Composition, proteolysis indices and coagulating properties of ewe milk as affected by bulk tank somatic cell count

Abstract

The aim of this study was to assess the effect of ovine bulk tank somatic cell count (BTSCC) on composition, proteose-peptone (p-p) content and casein fractions as indicating parameters for proteolysis and coagulating properties of milk. A total of 97 samples of bulk tank milk from Manchega breed ewe flocks were grouped according to somatic cell count (SCC) into four classes: fewer than 500 000 cells/ml, from 500 000 to 10 00 000 cells/ml, from 10 00 000 to 15 00 000 and more than 15 00 000 cells/ml. The casein : protein ratio and lactose content decreased with BTSCC. Proteolysis increased with BTSCC, causing a drop in β-casein and an increase in the γ-caseins from a concentration of 500 000 cells/ml. Regarding coagulation behaviour, the rennet clotting time (RCT) and firming time (k20) rose from 10 00 000–15 00 000 cells/ml of milk. The results showed that the impairment of milk quality and milk ability to make cheese as affected by intramammary infection (IMI) can be inferred from the bulk tank milk of flocks with poor udder health.