Plasminogen activation system in goat milk and its relation with composition and coagulation properties

The activity of plasmin (PL), plasminogen (PG), and plasminogen activator ( PA) and their correlation with goat milk components and milk clotting param eters were investigated. Seven late-lactating Saanen goats were used to pro vide milk samples that were analyzed for PL, PG, and PA activity (colorimet ric assay) fat, protein, noncasein nitrogen, nonprotein nitrogen, casein co ntent, and somatic cell count (SCC). Milk clotting parameters (rennet coagu lating time = coagulation time; K20 = firming rate of curd; A30 = curd firm ness) were measured with a formagraph. Average milk yield and composition w ere similar to those previously observed in other studies. Plasmin, PG, and PA activity, expressed as units/ml, were, respectively, 20.04 +/- 0.94, 3. 21 +/- 0.04, and 1154 +/- 57.61. Plasminogen activity was surprisingly low compared with other species (bovine, ovine), but it was consistent with the high activity of PA. A negative significant correlation was observed betwe en PL and milk casein content. The correlation coefficients between PL and casein/protein ratio and PA and casein/protein ratio were negative and sign ificant, A positive significant correlation was observed between PL and ren net clotting time and PA and rennet clotting time. Also positive was the co rrelation between PL and K20 and PA and K20. The plasmin activity was negat ively correlated with A30. High plasmin and plasminogen activator activity in goat milk appeared to be negatively related with coagulating properties in late lactation, most probably via degradation of casein due to plasmin a ctivity.