 1,500,000; and HSCC: 2,500,000 to 3,000,000 cells ml-1) were used to investigate changes in capillary electrophoresis protein profiles and cheese-making properties. The results do not reveal a significant effect of SCC on total casein contents, because the sum of beta-caseins decreased as SCC increased; no statistically significant differences were observed for the sum of alpha-caseins, and the values of kappa-casein were higher in the HSCC milk. However, the soluble proteins other than alpha-lactalbumin and beta-lactoglobulin increased with SCC. Regarding the effect of breed, the Assaf breed had the lowest contents of kappa-CN, alpha s1-I-CN, alpha s1-II-CN 1-CN, alpha s1-III-CN, beta1-CN and beta2-CN. The protein profile was significantly correlated with curd textural properties. alpha s1-I-CN was the most influential variant because it was positively correlated with a large number of textural parameters. Cheese yield was positively correlated with all casein variants except alpha s1-III-CN, showing that the milk from local breeds were more suitable for cheese-making due to their higher contents of all the casein variants. Regarding curd texture properties LSCC milk curds showed more cohesiveness, associated with its lower content of alpha s1-III-CN and Castellana milk curds showed the highest values for firmness owing to their higher content of alpha s1-I-CN.