15B-9 |
Differentiation of plasmin and plasminogen using Fourier transform infrared (FT-IR) spectroscopy |
K. D. HAYES, B. F. Ozen, and L. J. Mauer. Department of Food Science, Purdue University, 1160 Food Science Building, West Lafayette, IN 47907-1160 The major native protease in milk, plasmin, contributes to the proteolysis of milk proteins. Protein breakdown is desirable for some dairy products but detrimental for others. Plasminogen (PG), the precursor of plasmin, is initially present in milk at much higher concentrations than plasmin. Plasminogen activators activate PG to plasmin by cleaving an Arg-Ile bond, creating structural differences between PG and plasmin. With current plasmin activity assays and ELISA methods it is difficult to accurately differentiate between PG and plasmin; however, FT-IR is a good tool for monitoring subtle changes in protein conformation. The ability to differentiate between PG and plasmin is important for developing procedures to control plasmin activity in dairy products. The objective of this study was to differentiate between PG and plasmin in solution at various ratios using FT-IR spectroscopy. FT-IR spectra of PG and plasmin in water, as well as mixtures of PG and plasmin at various ratios, were obtained using a ZnSe-ATR attachment at 4 cm-1 resolution. The FT-IR was purged with dry nitrogen during measurements. Discriminant analysis and PLS were used to analyze data. Discriminant analysis was able to differentiate PG and plasmin using the 1700-1200 cm-1 region. Standard curves to determine PG and plasmin concentrations were constructed successfully using PLS (correlation coefficient >0.9). FT-IR was able to differentiate between PG and plasmin. This method will allow further study of the factors that influence PG and plasmin levels and locations (i.e. in casein or whey fractions) in milk and cheese products.
Session 15B, Dairy Foods: Chemistry, microbiology and sensory analysis of various cheeses
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