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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 Plasmin contributes many beneficial and detrimental characteristics in milk and dairy products and has been avidly studied to control these characteristics. However, there are many complications with comparing results from various research institutions due to the differences in sample preparation procedures and measurement methods. It is imperative to determine the most effective, reliable sample preparation and measurement methods for plasmin because it would allow for more accurate evaluation of plasmin and determination of the effectiveness of methods to control plasmin activity. The objective of this project was to identify the optimum sample preparation procedure and method of measuring plasmin in fresh milk at low, normal, and high levels. The procedures evaluated are those that are most commonly used to measure plasmin in milk. The fresh milk samples were (A) spiked with plasmin at four different levels and (B) diluted with a buffer at seven different levels. The first preparation method involved little clean-up for a more natural sample. The second procedure used intense sample clean-up to isolate plasmin and simplify measurement. In addition, three different substrates were used to measure plasmin (S-2251, SpectrozymeŽ PL, and coumarin). In the spiked milk, a significant difference (P <0.05) was found for the milk, level of plasmin, sample preparation, substrate, and all of the interaction factors except for level*sample preparation and level*sample preparation*substrate. Similarly, a significant difference (P < 0.05) was found in the diluted milk for level of plasmin, sample preparation, substrate, and interactions except for level*substrate and sample preparation*substrate. These results show that the amount of measured plasmin is significantly affected by the sample preparation and substrate. The combination of sample preparation and substrate should be chosen based on the condition of the experiment with the awareness of the significance of various interactions (sample preparation*substrate and level*sample preparation*substrate).
Session 46, Dairy Foods: General
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