Inactivate plasmin using sonication.Plasmin plasmin /plas·min/ (plaz´min) an endopeptidase occurring in plasma as plasminogen, which is activated via cleavage by plasminogen activators; it solubilizes fibrin clots, degrades other coagulation-related proteins, and can be activated is the major native milk protease. Plasmin, plasminogen and plasminogen activators are associated with the casein casein (kā`sēn), well-defined group of proteins found in milk, constituting about 80% of the proteins in cow's milk, but only 40% in human milk. micelles and milk fat globule globule /glob·ule/ (glob´ul) 1. a small spherical mass or body. 2. a small spherical drop of fluid or semifluid substance. 3. a little globe or pellet, as of medicine. membranes in milk. The activity of this enzyme is controlled by certain inhibitors, such as plasmin inhibitors or inhibitors of plasminogen activators, that reduce the activity of plasminogen activators so that plasminogen cannot be converted into plasmin. Most plasmin inhibitors are present in the serum phase of milk. Plasmin 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 processes and products, such as the ripening of cheddar and Swiss cheeses. But it is detrimental for others, such as the age gelation gelation /ge·la·tion/ (je-la´shun) conversion of a sol into a gel. ge·la·tion n. 1. Solidification by cooling or freezing. 2. The process of forming a gel. 3. that occurs in ultra-high-temperature (UHT UHT ultra-heat-treated (milk or cream) UHT adj abbr (= ultra heat treated): UHT milk → leche f uperizada UHT adj abbr (= ultra-heat treated); ) milk. Plasmin survives the direct and indirect heating of pasteurization pasteurization (păs'ch  rĭzā`shən, -rīzā`shən), partial sterilization of liquids such as milk, orange juice, wine, and beer, as well as cheese, to destroy and UHT
processes. Scientists at Purdue University wanted to learn how to better
control plasmin activity. For example, a decrease in plasmin activity
will delay the onset of age gelation in UHT milk.
Sonication sonication /son·i·ca·tion/ (son?i-ka´shun) exposure to sound waves; disruption of bacteria by exposure to high-frequency sound waves. son·i·ca·tion n. is able to inactivate in·ac·ti·vate v. 1. To render nonfunctional. 2. To make quiescent. in·ac  ti·va enzymes. However, its use to
inactivate plasmin has not been fully investigated. The
researchers' objective was to determine the effect of sonication on
plasmin activity in a buffer system.
Solutions containing 5 mU per mL of plasmin in a modified tris buffer (pH 7.6, 0.1M NaCl) were subjected to sonication treatment using a commercial sonication system with 20 kHz frequency, a constant duty cycle, a 3-mm ultra-high-intensity tapered microtip and a variable amplitude capability. Plasmin activity was quantified by using colorimetric analysis with a p-nitroanaline-based substrate that is specific for plasmin activity. The results showed that a 30-second treatment at 116-micron ultrasound amplitude decreased plasmin activity by 10%. An additional 60-second treatment at this amplitude decreased plasmin activity by 20% compared to a control sample that was not treated by ultrasound. A 15-second treatment at a 305-micron ultrasound amplitude decreased plasmin activity by 55%. So it appears that ultrasound can decrease plasmin activity, and that sonication has potential as an alternative way to control plasmin activity in UHT milk. Further information. Lisa Mauer, Whistler Center for Carbohydrate Research, Department of Food Science, Purdue University, 745 Agriculture Mall Dr., West Lafayette, IN 47907; phone: 765-494-9111; fax: 765-494-7953; email: mauer@foodsci.purdue.edu. |
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