17A-24 |
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S. E. SOMBERS1, L. J. Mauer2, S. S. Nielsen3, and K. D. Hayes2. (1) Department of Food Science, Purdue University, 745 Agricultural Mall Drive, West Lafayette, IN 47907, (2) Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009, (3) Dept. of Food Science, Purdue University, 745 Agricultural Mall Dr., West Lafayette, IN 47907 Plasmin system components (plasmin (PL), its inactive form plasminogen, and plasminogen activators) form a complex native enzyme/activator/inhibitor system that is involved in proteolytic breakdown of dairy proteins. This protein breakdown can cause desirable or undesirable flavor and texture changes in foods. The plasmin system components are very heat stable enzymes that are associated with the casein micelle in fresh milk. Most commercial dairy products have received heat treatments sufficient to start denaturing whey proteins, thereby enabling the whey proteins to adhere to casein micelles. This can increase cheese yield, but the effects of whey protein binding to casein micelles on plasmin system components have not been investigated. The objective of this research was to determine the influence of ß-lactoglobulin binding to casein micelles in a model buffer on the activity and location of plasmin. Samples were prepared by making a 3% casein solution in Jenness-Koops buffer, then allowing either plasmin or β-lactoglobulin (0%, 0.5% or 1.0%) to react with the casein for one hour at 21°C. The other component was then added, casein precipitated, and the supernatant assayed for PL activity using the chromogenic substrate Spectrozyme® PL. The results indicate that in a non-heated system, when added first, β-lactoglobulin influences plasmin binding to the casein micelle to result in more plasmin unbound to casein. When β-lactoglobulin was added second, more plasmin was found to remain with the casein micelle. This plasmin binding also was affected by the concentration of β-lactoglobulin, with increasing concentrations exhibiting a larger effect. These results are significant for cheese making, as whey proteins (specifically β-lactoglobulin) affect PL, resulting in higher levels of PL in cheese curd, potentially reducing cheese ripening times. A reduction in ripening time could result in significant cost savings for the cheese industry.
Session 17A, Dairy Foods: Cheese and microbiology
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