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Crosslinking and rheological changes of whey proteins treated with microbial transglutaminase |
V. D. TRUONG1, D. A. Clare2, G. L. Catignani, and H. E. Swaisgood. (1) Southeast Dairy Foods Research Center, Department of Food Science, North Carolina State University, Raleigh, NC 27695, (2) Dept. of Food Science, North Carolina State Univ., Schaub Hall, Box 7624, Raleigh, NC 27695-7624 In order to be competitive in the food ingredient markets, the functionality of whey proteins must be continuously improved and designed for specific uses. Heat and acid treatments are commonly used for modifying whey proteins. Enzymes including microbial transglutaminase (TG) have recently been applied. However, changes in rheological properties of whey proteins as affected by extensive TG crosslinking are not well studied. This study examined the factors affecting crosslinking of whey protein isolates (WPI) by TG, and characterized their rheological properties. Both soluble and immobilized TG were used. The enzyme was immobilized on amino-propyl glass beads (CPG-3000) following the biotin-avidin procedure developed in our laboratory. TG, 0.12-10 units/g proteins, was added to 4-8% w/w WPI in sodium phosphate buffer, pH 7.5 containing 10 mM dithiothreitol. The reaction was carried out in a jacketed bioreactor for 8 hrs at 40°C with continuous circulation. Aliquots were taken at time intervals for SDS-PAGE, Western blots and rheological characterization using a stress controlled rheometer. Gel point temperature of WPI solutions treated with 0.12 units of immobilized TG was slightly decreased but gel strength was unaffected. Ten units of soluble TG resulted in extensive crosslinking of a-lactalbumin and b-lactoglobulin in WPI as evident in SDS-PAGE and Western blotting results. Crosslinking of WPI was manifested with increases in apparent viscosity and changes in gelation properties. Interestingly, the gelling point of WPI solutions increased from 68°C at 0 min to 94°C after 4 hrs of reaction and the gel strength was drastically decreased (lower storage modulus, G¢). Thus, extensive intra- and inter-chain crosslinking probably caused formation of polymers that were too large for effective network development. Modified WPI having a wide range of gelling properties can be obtained with TG crosslinking reactions. The process can be applied to produce heat-stable whey proteins for various food applications.
Session 26, Dairy Foods: General developments in dairy technology
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