17A-16 |
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C. N. BURBRINK1, L. J. Mauer2, and K. D. Hayes2. (1) Department of Food Science, Purdue University, 745 Agriculture Mall, West Lafayette, IN 47907, (2) Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009 Plasmin is the major native milk protease, is very heat stable, and causes the breakdown of milk protein in a wide variety of dairy products. This protein breakdown is desirable for some dairy products (i.e. ripening of Cheddar and Swiss cheeses) but detrimental for others (i.e. age gelation in UHT, ultra high temperature, milk). Plasmin and Plasminogen activators survive the direct and indirect heating of pasteurization and UHT processes. A decrease in plasmin activity will delay the onset of age gelation in UHT milk. Sonication has been shown to inactivate enzymes; however, use of sonication to inactivate plasminogen activators has not been fully investigated. Our objective was to determine the effect on sonication on plasminogen activator activities in a buffer system. Solutions containing 720mU/mL plasminogen activator in modified Tris Buffer (0.05M Tris, 0.1M NaCl, 0.01% Tween 80, pH 7.6) were subjected to sonication treatment using Branson Sonifier 150 with 20k kHz frequency, constant duty, 3mm ultra-high intensity tapered microtip and variable amplitude. Plasminogen activator activities were quantified colorimetric analysis using SpectrozymeŽ UK (American Diagnostica, Greenwich, CT), a p-nitroanaline-based substrate that is specific for plasminogen activators. Our results showed that a 30 second treatment at an amplitude setting of 5 decreased plasminogen activator activity by 23%, and a 50 second treatment at this amplitude decreased activity by 52% compared to a control sample not treated by ultrasound. These results suggest that ultrasound treatment can be used to decrease plasminogen activity; therefore, sonication has potential as an alternate or additional method to control plasmin activity in UHT milk.
Session 17A, Dairy Foods: Cheese and microbiology
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