14A-2 |
Inactivation of plasmin by sonication |
L. J. MAUER 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, 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 survives 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 plasmin has not been fully investigated. Our objective was to determine the effect of sonication on plasmin activity in a buffer system. Solutions containing 5 mU/mL plasmin (Sigma) in modified tris buffer (pH 7.6, 0.1M NaCl) were subjected to sonication treatment using a Branson Sonifier 450 with 20 kHz frequency, constant duty cycle, 3mm ultra high intensity tapered microtip, and variable amplitude. Plasmin activity was quantified by colorimetric analysis using Spectrozyme®PL (American Diagnostica, Greenwich, CT), a p-nitroanaline-based substrate that is specific for plasmin activity. Our results showed that a 30 second treatment at 116 micron ultrasound amplitude decreased plasmin activity by 10%, and an additional 60 second treatment at this amplitude decreased plasmin activity by 20% compared to a control sample not treated by ultrasound. A 15 second treatment at 305 micron ultrasound amplitude decreased plasmin activity by 55%. These results suggest that ultrasound treatment can be used to decrease plasmin activity; therefore, sonication has potential as an alternate method to control plasmin activity in UHT milk.
Session 14A, Dairy Foods: General developments in dairy technology I
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