Relationship of somatic cell count and composition and coagulation properties of ewe’s milk

Abstract

The relationship between somatic cell count (SCC) and raw milk composition and its coagulation properties measured at native or standardised pH values were investigated in Manchega ewes’ milk. A total of 84 bulk tank milk samples from flocks included in the National Association of Manchega Sheep Breeders were used. According to their SCC, milk samples were divided into three terciles named low (562±138 cells/mL), medium (956±115 cells/mL) and high (1705±428 cells/ mL) SCC groups. Within each SCC group, two pH treatments were applied before determining coagulation properties (rennet clotting time, curd firming time and curd firmness): no acidification of milk (coagulation at native pH) and acidification of milk at pH 6.5. Native milk pH significantly increased (P<0.05) as SCC rose. With respect to raw milk composition, fat contents were not affected (P>0.05) by SCC, protein content tended to be higher in the high SCC group (P=0.05) and lactose content was significantly lower (P<0.05) in that group. At native pH, the high SCC group had longer rennet clotting time, higher curd firming time and lower curd firmness after 30 min of rennet addition than the low and medium SCC groups (P<0.05). Standardising milk pH at 6.5 prior to rennet addition clearly cancelled out (P<0.05) the negative effects of high SCC on milk coagulation properties. In conclusion, despite the fact that acidification before renneting improved the coagulation properties of milk with high SCC, more research would be needed to determine the sensorial properties of cheese manufactured under such conditions.