Activation of Plasmin with Urokinase in Ultrafiltered Milk for Cheese Manufacture

Havarti and Saint-Paulin cheeses were manufactured by traditional and UF techniques. Urokinase and KI$ were added individually and together to batches of retentate before cheese making. Cheeses were analyzed for solids, fat, total N, pH 4.6 soluble N, NPN, plasmin activity, plasmin plus plasminogen activity, and casein degradation. Eighty cheese sam- ples were analyzed (two varieties, two replications, and five treatments sampled after 1, 28, 56, and 84 d). Urokinase increased plasmin activity in UF Havarti and Saint-Paulin cheeses. This increased pH 4.6 soluble N levels and NPN, increased proteolysis of &casein, and slightly improved the flavor profile (only Havarti). Potassium iodate in UF cheese inhibited starter organisms, did not influence plasmin activity, and did not improve ripening. Activation of plasminogen may aid in ripening some UF cheese varieties.