71A-58 |
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L. A. PILLSBURY and K. D. Hayes. Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009 Plasmin is the major native milk protease, known to be very heat stable and to cause the breakdown of milk protein in a wide variety of dairy products. Plasminogen, the zymogen of plasmin, is converted to plasmin by the action of plasminogen activators, all of which are present in milk. In Swiss cheese, plasmin catalyzes the hydrolysis of a- and b-casein to result in improved flavor profile. The level and activity of plasmin system enzymes in mold-ripened cheeses previously has received limited attention. The objective of this research was to determine plasmin and plasminogen levels in various mold-ripened cheeses. The mold-ripened cheeses (Bleu, Brie, and Gorgonzola) were subjected to a curd preparation method, which included the addition of tri-sodium citrate and ε-amino-n-caproic acid, then pH reduction to remove casein proteins. The solution was centrifuged and the resulting supernatant was assayed for plasmin and plasminogen. A direct enzymatic assay with Spectrozyme®PL, a p-nitroanaline-based substrate that is specific for plasmin, was used to measure plasmin activity. Plasminogen was quantified by using a coupled enzymatic assay where exogenous urokinase-type plasminogen activator was added and the resulting plasmin was measured using Spectrozyme®PL. Results indicated that plasmin activity was highest in Bleu and Gorgonzola varieties, while Brie contained the least amount of plasmin. Plasminogen-derived activity was lowest in Brie and Gorgonzola, while Bleu cheeses contained the least amount of plasminogen-derived plasmin activity. These observations are likely due to differences in ripening times. Bleu and Gorgonzola are ripened between three and five mo, while Brie is ripened for two to three wk. During this longer ripening time for Bleu (and Gorgonzola), more plasminogen activation could occur, resulting in the higher plasmin levels observed. These results suggest that variations in plasmin and plasminogen content between Bleu, Brie, and Gorgonzola cheeses are due to differences in manufacturing conditions.
Session 71A, Dairy Foods: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |