Abstract
The aim of this work was to evaluate the effect of intramammary infection (IMI) on the endogenous proteolysis of milk. Four control checks were carried out in the half-udder milk of 10 ewes that acquired unilateral subclinical mastitis. Two of these checks were conducted before the infection was established and 2 after. Ten healthy ewes were tested as a control group. The presence of a subclinical IMI involved an increase of the products of casein hydrolysis, the proteose-peptone (p-p) fraction and minor (m) caseins, and a decrease of ß-casein. As a result, a significant increase in the proteolysis index (PI), calculated as the ratio of m-casein to the sum of caseins (¿ + ß + ¿), took place ¿-Casein and ¿-casein were not significantly affected by IMI. Correlations confirmed the scenario: log 10 of somatic cell count (SCC) was positively correlated with p-p content and negatively with ß-casein, whereas log 10 SCC was not correlated with ¿-casein or ¿-casein. On the other hand, p-p content was positively correlated with m-casein and PI and negatively with ß-casein, but no correlation was detected between p-p content and ¿- or ¿-casein. Furthermore, between casein fractions, m-casein was only significantly correlated with ß-casein. These results suggest that use of indices of proteolysis of caseins such as p-p, m-casein, and PI, could be applied together with SCC to evaluate the cheese-making quality of milk. © 2011 American Dairy Science Association.
