17A-23 |
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L. H. CHOI1, A. L. Kelly2, S. S. Nielsen1, and K. D. Hayes1. (1) Dept. of Food Science, Purdue Univ., 745 Agricultural Mall Dr., West Lafayette, IN 47907, (2) Dept. of Food & Nutritional Sciences, Univ. College Cork, Western Rd., Cork, Ireland Many researchers have studied the role of plasmin, plasminogen, and plasminogen activators (PA) in cheese systems due to their importance in cheese ripening. There have been many conflicting results from various institutions that cannot be based solely on regional and breed differences. Upon careful evaluation of various studies, some main differences noted were the methods of sample preparation and measurement of enzymes. The objective of this study was to determine the optimal sample preparation and measurement methods to evaluate plasmin, plasminogen, and plasminogen activators in parts of the cheese system (raw milk, pasteurized milk, whey, curd, and commercial cheese). Fresh, raw milk samples were used to produce a curd. Milk, whey, and curd were taken at the critical steps of the curd process. In addition, three different commercial Cheddar cheese samples were tested. The samples were prepared using two different methods and measured for plasmin, plasminogen, and plasminogen activators using three different substrates (coumarin, SpectrozymeŽ PL, and S-2251). After evaluating the results, a significant difference (P < 0.05) was found based on the type of product, enzyme, sample preparation, and substrate. However, the interaction of sample preparation*substrate was not significant. Unfortunately, it was discovered that tissue-type plasminogen activators could not be measured using coumarin due to natural fluorescence of one of the compounds needed for the procedure. These data indicates that careful consideration must be given when choosing the combination of sample preparation and substrate for experiments involving plasmin, plasminogen, and plasminogen activators.
Session 17A, Dairy Foods: Cheese and microbiology
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